AREAS OF USAGE
Approximate phase to earth fault current in 240-5000 V networks:
- Solidly grounded systems1000-6000 A
- Low resistance grounded systems: 100-1000 A
- High resistance grounded systems: 2-10 A
- Ungrounded (or delta) cable systems: 0,3-2,8 A/km: 2-10 A
High Resistance Grounding (HGR) systems are used in power systems where phase to ground short-circuit current is desired to be limited zero to a few amperes by placing highresistance between neutral point of transformer (or generator) and ground. As it is not possible to locate the fault point in delta connected systems, an artificial neutral point is created and delta connected system can be grounded. This allows a fault current of a few amperes thus locating the fault point gets easy. When the neutral point is grounded thru high resistance, both continuity of operation is provided during fault condition and sufficient current (typically between 2A and 10A) flow is provided for ease of locating the fault point.
- 0 - 10A analog ammeter and 0 - 250V analog voltmeter with setting on panel
- Automatic door switch for power shut down
- Test button to indicate fault
- Green light for normal conditions
- Intermittent alarm and red light during ground fault
- Pulse/Normal Selector swith to magnify current and intermittent pulse during ground fault.
- Auxilliary free contacts at pulse and alarm position during fault
- Dimensions (LxWxH)= 60 x 100 x 200 cm (Other enclosure types avaible on demand.)
- Suitable for 240....4160V three phase systems
While locating the ground contact point of phase - ground fault current that is limited to approximately 2A, generating approximately 10A pulses (approx. 1 second on, 1 second off) provides ease of measurement thus using short time pulses is the common application in HRG systems today.
Generally measurement is performed by analogue and wide clamp ammeters. The clamp ammeter outside the phase cable is traced until the pulse current disappears on the analogue display.
High Resistance Grounding Sstems are economical and practical choice especially systems under 5000 Volts.
As zero sequence (3Io) currents flow thru neutral point due to line capacitance of cables, HGR alarm level is set to a point that is greater than 3Io .