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procedures for replacing a sf6 11kv ring main unit

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polsk

Wed Apr 21 2010, 02:44PM

Registered Member #2815 Joined: Wed Apr 21 2010, 02:28PM
Location:
Posts: 1

Hi I'm in a bit of a dilema!
can you prove dead on a sf6 11kv ring main unit, or is simply switching both cables to cicuit earth at either end good enough, and what tests would be carried out under a sanction for test on a replacement ring main unit:-?

Dr. Slack

Wed Apr 21 2010, 03:12PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

I might be mistaken here, but I suspect you're on the wrong forum.

The procedure for replacing an 11kV ring main unit is to get someone who knows what they're doing to replace it.

radiotech

Wed Apr 21 2010, 04:37PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

In your jurisdiction, what agency writes the operating procedures for this class of voltage and you licensed to do these procedures?

Unless the switchgear can be drawn out for repairs, isolation, locking, and grounding of outgoing and incoming feeders is necessary before touching anything.

Grounding without isolation may be useless if any feeders connect directly or through transformers to overhead lines.

Patrick

Thu Apr 22 2010, 03:26AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

forgive my ignorance, what is a "11kv main ring" ?

radiotech

Thu Apr 22 2010, 07:30AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

High voltage power loops or rings are a way of connectiing substations together so if part of the system is shut down for maintenance the rest of the system will keep up. The breakers connecting the substations are called interties. To work on a section of the lines, it is isolated at two stations.The loop can have loads or sources, and some loads that become sources.

Often with pump stations an ATS automatic transfer switch can move the supply to another feeder should one go down.

Dilemma's happen when something already running on backup starts to go flakey.

Dr. Slack

Thu Apr 22 2010, 07:32AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

forgive my ignorance, what is a "11kv main ring" ?

It's a local power distribution system, which operates on the level of serving (say) 3000 homes or 100 light factories. It consists of a loop (ie ring) of cable running at 11kV, fed from a number of seperate grid downto 11kV transformers, and feeding the end loads by many smaller capacity 11kV downto 240v transformers. The purpose of connecting all of the transformers in a ring is that any one feeder can be taken out of service by isolators, and everything will still function. Any one transformer can be taken out of service, and the rest will still function. This allows it to be maintained and be somewhat fault tolerant while still giving a high percentage of uptime.

Obviously the ability to service a bit of kit, with 11kV just the other side of a breaker, means that rigourous safety procedures have to be maintained. The union of cable splicers and associated trades would not take kindly to one of their members being accidentally vapourised every so often.

If we are talking about 11kV ring main means that we are into major league stuff, 100s of MWatts and millions of annual revenue. This is not hobbyist territory.

Then again, if you simply have an 11kV to 240/110 pig sitting on your yard to test for your Tesla coil, then that's a different story.

Another, possibly slanderous, thought occurs to me. Have you spotted a redundant pig, and wonder whether it can safely be liberated?

Steve Conner

Thu Apr 22 2010, 09:08AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I've visited factories that were big enough to have their own 11kV ring mains, and these aren't covered by power company regulations because they're privately owned.

Officially, you shouldn't be anywhere near these things unless it's your job, and if it is your job then you should have received proper training and know what to do.

Common sense would suggest the following:

You should have a complete diagram of the system so you know what feeds what.

Isolate and earth the two feeders feeding the unit, at the two adjacent units in the ring. The isolation and earthing switches should be padlocked off, with tags attached explaining the reason why, and you should keep the keys on your person so that nobody can turn the power back on until you're done.

If the unit feeds a transformer that could be getting back-fed from the LV side, then you need to isolate and earth that too.

Operate the earthing switches on the unit you're about to replace, without the isolating switches. If it doesn't explode and black out half the town, then you have proved it dead, unless of course the earthing switches don't work.

Some of these things have meters on them, and you can look to see if the voltage is gone. But in this case, you should have looked at the meters before isolating it, to prove that they work.

The only test I know of on SF6 switchgear (apart from the RF partial discharge measurements that we're researching) is, check the gas pressure to make sure it's not leaking.

All of this advice is provided without warranty, use at your own risk.

radiotech

Thu Apr 22 2010, 05:52PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

"Have you spotted a redundant pig, "

Once I went to pick up some things from a military base and the quartermaster, said one item was currently 'not located',although documented, however there was another item that was located, but was currently undocumented.

The alternate item, was better than the one I had bought.

Patrick

Thu Apr 22 2010, 06:25PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

whoa ! find someone who is qualified dude!!! wholly shit !!!

Procedure:
1) locate sufficienct beer supply.
2) find qulified person
3) drink beer, watch them do the work.

Steve Conner

Fri Apr 23 2010, 10:20AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Patrick wrote ...

1) locate sufficienct beer supply.
2) find qulified person
3) drink beer, watch them do the work.

Hey! Electricians shouldn't be drinking beer on the job, even if that's what they do at Chico.

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