IRON CORE EARTHINGH
IRON CORE EARTHINGH
(OP)
Can some advise, whay the iron core of the transformers is earthed?
Elecme
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RE: IRON CORE EARTHINGH
Without this connection the potential of the core could be anywhere, making it impossible to design the insulation system
In case of some kind of insulation failures in the transformer there will be short circuit from the winding to the core. With an earthed core this will trip the transformers protection.
RE: IRON CORE EARTHINGH
Elecme
RE: IRON CORE EARTHINGH
Capacitive coupling is also the reason that you should always tie down unused windings in a transformer when doing an applied (hi-pot) test. You don't know the voltage that the other winding will float up to when applying volts to the winding under test. If the coupling is such, you may raise the winding not under test up to greater than its insulation level, and damage the insulation.
It is handy to have the core earth connection brought out through a bushing and earthed external to the tank with an earth cable, which allows the core insulation resistance can be measured. We have had situations where the earth connection was high resistance, and the core insulation was discharging, producing gas. It happens due to the core not being tied hard down to earth, and then the potential arcing over in the oil. With an externally connected earth, we could isolate it fairly easily, otherwise you have to do a lot more testing to try to determine the location of the discharge, whether its in the winding or not etc. Just make sure your technicians reconnect the earth after testing, otherwise you'll a step change in your gas results next time you analyse your oil sample.