Proposal on Active Ground Fault Detection System at

• Active ground fault monitoring at VMTF was discussed at the M&A group

• “Good” ground fault detection system: – – Should not depend on power

• AQD ground fault logic still active • Symmetric grounding required for all

Option A: • Everything protected: – Coil to Ground – Heater to Ground –

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Proposal on Active Ground Fault Detection System at VMTF RCMA 420

• Active ground fault monitoring at VMTF was discussed at the M&A group meeting on March 27, 2009 • Symmetric grounding was a prerequisite to an active ground monitoring at VMTF • The symmetric grounding for magnet in operation since June 2009 • The maximum coil voltage to ground reduced by factor of 2 • Ground current through the fault was significantly reduced (from 40 A to about 3 A) NEW SYMMETRIC OLD ASYMMETRIC

• “Good” ground fault detection system: – – Should not depend on power supply voltage and magnet inductance Is equally sensitive to ground fault at different locations Protects from coil to ground, coil to heater and heater to coil shorts Detects ground fault during and between magnet ramps • Active ground fault detection system is proposed: – Isolated 5 V voltage source connected in series with the ground resistor – Voltage drop develop across the ground resistor (100 -Ohm) in case of coil to ground short – “always armed” • Active ground fault system can be installed for magnet coils and strip heaters, or for magnet coils only 5 V

• AQD ground fault logic still active • Symmetric grounding required for all strip heaters (HFU) • Coil and strip heater grounding systems monitored by RCMA-420 relay • RCMA-420 will detect the non-zero current in 3 -500 m. A range and trigger the AQD • 20 A double-switch relay is connected to bypass the power supply in case of a failure Following options are considered: A. Protect both the magnet coil and strip heaters with an active ground fault system (see schematic on the left) B. Install an active ground system on the magnet coil and a passive ground system on strip heaters

Option A: • Everything protected: – Coil to Ground – Heater to Ground – Coil to Heater • Always protected – Detects ground fault during and between magnet ramps • Most expensive Option B: • Coils always protected • Ground fault in strip heaters will be detected only when they are fired • Strip heaters better protected because of the symmetric grounding • Can be easily upgraded to Option A