Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

Page: 524 / 1518

7.4
SEL-421 Relay Instruction Manual Date Code 20171021
Metering, Monitoring, and Reporting
Metering
where the current lags the applied voltage. Conversely, Q is negative when the
voltage angle is less than the current angle (

V
<

I
); this is when the current
leads the voltage, as in the case of capacitive loads.
The SEL-421 includes Relay Word bits to indicate the leading or lagging power
factor (see
Section 11: Relay Word Bits ). In the case of a unity power factor or
loss of phase or potential condition, the resulting power factor angle will be on
the axis of the complex power (P/Q) plane shown in
Figure 7.1 . This causes the
power factor Relay Word bits to rapidly change state (chatter). Be aware of
expected system conditions when monitoring the power factor Relay Word bits.
SEL does not recommend the use of chattering Relay Word bits in the SER or
anything that will trigger an event.
Figure 7.1 Complex Power (P/Q) Plane
Table 7.3 Instantaneous Metering Quantities—Power (Sheet 1 of 2)
Metered Quantity Symbol
Fundamental
(50 Hz/
60 Hz Only)
RMS
(Harmonics
Included)
Per-phase fundamental real power P

1
X
Per-phase true real power P

rms
X
Per-phase reactive power Q

1
X X
Per-phase fundamental apparent power S

1
X
Per-phase true apparent power U

rms
X
Three-phase fundamental real power 3P
1
X
Three-phase true real power 3P
rms
X
Three-phase reactive power 3Q
1
X X
Three-phase fundamental apparent power 3S
1
X
Q
P
+P
+Q
Comp
lex
Pow
er
S
1
Com
plex
Powe
r S
2
pf = Lead
pf = Lag
—P
+Q
+P
—Q
—P
—Q
Export power and
export reactive power
(inductive load)
Export power and
import reactive power
(capacitive load)