Calculation for CDG 61 Relay

The vendor will know.

What does your theoretical knowledge tell you?

You need the relay data sheet with the characteristic curve. Saturation effects occur.

32043 amp on 125 amp continuous is 256 times rated current.

That is exceptionally high, a supply impedance of <0.5%.

I would check the relay data sheet to be sure it is OK for 256 x In without damage!

Thanks to "Electric Power Systems" by Weedy and Cory, John Wiley & Sons page 456-7. ISBN0 47197677 6

Example 11.1

Determine the time of operation of a 1 A, 3 s overcurrent relay having....

a plug setting of 125 per cent

and a time multiplier of 0.6.

The supplying CT is rated 400: 1 A and the fault current is 4000 A.

Solution

The relay coil current = (4000/400) x 1 = 10 A.
The normal relay coil current 1 x (125/100) = 1.25A.
Therefore the relay fault current as a multiple of the plug setting = (10/1.25) = 8.
From the relay curve (Figure 11.16), the time of operation is 3.3 s for a time setting of 1.
The time multiplier (TM) controls the time of operation by changing the angle through

which the disc moves to close the contacts. The actual operating time = 3.3 x 0.6 = 2.0 s.

But note this is not a CDG61 curve. By memory, it may be very inverse time.

67model

There is some thing wrong on your input information.

On a 125/5 Amps CT, fault current can not be 32043 Amps

There is APP available developed by me to calculate the time.

I give Ramvinod a good answer.

Would Anonymous please explain why the fault current is so high?

The over current settings are two types

1. short circuit current - instantanious- setting will be 2-10 times to the rated current

2. Over current - IDMT. - 40% to 100% of rated current.

Hope U understood

Anand