Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 141 / 706

3.61
Date Code 20070117
Instruction Manual SEL-351-5, -6, -7 Relay
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Power Elements (Available in Firmware Version 7)
In Figure 3.38 , if the Phase A reactive power level is above pickup setting
PWR n P, Relay Word bit PWRA n asserts (PWRA n = logical 1) after time
delay setting PWR n D ( n = 1 through 4), subject to the “sufficient signal”
conditions.
Pickup setting PWR n P is always a positive number value (see Table 3.14 ).
Thus, if –WATTS or –VARS are chosen with setting PWR n T, the
corresponding real or reactive power values have to be multiplied by –1 so that
element PWRA
n asserts for negative real or reactive power.
Power Elements
Application—VAR
Control for a
Capacitor Bank
Figure 3.39 SEL-351(B) Provides VAR Control for 9600 kVAR Capacitor
Bank
The 9600 kVAR capacitor bank in Figure 3.39 is put on-line and taken off-line
according to the VAR loading on the transformer bank feeding the 21.6 kV
bus. The VAR loading is measured with the SEL-351(B) located at bus circuit
breaker 52-B.
Two SEL-351 relays control the capacitor bank-both relays are connected to
capacitor bank circuit breaker 52-C. The SEL-351(C) provides capacitor
overcurrent protection and trips circuit breaker 52-C for a fault in the capacitor
bank. The SEL-351(B) provides VAR control and automatically puts the
capacitor bank on-line (closes circuit breaker 52-C) or takes it off-line (trips
circuit breaker 52-C) according to the measured VAR level. The SEL-351(B)
also provides bus overcurrent protection and trips circuit breaker 52-B for a
fault on the 21.6 kV bus.
Transformer
Bank
Trip
Trip
Close
Trip
Block
Close
VAR Control
1.0 per unit
VARs (leading)
21.6 K
V
Bus
2000:5
CT Ratio
12,500:125
PT Ratio
To Other Feeder Positions
Block Close
SEL-351(B)
SEL-351(C)
52-B
52-C
9600 KVAR
Capacitor
Bank