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.

PHASE SHIFTING TRANSFORMER UNUSUAL SERVICE CONDITIONS

The unusual conditions shall be the same as those listed in IEEE Std C57.12.00-2000, 4.3.1 through 4.3.3. Additional unusual service conditions that may apply to PSTs are as follows:

Operation with two or more PSTs in parallel or in series
The purchaser shall ensure the manufacturer has all nameplate data, test data, and applicable system information necessary to design the PSTs for proper load sharing. The purchaser must specify in detail to the manufacturer the LTC’s controls that will be provided by the purchaser.

If the manufacturer provides the LTC’s controls, the purchaser shall provide the control scheme used with any existing PSTs to the manufacturer to ensure a compatible system.

Operation of PSTs in series with series capacitor banks
If the PST is, or may be, operated in series with a series capacitor bank, this operating condition shall be pointed out to the manufacturer by the purchaser. The operating conditions shall be specified and the protection scheme used by the purchaser to prevent series resonance shall be provided to the PST manufacturer for review and for considerations in design.

Unbalanced current flow through the PST
The purchaser must provide details of operating conditions that will subject the PSTs to unbalanced phase currents and voltages that may exceed allowable standard limits. The manufacturer will provide for these conditions during the design of the PSTs. The following are examples of operating conditions that could produce such problems:

a) Unbalances resulting from operation of parallel transmission lines in close proximity to the PST connected lines, where line transpositions are unequal resulting in unbalanced voltage at the PSTs and unequal current flow through the series windings.

b) Single-pole operation of the circuit breakers following line faults where single-pole reclosing is utilized


Transient recovery voltages
Transient voltage may exist circuit breakers are operated. These conditions may be between the PST and the circuit breaker.

Surge protection
Any condition where the PST may operate without surge protection applied at all S and L terminals.