H.V. Ring Main

[Pete999]

I have been looking through all of my paperwork, something to do now I'm retired, and an interesting question came to mind regarding H.V. Ring Mains.

I appreciate not every one would have worked on one but for those who have here is the question, When I was involved we always operated an open Ring, now for example if you needed to isolate a run of cable, say you needed to splice into the H,V, cable to, maybe add another DSS somewhere, the procedure I adopted was to close the ring, at where ever it was left open and proceed to isolate the cable that needed work done on it, we would isolate and earth down the cable, now for the life of me I cant recall if it needed earthing at both points of isolation, can't see the point of doing this really, but perhaps someone who is currently involved could throw some light on the subject, as I say it is just something that got stuck in my head, and I couldn't answer it, sad I know but hey hoe, grateful if someone could help me relax and put my mind at ease.

Not every ones cup of tea I know.

 

[pc1966]

Not my area but AFIK the HV ring main is designed as a loop with switch points at each transformer, etc, but normally it has one point left open to reduce fault currents if something goes wrong.

For maintenance, etc, you can close it if needed and open another point, or open two and earth the segment between them, etc.

 

[mhar]

My youngest is a dno hot glove technician who works on the 11 and 33kV networks (South West). He advises that the 33kV is a ring but the 11kV is an open ring so that different sections can be isolated to work on causing the minimum of disruption to the distribution network. Being an SAP and being authorised for HV switching I am sure that he can advise on any specific points, however most of his work is live - all to do money and how much the dnos get fined for customer minutes off supply.. Even in the height of summer he has to wear 5mm of neoprene plus leathers and has a dedicated observer watching him at all times.

 

[DPG]

My youngest is a dno hot glove technician who works on the 11 and 33kV networks (South West). He advises that the 33kV is a ring but the 11kV is an open ring so that different sections can be isolated to work on causing the minimum of disruption to the distribution network. Being an SAP and being authorised for HV switching I am sure that he can advise on any specific points, however most of his work is live - all to do money and how much the dnos get fined for customer minutes off supply.. Even in the height of summer he has to wear 5mm of neoprene plus leathers and has a dedicated observer watching him at all times.

My Mrs makes me wear leather and neoprene. But I'm not involved in any high voltage switching. Should I be worried?

 

[pc1966]

Should I be worried?

Not if this is your typical evening:

 

[pc1966]

On a more serious note (if I have one) the switching points are called Ring Main Units and started in the UK as a specific standardised (to a degree) pre-assembled design, etc.

 

[mhar]

There is actually a fair bit more to this than one might think at first. There have been occasions when he has had to isolate different sections of the 11kV network and power them by step up transformers, instead of 11kV down to 400V as is usual these are 400V to 11kV.
As regards to spiking he was quite looking foward to setting off the charge which fires the spike through the cable and into ground. He was quite disappointed when the bang he was expecting was more like the pop of an air rifle!

 

[wemejimmy]

My youngest is a dno hot glove technician who works on the 11 and 33kV networks (South West). He advises that the 33kV is a ring but the 11kV is an open ring so that different sections can be isolated to work on causing the minimum of disruption to the distribution network. Being an SAP and being authorised for HV switching I am sure that he can advise on any specific points, however most of his work is live - all to do money and how much the dnos get fined for customer minutes off supply.. Even in the height of summer he has to wear 5mm of neoprene plus leathers and has a dedicated observer watching him at all times.

Hi Thanks for info not sure it answers what Im asking but then again Im probably not asking the question correctly, we have a main incoming switch room 11kv that consists of Scottish power incomer plus two feeds to transformers, during power down we maintain the transformers one at a time, does the the feeds have to opened and earth down or can we isolate at the transformer OCB locally.

 

[Moley]

We would normaly isolate 1 TX at a time. Normaly in that situation the OCB would be withdrawn, the outgoing breaker would be racked out and busbar shutters locked and local earths applied to the transformer. I assume as you are using OCBs that they are quite old? What make/model are they? Are they being maintained at the same time? When was the last time they had an oil change? I've seen the after effects of a gassing OCB and it wasn't pretty. Took out a couple of walls and a roof!

 

[wemejimmy]

We would normaly isolate 1 TX at a time. Normaly in that situation the OCB would be withdrawn, the outgoing breaker would be racked out and busbar shutters locked and local earths applied to the transformer. I assume as you are using OCBs that they are quite old? What make/model are they? Are they being maintained at the same time? When was the last time they had an oil change? I've seen the after effects of a gassing OCB and it wasn't pretty. Took out a couple of walls and a roof!

Cheers mate Ive been given incorrect info notOCB'S its ACB's and yeah that's what I thought, one trans. at a time, main incomers can be left on, local ACB feeding transformers off and racked out earth down, allowing maintenance of transformers, LV side off and racked out, preventing back feed from generators.

 

[Moley]

I would say LV side racked out before applying earths. If you have a backfeed
from the LV applying earths to the HV could be a little bit 'eventful'. I don't know what size and what panels you have for your TX but we normally have control voltage available so any alarms and trips can be checked back to the relavent panel. What sort of maint. do you do to your TXs? Do you maintain the breakers at the same time?