Functions; Power Factor - GE 845 Instruction Manual

CHAPTER 4: SETPOINTS

Functions

Power Factor

845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The 8 Series relays provides two Power Factor elements.
It is generally desirable for a system operator to maintain the Power Factor as close to
unity as possible to minimize both costs and voltage excursions. Since the Power Factor is
variable on common non-dedicated circuits, it is advantageous to compensate for low
(lagging) Power Factor values by connecting a capacitor bank to the circuit when required.
The relay allows two stages of capacitance switching for Power Factor compensation.
The relay calculates the average Power Factor in the three phases as follows:
Average Power Factor = Total 3-Phase Real Power / Total 3-Phase Apparent Power
Figure 4-116: Capacitor Bank Switching
Two independent elements are available for monitoring Power Factor, each having a
Switch-In and a Switch-Out level. For each element, when the measured Power Factor
becomes more lagging or leading (depending on the user setting) than the Switch-In level,
the relay operates a user-selected output contact. This output can be used to control a
switching device which connects capacitance to the circuit, or to signal an alarm to the
system operator. After entering this state, when the Power Factor becomes less lagging or
leading than the Power Factor Switch-Out level for a time greater than the set delay, the
relay resets the output contact to the non-operated state.
For delta-connected VTs, the Power Factor feature is inhibited from operating unless all
three voltages are above a threshold and one or more currents are above 0.002 x CT.
Power Factor element delay timers are only allowed to time when the voltage threshold is
exceeded on all phases and the Power Factor remains outside of the region between the
programmed Switch-In and Switch-Out levels. In the same way, when a Power Factor
condition starts the Power Factor 1 or 2 delay timer, if all three phase voltages fall below
the threshold before the timer has timed-out, the element resets without operating. A loss
of voltage during any state returns both Power Factor elements to the Reset state.
MONITORING
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