600volt CT's on 34.5kv Feeder Cable???

[SLCC84]

I am just wondering if anyone has any experience with MV-HV feeder cables with severely under voltage CT's? Is this acceptable or what possible damage can be done? Cables burning up?

I recently came across a 3ph 34.5kv piece of switchgear with 2 CT's on phases A and C. They were both 600v CT's but it was a 34.5kv line?

Appreciate any help.

Thanks

 

[GoldDigger]

I am just wondering if anyone has any experience with MV-HV feeder cables with severely under voltage CT's? Is this acceptable or what possible damage can be done? Cables burning up?

I recently came across a 3ph 34.5kv piece of switchgear with 2 CT's on phases A and C. They were both 600v CT's but it was a 34.5kv line?

Appreciate any help.

Thanks

Not sure about the regulations, but it seems to me that as long as the insulation on the cable itself is good there is no problem on that end.
What could be a real problem is that if the secondary of the CT is open circuited it will act more like a saturated potential transformer and the voltage on the open output leads could be considerable.
Not anything like the voltage times the turns ratio though, since the 34.5kw will not be developed across the "primary" of the CT.

 

[jim dungar]

They were both 600v CT's but it was a 34.5kv line?

The 600V CT is adequate because the 'outside' surface of the 34.5kV insulation is at really at 0V to ground, otherwise it could not touch a grounded surface like the cable shield or a grounded raceway.

 

[electrofelon]

Does the shielding on the cable pose any issue or discrepancy with the current measured by the CT?

 

[iceworm]

Does the shielding on the cable pose any issue or discrepancy with the current measured by the CT?

My experience is 13.8KV and down.
Yes. Normal installation terminates the shield to a pigtail. The pigtail is run back through the CT and then is grounded. Running the shield pigtail back through the CT eliminates any currents on the shield.

ice

 

[GoldDigger]

Does the shielding on the cable pose any issue or discrepancy with the current measured by the CT?

If the cable shield carries return current then the CT output will be wrong. But the post above tells you how to fix that.
I suppose that if the shield is terminated only at one end there will be some capacitive current. I just do not know if it will be significant. Probably not.


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[electrofelon]

If the cable shield carries return current then the CT output will be wrong.


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Oh of course, silly me. In a typical 3 phase wye system, the three shields will make up the neutral conductor so they will carry current. On a single phase line to neutral circuit, the shield will be the neutral. But on a delta system or a ungrounded single phase system (2 cables), the shields will just be grounded. But in these latter cases I still couldn't CT over the entire cable? Does this effect the question in the OP then?