3phase urd transformerL:\Material Standards Committee\3 Phase URD transformer
S.C.Electric Cooperatives Specification for a Three-Phase, Padmounted URD Transformer (Revised 4/29/10)
This specification covers the electrical and mechanical characteristics of Three-Phase, Oil-Filled (certified non-PCB), Pad-Mounted URD Transformers.
All characteristics, definitions, and terminology, except as specifically covered in this specification shall be in accordance with the latest revision of the following ANSI and NEMA standards.C57.12.00 - IEEE Standard General Requirements for Liquid-Immersed Distribution, Power and Regulating Transformers.
C57.12.26 - Pad-Mounted, Compartmental-Type, Self-Cooled, Three-Phase Distribution Transformers With Separable Insulated High-Voltage Connectors; High Voltage, 34500GRDY/19920 Volts and Below; 2500 kVA and Smaller.C57.12.28 - Pad-Mounted Equipment - Enclosure Integrity.C57.12.90 - IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers and IEEE Guide for Short-Circuit Testing of Distribution and Power Transformers.In addition to the above requirements, the transformers shall also meet the requirements of the Rural Utility Service (RUS-formerly REA) Specification U-5and Department of Energy (DOE) 10 CFR Part 431 Efficiency Compliance.
The transformer shall be designed in accordance with this specification and shall have one of the following kVA ratings: 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000, 2500 The applicable kVA rating(s) shall be specified on Attachment k00;.100;V-00;.500; 00; -00;.00;l 00;-00;.00;.00; 00;i-00;.00; 00;.500; 00; -00;.00;.00; L:\Material Standards Committee\3 Phase URD transformer
2.2 The primary voltage and the basic insulation level (BIL) shall be 95 kV for 12,470 Grd.Y/7200 volts,125 kV for 24,940 Grd.Y/14,400 volts and 95 X125 kV for 12,470 Grd.Y/7200 X 24,940 Grd.Y/14,400 volts (dual voltage primary).
L:\Material Standards Committee\3 Phase URD voltage transformers shall have dual voltage primary windings connected to an externally operable, dual voltage selector switch for de-energized operation only.
Two operations (minimum) shall be required to change switch position.Unit to be shipped with voltage selector switch in highest voltage position.The primary voltage shall be specified on Attachment.700; p00;.700;.300;.200;y 00; -00;.00; 00;.700;l o00;n-00;.00; 00; .00; A.
2.3 The secondary voltage shall be 208Y/120 or 480Y/277 volts.The basic insulation level (BIL) of the secondary shall be 30 kV.
The secondary voltage shall be specified on Attachment AT-00;.00; 00;.600; 00;.600;l 00;-00;.00;.00; 00; 00;.600; 00; -00;.00;
.4If specified on Attachment A, the transformer shall be furnished with full capacity high-voltage taps.
The tap changer shall be clearly labeled to reflect that the transformer must be de-energized before operating the tap changer.If taps are required on dual voltage units, the
taps shall be on the higher voltage (series) position only.
The unit shall have one of the following tap configurations:
Two - 2% taps above and below rated voltage
Four - 2% taps below rated voltagePercent Voltage Impedance of units shall be as specified in table below with a tolerance of +/- 7.5%.500 KVA and KVA and larger
3.0 HIGH VOLTAGE BUSHINGS
There shall be six (6) high voltage bushings wells for dead front, loop feed operation rated for three-phase duty.These wells shall be externally clamped and removable to allow for field replacement of the bushings without opening the tank.
The bushing well studs shall be removable without removing the bushing wells.
The bushing configuration shall be per ANSI Figure 6A for loop feed configuration.
Cable accessory parking stands shall be provided and shall be located such that the separable insulated connectors designed for operation after the transformer is in place can be operated with hot-line tools.3.4 If specified on Attachment Abushing well inserts of the specified voltage shall be installed in the transformer.
These inserts shall have an all copper current carrying path.4.0 LOW VOLTAGE BUSHINGS AND TERMINALS
Bullets and NumberingFormattedL:\Material Standards Committee\3 Phase URD transformer
The configuration of the secondary bushings shall be per ANSI C57.12.26-staggered (Figure 8A - default configuration)
in-line (Figure 8B).
The applicable low voltage bushing configuration shall be specified on Attachment
These bushings shall be externally clamped and shall be removable to allow for field replacement without opening the tank if possible.The transformer shall have threaded, stud-type line and neutral bushings as per ANSI C57.12.26 Figure 9(d) with blade type spade terminals.Transformers larger than sizes listed in Figure 9(d) can have solid one-piece bushings with non-removable spades if threaded type bushings are not available in ampere range required.
The number of holes in the spade terminals shall be as follows:
Number of holes
225 kvA and smaller
10 1000 kvA
1500 & 2000 kvA
16 Spade terminals with ten (10) or more holes shall be equipped with an insulated, disconnectable support that prevents upward or downward movement of the terminal.
The low voltage neutral shall be a fully insulated bushing with a removable ground strap.5.0 PROTECTION The transformer primary shall include
loadbreak, hook stick operable bayonet dual elementfuse assemblies (RTE type 8 or equal) with oil valves to minimize oil spillage.