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APPLICATION EXAMPLE 2:
Starting from the following information:
Line details:

Transformation ratio of CT =500/1

Primary current: I
p
=500 A
50/51 function settings

Curve type: ANSI Extremely Inverse

Dial: 2.20

Tap: 1xI
n
50 function settings

Tap: 14xI
n

Operating time: 0.1 s
Figure 3. 50 and 50/51 ANSI Extremely Inverse
If overcurrent fault is 24xI
n
=12000 Ap, ANSI Extremely inverse curve defines a tripping value of
0.376 s (Figure 3) for 50/51 function. It is considered that this time is too high, so when current fault
reaches 24xI
n
, definite time overcurrent function will be work. 50 function tap is adjusted at 14xIn so
definite time overcurrent function will trip when current fault is higher than 14xIn (50 function does not
wait to reach 24xIn)