Skogsgurra
Electrical
- Mar 31, 2003
- 11,815
Hello,
I am studying recordings from a fire that occured in a plant. Data: 6 MVA transformers fed from 6.6 kV 50 Hz. Secondaries are 690 V. Isc is around 32 kA.
I see initial arcing at around 10 kA. It stays for 400 ms. Then an 1800 ms period with no arcing (breaker has not yet tripped) followed by a 500 ms 10 kA arcing period with a 700 ms no-arc period. Then, there is a 1600 ms long arcing period with a rather high current, random variation between 20 and 30 kA and then breaker trip.
Protection is set at 1 kA/1500 ms and 5 kA no delay.
There was a water damage almost a year before this happened. the equipment had not yet been connected at that time. The equipment was dried and inspected and commissioned. There were some problems with electronic modules and cooling fans that had been damaged by water. And a contactor that had become rusty was changed.
The inverter is situated in a heavily ventilated electrical room. There is a raised floor with cables entering cabinets from below. Cabinets are welded steel with galvanized mounting plates.
There is extensive damage, but we have not seen any bad connections (torque controlled wrenches were used when building the equipment, no connections to these parts made on site). The fuses have tripped, of course, but no fuse explosion.
We are trying to understand what really happened. Dirt collected in voids in insulator system? Zink whiskers being transported by cooling air and settling on insulator surfaces? Anything else?
It would help very much if there were some similar recordings with a known failure cause where one could study/compare to see if we can have a clue from such a comparison.
Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
I am studying recordings from a fire that occured in a plant. Data: 6 MVA transformers fed from 6.6 kV 50 Hz. Secondaries are 690 V. Isc is around 32 kA.
I see initial arcing at around 10 kA. It stays for 400 ms. Then an 1800 ms period with no arcing (breaker has not yet tripped) followed by a 500 ms 10 kA arcing period with a 700 ms no-arc period. Then, there is a 1600 ms long arcing period with a rather high current, random variation between 20 and 30 kA and then breaker trip.
Protection is set at 1 kA/1500 ms and 5 kA no delay.
There was a water damage almost a year before this happened. the equipment had not yet been connected at that time. The equipment was dried and inspected and commissioned. There were some problems with electronic modules and cooling fans that had been damaged by water. And a contactor that had become rusty was changed.
The inverter is situated in a heavily ventilated electrical room. There is a raised floor with cables entering cabinets from below. Cabinets are welded steel with galvanized mounting plates.
There is extensive damage, but we have not seen any bad connections (torque controlled wrenches were used when building the equipment, no connections to these parts made on site). The fuses have tripped, of course, but no fuse explosion.
We are trying to understand what really happened. Dirt collected in voids in insulator system? Zink whiskers being transported by cooling air and settling on insulator surfaces? Anything else?
It would help very much if there were some similar recordings with a known failure cause where one could study/compare to see if we can have a clue from such a comparison.
Gunnar Englund
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...