Megger SMART THUMP ST16, Руководство пользователя

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M
AVTMST16 Rev 1 May 2016
32
Detecting a Sheath Fault OR a Ground Fault in an
Unshielded, Low Voltage Cable (both must be directly
buried)
NOTE: The methods described to detect and pinpoint sheath faults in shielded
cables or ground faults in unshielded cables assumes that in both
situations the cables are direct buried; cables in conduit, especially PVC
conduit, will not respond to this method.
IMPORTANT
In contrast to the connection diagram on page 14 the HV Output lead has to be
connected to the cable shield (concentric neutral)
which in turn has to be
disconnected from the common bonding point on both ends
of the specific
cable to be tested. Consequently, the HV return lead has to be connected directly
to the system ground or a separately driven ground rod.
Fault locating on
unshielded, direct buried low voltage cables
must be
carried out in the sheath fault locating mode in order to ensure that the
maximum voltage is limited to 5kV; in this case the HV out put cable is
connected to the center conductor and the HV return to a driven ground rod.
The insulation of any high or medium voltage shielded power cable is protected
from water ingress by a jacket made from XLPE or PVC. The Sheath test
checks if the integrity of the jacket has been compromised, typically during
installation.
With a sheath test the dielectric strength of the cable jacket can be tested by
applying a DC voltage of up to 5 kV between the cable shield (concentric
neutral) and ground. Any leakage indicates a fault in the jacket.
Proceed as follows to perform a sheath test:
Step Description
1
Select the menu item from the submenu.
2
Confirm the following two notices with .