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Syed Ziauddin
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Join Date: Jul 2007
Posts: 37

Problem in power house

11/27/2007 2:33 AM

I am working in a container terminal. We have a power house of 7 x 1.2MW x 11kV capacity and all 7 DGs are connected to a common bus bar.

Recently we had a Earth fault in the "bus bars" and "generator in" compartment, found insulators were carbonized and moisture was in it. There is a Earth fault/short circuit relay which was not giving any indication initially, it gave earth fault indication when physically smoke and smell came out from one of the out going panel.

My question is that our Power house is about 3.5 year old, should we check the quality of insulators and protection relay or improve environment or we should induced some more safeties to the system so that to prevent recurrence of such faults. Any other suggestions will be most precious to us.
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calmade
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Join Date: Nov 2007
Posts: 9
#1

Re: Problem in power house

11/27/2007 3:57 AM

You should have to emplement the yearly preventive maintenace on all your HV CB. and also do a yearly check and calibration on all protection relay. Thare are some special instrument for calibration.
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PWSlack
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#2
In reply to #1

Re: Problem in power house

11/27/2007 4:14 AM

Quite. The manufacturer's maintenance manuals would be an excellent starting point for this poster.

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nesubra
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Join Date: Nov 2006
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#3

Re: Problem in power house

11/27/2007 9:57 AM
  1. Being a container terminal u will have saline atmosphere in addition to carbon.Saline atmosphere will reduce IR value.Breakdown of air is more easier.In fact u are lucky not to have phase phase flash over.Check whether u also have Corona even though it is 11kv.We have seen this in some Islands.The relay should have tripped unless some tampering of settings had taken place.The best in such circumstances is to revert back to good old electromechanical relays which are fail safe.Also have regular maintenance like cleaning the insulators and applying CTC.It may also be worthwhile to sectionalise the bus into two sections with a bus coupler .
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pwr2thepeople
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Join Date: Aug 2007
Location: Indiana, USA
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#4

Re: Problem in power house

11/27/2007 3:54 PM

Unfortunately, the problem you describe is fairly common. Although I agree with all the above comments, no one has addressed the moisture you describe. I suspect condensation is the root cause of the fault. If there are no heaters in the switchgear (and bus duct if you have it), install them. If there are heaters installed, they are probably non-functioning. This could be from a failed element, blown fuse or a loose connection.

Check the entire protective relay circuit from the current transformers through the relays to the breaker trip coils. If this is an electro-mechanical relay, the moisture may have corroded the bearings. If solid-state, check for moisture on the circuit boards inside the relay.

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Andy Germany
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#5

Re: Problem in power house

11/28/2007 6:19 AM

Buy a Megger and check insulation values yourself to earth when planned maintenance is made (as well as following the other good advice posted above!).

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