Sel SEL-421 - Page 119

R.1.77
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Inverse-Time Overcurrent Elements
Figure 1.51 U.S. Extremely Inverse—U4
3.00
2.00
1.00
0.50
15.00
12.00
10.00
8.00
6.00
5.00
4.00
.01
.5 .6 .7 .8 .9 1
.02
.03
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.09
.07
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.1
.2
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10
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100
80
10
2
3
6
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8
20
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90
Time in Seconds
Multiples of Pickup
Time in Cycles 60 Hz (50 Hz)
3 (2.5)
6 (5)
15 (12.5)
30 (25)
60 (50)
600 (500)
150 (125)
300 (250)
1500 (1250)
3000 (2500)
6000 (5000)