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Topic Title: Undervoltage trip on HV Breakers
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Created On: 22 June 2012 07:43 PM
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 22 June 2012 07:43 PM
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peterfile

Posts: 53
Joined: 17 April 2002

I'm wondering can anybody explain how an undervoltage trip actually works for HV circuit breakers? Do they operate by mechanical means and release a latch or is it by energising the shunt trip and preventing the close coil from energising?

I understand this has not normally been an option for many MV and HV breakers, but there are now some models which offer the function.

I have just provided a refurbished breaker into a generator installation, and the VMX breaker does not have an UV option. The generator manufacturer insists on the function, so we have installed a failsafe relay on their monitoring output, which when de-energised, will energise the shunt. They're not happy about that approach, so I'm trying to find out if the only alternative is to replace the breaker.

Thanks

Pete
 24 June 2012 12:04 PM
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ArthurHall

Posts: 737
Joined: 25 July 2008

Under voltage releases arent that uncommon. Normally a circuit VT feeds an undervoltage relay, the relay uses DC to energise the trip coil. The under voltage relay could be incorporated into a multi function relay.
 24 June 2012 12:52 PM
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alancapon

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Joined: 27 December 2005

With a generator circuit breaker, you will almost certainly have a VT for synchronisation. I would also expect that you would have an overcurrent relay on the panel, which will be directionalised. You should be able to change the relay settings (assuming that it has the functionality built in) to trip the circuit breaker with no voltage. It is usual also to block a "close" until you have sufficient voltage, although I would expect to accomplish this using a check-synch relay.


Regards,

Alan.
 24 June 2012 02:53 PM
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peterfile

Posts: 53
Joined: 17 April 2002

Thanks both for your replies.
The circuit breakers themselves don't have this function, but we are achieving that aim by an incorporated relay in the CB panel which energises the trip coil in the event of undervoltage or loss of the signal from the generator panel.
However the generator manufacturer insists on a direct action, which will mechanically release the breaker on the loss of signal. I'm struggling to find a manufacturer that provides it in this way. If the majority of HV breakers rely on energising the trip coil, then the generator supplier's requirements are not likely to be met. If it were LV, it would not be a problem. In addition, the undervoltage is not monitoring the supply, but is an external contact from the genny panel which monitors their control voltage.

Are there any manufacturers that come to mind, or any suggestion of how to rebut this demand?

Thanks very much.

Pete

Edited: 24 June 2012 at 03:33 PM by peterfile
 24 June 2012 05:07 PM
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alancapon

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I know of no manufacturer of HV circuit breaker that offers a no-volt release. Apart from anything else, you would need to use a VT signal anyway, simply due to the problems of dealing with 11kV or higher (safely) in a solenoid coil. Any risks of the CB failing to trip could be taken care of by implementing a CB Fail scheme. That, together with a "trip circuit fail" scheme to provide monitoring of the tripping circuit, I think the requirements of a no-volt release are over the top for an HV application.

Regards,

Alan.
 24 June 2012 07:41 PM
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stableford

Posts: 64
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Most electronic protection relays-ala Multilin and others, have the function built in, however configuration of the device is a different matter.
HV circuit breakers are energize to trip, hence the multiple trip parameters are up to the user.
I define everything above 1000V out there as HV.

Derrick
 24 June 2012 09:29 PM
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peterfile

Posts: 53
Joined: 17 April 2002

That seems to be a common theme - the breakers are tripped using an external signal on the shunt.
I have found that Schneider do an undervolt release, and possibly Siemens as well. However the Schneider selection only allows for either a shunt trip or undervolt release - not both.
I'll look at a few more manufacturers when they're open for business, but I may be going back to the generator supplier and advising them thay can't have what they expect.

Thanks for the help here.

Pete
 24 June 2012 09:31 PM
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ArthurHall

Posts: 737
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I would be suprised if you found an HV breaker with UV protection built in. Alstom MVTI or MVTD are two examples of relay that could be suitable but other makers produce them also.
 26 June 2012 12:54 AM
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stableford

Posts: 64
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Dont forget that on HV, there are 2 separate devices, the breaker, and the protection relay.

Regards

Derrick
 26 June 2012 05:27 AM
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ukmaharaja

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Joined: 26 May 2005

Simple under voltage relay with either built in time delay timer or external time delay relay some times becomes a part of protection scheme to prevent back charging of equipment in case upstream side supply fails. For additional safety , its one of the normally closed contact is wired in closing circuit of the breaker , to ensure preventing breaker from closing in under voltage condition.
Regards,
Umesh
 26 June 2012 03:48 PM
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peterfile

Posts: 53
Joined: 17 April 2002

My biggest headache is to find one which has a direct action on the latch.
We already have a protection relay.

However it is not the line voltage that is being monitored, but the status of an external system voltage that when lost will trip the breaker.

The company that refrubished the breaker have again advised that this sort of release is not an option. The breaker is a GEC VMX-C.
It has been suggested to me that the design was bought by Tamco and that there may be a trip unit available from them.

Any suggestions of a third party option or retrofit that might help?

Thanks

Pete
 26 June 2012 05:57 PM
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ArthurHall

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I dont realy see what the problem is, I am fairly familiar with VMX gear, it normally has a shunt trip coil wired through the protection relay contacts and fed from a battery. If you fit an undervoltage relay connected to the supply you want to monitor and wire the output contacts in parallel with your protection relay it should work. If the breaker is wired to a BS scheme you are looking for wires K1 and K3.
 26 June 2012 06:33 PM
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peterfile

Posts: 53
Joined: 17 April 2002

ArthurHall
That is exactly what we have done in this case, but GE Jenbacher apparently insist that is insufficient to provide their engine with the correct protection, unless it is a full failsafe direct-acting operation.
As far as I can see, if their control voltage drops, or if the interlock cabling is lost, then our monitoring relay drops out. This then operates the shunt trip.
The shunt trip would only not function if:
1 - The monitoring relay fails to de-energise or
2 - The monitoring relay contacts fail to close on de-energisation, or
3 - The shunt coil has failed or
4 - The VMX control voltage is too low to operate the shunt.

Item 4 is covered by the battery tripping circuit.
Item 3 is a maintenance issue
Items 1 and 2 can be covered by dual redundancy.

In any event, for a generator covered by this, surely a loss of synchronising would trip the G59 relay and isolate the generator from the grid - we have G59 monitoring on a bus coupler rather than just on the synchronising breaker. Would this be quick enough to avoid damage to the alternator?

Thanks

Pete
 27 June 2012 08:16 AM
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ArthurHall

Posts: 737
Joined: 25 July 2008

I would agree that the system you are proposing looks OK. I would add trip circuit supervision to cover your items 3&4.
Perhaps Alstom can supply a no volt release coil for the VMX? dont think I have ever seen one.
 29 June 2012 03:53 PM
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ToniSM

Posts: 26
Joined: 21 November 2006

Contact Merlin Gerin. Their range of 11KV VCB use the same operating mechanism as the LV Masterpack range which can have any combination of up to three shunt coils. (Or so I was told by one of their service engineers I was working with). Worth a phone call.

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