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amit_er1981
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Join Date: May 2009
Posts: 21

Current Transformers and Bidirectional Sensing

09/14/2009 4:20 AM

Is C.T will sense the current in both direction. As i know the C.T will sense the current in only one direction
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lyn
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Join Date: Oct 2008
Posts: 42355
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#1

Re: C.T will sense

09/14/2009 7:46 AM

Define C.T please. My crystal ball is in the shop being polished.
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sb
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Join Date: Mar 2007
Posts: 2550
Good Answers: 103
#2

Re: C.T will sense

09/14/2009 9:03 AM

How the CT (I think you mean current transformer) function ?

Think about it and the answer will be clear.

Ammeter (AC) does it sense current on both direction or one?

If you reverse the polarity of the voltage transformer does it become open circuit/shortcircuit/nonfunctional?

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ikhanuk
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Join Date: Aug 2009
Posts: 91
#3

Re: C.T will sense

09/14/2009 11:11 AM

CT can sense it but the direction of current will be change so u have to connect every thing upside down ..

regarding voltage transformer the direction will be reversed ..

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correct me if i am wrong

i am learner

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sb
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Join Date: Mar 2007
Posts: 2550
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#4
In reply to #3

Re: C.T will sense

09/14/2009 12:18 PM

The AC current is measured as RMS value, and on that there is no directional sense.

Let us talk in a relativistic approach shold we?

As far as ammeter (or CT) is concerned, it does not know what is phase and what is neutral.

Connect one end to red and call it phase and other to black (and call it neutral) one half of the cycle is + and other is - and it measures the voltage.

Connect otherway round and what happens? still one half is + (corresp to other) and other -

Got the concept?

This does not happen in DC.

In either CT or PT, not the direction the phase angle will be shifted by 1800.

The analogue/digital meters will be still reading the same values as the reverse connected. The problem happens when this signal is used for comparison/processing with some other signal (say Voltage for power) now the shifted phase angle creates problem.

Another problem may happen if the something CT/Meter has graded insulation ie the neutral side has a weaker insulation (the neutral-earth voltage is not expected to go high !) and the other side is connected to ground. But that is possible in even un-reversed connection.

BTW: Am I doing someone's home work?

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 Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
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msamad
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Join Date: Feb 2009
Location: Houston, USA
Posts: 946
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#5
In reply to #4

Re: C.T will sense

09/14/2009 12:20 PM

No doubt the CT will sense with same accuracy but the polarity will change. The change of polarity will affect if the CT burdens (loads) are polarity sensitive such as wattmeter, energy meter, PF meter, reverse power protection relay, directional current relay etc.

- MS

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sb
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Join Date: Mar 2007
Posts: 2550
Good Answers: 103
#6
In reply to #5

Re: C.T will sense

09/14/2009 1:31 PM

That's what I said

The problem happens when this signal is used for comparison/processing with some other signal (say Voltage for power) now the shifted phase angle creates problem.

__________________
 Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
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CJMcGill
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Join Date: Jul 2008
Location: SoCal USA
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#7
In reply to #6

Re: C.T will sense

09/15/2009 2:58 PM

Oh my. I have sensed some unusual sensitivity revealed by a normally very understanding and accommodating gremlin.

I do hope everything is well in your world sb.

CJM

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sb
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#8
In reply to #7

Re: C.T will sense

09/15/2009 10:19 PM

Not sensitive, just getting a bit irritated by the engineers. I am finding too many posts on the foundations of engineering.If people do not understand the basics then how do the will like to work on it?

And not only here, even on work i find quite senior so called engineering graduates with missing foundation.

Just a few days back I had to CONVINCE some whether megger test is destructive or non-destructive. One of the persons (senior) had to be forced to change the machine oil after the sump was flooded and there was some water entry in hydraulic tank of a critical machine. He wanted to use the drain plug and since water is heavier, remove it from there.

Now if one does not understand CBCT or its full form and its circuit, is it expected that we take this forum as one of teaching/ homework solving ? .

This OP's 1981 means he has not passed out from college long back plus he has a bit of working experience too. Should he ask all these questions?

(Solid vs Stranded every one missed the skin - AC/DC). My home telephone is solid, as is the cable connection. Stranded- costlier but necessary. Solid cheap - but ... (mechanical strength can be compensated by putting a steel wire at the core- as we learnt long back in college)

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