TL;DR
A coil ground fault alarm means insulation breakdown between the induction coil and the furnace shell or ground. Stop melting immediately and test the coil insulation resistance before restarting.
What you might see
- ground fault alarm on the power supply panel
- automatic shutdown of the melt power
- coil cooling water conductivity elevated
- power supply indicating coil-to-ground leakage
Likely causes
Coil insulation damaged by a steel splash that penetrated the insulation wrap
Cooling water conductivity elevated from a deionizer resin exhaustion allowing current leakage
Refractory lining cracked and allowing molten metal to contact the coil turns
Coil insulation degraded by long-term thermal cycling
Required tools
- Water conductivity meter
- Deionizer resin cartridge
- 500V megohmmeter
- LOTO kit
Safety first
- High voltage on the induction coil circuit. Isolate and lock out the power supply before any coil inspection.
- Molten metal in the furnace if the ground fault occurs during a melt. Follow the safe-hold or tap-out procedure before any coil work.
- Cooling water at elevated pressure. Bleed the circuit before opening any connections.
Procedure
- 1
Stop the melt power and allow the charge to solidify or safely hold. Do not restart until the fault is diagnosed.
Warning: High-voltage induction coil circuit. Only qualified persons with appropriate permits may work on the coil or power supply. - 2
Shut down and isolate the power supply from the coil using the main disconnect.[1]
- 3
Check the cooling water conductivity at the coil inlet and outlet. Conductivity above 10 microSiemens/cm indicates deionizer resin exhaustion.[1]
- 4
Replace the deionizer resin cartridge if conductivity is elevated and retest. If the fault clears, the water conductivity was the cause.
- 5
If conductivity is acceptable, perform an insulation resistance test on the coil to ground with a 500V megohmmeter. Below 1 MΩ confirms coil insulation damage.
- 6
Inspect the refractory lining for cracks or steel penetration toward the coil.
- 7
If coil insulation is failed, the coil must be removed and re-insulated or replaced. Consult the furnace manufacturer.
Sources
Inductotherm (Inductotherm Group) Inductotherm VIP-I / Power-Trak Induction Melting Furnace general technical documentation, Inductotherm (Inductotherm Group)
Inductotherm induction melting furnace operation and maintenance documentation, coil insulation and ground fault procedures (general)
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