The
design and operation of 240-5000 V systems, service continuity, personnel and equipment
safety are the most important aspects in industrial systems. The use of thehigh-resistance grounded (HRG) system can provide a safe, reliable and economic
system for 240-5000 V networks.
HRG systems limit the fault current by
placing high resistance 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 through high
resistance, both continuity of operation is provided during fault condition and
sufficient current (typically between 2 A and 10 A) flow is provided for ease
of locating the fault point.
Approximate phase to earth fault
current in 240-5000 V networks are:
Solidly grounded systems : 1000-6000 A
Low resistance grounded systems: 100-1000 A
High resistance grounded systems: 2-10 A
Ungrounded (or delta) cable system: 0.3-2.8 A/km:
2-10 A
High Resistance Neutral Grounding Devices General
Features:
0-10 A analog ammeter, 0-250 V 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 switch to
magnify current and intermittent pulse during ground fault
Auxiliary free contacts at pulse and
alarm position during fault
Dimensions (LxWxH)= 60 x 60 x 180 cm
(Other enclosure types available on demand)
Suitable for 240-5000 V three phase
systems
Optional data logging
Usage:
While locating the ground contact point of phase and ground, a 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.
Measurements are generally taken 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 Systems are economical and practical choice
especially for systems under 5000 Volts.
As zero sequence currents (3Io) flow thru neutral point due to line capacitance of cables, HGR alarm level is set to a point that is greater than 3Io.
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