Manual 37353A
MFR 13 Packages - Protection Relay
© Woodward
Page 23/91
Power Factor Definition
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The phasor diagram is used from the generator's view. This defines the following definitions.
Power Factor is defined as a ratio of the real power to apparent power. In a purely resistive circuit, the voltage
and current waveforms are instep resulting in a ratio or power factor of 1.00 (often referred to as unity). In an in-
ductive circuit the current lags behind the voltage waveform resulting in usable power (real power) and unusable
power (reactive power). This results in a positive ratio or lagging power factor (i.e. 0.85lagging). In a capacitive
circuit the current waveform leads the voltage waveform resulting in usable power (real power) and unusable
power (reactive power). This results in a negative ratio or a leading power factor (i.e. 0.85leading).
Inductive: Electrical load whose current waveform lags
the voltage waveform thus having a lagging power fac-
tor. Some inductive loads such as electric motors have
a large startup current requirement resulting in lagging
power factors.
Capacitive: Electrical load whose current waveform
leads the voltage waveform thus having a leading
power factor. Some capacitive loads such as capacitor
banks or buried cable result in leading power factors.
Different power factor displays at the unit:
i0.91 (inductive)
lg.91 (lagging)
c0.93 (capacitive)
ld.93 (leading)
Reactive power display at the unit:
70 kvar (positive)
-60 kvar (negative)
Output at the interface:
+ (positive)
- (negative)
Compared with the voltage, the current is …
lagging
leading
The generator is …
over excited
under excited
Control: If the control unit is equipped with a power factor controller, …
a voltage lower "-" signal is output as long as the
measured value is "more inductive" than the reference
set point
Example: measured = i0.91; set point = i0.95
a voltage raise "+" signal is output as long as the meas-
ured value is "more capacitive" than the reference set
point
Example: measured = c0.91; set point = c0.95
