You’ll love this.

[Knobhead]

This is one for any guys that have worked on HV stuff

Asked by a mate to check a switching schedule for an 11KV system. 3off 20MVA 33/11KV ATC transformers feeding a large site. He needed to parallel two 1MVA 11/.44KV transformers for a short while.
So I read through his schedule and noticed he’d missed out balancing the ATC’s voltage (you put them in to leader and follower mode not independent as is normal). Phoned him up and pointed it out. “Yes OK will have a look at that” he didn’t!

He closed the bus section ACB and two 1MVA transformers are now trying to sort out a fight between two unbalanced 20MVA transformers. I don’t know who set up the O/L protection but it must have been perfect. TX1 went out on HV O/L, TX2 went out on LV O/L at the same time!

Data centre, pub, a large potion of the works plus half the village all blacked out!

 

[VoltzElectrical]

is this sort of thing additional training? I don't have a clue what you're on about. But I'd like too.

Input needed.

 

[madmac]

Lucky the fault protection panels were wired by electricians and not labourers/fitters as will happen soon unless things are tightened up!!!

 

[DurhamSparky]

sweet!!!

where was this balls up located!!

 

[VoltzElectrical]

Oi, you lot in the know... fill me in, or is this secret society training?

 

[DurhamSparky]

specialist training buddy!! unless your company you work for requires it then chances of you doing the courses are slim to none!! my company paid 1.3k for my 2week HV AP course alone...! not to mention others that will intotal cost approx 10K AND take 5 - 6 months

 

[VoltzElectrical]

no probs. Just wanted to check I didn't miss anything at evening class!

 

[madmac]

HV work is quite specialist, however, with the up-grading of the system to incorporate these new wind farms and the general run down state of the subs, it's only a matter of time before the contracting mentality swamps the industry and labourers and the like will be wrecking the joint!!! as is already happening in Scotland with the likes of BBESL who seem hell bent on using ex-fishermen and calling them electrical fitters and using them to install the new primary works!!! won't be long till they're shown and then let loose in the relay rooms!!!!!!!!!!!!!!!!!!!!!!!!!!!!!:crazy: God help us!!!

 

[Engineer54]

To be honest i'm a little confused myself!!! The bus coupler shouldn't have been able to close, via the control circuitry and protection relays if the two primary supplies were not compatible in any way at the time of closing. That would apply to manual or auto closing.
Not even sure why you would need to parallel the two TXs, as both would be supplying each side of the bus couplers outgoing circuits anyway??


Generally speaking, only TXs derived from the same upstream source, should be able to be paralleled on a single bus. Even then, depending on the complexity of the upstream system could be hazardous, ...say if due to a TX being taken out of the normal supply system and a supply from a completely different system, switched in to temporarily take up the load....

 

[Knobhead]

The two 1000KVA Tx’s were paralleled with the intension of not loosing supply to the data centre. It was so one of the Tx’s could be shut down to fix an oil leak. So the parallel operation should have been just for a matter of seconds. Unfortunately the unbalanced load and voltage on the main incoming board caused the trips to operate. Had my mate balanced the voltage he wouldn’t have had the problem. All his own fault!
Fortunately the UPS system took care of the data centre but the other uses weren’t to pleased.