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Anonymous Poster #1

Calculation for CDG 61 Relay

01/02/2014 5:24 AM

let's know how to calculate tripping time for CDG61EG111ZM(M) relays for a particular settings with detailed formula.

For example : CT ratio 125/5, plug setting : 6.25, TMS : 0.3,

Fault current : 32043AMP.

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#1

Re: calculation for cdg 61 relay.

01/02/2014 7:29 AM

The vendor will know.

What does your theoretical knowledge tell you?

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#2

Re: Calculation for CDG 61 Relay

01/02/2014 2:17 PM

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!

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#3

Re: Calculation for CDG 61 Relay

01/02/2014 3:15 PM

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

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#4

Re: Calculation for CDG 61 Relay

01/02/2014 11:28 PM

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.

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Ramesh,Freelance Electrical/automation Consultant
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#5
In reply to #4

Re: Calculation for CDG 61 Relay

01/02/2014 11:38 PM

For CDG 61 applicable IEC curve is standard inverse. The formula for calculating tripping time t= (0.14 x tms) / ( [(If/Is)power 0.2]-1)

The CDG 61 relay has got settings 50 -200 %

For 5Amps relay settings available are

2.5 Amps-50 %

3.75 Amps-75%

5 Amp-100%

6.25 Amp-125%

7.5 Amp-150%

8.75 Amp-175 %

10 Amp-200%

Calculated Tripping time based on the above formula ,for following fault currents will be as follows;

If-200A- 8.49 sec

If-250 A-4.45 sec

If-375 A-2.38 sec

If-500 A-1.78 sec.

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#6
In reply to #5

Re: Calculation for CDG 61 Relay

01/03/2014 6:01 AM

I give Ramvinod a good answer.

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

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#7
In reply to #6

Re: Calculation for CDG 61 Relay

01/25/2014 7:50 AM

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

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