49
Use of GUARD Terminal
Measurement using G (GUARD) terminal grounding
G terminal grounding is used for measuring the insulation resistance between
the core and the metallic shielding layer of a high-voltage cable with the cable
connected to other high-voltage equipment. The diagram below shows an example of
measurement.
Cable
Core wire
Power supply
Meter transformer
Grounding
wire
Disconnector
Remove
Metallic
shielding layer
of the cable
Current detector
GUARD
Rn
N
Ro
Rc
Rs
P
Load side
Power supply side
Rc: Insulation resistance of the insulating material of the high-voltage cable (Between
core and metallic shielding layer)
Rs: Insulation resistance of the sheath of the high-voltage cable (Between metallic
shielding layer and ground)
Rn: Insulation resistance between insulator or high-voltage equipment and ground
Ro: Instrument’s internal resistance (approx. 3 k
Ω
)
Inuence of Rs and Rn is removed and solely Rc is measured.
For details, refer to regulations for high-voltage power receiving facility.
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