Earth Monitoring Check On IT System(Neural Non-ground)

[shkim2000]

I'm involved with commissioning on 690V 3phase, IT(Unearthed system). The system has earth monitoring system, supplied by Bender. The monitoring system consists of BENDER IRDH575 monitoring insulation resistance and EDS470-12 evaluating/locating insulation.
Anybody tell me how earth is simulated in order to verify total earth monitoring system with easiness ?

 

[drivechanger]

I've never used BENDER but have evaluated it several times for retrofit to existing IT or ungrounded power system.s It requires a single high-impedance connection to earth and a connection to one power phase, through which it pulses a low-energy, high-frequency signal that is able to propogate throughout all three phases of the system (through trafo windings). For systems that cannot be converted to High-Resistance Ground (preferred), this type of monitoring should be installed to provide early detection of ground faults.

 

[Skogsgurra]

As above. Only that the pulsating test voltage is not exactly high frequency. It is more like half a cycle/second (0.5 Hz). If you have a display on your unit, you can actually see the square wave going positive and negative.

You can test the instrument by introducing a leakage current anywhere in the system - from center point to ground or from any phase to ground. The Bender will detect any earth fault.

The setting range is usually from a high 10 Mohm to a low 10 kohm with special units going down to 1 kohm for inverter loads. Use a string (to accomodate the possible 690 V) of low wattage lamps and test by connecting it between one phase and ground. The Bender shall trip immediately. For more accurate testing, you need resistors with known resistance. Be careful with these voltages! And never connect an unfused voltage to ground.

Gunnar Englund

http://www.gke.org