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#47079 - 01/07/05 10:01 PM Problem Voltage transformers,
bdg Offline
Junior Member

Registered: 01/07/05
Posts: 6
Dear,

I live in Europe and I work in an energy company at this time we have some troubles to locate faults in a medium voltage network, We have 40 clients connected on 1 feeder departing out of our main network, due the new voltage transformers the secundary and also the primary windings are now connected to earth, that means if you want to find a fault in the network with a megger (earth fault testers) you always get a fault even there is no fault in the line, this is due the new type of current and voltage transformers.

Any suggestions? to locate a fault with this new types of current and voltage transformers?


Regards Ben


[This message has been edited by bdg (edited 01-08-2005).]

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#47080 - 01/07/05 11:10 PM Re: Problem Voltage transformers,
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Welcome Ben!.
I don't want to sound rude, but I would'nt like to give this sort of advice over the Internet without knowing what sort of protection on the system has operated and where that protection is in the system.
I would personally be checking any underground cabling first with the megger, before doing anything else.
Obviously, if the system was working before the new Current and Potential Transformers were installed, logic would dictate that there is a fault in the installation of the CT's and PT's.
BTW, what brand/type of transformers are they?

[This message has been edited by Trumpy (edited 01-08-2005).]
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#47081 - 01/08/05 10:40 AM Re: Problem Voltage transformers,
bdg Offline
Junior Member

Registered: 01/07/05
Posts: 6
hi,

Very thx for the response, yes I'm testing all the underground cables, but that's the problem, al the Medium voltages cabines are connected to each other and before the new current & voltage transformers there was a possibility to check in the beginning or the end of the line? I put the megger between R or S or T phase and ground and if there was no shortage I got a good result, if you know what I mean, difficult to explain, but now with the new current and voltage transformers the primary is also connected to the ground, this calls unipolar shielded in europe, the system is protected with a SIEMENS SJ5005 earth protective relay.

thx

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#47082 - 01/08/05 10:48 AM Re: Problem Voltage transformers,
bdg Offline
Junior Member

Registered: 01/07/05
Posts: 6
the current transformers that we use are 11000/110/3 ABB VT series

or AEG 11000/110/3

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#47083 - 01/09/05 01:45 AM Re: Problem Voltage transformers,
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Ben,
Thanks for the reply!.
I'm a HV Faultsman here in New Zealand and this sort of thing is "Bread and Butter" to me.
Also I have quite a bit of experience with the ABB VT series of Circuit protection.
Tell me, was the new equipment of the same "ratio" as the old?.
Also, we use the Siemens SJ5005 on a few of our systems here.
Are you sure that you haven't got a conductor going through the loop in the wrong direction?.
I can only sort of help, I think.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#47084 - 01/09/05 03:04 AM Re: Problem Voltage transformers,
bdg Offline
Junior Member

Registered: 01/07/05
Posts: 6
hi, I would like to talk to you directly over msn? is that possible?

my msn adres is benoitdeguffroy@hotmail.com

or at AOL AIM bdgtrader@aol.com

regards and thx

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#47085 - 01/09/05 08:20 PM Re: Problem Voltage transformers,
bandb12 Offline
Member

Registered: 01/09/05
Posts: 23
Loc: Crown Point, NY, USA
I am a HV test tech, and you will need to isolate the equipment being tested from ground.

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#47086 - 01/14/05 08:26 AM Re: Problem Voltage transformers,
bdg Offline
Junior Member

Registered: 01/07/05
Posts: 6
I think that's the best way, I work on a tester based on a unique technology

Regards
ben

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