Schweitzer Engineering Laboratories SEL-787, Instruction Manual, Page: 132 / 564

4.54
SEL-787 Relay Instruction Manual Date Code 20081022
Protection and Logic Functions
Voltage-Based Protection
Volts/hertz tripping elements are usually used to trip the transformer breaker.
Volts/hertz logic is discussed in the following section.
Figure 4.32 and Figure 4.33 are similar to IEEE C37.102 : 2006 IEEE Guide
for AC Generator Protection Figure 4.5.4-1 and Figure 4.5.4-2 .
Figure 4.32 Dual-Level Volts/Hertz Time-Delay Characteristic 24CCS = DD
Figure 4.33 Composite Inverse/Definite-Time Overexcitation Characteristic, 24CCS = ID
.01 0.1 1.0 10 100 1000
100
110
120
130
140
24D2P2 = 118%
24D2D2 = 6 s
24D2P1 =
110%
Time (Minutes)
Transformer Limit Curve
on Gen. Voltage Base
Mfg-Generator
Limit Curve
Volts/Hertz (%)
Relay Characteristic
Time (Minutes)
Generator Manufacturer's
Recommended Protection Curve
Transformer Limit Curve on
Generator Voltage Base
.001 .01 0.1 1.0 10 100
100
110
120
130
140
Volts/Hertz (%)
1000
24D2P2 = 118%
24D2D2 = 1.2 s
24IP=108%