Of 109 substations in our network, we have one infeed 4 transformer substation (4x 275Mw)with incoming voltage of 400kV.

Recently one transformer was struck by lightening, burned for 9 days straight (transformer oil in chamber beneath could not be accessed) Total write off, and long delivery period from manufacturer meant three remaining had to carry the load.

Then another transformer kinda blew up (don't have the exact details) and the spares have to come from United Kingdom, and we are now down to two operational transformers, same load.

Thats where the continuous water sprayers come in, 24 hours a day waterspray is used to cool down the transformers. It costs $10 000 per month for the water alone. We are still months away from replacement transformer / spares arriving. So never mind Year 2000 problems, we have an operational problem right now.

Regards

James Prosser

-- Anonymous, August 19, 1999

Answers

James,

Thanks for that story. I have read that this will be the biggest problem over the long term for Y2k related failures. The parts problems as well as availability for specialized equipment has very long lead times, measured in terms of 6-12-18 months. If and when a bunch of failed components are finally put on order, it could be a very long wait to actually get the part. I was a pilot in commercial aviation and flew 4-engine jets mostly. One generator for each engine and all of them synched to run together. Lose one, no big problem. Lose 2 and contingency planning and load management become important. You are now down to cool spraying the remaining 2, keeping your fingers crossed, I imagine, that they both stay up and running. Lose 1 more and it's crisis management time. It is this sort of slow degradation of the equipment, with no replacements in stock, that will be the longer term danger next year, I think.

-- Anonymous, August 19, 1999

James,

A very interesting dilemma you have there and one I do not envy. Sounds like you are taking the only steps practical for the moment. If and when you are able, I would be very interested in hearing the cause of the second transformer failure. Was the second transformer in close proximity to the one that burned? What was the separation in time between failures?

In early April, we lost a much smaller transmission/distribution transformer (138Kv to 12kv) in one of our local substations that was configured as a duel transformer (total 66 MVA) station. The cause of the failure was internal arcing in the reactor windings just under the tap changer (30 year old unit). Fortunately, our protective relaying isolated the transformer very quickly and the automatic transfer scheme moved the load to the adjacent transformer so that if our customers saw anything at all, it was very brief. According to our distribution fault recorder, the load was transferred within 7 cycles from the initial fault or about 12/100 of a second.

We immediately dispatched personnel to check the surviving transformer before securing and opening the failed unit. We then initiated contingency field switching to prevent possible overloading of the surviving transformer. Fortunately, as it turned out, this was not a critical step due to the mild temperatures and lower demand in April here in Florida. We were forced to ship the transformer off to south Florida for repairs and expect it back in mid to late October. Going through the summer has been interesting to say the least but we were able to move a spare to bring us back to normal operations and restored our contingency field switching.

I sincerely hope things work well for you, James. Best of luck.

-- Anonymous, August 19, 1999

James,

We had a similar experience here in NZ about 10 years ago when we lost the ONLY 150 MVA 220/110 KV interconnector at a substation in the North Island. We were able to maintain some limited supply by backfeeding on the 110KV system, but because of the long lead times required to replace transformers, we borrowed a 200 MVA 220/110 KV transformer from another substation that had 4 and could get by with 2. Problem solved.

Keep us informed on how effective the water spraying is. It may be a handy solution to assist in overcoming expected overloads.

Malcolm.

-- Anonymous, August 19, 1999

James,

I am having some trouble comprehending this, would you be kind enough to provide some clarifications.

"Of 109 substations in our network, we have one infeed 4 transformer substation"

Does each substation have four transformers? It sounds from the text that there is a single feed for all of the generating capacity, processed through 4 transformer substations then distributed to 109 regional substations. Do the two out of service transformers affect one out of 109 substations or potentially all substations? I realize as an industry outsider I am being thick on this but I do understand earlier threads

"Eskom (Electricity Supply Commission of South Africa)is the fourth largest generator of electricity in the world, and it stands to reason that it is thus the largest in Africa. Anything else by comparison is a pimple on a pumpkin" (James Prosser - Y2K and electricity in Africa: posted by Chris Byrne)

"Eskom is the ONLY generator for the whole country" (James Prosser - Y2K and electricity in Africa: posted by Chris Byrne)

This may be just a bad break in uncertain times but are you telling me that all of the electrical generating capacity for all of South Africa from the fourth largest plant in the world is hanging on a jury rigged sprinkler system?

-- Anonymous, August 20, 1999