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What are the risks of arcing between the primary voltage terminals and the transformer frame on energising?
The arcing phenomenon observed on TRIHAL devices is known and is not related to any equipment problem.
Explanation: When a transformer is energised, the peak switching currents can reach approximately 10 times the nominal current. The time constant for 2000kVA TRIHAL devices is approximately 0.6 sec. These switching currents generate leakage fluxes of the same duration which, as they re-close in the air, induce high currents in all the metal parts around the transformer. These induced currents trigger short duration arcing phenomena at the joints between the panels of the housing of these devices.
To summarise: These phenomena are mainly seen on devices whose power is greater than 1000kVA. They are not at all serious and are definitely not evidence of a transformer problem. Moreover, these phenomena are totally random and their intensity is dependent on the moment of energisation on the voltage sinus wave.
Explanation: When a transformer is energised, the peak switching currents can reach approximately 10 times the nominal current. The time constant for 2000kVA TRIHAL devices is approximately 0.6 sec. These switching currents generate leakage fluxes of the same duration which, as they re-close in the air, induce high currents in all the metal parts around the transformer. These induced currents trigger short duration arcing phenomena at the joints between the panels of the housing of these devices.
To summarise: These phenomena are mainly seen on devices whose power is greater than 1000kVA. They are not at all serious and are definitely not evidence of a transformer problem. Moreover, these phenomena are totally random and their intensity is dependent on the moment of energisation on the voltage sinus wave.
Released for:Schneider Electric UK
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