Substation Fuse

[linuxthefish]

What would the rating be for a substation fuse and has anyone ever seen one go while on a job? Had a mate asking me this earlier, and now i feel interested.

As i understand it goes: substation fuse > DNO fuse > CU?

 

[mechelec]

Depends on the size of the dno transformer. This is protected by Hv fuses in the transformer switch fuse. This in ground mounted gear. Overhead is a bit different with a number of pt's being protected by oh fuses. Lv distribution fuses need to grade with the Hv fuses, you don't want an Lv fault taking out an hv fuse and the entire sub. Lv fuses can vary between 100A and 630A
Yes I have heard them operate. When you have replaced one and a fault on the Lv feeder makes the tx rumble and grumble until the fuse operates. I have also banged them in onto a fault. You want safety glasses on for that!!! 400A onto a dead short makes a big bang
It should be primary circuit breaker-pmr-oh hv fuses- switch fuse- Lv feeder fuse- etc

 

[Knobhead]

Have a look at Low Voltage Switchgear & Feeder Pillars | Schneider Electric UK

As mechelec says it’s fun (not) replacing a fuse on to a fault, where people come unstuck is by pulling the fuse back out rather than wait for the fuse to blow safely. Pulling the fuse causes a tremendous arc and probably an explosion. PPE is essential, a colleague of mine was badly injured by a short on a circuit protected by a 1200A ACB. His sight fortunately was saved by his glasses, his face and hands were a mess.

The transformer isn’t exactly happy while this is going on. One particular fault we had was caused by the checker plate over a cable trench being dropped edge on, on to the transformer tails, it blew the plate 6’ in the air.

 

[linuxthefish]

Thanks both of you, i was expecting something along the lines of "Don't ask silly questions". HV/DNO looks interesting, i'm looking at going down that route soon hopefully!

 

[mechelec]

Thanks both of you, i was expecting something along the lines of "Don't ask silly questions". HV/DNO looks interesting, i'm looking at going down that route soon hopefully!

I would recommend it. I have worked for a DNO for 4 years now after various other electrical and mechanical maintenace type jobs, installation, testing etc over a good few years. I find the the work is interesting and you can work towards the authorisation level you want to acheive. It comes with regular pay and the usual big company benefits.

 

[Guest111]

I saw an overhead line come down once 33kv took 2 pole fuses but didnt take the third,arcing all over the place anyway rang dno who panicked as it was on a main rd and lots of oh lines so they didn,t know which one it was,anyway guy calmed down quite a bit when i told him i was a sparks,they sent out fire service and asked me to supervise incident till they arrived,which they did 3 hours later and it was early hours of new years day,wish I had got paid for it lol

 

[Knobhead]

Yeh right. Supervise? Show them there it is maybe.
The first to tell you where to go would be the fire brigade if you tried to interfere! They arrested my boss for sticking his oar in.
As far as I know blow out fuses are used up to 11KV only.

 

[mechelec]

You are right Tony I have never seen DOEF's on 33KV OH yet in my area either.

 

[Knobhead]

I wouldn’t want to see one go, I damn near jumped out of my skin when an 11KV blow-out fuse went. Dread to think what a 33KV would be like.

 

[Guest111]

well thats what they said it was 33kv,and as regards fb apparently they were told to take advice from me by the guy at the dno,personally I,d rather have been in a warm bed than stuck outside but round here you just get used to helping out.

 

[Knobhead]

The DNO would not ask you to do anything other that keep out of the way. If they had and anything happened their --- would be in a legal sling.
The fire brigade are trained to do the shuffle walk. Are you? If you don’t know what the “shuffle” is, read up on ground voltage gradients. It looks comical but it is a lifesaver, fatal if you’re a cow.
The last time I saw an 11KV line come down there were 6 dead cows dotted around and nearly a dead farmer if he hadn’t been stopped approaching them.

 

[Bobster]

I've only ever heard 3.3kv motor fuses go. That was an experience.

A couple of brushes had gotten stuck to the slip ring, flames everywhere. The cb downstream of the fuses failed to operate.

Was only there because we were having trouble with the excitation voltage.

 

[Knobhead]

We had a 3.3 motor that the brush gear failed regularly. Saturday afternoon used to be like a kids Easter egg hunt with us searching for bits blown out of the motor inspection cover. It took me 6 months to get the company to agree a new ring cleaning regime, after that no problems. First time it went I was stood next to the ACB when it tripped, it lit the room up. (Didn’t do me a lot of good either).

 

[mechelec]

11kv DOEF's sound like a shotgun going off above your head. A "Close to possible fault" instruction always makes you twitchy when you can't see why they operated in the first place

 

[Guest111]

yes tony i am trained actually also i was a volunteer with the major incident support team at our local fire station for over a year,dont know why you seem to be getting wound up over this could it be someone has done something you haven,t perhaps?