Megger SG32-1500M, Руководство пользователя

Страница: 49 / 76

SG32-UG-EN-V01 Dec 2016
39
ADDENDUM 2
Typical Fault Locating Strategy
The most important aspect of locating a cable fault is the development of a
strategy that will allow the fault location to be safely and positively identified.
This is achieved by following the “Methodical Approach to Cable Fault
Location” , see previous flowchart.
1. Use only suitably rated, equipment, making sure that all company and
equipment manufacturers' safety guidelines are followed.
2. Positively identify the faulted cable. Following isolation and
Earthing/Grounding of all of the suspect cables and cores, this can be done
by either using an Insulation Continuity Tester, to determine the condition of
each of the cables and cable cores, or by using a TDR to see if all of the
cores appear to have the same characteristics, i.e. (splices, joins, transformers,
etc., at approximately the same distance.
3. If all circuit elements appear to be equal, determine if the electrical length of
the circuit elements agree with the known physical length of the circuit. If it
does not verify, then adjust the TDR propagation velocity accordingly.
4. If the TDR data is inconclusive, use the DC (Proof/Dielectric Test) function
to positively identify the faulted phase. Separately bring each phase up to a
test voltage as agreed by “local” conditions or regulations. Note the
breakdown voltage from the faulty phase or phases.
a. After the faulted phase (or phases) has been positively identified, begin
pre-location by engaging the Arc Reflection method and configuring the
MTDR and SG32 for Arc Reflection. Apply a test voltage as defined by
the breakdown voltage noted during the previous step. Increase the test
voltage slowly, noting that the longer the cable, the greater the cable
capacitance, hence the Arc Reflection breakdown voltage can be higher
than the breakdown voltage. If the fault appears to be unstable, try
increasing the discharge voltage slightly.
b. If the fault does not consistently breakdown, or is unstable, at the
maximum allowable voltage, select the Proof/Burn function on the
SG32. Raise the voltage to either the maximum allowable voltage or until
the fault breaks down in a relatively stable manner as indicated by stable
current and voltage. Continue this proof/burn function until the
discharge current is stable, after a few minutes of stable discharge, return
to Arc Reflection. Do not use proof/burn excessively as you could create