FANOX SIL-A A Series, Руководство пользователя

Страница: 66 / 112

www.fanox.com Rev.04 66/112
7.3 Application examples
It is important to know that if both overcurrent protection functions (50 and 50/51), phase or neutral, are
enable, definite time function (function 50) must be more restrictive. So, if overcurrent fault values are
low, inverse time overcurrent function (function 50/51) must work, and if overcurrent fault reaches a
certain value, definite time overcurrent function will always work. This is because, when overcurrent fault
reaches high values (I>>), it is necessary to be sure that trip is going to be instantaneous to get that the
element we are protecting, does not be damaged.
Some examples are shown below:
APPLICATION EXAMPLE 1
Starting from the following information:
Line details :
•
Transformation ratio of CT =100/1
•
Primary current: I
p
=100 A
50/51 function settings
•
Curve type: IEC Inverse
•
Dial: 0.05
•
Tap: 1xI
n
50 function settings
•
Tap: 11xI
n
•
Time delay: 0.05 s
Figure 1. 50 y 50/51 IEC Inverse
If overcurrent fault is 11xI
n
=1100 A, IEC inverse curve defines a tripping value of 0.1425s (Figure1) for
50/51 function. It is considered that this time is too high, so when current fault reaches 11xI
n
, definite
time overcurrent function will be work.