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coolyaar
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Generator CT

11/13/2019 9:49 AM

In a power plant, a small blue cable is connected between the generator (11KV,50MW) phase terminal and the CT moulding/casing of window type CT mounted on the generator phase terminal. The cable is the blue one shown in the picture. Can someone explain what the purpose of this cable is?
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redfred
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#1

Re: Generator CT

11/13/2019 12:01 PM

The purpose is to electrically connect them together.

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PWSlack
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#2

Re: Generator CT

11/13/2019 12:11 PM

Yes. The person who created the "as built" drawing for the installation can do that.

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Rixter
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#3

Re: Generator CT

11/13/2019 12:30 PM

Are you sure that it's around a phase and not the neutral?

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coolyaar
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#10
In reply to #3

Re: Generator CT

11/14/2019 7:32 AM

Yes , see my question where it is written as "CT mounted on phase terminals". the 3 No. CTs mounted on 3 No. Phase terminals have same small cables connected between CT casing and phase terminal bars.
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SolarEagle
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#4

Re: Generator CT

11/13/2019 12:43 PM

Looks like a neutral wire connection to me...

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Rixter
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#6
In reply to #4

Re: Generator CT

11/13/2019 2:52 PM

I don't know if this is applicable, but in Europe, Blue is Neutral...

https://electricalfundablog.com/wiring-color-codes-usa-uk-europe-canada/
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PWSlack
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#14
In reply to #6

Re: Generator CT

11/14/2019 11:55 AM

Ah! Those are the latest harmonised colours. Prior to 2004 the colours in the UK were red/yellow/blue for the three phase colours, and black was the neutral.

The forum has no information about the age of this installation, nor its location.

It's still looking as though a copy of the "as built" drawing will answer all of the Original Poster's questions. Such a document should always be the first port of call on queries like this.

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coolyaar
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#11
In reply to #4

Re: Generator CT

11/14/2019 7:34 AM

Why would CT neutral be connected to 11KV bar?
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PWSlack
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#12
In reply to #11

Re: Generator CT

11/14/2019 10:55 AM

The question is impossible to answer without sight of the "as built" drawing.

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redfred
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#13
In reply to #12

Re: Generator CT

11/14/2019 11:19 AM

From the angle of the single image, I'm not sure that right angle bus bar is connected to anything else but the blue wire. I realize that the image taken may be the best image possible in a cramped space but this is exactly why a drawing should be examined.

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redfred
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#5

Re: Generator CT

11/13/2019 1:17 PM

Whatever this wire does, I don't like how it is installed. That's a very sharp bend around the bus bar. If it was connected to the other side of the bus bar the strains would be much less on the wire.

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lyn
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#7

Re: Generator CT

11/13/2019 8:23 PM

Look at the schematic.

Ask the electrician.

You could have the electrician use a meter to identify its function.
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rwilliams
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#8

Re: Generator CT

11/14/2019 12:21 AM

The only entity that can answer this question accurately is the manufacturer of the current transformer. I’d guess that this wire assures the iron core of the CT is at the same potential as the primary conductor. They may have had problems with the secondary insulation they attributed to static charges in the insulated case?

This is unusual construction in my +20yr experience with 15kV class window type current transformers.
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raghun
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#9

Re: Generator CT

11/14/2019 6:44 AM

Window type CT encounters two layers of insulation - one is air between the 11kV phase conductor and the epoxy outer of the CT, the second is the epoxy insulation to the earthed secondary of the CT.

In some designs, the two layers cause potential grading issues due to unequal capacitances of two layers. Hence, some of the CT vendors provide a metallic shield in the outer part of the epoxy and connect it to the phase conductor. With this, the epoxy only has to be rated to withstand 11kV potential with no capacitive grading issues.

I have seen a case where the CT burst as the shield was not connected to thephase conductor and sustained discharges that ensued, led to CT damage over a period of time.

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Users who posted comments:

coolyaar (2); lyn (1); PWSlack (3); raghun (1); redfred (3); Rixter (2); rwilliams (1); SolarEagle (1)

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