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Percentage differential relay - What is the calculated imbalance?

1.  Junior Member Pro Subscriber
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Mar 2019
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Reputation Percentage differential relay - What is the calculated imbalance?

A percentage differential relay with a 25 percent slope characteristic has 4.9 A in one restraint coil and 4.2A in the other. What is the calculated imbalance?

I have the answer from the help link of 16.6% but need help on the formulas used and calculation process.  Reply With Quote

2. Originally Posted by jbren81 A percentage differential relay with a 25 percent slope characteristic has 4.9 A in one restraint coil and 4.2A in the other. What is the calculated imbalance?

I have the answer from the help link of 16.6% but need help on the formulas used and calculation process.
First determine the difference between the restraint coils:
4.9A - 4.2A = 0.7A

Then calculate the % slope by using the smaller restraint coil current (can use either but the higher % slope is from the smaller restraint current):
0.7A / 4.2A = 0.166 * 100% = 16.6%.

16.6% < 25% so the relay will not operate.  Reply With Quote

3.  Junior Member Pro Subscriber
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Mar 2019
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Reputation  Originally Posted by Kalbi_Rob First determine the difference between the restraint coils:
4.9A - 4.2A = 0.7A

Then calculate the % slope by using the smaller restraint coil current (can use either but the higher % slope is from the smaller restraint current):
0.7A / 4.2A = 0.166 * 100% = 16.6%.

16.6% < 25% so the relay will not operate.
Thank you, I appreciate the help!  Reply With Quote

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