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.

 

[malcolmsanford]

Ahhhhhhhhhhh have the days gone when you walked into a generating plant and saw all the gennes coupled together with cam rods so they run at the frequency, I bet it is all done by electronics now.

No was very glad when I missed the HV stuff .....not my cup of tea all the Mvolts

 

[Knobhead]

All the sites I’ve worked on have had at least 11KV supplies so I’ve been brought up with it.
The only thing I’m not keen on is phasing out with 11KV hot sticks.

 

[ian.settle1]

Who may I ask was the second person who put their signature to the switching schedule to say it was OK or was there not one which would mean your mate is in the deep mire for doing the switching in the first place.

 

[Knobhead]

He was on his own! Totally in the wrong! But I don’t work there so no fault of mine, I just checked his switching schedule for him. He’s the only HV guy on site so in the sh*t before he starts! I’ve found myself in the same situation where I’ve had to do emergency switching to restore essential supplies. Not a good situation to find ones self in, but in the middle of the night needs must.

 

[Engineer54]

Fortunately the UPS system took care of the data centre but the other uses weren’t to pleased.

Then surely, ...No Need to parallel 2 x 11KV TXs then, if the UPS is going to look after the data centre?? Auto or manual changeover of the bus coupler, will be complete in say 2 seconds (or even quicker), UPS will take up the data loads during that time, plus any built in time delay for return to prime power, so still can't see any reason to parallel the 2 TXs???

 

[Knobhead]

As I said in my first post, there were other loads, not just the data centre. I’ve worked on this system and it’s not a simple one to understand. Two villages, a medical centre, several pubs, farms and a number of separate companies supplied from it. The system wasn’t designed, it evolved over about 60 years.

 

[mechelec]

In the area I work often two transformers are run in parallel at the same time and it is the nornal running arrangement. As Tony mentioned the tap changers are run in a master slave arrangement. The protection side is a work of art and I have been trying for some time to get involved. Directional protection, restricted earth fault etc very interesting and specialised stuff

 

[Engineer54]

As I said in my first post, there were other loads, not just the data centre. I’ve worked on this system and it’s not a simple one to understand. Two villages, a medical centre, several pubs, farms and a number of separate companies supplied from it. The system wasn’t designed, it evolved over about 60 years.

Fair enough Tony, i know only too well, sometimes explaining or describing things that are not exactly as one would expect, ...can be a real pain in the bot!! Especially when they have evolved over that period of time...

 

[Engineer54]

In the area I work often two transformers are run in parallel at the same time and it is the nornal running arrangement. As Tony mentioned the tap changers are run in a master slave arrangement. The protection side is a work of art and I have been trying for some time to get involved. Directional protection, restricted earth fault etc very interesting and specialised stuff

I know it's not unheard of to run 2 11KV TXs in parallel, but i can assure you it's not your normal standard practice to do so. The main Switchboard along with it's ACBs/GCBs/SW Fuses etc, would need to be rated at the combined fault level (bracing etc) of those 2 TX's, ...That tends to make such switchboards a rather expensive proposition.

It's also one of the reasons why a ring of RMUs fed from 2 TXs on the same switchboard are normally run in an open ring configuration.

As you say, it's the art of setting up protection relays and controls that is the real specialised area, be it for HV/MV/LV switchboards, and systems.

 

[Knobhead]

I’ve paralleled 11/.44KV 1600KVA transformers several times and each time we knew we would be exceeding the boards maximum fault level but for only a mater of seconds. The chances of a fault on the board in that space of time would be minimal.
This was a modern system but due to the failure of a VCB it was decided all VCB’s were to be taken out of service in turn and tested. We did all we could to make the operation as safe and quick as possible, it wasn’t possible to shut the plant down. One beauty of this particular system was every boards loading was such that if one transformer failed the other could take the full load. When I first saw the system I thought it laughable that a transformer capable of supplying 2133A was bumbling along at say 900A only when we had to go through this exercise did I realise how good it was. OK some bits of kit had to be shut down where there was no parallel feed, (11KV motors) for a few minutes while we swapped the VCB for a stand by one.
The four incoming 33/11KV 20MVA transformer OLTC’s were always in leader and follower mode.

At another works two of us were separately asked to write a switching procedure so part of the intake board could be shut down, we compared them and made the final out of the two. There were 77 steps to the procedure, a lot of load shedding, a lot of driving and radio contact, but most things kept going!