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pareshh_joshi
Member

Join Date: Dec 2008
Posts: 8

how to desing Earth faulty Relay??

02/15/2009 2:46 AM

i have core balance CT

so pass three phase of the motor in this CT when any phase is imbalance or earth faulty in any phase or both or three phase so current direction is one state

so current will flow in CT out put

CT is 100/5 415v 50hz

so whts is the out put voltage/current and whts the rating of the realy and current limiting circuit how to desing this thing if any have idea so plz suggest with calculation.

Paresh Joshi
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benbenben
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Join Date: Feb 2009
Location: florida
Posts: 72
Good Answers: 4
#1

Re: how to desing Earth faulty Relay??

02/16/2009 4:02 AM

um.... what?

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sb
Guru

Join Date: Mar 2007
Posts: 2550
Good Answers: 103
#2

Re: how to desing Earth faulty Relay??

02/16/2009 5:11 AM

Are we talking about CT as we know ?

What is the expected voltage at out put ? I always thought it should be zero.

The current limiting circuit - on CT secondary ? never heard the term.

Relay rating and settings depends on the load.

Please assign the job to some professional or else not only the motor will be un protected but also it may be dangerous if you put current limit on CT secondary.

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marcot
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Canada - Member - Specialized in power electronics

Join Date: Feb 2008
Location: Montreal, Canada.
Posts: 1372
Good Answers: 80
#3

Re: how to desing Earth faulty Relay??

02/16/2009 9:28 AM

The voltage coming out of the CT will be the imbalanced of current divided by the ratio (100/5 = 20) times the burden resistor you will be using.

Normally, you want this voltage to stay below a few volts to avoid core saturation.

In this application, the CT is sized for only a fraction of the supply current to have enough sensitivity.

E.G. A 100A CT would likely be used on a 1000A supply or more. If the imbalance is 5% (50A), the current in the burden will be 50A/20 = 2.5A. Using a common 0.47Ω 25W resistor, the voltage will be ~1.2V.

Other values of resistors could be used depending on the VA capacity of your CT.

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pareshh_joshi
Member

Join Date: Dec 2008
Posts: 8
#4
In reply to #3

Re: how to desing Earth faulty Relay??

03/11/2009 2:00 AM

Thanks for all the reply

but can any one give the realy rating which one i use it for that

i have a 24V ac/dc realy

its is advisable that it will be connected or not ? or any possibilities of burning the realy coil when i connect in CT secondary????????
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