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Anonymous Poster

# Calculation of relay settings

05/17/2010 10:07 AM

Can anyone please show me how to calculate the relay settings. I would like all the steps of how to carry out the calculations. Thanks. I'll wait for a reply(ASAP)

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Commentator

Join Date: Mar 2009
Posts: 82
#1

### Re: Calculation of relay settings

05/17/2010 10:32 AM

I found these...

The easiest way is to run all 6 (3 phases, 3 neutrals) or 4 (3 phases and neutral) leads through a large window CT and connect it to a simple overcurrent relay. This is not always very easy. You can also use individual CT's, wire all the secondaries in parallel and in parallel with the overcurrent relay. It is very important the CT's are matched exactly. Thus the percentage comes into play.

Percentage differential is the difference between the operating current and the restraint current. Think of it this way, operating current (phase current) tries to close the relay and the restraint current (neutral) tries to hold it open. If it closes, the breaker trips. So a 10% differential relay setting says that the operating current needs to be over 10% more than the restraint current.

This gets much more complicated when you have a zone that includes the generator and the transformer

Or this one?

(a) Time/ p.s.m curve

(b) Current setting

(c) Time setting

(d) Fault current

(e) Current transformer ratio

The procedure for calculating the actual relay operating time is as follows

<!--[if !supportLists]-->(i) <!--[endif]-->Convert the fault current into the relay coil current by using the current transformer ratio.

<!--[if !supportLists]-->(ii) <!--[endif]-->Express the relay current as a multiple of current setting i.e. calculate the P.S.M.

<!--[if !supportLists]-->(iii) <!--[endif]-->From the Time P.S.M. curve of the relay, read off the time of operation for the calculated P.S.M.

<!--[if !supportLists]-->(iv) <!--[endif]-->Determine the actual time of operation by multiplying the above time of the relay by time setting multiplier in use.

Problem 1: – Determine the time of operation of a 5-ampere, 3-second over current relay having a current setting of 125% and a time setting, multiplier of 0.6 connected to supply circuit through a 400/5 current transformer when the circuit carries a fault current of 4000A. The time of operation is 3.5 for a P.S.M value of 8.

Solution

Rated secondary current of CT = 5 A

Pickup current = 5 x 1.25 = 6.25 A

Fault current in relay coil = 4000 x 5/400 = 50 A

Plug-setting multiplier (P.S.M.) = 50/6.25 = 8

Given when P.S.M is 8 time operation is 3.5 Sec.

Actual relay operating time = 3.5 x Time-setting = 3.5 x 0.6 = 2.1 seconds

Guru

Join Date: Oct 2009
Posts: 2031
#2

### Re: Calculation of relay settings

05/18/2010 9:20 AM

I suggest that you attend to our four days' duration training programme on "Digital Protective Relaying & Feeder Protection and Protection of Generators & Transformers" conducted at our Switchgear Training Centres located at Pune, Lucknow & Coonoor (near Ooty in Tamilnadu). In this programme we do have a session on relay co-ordination with a detailed case study. You may mail me thro the mailbox in this forum for further details.

Power-User

Join Date: May 2009
Location: Some where on Earth !!!.
Posts: 205
#3

### Re: Calculation of relay settings

05/27/2010 12:56 PM

Sir,pls provide me also the details about the training:my mail id is sent in your mail box.

Thank you

__________________
Anonymous Poster
#4

### Re: Calculation of relay settings

06/16/2010 12:12 AM

Sir,

I need to know more details about 4 day course including relay setting study.

Guru

Join Date: Oct 2009
Posts: 2031
#6

### Re: Calculation of relay settings

08/31/2010 5:06 AM

Send your mail ID; I will send the details.

Anonymous Poster
#7

### Re: Calculation of relay settings

11/16/2010 3:21 AM

Please send the program details so as to attend this program. thanks and regards Madhu

Anonymous Poster
#8

### Re: Calculation of relay settings

12/23/2010 10:36 PM

my email id mvamsikiran@yahoo.com.please se how to calculate the relays

Anonymous Poster
#5

### Re: Calculation of relay settings

08/31/2010 4:27 AM

Dear Sir,

I would like to know the particulars of this course.

Can you brief me.

BR

Bhuvaneswar

Off Topic (Score 5)
Participant

Join Date: Mar 2011
Posts: 1
#9

### Re: Calculation of relay settings

03/19/2011 2:38 PM

email:- <email removed>

From the CR4 Rules: Do not post phone numbers or email addresses. The CR4 Admin will delete all phone numbers posted in threads or comments, and we strongly urge you not to put up email addresses. You can share this information via the CR4 internal messaging system.

Member

Join Date: Jun 2011
Posts: 6
#10

### Re: Calculation of relay settings

07/05/2011 5:53 AM

Dear Sir,

Please send me details of training forth coming programs.

Thanks & Best Regards,

From the CR4 Rules: Do not post phone numbers or email addresses. The CR4 Admin will delete all phone numbers posted in threads or comments, and we strongly urge you not to put up email addresses. You can share this information via the CR4 internal messaging system.

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