PHASE SHIFTING TRANSFORMER CONSTRUCTION

In general, construction requirements for PSTs should be in accordance with the requirements for power transformers, as covered in IEEE Std C57.12.00-2000 and other applicable IEEE standards based on kV and kVA ratings, with the following exceptions or additions.


Enclosed throat connections
Enclosed throat connections in fully assembled condition must meet the pressure and vacuum requirements of PST tanks for all designs that subject the enclosed throat connection to the same operating pressures and vacuum levels as the transformer tank.

Liquid insulation and preservation system 
Liquid insulation and preservation systems shall be in accordance with IEEE Std C57.12.00-2000 with the following addition.

Two tank designs with enclosed liquid-filled throat connection
Enclosed liquid-filled throat connections may be either sealed from each tank or opened to the insulating fluid from one or both tanks. Enclosed throat connections shall be designed for installation or removal without the need to jack or move either or both of the transformer tanks and shall accommodate thermal expansion and contraction of the throat assembly and both tanks. For a sealed throat system that isolates the insulating fluid, the throat connections require a separate conservator system.

For a system where the throats are not directly connected to a main tank and the isolation of the insulating fluid in different compartments is not important, the throats may be connected to the conservator system of the main tank. If this approach is used, the user should be aware that the use of oil and gas analysis to isolate problems will be complicated.

For throat connections that place barriers between both the tanks and the throat, the throat shall be equipped with the following accessories:

— Gas accumulation relay
— Pressure relief device/relay
— Liquid filling and draining valves
— Rapid rate of rise relay
— Liquid level gauge

PHASE SHIFTING TRANSFORMER RATING DATA REQUIREMENT BASIC INFORMATION

In general, rating data for PSTs should be in accordance with the requirements for power transformers as covered in IEEE Std C57.12.00-2000 with the following exceptions or additions.


Polarity, angular displacement, and terminal markings
Terminal markings unique to PSTs
The designations H and X shall not be used and shall be replaced by S and L to indicate the source and load. The S terminals shall be marked S1, S2, S3, and (if applicable) S0. The L terminals shall be marked L1, L2, L3, and (if applicable) L0. Y and Z designations shall be used for additional windings that are brought out of the tank.

Enclosed throat connection terminal markings
Enclosed throat winding terminal connections shall be marked in any manner that will permit convenient reference and cannot be confused with the markings of the external transformer terminals.

Impedance
Impedance shall be in accordance with IEEE Std C57.12.00-2000 with the following additions.

General
Rated impedance shall be at zero phase-shift connections.

Change in impedance with phase-angle regulation
The impedance of PSTs can vary substantially over its range of phase-angle regulation. The user must specify the acceptable ranges of impedances and the manufacturer shall calculate and provide a matrix of impedances as required by the user. The extent of test verification of impedance values other than rated impedance should be specified and agreed upon by the purchaser and manufacturer.

Nameplates
Nameplates shall be in accordance with IEEE Std C57.12.00-2000 with the following addition: The nameplate of the PST shall show the phase shift in degrees from the S to the L terminals starting at the zero phase-shift tap and for each tap position in the advance and retard direction while operating at no-load.

The nameplate shall also show the phase shift in degrees from the S to the L terminals while operating at maximum rated kVA output at unity power factor at the S terminal for all tap positions which result in acceptable service conditions.

Intermediary phase shifts at varying loads may be specified by the purchaser for inclusion on the nameplate. The user may request impedance changes be indicated on the nameplate for any tap position.