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Topic Title: RMU Fuse switch tripping reenergizing locally
Topic Summary: Criteria for reenergizing and distance between RMU and Transformer
Created On: 28 August 2013 09:08 AM
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 28 August 2013 09:08 AM
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Badshah

Posts: 38
Joined: 22 July 2009

During Fuse switch(F/S) tripping, if it is oil RMU, we carry out all the isolation and reenergization from far ends.. i.e. the fuse switch will not be operated locally.
But for SF6 type RMUs we close the fuse switch locally during tripping(1 fuse blown out of 3 fuses). But recently while doing so, during an tripping, there was abnormal noise from transformer and we tripped F/S manually didn't wait for it to trip automatically.
In this particular station, the TR & RMU was placed nearby and i want to know, is there any standard which defines the min. distance between TR and RMU within a substation, considering the worst case scenario. Based on it, we have to identify the station where local operation should not be carried out.
Also if there is any better practice, please advice..

Thanks & Regards,
 29 August 2013 12:22 AM
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alancapon

Posts: 5834
Joined: 27 December 2005

There is no minimum distance, however, the best option is not having to pass the transformer on the way out of the substation. It is also useful if the RMU is arranged so that a lanyard can be used easily - most switchgear can be operated with some rope and a couple of pulleys.

I am surprised you tripped the faulted transformer manually. To be honest, I would already have left the substation in that scenario (and have done in practice).

Your final question about working out which RMUs should be switched live, is to undertake an analysis of their insulating oil.


Regards,

Alan.
 29 August 2013 06:54 AM
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Badshah

Posts: 38
Joined: 22 July 2009

Hi Alan,
Thanks for the reply, When our staff heard the abnormal sound, he was in front of RMU and just pulled the tripping mechanism and left the substation immediately.
Regarding the Rope & Pulley arrangement, is this approved practice? and any supplier/manufacturer available in the market?
 30 August 2013 12:17 AM
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alancapon

Posts: 5834
Joined: 27 December 2005

I had a transformer short between HV and LV windings while re-energising the LV with solid links a few years back. I did not wait for the HV fuse to operate or trip the mechanism - I was in "running mode" as soon as the first odd sound was heard.

Regarding the rope and pulley, we usually refer to it as "closing by lanyard". I am sure you can get proper ones, but mine is some insulating draw rope, and a couple of pulleys from the local diy store. With the addition of a reel of insulating tape foe helping to attach the rope to the operating handles, you can operate most switchgear. The rope is long enough to be able to get out of the substation and a few metres away. Where a lanyard cannot be used, we would operate the switchgear dead, then re-energise remotely. Our safety rules allow the person "on the end of the handle" to refuse a switching instruction for safety reasons.

Regards,

Alan.
 03 September 2013 07:48 PM
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neilmcd84

Posts: 56
Joined: 02 June 2003

I am surprised that you don't switch locally. It is very common practice to stand in front of gear and operate it. As long as you have good maintenance practices, take account of any operational restrictions (eg the recent 'no live operation' restriction on Long and Crawford FSWs) and consider your escape route/s then you will be fine.
The gear is rated to be operated live, usually including closing onto faults.
However I would never interrupt potential fault current while standing in front of gear. Let it burn! I have only had to make real emergency escapes from substations twice, and on both occasions I found myself 30 metres+ from the sub with no memory of how I got there. I would never have tried the switching your colleague carried out.
 03 September 2013 11:51 PM
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alancapon

Posts: 5834
Joined: 27 December 2005

You need to risk assess all your switchgear for its condition / known defects. This will allow you to separate your switchgear into equipment with little risk, equipment that should be operated with a lanyard and equipment that should be operated dead. You also need to carry out some training, as virtually no RMUs are rated for breaking fault current - that is what the fuse is for.

Regards,

Alan.
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