SYNC™

SynC · Historical revision

Secondary Unit Substations

Revision3
EditedOct 8, 2026
StatusSuperseded
Contents

View changes in this revision   Revision history

Historical revision. This is editorial revision 3, kept so citations to it stay resolvable. It is not the current text of this standard — see the current revision.

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)
Remade from scratch to the authoring rules: defaults asserted only where four of five projects would choose them, and scope boundaries matched to the neighboring standards

1 Scope

NOTE A secondary unit substation is one assembly in which a primary medium-voltage section, a step-down transformer, and a secondary low-voltage distribution section are mechanically and electrically close-coupled, and in which one manufacturer of record is responsible for the ratings, the connections between the sections, the factory tests of the assembled lineup, and the warranty of the whole. (1.1)
NOTE This standard governs what only the assembly decides: the arrangement and the tie transfer scheme, the ratings that must agree across the three sections, the throats and transitions, the assembly enclosure, the protective-device actions wired from one section to another, the factory and field tests of the assembled unit, and its installation. The construction of each section is invoked by reference to the standard that governs that product, and each section meets that standard except where this standard states otherwise. (1.2)
NOTE The following are governed elsewhere and are outside this standard: (1.3)
  • a transformer furnished on its own rather than as a section of this equipment, under Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers or Low Voltage Dry Type TransformersLow-Voltage Dry-Type TransformersResolves to the current adopted revision.sync/low-voltage-dry-type-transformers
  • metal-clad switchgear that stands alone, under Medium Voltage SwitchgearMedium Voltage SwitchgearResolves to the current adopted revision.sync/medium-voltage-switchgear
  • low-voltage switchgear, switchboards, and motor control centers purchased separately rather than as a section of the assembly, under Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current adopted revision.sync/low-voltage-switchgear, Low Voltage SwitchboardsLow Voltage SwitchboardsResolves to the current adopted revision.sync/low-voltage-switchboards, and Motor Control CentersMotor Control CentersResolves to the current adopted revision.sync/motor-control-centers
  • the medium-voltage feeder cable that supplies the assembly, up to its termination, under Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables
  • the low-voltage conductors leaving the secondary section and their raceways, under Conductors And CablesConductors and CablesResolves to the current adopted revision.sync/conductors-and-cables and Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit
  • the low-voltage grounding electrode system the secondary is bonded into, under Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding
  • the concrete pad as a structure, under Concrete PadsConcrete Equipment PadsResolves to the current adopted revision.sync/concrete-pads
  • the room that houses the assembly, under Electrical RoomsElectrical RoomsResolves to the current adopted revision.sync/electrical-rooms
  • the short-circuit, coordination, and arc-flash studies, under Short Circuit StudyShort-Circuit StudyResolves to the current adopted revision.sync/short-circuit-study, Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study, and Arc Flash StudyArc-Flash StudyResolves to the current adopted revision.sync/arc-flash-study
  • automatic transfer switches for emergency and legally required standby systems, under Automatic Transfer SwitchesAutomatic Transfer SwitchesResolves to the current adopted revision.sync/automatic-transfer-switches
  • primary substations above 38 kV and substations owned by the serving utility
1.4 The assembly shall be furnished as a close-coupled lineup in which the transformer is mechanically and electrically integrated with the primary section and with the secondary section.
1.5 The assembly location, its orientation, and the position of the transformer relative to the primary and secondary sections shall be as indicated on the electrical room layout or the site electrical plan.
1.6 The Contractor shall coordinate the primary cable terminations, the secondary feeders, the pad, the room or yard, and the grounding of the assembly with the standards named in this section before the assembly is released for manufacture.

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 Where the contract documents, the serving utility's requirements, the Authority Having Jurisdiction, or two referenced standards impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
IEEE C37.121 Guide for Switchgear: Unit Substation Requirements
IEEE C37.20.1 Metal-Enclosed Low-Voltage AC Power Circuit Breaker Switchgear
IEEE C37.20.2 Metal-Clad Switchgear
IEEE C37.20.3 Metal-Enclosed Interrupter Switchgear (1 kV to 38 kV)
IEEE C37.20.7 Guide for Testing Switchgear Rated Up to 52 kV for Internal Arcing Faults
IEEE C37.46 High-Voltage Expulsion and Current-Limiting Type Power Class Fuses and Fuse Disconnecting Switches
IEEE C37.48 Guide and Tutorial for the Application of High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories
IEEE C57.12.00 General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers
IEEE C57.12.01 General Requirements for Dry-Type Distribution and Power Transformers
IEEE C57.12.36 Requirements for Liquid-Immersed Distribution Substation Transformers
IEEE C57.12.55 Dry-Type Transformers Used in Unit Installations, Including Unit Substations, Conformance Standard
IEEE C57.12.90 Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers
IEEE C57.12.91 Test Code for Dry-Type Distribution and Power Transformers
IEEE C62.22 Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current Systems
IEEE 80 Guide for Safety in AC Substation Grounding
UL 1062 Unit Substations
UL 1558 Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear
UL 891 Switchboards
UL 845 Motor Control Centers
UL 1562 Transformers, Distribution, Dry-Type, Over 600 Volts
NEMA 250 Enclosures for Electrical Equipment (1000 Volts Maximum)
NFPA 70 National Electrical Code (Articles 110, 215, 230, 240, 250, 450, and 490)
NFPA 70E Standard for Electrical Safety in the Workplace
ANSI/NETA ATS Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems
ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Chapter 13)
ICC-ES AC156 Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components
10 CFR Part 431 Subpart K Energy Conservation Standards for Distribution Transformers

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for review before the assembly is released for manufacture:
  • an assembly outline drawing showing every section in plan and elevation, the shipping splits, the weight and center of gravity of each shipping section, the lifting and jacking provisions, the anchor pattern, the conduit entry areas, and the clearances the manufacturer requires around the assembly
  • a one-line diagram of the assembly showing the primary device, the transformer, the secondary main and tie devices, the feeder devices, the metering, and every instrument transformer, with the rating of each
  • a ratings coordination table stating, for the primary section, the transformer, and the secondary section, the rated voltage, the continuous current, the short-circuit rating, and the basis on which each was established
  • throat and transition drawings showing the bus arrangement through each throat, the flexible connectors, the bracing, the barriers, and the covers
  • the transfer scheme schematic, the sequence of operation, and the interlock diagram for a double-ended assembly
  • the action submittals that Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers requires for the transformer section, that Medium Voltage SwitchgearMedium Voltage SwitchgearResolves to the current adopted revision.sync/medium-voltage-switchgear requires for a metal-clad primary section, and that the governing standard requires for the secondary section construction selected
  • the seismic qualification certificate for the complete assembly as configured, where seismic qualification is required
  • the nameplate schedule listing the text to appear on the assembly, section, and device nameplates
Action Submittal Packagecheckbox
☑ Assembly outline drawing
☑ Assembly one-line diagram
☑ Ratings coordination table
☑ Throat and transition drawings
☐ Transfer scheme schematic and sequence of operation
☑ Section submittals required by each governing standard
☐ Seismic qualification certificate
☑ Nameplate schedule
3.1.2 The assembly shall not be released for manufacture until the action submittals covering it have been reviewed and returned.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following with or before the action submittals:
  • the manufacturer of record's statement of responsibility, identifying the maker of each section and confirming that one party is responsible for the coordinated ratings, the throats, the factory tests of the assembled lineup, and the warranty of the whole
  • the manufacturer's qualification statement required under Quality Assurance
  • the factory test procedure for the assembled lineup, where witnessed testing is selected in the datasheet
  • the field acceptance testing firm's qualification statement and the proposed field test procedure for the assembly
  • the manufacturer's published derating factors applied for ambient temperature and altitude, where either exceeds the usual service conditions of the governing standards
Informational Submittal Packagecheckbox
☑ Manufacturer of record statement of responsibility
☑ Manufacturer qualification statement
☐ Factory test procedure
☑ Field testing firm qualification and test procedure
☐ Ambient and altitude derating factors

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following before the assembly is accepted:
  • the certified factory test report for the assembled lineup and for each section, identified by serial number
  • the field acceptance test report for the assembly, giving every measured value, the acceptance criterion applied, and the tester's determination
  • the recorded sequence of the transfer scheme as tested, for a double-ended assembly
  • record drawings reflecting every field change to the arrangement, the wiring, and the settings
  • the final settings of every protective device, the transformer tap position as set, and the fuse ratings installed
  • the arc-flash incident energy labels installed, with the study revision they were taken from
  • operation and maintenance data covering each section and the assembly as a whole
  • the warranty certificate identifying the assembly serial numbers and the warranty commencement date
  • a signed receipt from the Owner for the spare parts delivered
Closeout Submittal Packagecheckbox
☑ Factory test reports
☑ Field acceptance test report
☐ Transfer scheme as-tested sequence record
☑ Record drawings
☑ Final settings, tap position, and fuse ratings
☐ Arc-flash label record
☑ Operation and maintenance data
☑ Warranty certificate
☑ Spare parts receipt

4 Quality Assurance

4.1 Manufacturer of Record

4.1.1 The source arrangement for the sections of the assembly shall be as indicated in the datasheet.
Source Arrangementradio
○ All three sections manufactured by one manufacturer
○ Transformer of another make integrated by the manufacturer of record
4.1.2 One manufacturer of record shall be responsible for the coordinated ratings of the assembly, the design and construction of every throat and transition, the factory tests of the assembled lineup, the seismic qualification of the assembly, and the warranty of the whole, regardless of who manufactured each section.
NOTE A manufacturer that builds all three sections controls every interface from its own drawings; a manufacturer of record that integrates a transformer of another make draws on a wider choice of transformer designs and prices, and carries the fit-up of a throat to a tank or enclosure it did not draw. In either arrangement the Owner has one party to call, which is what the manufacturer of record requirement secures. (4.1.3)
NOTE A transformer rated to withstand a through-fault and a secondary bus braced for a fault current do not, when bolted together, establish a rating for the assembly; the ratings coordination table and the manufacturer of record's statement are how the assembly's ratings become one party's responsibility. (4.1.4)

4.2 Manufacturer Qualifications

4.2.1 The assembly shall be produced by a manufacturer of record that has furnished unit substations of the voltage class and the secondary construction selected for not less than the period indicated in the datasheet.
Minimum Manufacturer Production Experiencerange
years
351020
4.2.2 The manufacturer of record shall maintain a factory-trained field service organization able to reach the site, and shall state the location of the nearest such office in the qualification statement.

4.3 Listing and Certification of Each Section

4.3.1 The complete assembly shall be listed to UL 1062, or each section shall be listed or certified to its governing standard as stated in this article, as indicated in the datasheet.
Assembly Listing Basisradio
○ Complete assembly listed to UL 1062
○ Each section listed or certified to its own governing standard
NOTE A UL 1062 listing covers the assembly as one product, including the throats, and is the basis an Authority Having Jurisdiction accepts without evaluating the interfaces; a per-section basis covers each section under its own listing or certification and leaves the throats to the manufacturer of record's certification, and it is the basis under which a metal-clad primary section or a transformer of another make is most often furnished. (4.3.2)
4.3.3 The secondary section shall be listed by a Nationally Recognized Testing Laboratory to UL 1558 where low-voltage power circuit breaker switchgear construction is selected, to UL 891 where switchboard construction is selected, or to UL 845 where motor control center construction is selected.
4.3.4 A dry-type transformer section shall be listed to UL 1562 and shall comply with IEEE C57.12.55.
4.3.5 A liquid-immersed transformer section shall comply with IEEE C57.12.00 and IEEE C57.12.36 and shall bear the manufacturer's certification of compliance.
4.3.6 A load-interrupter switch primary section shall comply with IEEE C37.20.3, and a metal-clad primary section shall comply with IEEE C37.20.2, each with the manufacturer's certification of compliance.
4.3.7 The transformer section shall meet the efficiency 10 CFR Part 431 Subpart K requires for its category, and the certification of compliance shall be furnished with the action submittals.

4.4 Field Testing Firm

4.4.1 Field acceptance testing of the assembly shall be performed by the firm indicated in the datasheet.
Field Acceptance Testing Firmradio
○ Independent testing firm accredited to ANSI/NETA ATS
○ Manufacturer of record's field service organization
○ Installing contractor's own technicians
NOTE An independent firm has no stake in whether the assembly passes and reports against a published acceptance standard; the manufacturer of record's organization knows the throats and the transfer scheme best and is already on site for start-up; the installing contractor's own technicians cost least and are available on the installer's schedule. Which of these the Owner wants depends on how the results will be used, and on whether a report from the party who built or installed the equipment would satisfy the Owner's insurer and the Authority Having Jurisdiction. (4.4.2)
4.4.3 The field testing firm shall be qualified in accordance with Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing, and its technicians shall hold a current certification for medium-voltage and low-voltage equipment testing from NETA or from the manufacturer of the equipment tested.

5 Environmental and Service Conditions

5.1 Ambient Temperature

5.1.1 The assembly shall carry its nameplate ratings at the design ambient temperature of the room indicated in the datasheet.
Indoor Design Ambient Temperaturerange
°C
30404550
NOTE The usual service conditions of IEEE C37.20.1, IEEE C37.20.2, IEEE C37.20.3, IEEE C57.12.00, and IEEE C57.12.01 all establish the ratings at a 40 °C maximum ambient, so a 40 °C design ambient is the condition at which every section's nameplate applies without correction; a higher value buys margin for a room whose ventilation cannot hold that ambient with the transformer at design load, at the cost of a larger bus or a larger transformer for the same nameplate. (5.1.2)
5.1.3 Where the assembly is installed outdoors and Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum exceeds 40 °C, the manufacturer of record shall derate each section in accordance with the published factors of its governing standard and shall state the derated ratings in the ratings coordination table.
5.1.4 Where the assembly is installed outdoors or in an unconditioned space, the enclosure space heaters shall be sized to hold the interior of every section above the dew point at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum.

5.2 Altitude

5.2.1 Each section of the assembly shall be derated for AltitudeAltitudeParameterEach project supplies its own value.altitude in accordance with the correction factors of its governing standard where the altitude exceeds that standard's usual service condition, and the derated ratings shall be stated in the ratings coordination table.
NOTE Air thins with altitude, which reduces both the dielectric strength of the air clearances in the primary section and the convective cooling that sets the transformer rating and the secondary bus rating, so the three sections lose capability at different rates and the assembly rating at elevation is the lowest of the three corrected values. (5.2.2)
5.2.3 Ambient temperature derating and altitude derating shall be applied cumulatively where both conditions apply.

5.3 Seismic Qualification

5.3.1 The seismic qualification of the assembly shall be as indicated in the datasheet.
Seismic Qualificationselect
Not required
Shake-table qualification per ICC-ES AC156 with component importance factor 1.0
Shake-table qualification per ICC-ES AC156 with component importance factor 1.5
Qualification by analysis per ASCE 7 Chapter 13
Derived — Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category and the component importance factor ASCE 7 Chapter 13 assigns to the assembly (by default)
5.3.2 Where seismic qualification is required, it shall be performed in accordance with the seismic provisions of Adopted Building CodeAdopted Building CodeParameterEach project supplies its own value.adopted-building-code and ASCE 7 Chapter 13.
NOTE Whether the assembly must be qualified follows from the seismic design category, and whether it must remain operable after the design earthquake, rather than merely stay anchored, follows from the component importance factor; neither is decided within this standard. (5.3.3)
5.3.4 Seismic qualification shall cover the complete assembly in the configuration shipped, including the transformer, every throat, and the heaviest arrangement of devices in any section, and a certificate covering one section apart from the others shall not be accepted as qualification of the assembly.
NOTE The transformer and the sections it is coupled to respond to ground motion as one body only if the throats and the anchorage make them one; a certificate for the transformer alone and another for the switchgear alone say nothing about the throat between them, which is the part that fails when the two move differently. (5.3.5)

6 Substation Arrangement

6.1 Single-Ended and Double-Ended Arrangement

6.1.1 The substation arrangement shall be as indicated in the datasheet.
Substation Arrangementselect
Single-ended
Double-ended, tie normally open
Double-ended, tie normally closed with transformers paralleled
Per drawings — the one-line diagram (deferred by default)
NOTE A single-ended substation has one primary section, one transformer, and one secondary section, and a loss of the transformer or its primary feeder drops every load it serves. A double-ended substation has two of each joined by a tie device in the secondary bus, so that either transformer can carry the loads of both when the other is out of service; with the tie normally open each transformer carries its own bus and the loads see a transfer when one source is lost, and with the tie normally closed the two transformers share every load continuously and the loads see no transfer, at the cost of a secondary fault current that is the sum of both transformers' contributions and of protection that must distinguish a fault on one side from a fault on the other. (6.1.2)
6.1.3 Where a double-ended arrangement is selected, each transformer and each secondary bus shall be rated to carry the combined load of both buses with the tie closed and one primary source out of service, at the transformer's highest cooling stage.
6.1.4 Where a double-ended arrangement is selected, the two transformers shall have the same kVA rating, the same voltage ratings, the same vector group, and impedances within 7.5 percent of each other on a common kVA base.
NOTE Two transformers that will share a bus, even briefly during a closed-transition retransfer, divide the load in inverse proportion to their impedances and circulate current between them where their vector groups or tap positions differ, so the matching requirements are what make the tie safe to close. (6.1.5)

6.2 Tie Transfer Scheme

6.2.1 Where a double-ended arrangement is selected, the tie transfer scheme shall be as indicated in the datasheet.
Tie Transfer Schemeselect
Manual transfer at the devices
Automatic open-transition transfer with manual retransfer
Automatic open-transition transfer and automatic open-transition retransfer
Automatic open-transition transfer with closed-transition retransfer
Not applicable, single-ended arrangement
NOTE A manual scheme leaves the operator to open the failed main and close the tie, which costs an outage lasting as long as it takes someone to reach the substation and is the arrangement where the loads can tolerate that or where an attendant is always present. An automatic open-transition scheme senses loss of voltage on one bus, opens that main, and closes the tie after a time delay, so the outage lasts seconds; manual retransfer leaves the return to normal to an operator who can choose the moment, where automatic retransfer returns the substation to normal unattended and imposes a second brief outage on the transferred loads when it does. A closed-transition retransfer parallels the two sources for the moments it takes to close the returning main and open the tie, so the loads see no second outage, at the cost of a synchronism check, a short-circuit duty on the secondary that briefly includes both transformers, and a primary system that both sources must be in phase with. (6.2.2)
6.2.3 Where an automatic transfer scheme is selected, loss of source shall be sensed by undervoltage relays on each secondary bus, with an adjustable time delay before transfer so that a momentary primary voltage dip does not initiate a transfer.
6.2.4 Where an automatic transfer scheme is selected, the scheme shall not transfer where the main device opened on an overcurrent or ground-fault trip, and shall indicate a lockout that requires a manual reset.
NOTE Closing the tie onto a bus whose main tripped on a fault puts the second transformer onto the same fault, so the scheme distinguishes a lost source from a cleared fault before it acts. (6.2.5)
6.2.6 Where automatic retransfer is selected, retransfer shall be delayed for an adjustable period after the source returns so that an unstable source does not cause repeated transfers.
6.2.7 Where closed-transition retransfer is selected, the parallel shall be permitted only through a synchronism check, and the scheme shall limit the paralleled period to the duration stated in the submittal and shall trip the tie where that duration is exceeded.
6.2.8 The transfer scheme controls, including an automatic-manual selector switch, mode and position indication, and a test provision, shall be mounted in a control compartment of the secondary section and shall be powered from a control source that remains available with either main device open.

6.3 Tie Interlocking

6.3.1 Where a double-ended arrangement is selected, the interlocking of the two main devices and the tie device shall be as indicated in the datasheet.
Main and Tie Interlocking Methodselect
Mechanical key interlock
Electrical interlock in the device control circuits
Mechanical key interlock and electrical interlock
Not applicable, single-ended arrangement
NOTE A key interlock enforces the two-of-three rule with a physical key that cannot be in two locks at once, which no loss of control power or wiring error defeats, and it governs only manually operated devices; an electrical interlock enforces the same rule through the devices' control circuits and is what an automatic scheme depends on, and it is only as good as the control power and the wiring behind it. Both together give an automatic scheme a backstop that holds when its control power fails, at the cost of keys that must be managed. (6.3.2)
6.3.3 Unless the datasheet selects a tie normally closed with transformers paralleled or a closed-transition retransfer, the interlocking shall prevent more than two of the two main devices and the tie device from being closed at one time.
6.3.4 Where the datasheet selects a tie normally closed with transformers paralleled, the interlocking shall instead prevent the tie from being closed where either main device is open and the opposite bus is de-energized, and the secondary protection shall be arranged so that a fault on one bus trips the tie and that bus's main while the other bus remains energized.
6.3.5 An electrical interlock shall be wired so that a loss of control power leaves every device in its position and blocks further operation rather than opening or closing any device.

7 Coordinated Ratings Across Sections

7.1 System Voltage and Frequency

7.1.1 The primary nominal system voltage shall be as indicated in the datasheet.
Primary Nominal System Voltagerange
kV
2.44.164.86.97.21212.4713.213.814.420.822.92324.934.5
Per drawings — the one-line diagram (deferred by default)
7.1.2 The secondary system voltage and configuration shall be as indicated in the datasheet.
Secondary System Voltageselect
208Y/120 V 3Φ 4-wire
240 V 3Φ 3-wire delta
240/120 V 3Φ 4-wire high-leg delta
480Y/277 V 3Φ 4-wire
480 V 3Φ 3-wire delta
600Y/347 V 3Φ 4-wire
600 V 3Φ 3-wire delta
Per drawings — the one-line diagram (deferred by default)
7.1.3 The system frequency shall be as indicated in the datasheet.
System Frequencyradio
● 60 Hz
○ 50 Hz
7.1.4 Whether the primary section is the service disconnecting means shall be as indicated in the datasheet.
Service Configurationradio
○ Primary section is the service disconnecting means for a medium-voltage service
○ Fed from premises medium-voltage distribution downstream of the service
Per drawings — the one-line diagram (deferred by default)
7.1.5 Where the primary section is the service disconnecting means, it shall comply with NFPA 70 Article 230 Part VIII and Article 490, shall carry the available fault current marking NFPA 70 110.24 requires, and shall provide the metering, sealing, and access provisions the serving utility requires.
7.1.6 The Contractor shall confirm the serving utility's nominal primary voltage, its system grounding, and the available fault current at the point of connection with the utility before the assembly is released for manufacture, and shall report any difference from the one-line diagram to the Engineer of Record.

7.2 Transformer Rating and Impedance

7.2.1 The transformer self-cooled kVA rating shall be as indicated in the datasheet.
Transformer Self-Cooled kVA Ratingrange
kVA
112.51502253005007501000150020002500300037505000750010000
Per drawings — the one-line diagram (deferred by default)
7.2.2 The transformer cooling stages shall be as indicated in the datasheet.
Transformer Cooling Stagesselect
Self-cooled only
Self-cooled with one forced-air stage
Self-cooled with provisions for a future forced-air stage
NOTE A forced-air stage adds capacity without adding core and is the least expensive kVA a transformer can carry, but a secondary bus sized for the self-cooled rating cannot carry the forced-air output, and a bus cannot be enlarged in the field; so the cooling stage is decided with the secondary bus in view, and a future stage is bought by sizing the bus for it now. In a double-ended substation the forced-air stage is often what lets one transformer carry both buses. (7.2.3)
7.2.4 The transformer percent impedance at the rated tap shall be as indicated in the datasheet.
Transformer Percent Impedance at Rated Taprange
%
22.533.544.555.55.7566.577.588.5910
7.2.5 Where no impedance is selected in the datasheet, the manufacturer of record shall apply its standard impedance for the rating and construction and shall report the design value in the ratings coordination table for use in the short-circuit study.
NOTE Impedance sets the secondary fault current and the voltage regulation together: a lower impedance delivers a stiffer secondary and a higher fault current the secondary section must withstand and interrupt, and a higher impedance limits the fault current at the cost of more voltage drop under load. In a unit substation the impedance is the single transformer value the secondary section's rating depends on most, which is why it is reported in the coordination table even when the manufacturer's standard value is accepted. (7.2.6)
7.2.7 The transformer impedance shall not be changed from the value in the reviewed ratings coordination table without the short-circuit study being revised and the secondary section rating being confirmed against the revised study.

7.3 Primary Section Ratings

7.3.1 The rated maximum voltage of the primary section shall be as indicated in the datasheet.
Primary Section Rated Maximum Voltagerange
kV
4.768.251515.52738
Derived — the primary nominal system voltage, per the voltage classes of IEEE C37.20.3 for a load-interrupter switch section or IEEE C37.20.2 for a metal-clad section (by default)
7.3.2 The short-circuit rating of the primary section shall be as indicated in the datasheet.
Primary Section Short-Circuit Ratingrange
kA
12.516202531.5405063
Derived — the available symmetrical fault current at the primary terminals established by the short-circuit study, with the momentary, fault-closing, and interrupting ratings of the section each not less than the corresponding duty (by default)
NOTE A load-interrupter switch carries a momentary and a fault-closing rating but no interrupting rating, and its fuses interrupt the fault; a circuit breaker carries all three. The study establishes the duty, and the section is rated to it, so the field records a consequence of the one-line diagram rather than a preference. (7.3.3)
7.3.4 The continuous current rating of the primary section shall be not less than the transformer's full-load primary current at its highest cooling stage, and where the primary section also feeds through to other equipment, not less than the sum of that current and the feed-through load.
7.3.5 The primary section insulation level shall be the BIL IEEE C37.20.3 or IEEE C37.20.2 assigns to its rated maximum voltage, corrected for AltitudeAltitudeParameterEach project supplies its own value.altitude where the altitude exceeds the usual service condition.

7.4 Secondary Section Ratings

7.4.1 The secondary main bus continuous current rating shall be as indicated in the datasheet.
Secondary Main Bus Continuous Currentrange
A
6008001000120016002000250030003200400050006000
Derived — the transformer's full-load secondary current at its highest cooling stage and the secondary system voltage, with the bus rated not less than that current (by default)
7.4.2 Where a double-ended arrangement is selected, the tie device and the bus on each side of it shall be rated not less than the secondary main bus continuous current rating, so that either transformer can carry both buses through the tie.
7.4.3 The secondary section short-circuit current rating shall be as indicated in the datasheet.
Secondary Section Short-Circuit Current Ratingrange
kA
2225303542506585100150200
Derived — the available symmetrical fault current at the secondary bus established by the short-circuit study, including the contribution of both transformers where the tie can be closed and the contribution of connected motors (by default)
NOTE A bus stamped 65 kA looks the same as one stamped 42 kA, and the only thing that tells whether either is enough is the fault current the transformer's kVA and impedance deliver, so the rating is a consequence of the transformer selected and the study that evaluates it. In a double-ended substation the duty with the tie closed, even for the moments of a closed-transition retransfer, is the duty the bus is rated for. (7.4.4)
7.4.5 The secondary section short-circuit current rating shall be established as a rating of the assembled secondary section under its governing standard, and shall not be established by combining the ratings of its components on paper.
7.4.6 Every feeder device in the secondary section shall be fully rated for the secondary section short-circuit current rating, unless the datasheet of the governing secondary section standard selects series rating and the tested combinations are marked in accordance with NFPA 70 110.22.
7.4.7 Where the datasheet of the governing secondary section standard selects series rating in a double-ended assembly, each series-rated combination shall be tested with the main device and with the tie device as the upstream device.

7.5 Ground-Fault Protection and System Grounding

7.5.1 The secondary system grounding shall be as indicated in the datasheet.
Secondary System Groundingselect
Solidly grounded
High-resistance grounded
Low-resistance grounded
Ungrounded
NOTE A solidly grounded secondary is the arrangement a four-wire system with line-to-neutral loads requires and is the arrangement most building substations are built with; a high-resistance grounded secondary limits a ground fault to a few amperes so that a faulted feeder keeps running until it is found, which suits a three-wire process system where an unplanned stop costs more than a controlled one, and it cannot serve line-to-neutral loads; a low-resistance grounded secondary limits the ground fault to hundreds of amperes so that relays can clear it selectively, which is the arrangement of medium-voltage practice carried down to a 600 V process system; an ungrounded delta secondary is the arrangement of some older plants and carries transient overvoltages during an arcing ground fault that the other three limit. (7.5.2)
7.5.3 Where high-resistance grounding is selected, the grounding resistor, its pulsing contactor, the ground-fault alarm, and the fault-locating indication shall be furnished within the assembly by the manufacturer of record, and the resistor shall be sized so that its let-through current exceeds the system's capacitive charging current.
7.5.4 Where high-resistance or low-resistance grounding is selected, the resistor shall be connected between the transformer secondary neutral terminal and the assembly ground bus, and no other connection between the secondary neutral and ground shall be made anywhere in the assembly.
7.5.5 Ground-fault protection of equipment on the secondary main device shall be as indicated in the datasheet.
Ground-Fault Protection of Equipment on the Secondary Mainradio
○ Not provided
○ Provided
Derived — NFPA 70 230.95 and 215.10 applied to the secondary system voltage to ground, the secondary system grounding, and the secondary main device rating (by default)
NOTE Whether the secondary main must carry ground-fault protection of equipment is fixed by code from the system grounding, the voltage to ground, and the device rating, so the field records the consequence of those inputs rather than a preference; a project may add ground-fault protection where code does not require it. (7.5.6)
7.5.7 Where ground-fault protection of equipment is provided on a double-ended assembly, the tie device shall carry ground-fault protection coordinated with that on the main devices, and the ground-fault sensing shall be arranged so that a fault on either bus is sensed correctly with the tie open and with the tie closed.
NOTE A ground-fault scheme that reads the neutral current of one transformer reads wrong the moment the tie closes and the neutral current divides between two transformers, which is why the sensing on a double-ended substation is designed for both states rather than copied from a single-ended one. (7.5.8)
7.5.9 Where ground-fault protection of equipment is provided, it shall be performance-tested at the site in accordance with NFPA 70 230.95(C) before the assembly is energized, and the test record shall be included in the field acceptance test report.
7.5.10 The location of the system bonding jumper shall be as indicated in the datasheet.
System Bonding Jumper Locationradio
● At the transformer secondary neutral terminal
○ At the secondary main device
7.5.11 The system bonding jumper and the grounding electrode conductor connection shall be installed at the location selected and at no other point, in accordance with NFPA 70 250.30, and the secondary neutral bus shall be insulated from the structure everywhere else.

8 Primary Section

8.1 Primary Section Type

8.1.1 The primary section type shall be as indicated in the datasheet.
Primary Section Typeselect
Air terminal chamber with no switching device
Load-interrupter switch without fuses
Load-interrupter switch with power fuses
Metal-clad drawout circuit breaker switchgear
Per drawings — the one-line diagram (deferred by default)
NOTE An air terminal chamber terminates the primary cable at the transformer and leaves both switching and protection to the upstream device, so it is the smallest and least costly primary and depends on that device being dedicated to the transformer and reachable to isolate it. A load-interrupter switch adds a visible, lockable means to isolate the transformer at the substation and can make and break load current but not fault current; with power fuses it also clears a transformer fault, and the fuse is replaced rather than reset. A metal-clad circuit breaker section interrupts faults and is reset after them, carries protective relays that can be set for the transformer's damage curve and coordinated with the rest of the system, and offers drawout maintenance, at the largest footprint and the highest cost, which is what recommends it where the primary is looped or utility-interconnected, where the transformer protection must coordinate closely, or where a fuse outage cannot be tolerated. (8.1.2)
8.1.3 Where an air terminal chamber with no switching device is selected, the Contractor shall confirm that the upstream device shown on the one-line diagram provides the transformer primary overcurrent protection NFPA 70 450.3 requires and a lockable disconnecting means for the transformer, and shall report any shortfall to the Engineer of Record before the assembly is released for manufacture.
8.1.4 Where a load-interrupter switch without fuses is selected, the transformer primary overcurrent protection shall be provided by the upstream device shown on the one-line diagram, and the switch shall be interlocked with that device so that the switch cannot be opened or closed with the upstream device closed, unless the switch is rated for the load-break duty and the Engineer of Record accepts live switching in writing.

8.2 Load-Interrupter Switch and Power Fuses

NOTE Requirements in this article apply where the datasheet selects a load-interrupter switch primary section. (8.2.1)
8.2.2 The load-interrupter switch shall be a three-pole, two-position, gang-operated air switch complying with IEEE C37.20.3, with a quick-make, quick-break stored-energy operating mechanism independent of the operator's speed, rated for the primary section rated maximum voltage, the continuous current, and the momentary and fault-closing duty established under Coordinated Ratings Across Sections.
8.2.3 The switch shall be furnished with a viewing window through which the position of every blade can be verified with the door closed, and with mechanical position indication at the operating handle.
8.2.4 The switch operating handle shall be lockable in the open and closed positions and shall accept not fewer than three padlocks in the open position.
8.2.5 The switch compartment door shall be interlocked so that it cannot be opened with the switch closed and the switch cannot be closed with the door open, with a tool-operable defeat for authorized testing.
8.2.6 Where power fuses are selected, the power fuse type shall be as indicated in the datasheet.
Power Fuse Typeradio
○ Current-limiting power fuses
○ Solid-material expulsion power fuses
NOTE A current-limiting fuse clears a high-magnitude fault within the first half cycle and limits the peak current the transformer and the secondary section see, which is what lets the downstream equipment carry a rating below the prospective fault current, and it vents no gas, so it is applied indoors without provision for discharge; a solid-material expulsion fuse clears every current within its range in a single element with a time-current characteristic that coordinates more easily with the transformer's inrush and damage curve, and it discharges gas on operation, which an indoor installation handles with a muffler or an exhaust provision. (8.2.7)
8.2.8 Power fuses shall comply with IEEE C37.46 and shall be applied in accordance with IEEE C37.48, with a fuse interrupting rating not less than the primary section short-circuit rating.
8.2.9 The fuse ratings shall be those established by the coordination study performed under Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study for the transformer's inrush and through-fault damage characteristics, and the Contractor shall not install fuse elements of a rating other than the rating the study establishes.
8.2.10 Fuse mountings shall be of the disconnect type, de-energized and isolated with the switch open, and accessible for replacement from the front of the section with the door open.
8.2.11 Where current-limiting fuses are selected, each fuse shall carry a blown-fuse indicator visible with the door closed, and the fuse mountings shall accept a blown-fuse trip device where the datasheet selects one.

8.3 Metal-Clad Circuit Breaker Primary

NOTE Requirements in this article apply where the datasheet selects a metal-clad drawout circuit breaker primary section. (8.3.1)
8.3.2 A metal-clad primary section shall comply with Medium Voltage SwitchgearMedium Voltage SwitchgearResolves to the current adopted revision.sync/medium-voltage-switchgear as requirements of this standard, except that its ratings shall be those established under Coordinated Ratings Across Sections and its enclosure, throat, and factory testing shall be as this standard requires for the assembly.
8.3.3 The transformer protective relaying in a metal-clad primary section shall include phase and ground overcurrent protection set in accordance with the coordination study, and shall accept the transformer protective-device actions wired to it under Transformer Section.
8.3.4 Where a metal-clad primary section is selected for a double-ended assembly, each primary breaker shall be interlocked with the transfer scheme so that a primary breaker trip initiates the same transfer as a loss of source.

8.4 Primary Cable Termination

8.4.1 The primary cable termination arrangement shall be as indicated in the datasheet.
Primary Cable Termination Arrangementselect
Air-insulated cable terminations on bus stabs in a cable compartment
Dead-front separable connectors, 200 A loadbreak
Dead-front separable connectors, 600 A deadbreak
Medium-voltage bus duct entry
NOTE Air-insulated terminations land a stress-cone termination on a bus stab in a compartment sized for the bending and training of the cable, and accept any cable size the compartment is sized for; separable connectors mate the cable to the section through elbows on bushings so that no energized primary part is exposed once the connectors are made up, with a 200 A loadbreak elbow limited to the cable and current that rating accepts and a 600 A deadbreak connector for larger cable and higher loop current; a bus duct entry receives a medium-voltage bus duct from the upstream switchgear and has no cable at all. (8.4.2)
8.4.3 The primary cable compartment shall be sized to receive the number and size of primary cables as indicated on the one-line diagram and the conduit and cable schedule, with space to make up a termination on each cable without bending the cable below its minimum radius, and the terminations themselves shall comply with Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables.
8.4.4 The primary cable compartment shall be furnished with a grounding provision for the cable shields and for a portable grounding set, and with a barrier between the cable compartment and the switch or breaker compartment.

8.5 Primary Section Provisions

8.5.1 The primary section shall be furnished with the provisions indicated in the datasheet.
Primary Section Provisionscheckbox
☐ Integral grounding switch, interlocked with the main switch
☐ Key interlock with the upstream device
☐ Blown-fuse trip of the switch
☐ Motor operator for the switch
☐ Metal-oxide surge arresters in the primary section
☐ Shunt trip of the switch from the transformer protective devices
☐ Capacitive voltage indicators on the primary bus
☐ Infrared inspection windows at the cable terminations
NOTE A grounding switch grounds the de-energized primary bus and the transformer winding before work begins and depends on an interlock to keep it off an energized bus; a blown-fuse trip opens the switch when one fuse operates, so that the transformer does not run single-phased on the remaining two, which is the condition that overheats a transformer and the motors it serves; a motor operator lets a switch be opened or closed from outside the arc-flash boundary and is what a transfer scheme needs if it is to act on the primary side; surge arresters at the primary terminals protect the transformer winding against surges arriving on the cable, with protective margin applied per IEEE C62.22; a shunt trip lets a winding temperature or sudden-pressure device remove the transformer from the system rather than only alarm. (8.5.2)
8.5.3 Where a motor operator is furnished on a load-interrupter switch, the switch shall be manually operable with the motor operator installed, and the manual operation shall be blocked while the motor operator is in motion.

8.6 Primary Arc-Resistant Construction

8.6.1 Arc-resistant construction of the primary section shall be as indicated in the datasheet.
Primary Section Arc-Resistant Constructionselect
Not required
Type 1 accessibility per IEEE C37.20.7
Type 2 accessibility per IEEE C37.20.7
Type 2B accessibility per IEEE C37.20.7
NOTE Arc-resistant construction directs the products of an internal arcing fault away from the front of the section, Type 2 extends that protection to the sides and rear, and Type 2B keeps it with the low-voltage control compartment door open. On a medium-voltage section the incident energy is high enough that arc-resistant construction, a motor operator, or both are often what brings the labeled personal protective equipment category to a workable level, and the construction adds a plenum, reinforced doors, and pressure-relief flaps that raise the height and the cost of the section and that must discharge somewhere the room can accept. (8.6.2)
8.6.3 Where arc-resistant construction is selected, the section shall have been tested to IEEE C37.20.7 in the configuration furnished, including the throat to the transformer, and the exhaust plenum and its discharge location shall be shown on the shop drawings and coordinated with Electrical RoomsElectrical RoomsResolves to the current adopted revision.sync/electrical-rooms.
NOTE Arc-resistant construction does not lower the incident energy at a section whose door is open, and the throat between an arc-resistant section and a transformer that is not arc-resistant is the boundary of the tested protection. (8.6.4)

9 Transformer Section

9.1 Transformer Medium

9.1.1 The transformer insulating medium and winding encapsulation shall be as indicated in the datasheet.
Transformer Insulating Medium and Winding Encapsulationradio
○ Liquid-immersed
○ Dry-type, open-wound, vacuum-pressure-impregnated
○ Dry-type, vacuum-pressure-encapsulated
○ Dry-type, cast-resin
NOTE A liquid-immersed section is the smallest and lowest-loss transformer for a given rating and tolerates outdoor exposure in its own tank, and it brings a fire-point and spill-containment obligation that decides whether the assembly can stand in a room, needs a vault, or belongs outdoors; a dry-type section has no liquid to contain or burn and is the construction most often set inside an occupied building, and it is larger, heavier, and higher in loss, and depends on the room's ventilation to carry away the heat a liquid unit sheds through its tank. Vacuum-pressure-impregnated windings are the lowest-cost dry-type construction, vacuum-pressure-encapsulated windings seal the coil surface against moisture and contaminants, and cast-resin windings are impervious to moisture and strongest against short-circuit forces at the highest first cost. (9.1.2)
NOTE The transformer type decides the fire-protection and vault requirements of the whole installation, the enclosure the assembly needs, and the standard the transformer section is built to, so it is decided with the room or yard in view rather than against first cost alone. (9.1.3)

9.2 Transformer Requirements by Reference

9.2.1 The transformer section shall comply with Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers as a substation-type transformer of the medium selected, applied as requirements of this standard, except that its kVA rating, cooling stages, impedance, and secondary voltage shall be as established under Coordinated Ratings Across Sections, its terminations shall be the throats this standard requires, and its enclosure and factory testing shall be as this standard requires for the assembly.
9.2.2 A dry-type transformer section shall in addition comply with IEEE C57.12.55 for its integration with the primary and secondary sections, and a liquid-immersed transformer section shall in addition comply with IEEE C57.12.36.
NOTE IEEE C57.12.55 and IEEE C57.12.36 carry the throat dimensions, the terminal arrangements, and the enclosure interfaces that let a transformer couple to switchgear, which the general requirements standards do not, so a transformer section built only to IEEE C57.12.00 or IEEE C57.12.01 is a transformer and not yet a section. (9.2.3)
9.2.4 The transformer vector group shall be a delta primary with a grounded-wye secondary, Dyn1, unless the datasheet of Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers as applied to this section selects otherwise.
9.2.5 Where the transformer is a dry-type unit, its enclosure shall be ventilated so that the full-load losses at the highest cooling stage are carried away at the indoor design ambient temperature with the throats and the adjacent sections in place, and the ventilation openings shall not be obstructed by either throat.

9.3 Transformer Protective Device Actions

9.3.1 The transformer protective devices shall be wired within the assembly to produce the actions indicated in the datasheet.
Transformer Protective Device Actions Wired Within the Assemblycheckbox
☑ Winding temperature alarm to the annunciator or the monitoring interface
☐ Winding temperature trip of the secondary main device
☐ Winding temperature trip of the primary device
☑ Forced-air fan start from winding temperature
☐ Sudden-pressure relay trip of the primary device on a liquid-immersed section
☐ Liquid level and liquid temperature alarms on a liquid-immersed section
☐ Pressure-relief device operation alarm on a liquid-immersed section
☐ Transformer differential protection across the primary device and the secondary main
NOTE An alarm tells an operator the transformer is in trouble and leaves the response to them; a trip of the secondary main removes the load and leaves the transformer energized, which stops the overload but not an internal fault; a trip of the primary device de-energizes the transformer and is the action that stops an internal fault, and it is available only where the primary device can be tripped, which an unfused switch or a terminal chamber cannot. A sudden-pressure relay detects the pressure wave of an internal arc in a liquid-immersed tank faster than any device that senses current. Differential protection compares the current entering the primary with the current leaving the secondary and trips on the difference, which clears an internal fault without waiting for an overcurrent device to reach into the transformer, at the cost of current transformers on both sides and a relay to compare them. (9.3.2)
9.3.3 Where a trip of the primary device is selected, the primary section shall be furnished with the shunt trip or the motor operator the action requires, and the action shall be wired through a lockout relay that requires a manual reset at the assembly.
9.3.4 Every protective-device action wired between sections shall be routed through the throats or through a wireway furnished by the manufacturer of record, shall be terminated on terminal blocks in each section, and shall be shown on the schematic diagrams submitted.

10 Secondary Section

10.1 Secondary Section Construction

10.1.1 The secondary section construction shall be as indicated in the datasheet.
Secondary Section Constructionselect
Low-voltage power circuit breaker switchgear
Low-voltage switchboard
Motor control center
NOTE Low-voltage power circuit breaker switchgear carries drawout breakers that are each rated to carry and interrupt the full bus fault current and that can be withdrawn for maintenance with the bus energized, in a compartmentalized structure tested to IEEE C37.20.1, at the largest footprint and the highest cost; a switchboard carries group-mounted or individually mounted molded-case or insulated-case breakers in a structure tested to UL 891, at a smaller footprint and lower cost, with maintenance that generally requires a bus outage; a motor control center puts plug-in motor controllers directly on the transformer secondary and suits a substation whose loads are predominantly motors controlled from the substation. The choice follows from how the secondary will be maintained, what it serves, and how much floor the room has. (10.1.2)
10.1.3 A secondary section of low-voltage power circuit breaker switchgear construction shall comply with Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current adopted revision.sync/low-voltage-switchgear as requirements of this standard, a secondary section of switchboard construction shall comply with Low Voltage SwitchboardsLow Voltage SwitchboardsResolves to the current adopted revision.sync/low-voltage-switchboards, and a secondary section of motor control center construction shall comply with Motor Control CentersMotor Control CentersResolves to the current adopted revision.sync/motor-control-centers, in each case except that its ratings shall be those established under Coordinated Ratings Across Sections, its incoming connection shall be the throat this standard requires, and its enclosure and factory testing shall be as this standard requires for the assembly.
10.1.4 The feeder devices, their frame and trip ratings, and the loads they serve shall be as indicated on the one-line diagram.

10.2 Secondary Main Device

10.2.1 The secondary main device shall be as indicated in the datasheet.
Secondary Main Device Typeselect
Drawout low-voltage power circuit breaker
Fixed-mounted insulated-case circuit breaker
Fixed-mounted molded-case circuit breaker
Bolted-pressure fused switch
No secondary main device
Per drawings — the one-line diagram (deferred by default)
NOTE A drawout power circuit breaker is the main a switchgear section is built around and can be withdrawn for maintenance; an insulated-case breaker is the main most switchboard sections carry and is fixed-mounted or individually drawout; a molded-case breaker is the smallest and least costly main and is available at the lower bus ratings; a bolted-pressure fused switch carries the highest interrupting rating in the smallest space and clears a high-magnitude fault fastest, at the cost of a fuse replacement after every fault; a secondary with no main device connects the bus directly to the transformer and relies on the primary device for the transformer's secondary protection, which NFPA 70 450.3 permits only within stated limits in a supervised location. (10.2.2)
10.2.3 Where no secondary main device is selected, the transformer primary overcurrent protection shall satisfy NFPA 70 450.3 for a transformer without secondary protection, and the installation shall be one NFPA 70 450.3 recognizes as a supervised location, confirmed by the Engineer of Record in writing before the assembly is released for manufacture.
10.2.4 Where a double-ended arrangement is selected, the tie device shall be of the same type and frame as the main devices, and the two main devices and the tie device shall be electrically operated where an automatic transfer scheme is selected.
10.2.5 Where a circuit breaker main or tie device is rated or can be adjusted to 1200 A or more, arc energy reduction shall be provided in accordance with NFPA 70 240.87 by the method the governing secondary section standard selects, and the method shall act on the main and the tie alike.

10.3 Secondary Arc-Resistant Construction

10.3.1 Arc-resistant construction of the secondary section shall be as indicated in the datasheet.
Secondary Section Arc-Resistant Constructionselect
Not required
Type 1 accessibility per IEEE C37.20.7
Type 2 accessibility per IEEE C37.20.7
Type 2B accessibility per IEEE C37.20.7
NOTE The low-voltage section is where most of the hands-on work happens and where a transformer's full fault current arrives, so its arc-resistant construction protects the workers who most often stand at the assembly; it is available in switchgear construction and in some switchboard and motor control center constructions, it adds a plenum and height to the section, and it does not reduce the incident energy at a section whose door is open, which is what arc energy reduction under NFPA 70 240.87 addresses. (10.3.2)
10.3.3 Where arc-resistant construction is selected for the secondary section, the section shall have been tested to IEEE C37.20.7 in the configuration furnished, including the throat to the transformer, and the exhaust plenum and its discharge location shall be shown on the shop drawings.

10.4 Secondary Metering and Monitoring

10.4.1 Metering in the secondary section shall be as indicated in the datasheet.
Secondary Meteringselect
No metering
Multifunction power meter on each secondary main
Multifunction power meter on each secondary main and on each feeder
NOTE A meter on the main records what the transformer carries, which is the figure a loading study, an energy submeter, and a demand record all want; a meter on every feeder adds the split of that load among the feeders, which serves a tenant allocation or a measurement and verification program, at the cost of a meter and current transformers in every feeder compartment and a compartment deep enough to hold them. (10.4.2)
10.4.3 Meters and their current and potential transformers shall comply with Electrical Power MonitoringElectrical Power Monitoring and MeteringResolves to the current adopted revision.sync/electrical-power-monitoring and shall be installed by the manufacturer of record in a compartment of the secondary section of its own construction.
10.4.4 Primary metering shall be as indicated in the datasheet.
Primary Meteringselect
No primary metering
Utility revenue metering compartment in the primary section
Owner's primary metering with current and potential transformers
Per drawings — the one-line diagram (deferred by default)
NOTE Utility revenue metering at the primary is furnished where the service point is at medium voltage and the utility bills on the primary side; it is built to the utility's metering requirements, which fix the compartment, the instrument transformers, and the sealing, and it must be coordinated with the utility before the primary section is drawn. Owner's primary metering serves a campus distribution system that allocates energy by substation, and it is built to the Owner's monitoring standard rather than the utility's. A metering compartment cannot be added to a primary section in the field, so an omitted metering decision is discovered when the meter will not fit. (10.4.5)
10.4.6 The remote monitoring interface of the assembly shall be as indicated in the datasheet.
Remote Monitoring Interfaceselect
No remote interface
Dry contacts for every alarm and position to a terminal block
Network interface through the meters, relays, and trip units
Dry contacts and network interface
NOTE Dry contacts carry a state and nothing more, need no protocol, and are read by any supervisory system; a network interface carries every measured value and every event the meters, relays, and trip units record, and it must match the protocol of the system the assembly reports to; a substation whose alarms must reach a plant control system while its energy data reach a building system often carries both. (10.4.7)
10.4.8 Where a network interface is selected, the network devices, cable, and power supplies within the assembly shall be furnished and installed by the manufacturer of record and brought to a terminal or connector in a designated compartment for the field connection, and the protocol shall be as indicated on the electrical power monitoring riser.

11 Close-Coupled Throats and Transitions

11.1 Primary-to-Transformer Connection

11.1.1 The connection between the primary section and the transformer shall be as indicated in the datasheet.
Primary-to-Transformer Connectionradio
○ Close-coupled throat with bus connection
○ Cable connection through an air terminal chamber on the transformer
NOTE A close-coupled throat bolts the primary section to the transformer and carries insulated bus through a flanged enclosure, so no primary cable is pulled at the site and no energized part is exposed; a cable connection sets the primary section apart from the transformer and runs medium-voltage cable between them through an air terminal chamber, which lets the primary section stand where the room needs it and lets a transformer be replaced without disturbing the switch, at the cost of a cable, two terminations, and a raceway the Contractor furnishes. (11.1.2)
11.1.3 Where a cable connection is selected, the cable, its terminations, and its raceway between the primary section and the transformer shall comply with Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables and Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit, and the air terminal chamber shall be sized for the cables as indicated on the one-line diagram and the conduit and cable schedule.

11.2 Transformer-to-Secondary Connection

11.2.1 The connection between the transformer and the secondary section shall be as indicated in the datasheet.
Transformer-to-Secondary Connectionselect
Close-coupled throat with bus connection
Cable connection through a terminal chamber on the transformer
Low-voltage busway connection
NOTE A close-coupled throat is the connection that makes the assembly a unit substation and the one nearly every assembly is built with: the full secondary current passes through braced bus inside a flanged enclosure with no field conductors and no field terminations. A cable connection sets the secondary section apart and carries the secondary current in parallel conductors sized under Conductors And CablesConductors and CablesResolves to the current adopted revision.sync/conductors-and-cables, at a cost in copper, terminations, and lugs that rises steeply with the bus rating, and it is used where the room cannot hold the lineup in one line; a busway connection does the same with a low-voltage busway under BuswayBuswayResolves to the current adopted revision.sync/busway where the distance is longer than a throat and the current is higher than cable serves economically. (11.2.2)
11.2.3 Where a cable or busway connection is selected, the transformer secondary terminal chamber or busway flange and the secondary section incoming compartment shall be sized by the manufacturer of record for the conductors or busway as indicated on the one-line diagram, and the conductors or busway between them shall be furnished under the standard that governs them.

11.3 Throat Construction

11.3.1 Each throat shall be a flanged, gasketed, grounded metal enclosure furnished by the manufacturer of record, bolted to the transformer and to the adjoining section so that the three sections form one continuous grounded enclosure with no exposed bus.
11.3.2 The bus through each throat shall be rated and braced for the continuous current and the short-circuit rating of the section it connects, shall be insulated where the governing standard of that section requires insulated bus, and shall be supported in the throat independently of the transformer terminals.
11.3.3 The connection between the throat bus and the transformer terminals shall be made with flexible connectors that accommodate the differential movement, thermal expansion, and vibration between the transformer and the section without transmitting load to the transformer bushings or terminals.
NOTE A transformer hums and warms, and the switchgear beside it does neither to the same degree; a rigid bus between them works the transformer terminal through every load cycle until a connection loosens or a bushing cracks, which is why the throat carries the compliance and the terminal carries none of the load. (11.3.4)
11.3.5 Each throat shall have removable covers giving access to every bolted connection within it for torque verification and infrared inspection, and shall be arranged so that the covers can be removed without de-energizing the adjoining section where the throat bus is insulated.
11.3.6 Where the transformer section is liquid-immersed, the throat flanges on the tank shall be furnished with air-filled terminal chambers so that no liquid-filled compartment communicates with the switchgear, and where the transformer section is dry-type, the throat openings in the transformer enclosure shall be barriered so that the transformer's ventilation air does not pass through the switchgear.
11.3.7 Shipping splits shall be located at the throat flanges, and each flange connection shall be designed so that the sections can be set, aligned, and bolted together at the site with the bus connection made up through the removable covers.
11.3.8 The manufacturer of record shall verify the throat dimensions of the transformer and of each section against each other before the assembly is released for manufacture, and where the transformer is of another make shall obtain that maker's certified throat drawing and shall state in the action submittals that the fit has been verified.

12 Assembly Enclosure

12.1 Enclosure Type

12.1.1 The enclosure type of the primary and secondary sections and of a dry-type transformer section shall be as indicated in the datasheet.
Enclosure Type per NEMA 250select
Type 1
Type 1 gasketed
Type 12
Type 3R
Type 3RX
NOTE A dry, conditioned electrical room is the installed location on most projects, and a Type 1 enclosure is the construction rated for it; the gasketed and Type 12 constructions keep out the dust of an unconditioned mechanical or process space, Type 3R is the outdoor construction, and Type 3RX adds corrosion resistance for a coastal, industrial, or de-icing-salt exposure. A liquid-immersed transformer section stands in its own tank and compartments and carries the enclosure integrity of its governing standard rather than a NEMA 250 type. (12.1.2)
12.1.3 Where the assembly is installed outdoors, the enclosure of every section shall be Type 3R at minimum, with rain hoods over ventilation openings and a drip shield over each door, and the throats shall be weatherproofed to the same type.
12.1.4 Where the assembly is installed within reach of salt air, chemical fallout, or de-icing spray, the enclosure of every section shall be Type 3RX at minimum or the sections shall be of a corrosion-resistant construction the manufacturer of record certifies as equivalent.
12.1.5 Where the assembly is installed in an unconditioned space subject to dust or dripping liquid, the enclosure shall be Type 12 at minimum.
12.1.6 The enclosures of the three sections shall match in height and depth at every throat and shall present one continuous front, and where a liquid-immersed transformer section stands taller than the switchgear the manufacturer of record shall furnish the transition pieces that close the enclosure at the throats.

12.2 Outdoor Housing

12.2.1 Where the assembly is installed outdoors, the outdoor housing arrangement shall be as indicated in the datasheet.
Outdoor Housing Arrangementradio
○ Non-walk-in
○ Walk-in aisle
NOTE A walk-in housing puts the working space in front of the primary and secondary sections inside a weatherproof aisle so that the equipment can be operated and serviced in any weather, at the cost of a larger and heavier structure; a non-walk-in housing is the smaller and lighter structure, and its working space is the outdoor pad in front of it. (12.2.2)
12.2.3 Where a walk-in housing is furnished, the aisle shall provide the working space NFPA 70 110.26 requires in front of every low-voltage device and NFPA 70 110.34 requires in front of every medium-voltage device, and the housing shall have lighting, a convenience receptacle, and a door openable from inside without a key at each end of the aisle.
12.2.4 An outdoor housing shall be furnished with thermostatically controlled space heaters in every section, supplied from a circuit that stays energized with the secondary main device open.

12.3 Finish

12.3.1 The finish system applied to the painted steel enclosures shall be as indicated in the datasheet.
Painted Steel Finish Systemselect
Polyester powder coat over a phosphate pretreatment
Epoxy powder coat over a phosphate pretreatment
Two-coat epoxy primer and polyurethane topcoat
Manufacturer's standard (by default)
12.3.2 The manufacturer of record shall state the finish system and its dry film thickness in the product data.
NOTE A polyester powder coat is the finish the sections are built with and holds up indoors and in ordinary outdoor exposure; an epoxy powder coat resists chemical splash better and chalks faster in sunlight; a two-coat liquid system is applied where a chemical or marine exposure has already been identified and the enclosure is not being made of a corrosion-resistant metal. (12.3.3)
12.3.4 The finish color shall be as indicated in the datasheet.
Finish Colorselect
ANSI 61 light gray
ANSI 49 medium gray
ANSI 70 sky gray
Custom color matched to a sample furnished by the Owner
12.3.5 The three sections and the throats shall be finished in the same color and the same finish system, and a transformer section of another make shall be finished to match the switchgear.

13 Identification

13.1 Nameplates shall be furnished on the assembly, on each section, and on each main, tie, and feeder device, and shall comply with Electrical IdentificationWiring System IdentificationResolves to the current adopted revision.sync/electrical-identification for material, lettering, and attachment.
13.2 The assembly nameplate shall state the assembly designation, the primary and secondary system voltages, the transformer kVA rating at each cooling stage and its impedance, the primary section and secondary section short-circuit ratings, the secondary main bus rating, the source that feeds each primary section, and the manufacturer of record.
NOTE The ratings on the assembly nameplate are the coordinated ratings of the whole, which are not the same as the ratings on any one section's own nameplate, and they are what a later engineer reads when the one-line diagram has been lost. (13.3)
13.4 Each main and tie device shall carry a nameplate stating its designation, its position in the transfer scheme, and the source it connects, and the transfer scheme control compartment shall carry a permanently mounted sequence-of-operation placard.
13.5 Arc-flash incident energy labels shall be applied to each section in accordance with NFPA 70 110.16 and NFPA 70E, with the values taken from the study performed under Arc Flash StudyArc-Flash StudyResolves to the current adopted revision.sync/arc-flash-study, and the label on the secondary section shall state the value with the tie open and the value with the tie closed where they differ.
13.6 The available fault current at the secondary bus and the date it was calculated shall be marked on the secondary section in accordance with NFPA 70 110.24 where the assembly is service equipment.

14 Testing

14.1 Factory Assembly and Testing

14.1.1 The extent of factory assembly before shipment shall be as indicated in the datasheet.
Factory Assembly Before Shipmentradio
● Complete lineup assembled, aligned, and tested at the factory before shipment
○ Sections tested individually with throat fit verified against certified drawings
NOTE Assembling the lineup at the factory proves the throat fit, the bus alignment, and the inter-section wiring before anything ships, and it is the practice of a manufacturer that builds all three sections; testing sections individually against certified drawings is the practice where a transformer of another make ships from its own factory, and it moves the first fit-up to the site, where a misaligned throat is corrected at the Contractor's schedule rather than the manufacturer's. (14.1.2)
14.1.3 Each section shall receive the production tests its governing standard requires: IEEE C37.20.3 or IEEE C37.20.2 for the primary section, IEEE C57.12.90 or IEEE C57.12.91 for the transformer section, and UL 1558, UL 891, or UL 845 for the secondary section construction selected, with a certified report for each.
14.1.4 In addition to the section tests, the manufacturer of record shall perform the following tests on the assembled lineup, or where sections are tested individually, on each throat and on the inter-section wiring as far as it can be exercised:
  • a dielectric withstand test of the bus through each throat at the test voltage the governing standard of the connected section requires
  • a continuity and functional check of every protective-device action wired between sections against the schematic diagrams
  • a functional test of the transfer scheme through every sequence, including transfer, retransfer, lockout on a simulated overcurrent trip, and loss of control power, with the devices operated
  • a functional test of every key and electrical interlock in every combination of device positions
  • a check of the phasing through the throats and across the tie
  • a dimensional check of each throat against the certified throat drawings
14.1.5 Factory acceptance test witnessing shall be as indicated in the datasheet.
Factory Acceptance Test Witnessingradio
○ Witnessed by the Owner's representative
● Unwitnessed with a certified test report
14.1.6 Where witnessed testing is indicated, the manufacturer of record shall give the Owner not less than two weeks notice of test readiness, and the test procedure shall have been submitted and returned before the test date.
NOTE A witnessed test lets the Owner see the transfer scheme run and every interlock work before the assembly ships, and it commits a representative to a trip to the factory; a certified report records the same tests without the trip, and leaves any discrepancy to be found at field acceptance testing instead. (14.1.7)

14.2 Field Acceptance Testing

14.2.1 Field acceptance testing shall be performed after the assembly is installed and before it is energized, in accordance with ANSI/NETA ATS and with Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing, and each section shall receive the field acceptance tests its governing standard requires.
14.2.2 In addition to the section tests, the assembly shall receive the tests indicated in the datasheet.
Assembly Field Acceptance Testscheckbox
☑ Torque or contact-resistance verification of every bolted connection in every throat
☑ Insulation resistance of the bus through each throat with the transformer isolated
☑ Phasing verification through each throat and across the tie
☑ Functional test of the transfer scheme through every sequence with the devices operated
☑ Functional test of every key and electrical interlock in every combination
☑ Functional test of every protective-device action wired between sections
☐ Performance test of ground-fault protection of equipment per NFPA 70 230.95(C)
☑ Verification of every protective device setting and fuse rating against the coordination study
☑ Verification of the transformer tap position against the one-line diagram
NOTE The throat is the one part of the assembly no section's own test reaches, and the transfer scheme is the one function that does not exist until the sections are joined, so the assembly tests are the tests of what the shipping splits took apart. (14.2.3)
14.2.4 A section, a throat, or a scheme that fails an acceptance test shall be corrected and retested, and the cost of the correction and the retest shall be borne by the Contractor.
14.2.5 No section shall be energized until the field acceptance tests covering it and the throats connected to it have passed and the arc-flash labels have been installed.

14.3 Start-Up and Initial In-Service Inspection

14.3.1 Manufacturer start-up shall be provided where indicated in the datasheet.
Manufacturer Start-Upradio
○ Manufacturer of record's field service present at energization and start-up
○ Not required
14.3.2 The assembly shall be energized from the primary side with every secondary feeder device open, held for not less than one hour while the transformer sound level, the temperature indicators, and the throats are observed, and then loaded one bus at a time.
14.3.3 Infrared thermographic inspection shall be as indicated in the datasheet.
Infrared Thermographic Inspectionselect
Not required
One inspection within 90 days of energization
One inspection within 90 days of energization and a second at eleven months
14.3.4 Where infrared inspection is indicated, it shall be performed with the assembly carrying not less than 40 percent of the transformer self-cooled rating, shall include every throat connection through its inspection covers or windows, and every connection showing a rise of more than 10 °C above a comparable connection under the same load shall be reported and corrected.
NOTE A second inspection near the end of the first year finds the throat connection that loosened through the first full cycle of seasonal load, which the first inspection cannot see; it costs a second visit under load and a warranty claim filed before the warranty ends. (14.3.5)

15 Installation

15.1 Room, Vault, and Yard

15.1.1 An indoor assembly shall be installed in a room complying with Electrical RoomsElectrical RoomsResolves to the current adopted revision.sync/electrical-rooms, and the room ventilation shall carry away the full-load losses of the transformer at its highest cooling stage and the losses of both sections so that the room ambient does not exceed the indoor design ambient temperature selected in the datasheet.
15.1.2 The Contractor shall furnish the transformer and section loss data from the reviewed submittals to the mechanical trade before the room ventilation design is fixed.
15.1.3 Where the transformer section is liquid-immersed and installed indoors, the vault or the less-flammable-liquid installation provision shall be as Medium Voltage TransformersMedium-Voltage Distribution TransformersResolves to the current adopted revision.sync/medium-voltage-transformers requires for the liquid selected, applied to the transformer section, and the primary and secondary sections shall stand outside the vault with the throats passing through the vault wall only where the Authority Having Jurisdiction accepts the penetration detail.
NOTE A vault wall between the transformer and the switchgear turns the throats into fire-rated penetrations and separates the sections the throat was meant to join, which is a reason a liquid-immersed assembly indoors is most often built with a less-flammable liquid under NFPA 70 450.23 or set outdoors. (15.1.4)
15.1.5 Where the transformer section is dry-type and installed indoors, the room shall satisfy NFPA 70 450.21 for the transformer's rating and voltage.
15.1.6 Where the assembly is installed outdoors in a dedicated yard, the yard grounding grid shall be designed for step and touch potential in accordance with IEEE 80 and shall be as indicated on the yard grounding plan, and the fence, the gate, and the warning signs shall comply with NFPA 70 110.31.

15.2 Foundation and Anchorage

15.2.1 The assembly shall be set on a concrete pad constructed under Concrete PadsConcrete Equipment PadsResolves to the current adopted revision.sync/concrete-pads, of the height indicated in the datasheet, extending not less than 3 in. beyond the assembly base on every side.
Housekeeping Pad Heightrange
in.
346
NOTE A pad keeps the base of the assembly above a wet floor and gives the anchors something to bite into that is not the slab's reinforcing; a pad height of zero is the direct-to-slab installation used where the floor is a structural slab designed for the anchors, and an outdoor assembly stands on a pad whose height the site grading sets. (15.2.2)
15.2.3 The pad shall be level across its full length so that the three sections align at the throats without shimming beyond the manufacturer of record's stated limit.
15.2.4 The assembly shall be anchored to the pad as indicated on the seismic anchorage details, using the anchor type, size, and embedment stated there, and where seismic qualification is required the anchorage shall be that on which the qualification depends.
15.2.5 The Contractor shall confirm the pad dimensions, the conduit stub-up locations, the anchor locations, and the weight of each shipping section against the reviewed shop drawings before the pad is placed, and shall report a discrepancy to the Engineer of Record before concrete is placed.
NOTE An assembly weighs from a few thousand pounds to more than 50,000 lb, and the pad, the anchor pattern, and the stub-ups are fixed in concrete before it arrives; the check against the shop drawings is where the RFIs this equipment is known for are avoided. (15.2.6)

15.3 Setting and Reassembly

15.3.1 Shipping sections shall be set, aligned, and bolted together at the throat flanges in accordance with the manufacturer of record's instructions, and the bus connection through each throat shall be made up with the manufacturer's hardware torqued to the manufacturer's values with a calibrated tool.
15.3.2 Every shipping brace, block, and desiccant shall be removed from every section and every throat before the assembly is energized, and their removal shall be recorded on the field test report.
15.3.3 Where the transformer is liquid-immersed, the liquid level shall be verified at the 25 °C mark and the tank pressure recorded before the throats are closed.
15.3.4 Conduit entry to the assembly shall be as indicated in the datasheet.
Conduit Entryradio
○ Top entry
○ Bottom entry
○ Top and bottom entry
Per drawings — the electrical plans (deferred by default)
15.3.5 Conduit shall enter only through the areas designated on the shop drawings, and no raceway shall enter a throat, a bus compartment, or a transformer ventilation path.

15.4 Field Wiring and Grounding

15.4.1 The primary cables and their terminations shall comply with Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables, the secondary conductors with Conductors And CablesConductors and CablesResolves to the current adopted revision.sync/conductors-and-cables, and the raceways with Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit.
15.4.2 The ground bus of the primary section, the transformer tank or enclosure, and the ground bus of the secondary section shall be bonded to one another through the throats by the manufacturer of record, and the assembly shall be bonded to the grounding electrode system in accordance with NFPA 70 250.30 and Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding.
15.4.3 The grounding electrode conductor shall be connected at the system bonding jumper location selected in the datasheet and at no other point.
15.4.4 Every field termination shall be torqued to the device manufacturer's published value with a calibrated tool, and the torque values applied shall be recorded in the field test report.
15.4.5 The protective device settings shall be applied in the field from the coordination study performed under Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study before the assembly is energized, and the transformer tap shall be set to the position indicated on the one-line diagram, or where none is indicated to the rated-voltage tap.

15.5 Working Space

15.5.1 Working space in front of, behind, and beside the assembly where it is accessible there shall comply with NFPA 70 110.26 for the secondary section and NFPA 70 110.34 for the primary section, and the clearance the manufacturer requires to remove a throat cover, withdraw a drawout device, or open every door fully shall be maintained in addition.
15.5.2 The dedicated electrical space above the assembly required by NFPA 70 110.26(E) shall be kept clear of piping, ductwork, and equipment not associated with the assembly.
15.5.3 Working space shall not be used for storage at any time.

16 Delivery, Storage, and Handling

16.1 The assembly shall be shipped in the largest sections that the route from the delivery point to the final location will pass, with the shipping splits at the throat flanges, and the Contractor shall verify door, corridor, hoistway, and crane dimensions along that route before the shipping splits are fixed on the shop drawings.
16.2 Each shipping section shall be lifted only at the lifting provisions the manufacturer furnishes, and a liquid-immersed transformer section shall be lifted by its tank lifting lugs with a spreader that keeps the slings clear of the bushings and the throat flanges.
16.3 Each throat flange shall be shipped covered so that the bus, the flexible connectors, and the gasket surfaces are protected until the sections are joined.
16.4 The sections shall be stored indoors in a clean, dry location protected from construction dust and water until they are set, except that a liquid-immersed transformer section may be stored outdoors on its pad with its throats covered and its tank pressure maintained.
16.5 Where a section must be stored for more than 30 days or in a space that is not conditioned, its space heaters shall be connected to a temporary supply and energized for the duration of storage.
16.6 A section that has been wetted in transit or in storage shall be dried, inspected by the manufacturer of record's field service organization, and released in writing before it is energized, and a dry-type transformer section that has been wetted shall have its insulation resistance verified before energization.

17 Warranty

17.1 The manufacturer of record shall warrant the complete assembly, including every section, every throat, and every factory-installed device, against defects in materials and workmanship for the period indicated in the datasheet.
Warranty Periodrange
years
1235
17.2 The warranty period shall commence on the date indicated in the datasheet.
Warranty Commencementselect
Date of substantial completion
Date of energization
Date of shipment
NOTE Warranty commencement at shipment is the manufacturer's usual term, and it consumes the warranty during storage and construction; commencement at energization or substantial completion moves the coverage to the period the Owner is operating the equipment, and the manufacturer prices the added months into the assembly. (17.3)
17.4 The warranty coverage scope shall be as indicated in the datasheet.
Warranty Coverage Scoperadio
○ Parts only
○ Parts and labor
17.5 The warranty shall be one warranty from the manufacturer of record covering the three sections as an assembly, and a defect at a throat or at an interface between sections shall be the manufacturer of record's responsibility regardless of which maker built the sections on either side of it.
NOTE One warranty on the whole is the practical payoff of the manufacturer of record requirement: a coordination gap revealed by a fault has one responsible party, and not a transformer vendor and a switchgear vendor each pointing at the other. (17.6)
17.7 A repair or replacement performed under this warranty shall itself be warranted for a full new term equal to the original period from the date the repair is completed, or for the remainder of the original period, whichever ends later.
17.8 The Contractor shall warrant the installation, including every field connection, the anchorage, the grounding, and the field-applied settings, for the project warranty period.

18 Spare Parts

18.1 The Contractor shall deliver the spare parts indicated in the datasheet to the Owner before the assembly is accepted, and shall obtain a signed receipt for them.
Spare Parts to Be Furnishedcheckbox
☑ One set of primary power fuses of each rating installed, on a fused primary section
☑ One set of control fuses of each type and rating installed
☑ One set of indicating lamps and lenses of each type installed
☐ One spare undervoltage relay of each type in the transfer scheme
☐ One set of throat gaskets for each throat
☐ One cooling fan for a transformer furnished with a forced-air stage
☐ One winding temperature sensor for a dry-type transformer section
☐ Touch-up finish in the exterior color
NOTE A blown primary fuse is otherwise an outage that lasts until a replacement is sourced, and a fuse of a different rating installed to end the outage defeats the coordination study and the current-limiting protection the secondary section may depend on, so a fused primary without spare fuses on the site is a substation waiting for a substitution. (18.2)
18.3 Spare parts shall be of the same manufacturer and rating as the installed items, shall be delivered in their original packaging, and shall be labeled with the designation of the section and device they serve.

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