Arc flash question

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barrymac20

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I hope i have the correct sub forum

Looking for opinions on an arc flash incident in a 3 phase LV 690V substation.
MV/LV Transformer energised. Main incomer in substation is open. Control circuitry fed from live side via a set of 690V fuses connected to live side busbar.
Voltage meter fed from live side was measuring voltages of up to 750V.
As a part of the investigation into spurious voltage readings the control fuses were subsequently pulled and replaced a couole of times and while this was being done there was a flash over and a bang.
As the voltages were reading 750V and the fuses were only rated for 690V is there a chance that the removing/replacing of these fuses while under load could have caused arcing which led to arc flash? Or any other guesses as to what coukd have caused the flash.
 
barrymac20 said:
I hope i have the correct sub forum

Looking for opinions on an arc flash incident in a 3 phase LV 690V substation.
MV/LV Transformer energised. Main incomer in substation is open. Control circuitry fed from live side via a set of 690V fuses connected to live side busbar.
Voltage meter fed from live side was measuring voltages of up to 750V.
As a part of the investigation into spurious voltage readings the control fuses were subsequently pulled and replaced a couole of times and while this was being done there was a flash over and a bang.
As the voltages were reading 750V and the fuses were only rated for 690V is there a chance that the removing/replacing of these fuses while under load could have caused arcing which led to arc flash? Or any other guesses as to what coukd have caused the flash.
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Yes, under load, sure it could've caused a flash, arc, etc...
What type of fuses were they?
 
Pulling fuses, one at a time, can result in a ferroresonant condition resulting in higher voltages and flashovers. This is not typically a situation below 1kV.
 
It was necessary to pull the fuses under load? There was no disco ahead of them?
 
@Buck Parrish
Fuse holders top right of page 28 at the below link. Bfb63a3. So live connection extends through plate where fuse holders mounted into busbar section.
Fuses page 12. Type A3 690V 40A.
Fuses

the flash occurred behind the compartment where the fuses are mounted
 
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