PHASE SHIFTING TRANSFORMER USUAL SERVICE CONDITION BASIC INFORMATION

These conditions shall be as stated in IEEE Std C57.12.00-2000, 4.1.1 through 4.1.7, and 4.1.9; 4.1.8 shall not apply. In 4.1.6.1 (a), the word secondary shall mean the L terminals of the PST.

a) The purchaser of the PST shall specify the switching arrangements that will be used to place the PST in and out of service. This shall include breaker or switch operations resulting from faults external and internal to the PST.

b) The PST shall be suitable for energization by voltage applied to either the S or L terminals.

c) The PST shall be capable of transferring rated kVA with the electrical source of power connected to the S or L terminals. Limited power transfer in the retard position has to be considered.

d) Seismic requirements shall be as specified in IEEE Std 693-1997. The seismic zone shall be provided by the purchaser. The foundation design shall be provided to the PST manufacturer by the purchaser.

The manufacturer shall provide for differential motion between the two tanks, if used, and in the case of remotely mounted radiators provide for their differential motion.

e) The manufacturer of the PST shall make provisions for differential alignments that will occur when two tanks are connected. The foundation tolerance shall be defined by agreement between purchaser and manufacturer.

f) Unless specified otherwise, the PST shall be manufactured for operation in the bypassed state with the source and load bushing connected through bus work. This shall require special consideration in design for lightning impulse and switching surges.

This condition will require additional testing with the terminals connected, as in operation, to demonstrate that the insulation level meets the specified BIL.

TRANSFORMER PERCENT (%) REGULATION BASIC AND TUTORIALS

When a transformer is energized with no load, the secondary voltage will be exactly the primary voltage divided by the turns ratio (NP/NS). When the transformer is loaded, the secondary voltage will be diminished by an amount determined by the transformer impedance and the power factor of the load.

This change in voltage is called regulation and is actually defined as the rise in voltage when the load is removed. One result of the definition of regulation is that it is always a positive number.

The primary voltage is assumed to be held constant at the rated value during this process. The exact calculation of percent regulation is given in Equation

where cos 􀁕 is the power factor of the load and L is per unit load on the transformer.

The most significant portion of this equation is the cross products, and since %X predominates over %R in the transformer impedance and cos 􀁕 predominates over sin 􀁕 for most loads, the percent regulation is usually less than the impedance (at L = 1).

When the power factor of the load is unity, then sin 􀁕 is zero and regulation is much less than the transformer impedance.

A much simpler form of the regulation calculation is given in Equation

For typical values, the result is the same as the exact calculation out to the fourth significant digit or so.