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anbarasu.pr
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Join Date: May 2009
Location: INDIA
Posts: 25

Homopolar Transformer (Neutral)

06/06/2010 1:07 AM

Kindly can any one give me the details of Homopolar Transformer (Neutral), which is used in a system instead of Neutral Grounding Resistor (NGR).

Ie. NGR we use to connect it in the Neutral of Generator.

But Homopolar Transformer is connected to the bus where the generator is connected.

If any article available on this kindly provide.

Thanks in advance for your reply.
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North of 60
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#1

Re: Homopolar Transformer (Neutral)

06/06/2010 1:14 AM

Do you mean a zigzag transformer? Is your genset wound delta?

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anbarasu.pr
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Location: INDIA
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#2
In reply to #1

Re: Homopolar Transformer (Neutral)

06/06/2010 1:19 AM

Generator is Star wounded,

Homopolar Transformer Primary is Star & connected to earth & Secondary Delta kept open.
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Anonymous Poster
#3
In reply to #2

Re: Homopolar Transformer (Neutral)

06/06/2010 5:40 AM

Ohhh.. poor thing. How could a star have wounded it?

Anyway, google with the keywords "Homopolar transformer" and see what you get. Some current transformers, some rotary machines, lots of patents...
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pwr2thepeople
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#4

Re: Homopolar Transformer (Neutral)

06/07/2010 9:46 AM

The device you describe is a toroidal current transformer with all 3 phases passing through the center. It senses the direct residual current (Ir) produced by unbalanced current in a 3-phase circuit. When an earth fault occurs, fault current in the affected phase does not return to the generator via the other phases. It returns through ground to the neutral star connection of the generator. The fault current through the phase conductor is sensed by the CT, causing a current imbalance which is sensed by the CT. The output of the CT is connected to an earth fault relay.

This type of sensing can also be accomplished with a separate CT on each phase conductor. The CT secondaries are wired in a star connection. The earth fault relay is then connected in series with the neutral (star) of the CT secondaries.

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kvsridhar
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#5
In reply to #4

Re: Homopolar Transformer (Neutral)

06/07/2010 10:27 AM

Interesting. i didn't know this before, thank you.

Is it not doing the same function as a CBCT (Core balance current transformer) for ELCBs in India? The difference in that is that all four wires (3Ph+N) pass through this CT, and whatever extra has to be an earth leakage current.

i expect that the areas of application are quite different, what i mention being a domestic supply.

"Homopolar" to me meant "One pole" "homopolar motor"...some distant memory from a long time ago, very misty

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