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What is the Spring's Function in CT Measure?

07/08/2017 10:16 PM

Hi all
When maintenance transmission system from generator to SF6 Breaker (20kv). i detected on transmission line from SF6 to Transformer have two spring which connect from CT to phase line (1 touch, 1 don't touch). Near location have electrical discharge from phase line (phase line coated by insulation paint) to spring (don't touch) to. I don't know spring's function in CT measure. I have picture show it. Many thanks

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#1

Re: what is the spring's function in CT measure?

07/09/2017 7:04 AM

Maybe it doesn't belong there. Someone dropped it and it was attracted by the magnetic field.

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#3
In reply to #1

Re: what is the spring's function in CT measure?

07/09/2017 12:05 PM

it is attached by a screw bolt.

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#2

Re: what is the spring's function in CT measure?

07/09/2017 9:09 AM

Maybe it's one spring broken in half.......did you try to remove it?

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#4
In reply to #2

Re: what is the spring's function in CT measure?

07/09/2017 12:14 PM

No. i don't try to remove. that is design. I just want to know why have spring in there. it is 600MW power plant.

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#5

Re: what is the spring's function in CT measure?

07/09/2017 3:13 PM

Here's a guess...Maybe it's part of some mounting hardware which was once there to hold the CT in place in a permanent installation.

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#6

Re: what is the spring's function in CT measure?

07/09/2017 4:36 PM

It's quite hard to understand your question.

It almost sounds like the spring is there to make a flexible contact with a semi-conductive layer of insulation and prevent a capacitive charge build up, but then again this is only a guess and I have never seen a spring used this way before myself.

Who is the manufacturer, and have you contacted them? I doubt this sort of detail is shown in the drawings or in the manual but it would be worth while checking those just in case it answers your question.

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#7

Re: What is the Spring's Function in CT Measure?

07/10/2017 12:09 AM

Question is not clear.The spring is not a part of CB if we go by your statement.Can u post a clear picture or draw a schematic and post.It appears to be apart of transmission system.Why it is there can be understood only after getting the above

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#8

Re: What is the Spring's Function in CT Measure?

07/10/2017 6:10 AM
  1. The CT has earthed windings. It is insulated by solid insulation.
  2. The phase line is live.
  3. The CT to phase gap is far less than the usual clearance in air. Hence need for its solid insulation.
  4. The thickness and permittivity of the solid CT insulation means most of the voltage appears across the air gap - which will certainly break down in a "corona" way - although current is initially limited by the capacitance of the solid insulation.
  5. Solid insulation for high voltage ends with a semiconducting layer to reduce the surface field strength, particularly evident in HV cables where geometry makes the field strength at the inner conductor higher.
  6. So I think the inner surface of the CT insulation has a conductive layer, which is connected to the phase line by two springs [one to do the job and one to back it up to make absolutely sure].
  7. Without the connection 6, discharge in the air gap 4 would cause deterioration and failure.
  8. The coating on phase line may be "insulating", but this will break down with the thin film between spring and phase line.
  9. Considering the above, I think the two springs are too important not to be shown on drawings, or at least mentioned in assembly instructions. Obviously, phase conductor size may vary & CT may not be concentric with phase line in practice, so the connection is a spring.
  10. An enquiry to the CT makers service department should "put your mind at rest". Send picture & ask if the evidence of electric discharge seen is normal and what kind of paint should be on phase line, should you repair it?? - maybe it should be a "semiconducting" type.
  11. They will be pleased that you have noted the details and have the sense to enquire if the slight damage is normal or a warning of future failure.
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#9
In reply to #8

Re: What is the Spring's Function in CT Measure?

07/10/2017 6:37 AM

Further to my post #8. Considering what OP wrote & photo, I realise spring in photo is not touching phase line. It is obviously best both springs contact & this must be highlighted in query to CT maker.

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#13
In reply to #8

Re: What is the Spring's Function in CT Measure?

07/14/2017 11:44 AM


With above picture, the Spring is sure in the design of product. " it connected solid CT insulation. @67model: What technical documents have you seen or mentioned?

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#16
In reply to #13

Re: What is the Spring's Function in CT Measure?

07/16/2017 5:55 AM

I have not looked at, or given reference to any documents.

Remember, you have not identified the type or make of CT to us.

As I wrote, the manufacturer is best placed to explain the function, maintenance and acceptable condition of this spring connection.

You are best placed to see or test if the springs are connected to the wires "ringed" in your latest photo.

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#17
In reply to #13

Re: What is the Spring's Function in CT Measure?

07/16/2017 7:43 PM

The wiring shown connected to the springs is green/yellow wire, a colour code that is almost exclusively used for earth wiring so my comments in post #6 stand.

If you have any concerns check that the springs are in fact connected to earth and leave them be, or contact the manufacturer for more details. Do not attempt to disconnect the springs as they are there for a good reason.

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#10

Re: What is the Spring's Function in CT Measure?

07/10/2017 10:27 AM

What voltages are present? I have seen instances where something like this surrounds a high voltage, small radius location for the purpose of suppressing corona discharge.

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#14
In reply to #10

Re: What is the Spring's Function in CT Measure?

07/14/2017 12:00 PM

it is system rrom Generator to Transformer (20/220kv). Electrical discharge on conductor 20kv live.

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#15
In reply to #14

Re: What is the Spring's Function in CT Measure?

07/14/2017 12:33 PM

OK, then those little springs are actual pick up for the CT? Or are they there to dissipate any static charge present, not part of the high tension potential?

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#11

Re: What is the Spring's Function in CT Measure?

07/10/2017 10:38 AM

Well if we are just going to guess, then it could be monitoring the condition of the SF6 insulating properties, as the gas leaks down the voltage or temperature on the containment builds up signalling it's time to replace gas....

http://www.utilityproducts.com/articles/print/volume-7/issue-5/product-focus/power-monitoring/high-voltage-remote.html

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#12

Re: What is the Spring's Function in CT Measure?

07/10/2017 2:13 PM

Those springs are not belonging in this CT in this configuration. Remove them, contact OEM, (for the CT), and see if to back-install them in correct position.

Bad Bad Bad.

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