Hi,
I'm an electrical station operator. Today, one of my co-workers (let's call him "M") had an incident at an electrical substation and we're trying to figure out the cause of it. The station has two 25MVA open delta transformers that feed a front & rear bus. Each transformer has two 5kV cbs, one for each bus. The station is normally configured with one bank feeding the front bus & the other feeding the rear bus. M had transferred the entire station load to one transformer and opened the cbs to the other transformer. The two buses were now in parallel thru the bank's 5kV cbs. (It should be noted that each bus feeds approximately 8 feeders that are part of our distribution system. Each fdr position is made up of a 5kV CB that is fed from the bus thru disconnects & then goes thru two step voltage regulating transformers on the load side of the CB before it goes thru a pothead out to the field. Sorry - this is getting kind of long. The two regulators are wired open delta with one AB & one BC regulator.)
M then made a huge mistake. He began to open the A phase disconnect on one of the bank cbs. Doing this broke the parallel between the buses and also interrupted approx. 20 MW of load on A phase on one of the buses. When M saw the resulting arc forming (he said it was a ball of fire about 3 feet wide which also set off car alarms next door due to the sound) He slammed closed the disconnect picking up the load. But, this is the weird part. The fdr position right next to him exploded at the CB's A phase load side bushing. It was far enough away from the initial fireball that it didn't get any damage from it. Is it possible that B & C phase back fed thru the regulators to feed the interrupted A phase load on the bus and blew up the bushing by sheer overcurrent? Is it possible? Or do you think it was just ready to go anyhow? I've been in this field for over 30 years and never seen anything like it. I'd love some opinions from people with high voltage experience.
Thanks
I'm an electrical station operator. Today, one of my co-workers (let's call him "M") had an incident at an electrical substation and we're trying to figure out the cause of it. The station has two 25MVA open delta transformers that feed a front & rear bus. Each transformer has two 5kV cbs, one for each bus. The station is normally configured with one bank feeding the front bus & the other feeding the rear bus. M had transferred the entire station load to one transformer and opened the cbs to the other transformer. The two buses were now in parallel thru the bank's 5kV cbs. (It should be noted that each bus feeds approximately 8 feeders that are part of our distribution system. Each fdr position is made up of a 5kV CB that is fed from the bus thru disconnects & then goes thru two step voltage regulating transformers on the load side of the CB before it goes thru a pothead out to the field. Sorry - this is getting kind of long. The two regulators are wired open delta with one AB & one BC regulator.)
M then made a huge mistake. He began to open the A phase disconnect on one of the bank cbs. Doing this broke the parallel between the buses and also interrupted approx. 20 MW of load on A phase on one of the buses. When M saw the resulting arc forming (he said it was a ball of fire about 3 feet wide which also set off car alarms next door due to the sound) He slammed closed the disconnect picking up the load. But, this is the weird part. The fdr position right next to him exploded at the CB's A phase load side bushing. It was far enough away from the initial fireball that it didn't get any damage from it. Is it possible that B & C phase back fed thru the regulators to feed the interrupted A phase load on the bus and blew up the bushing by sheer overcurrent? Is it possible? Or do you think it was just ready to go anyhow? I've been in this field for over 30 years and never seen anything like it. I'd love some opinions from people with high voltage experience.
Thanks
