Partial discharge measurement (PD)
The partial discharge measurement is a
non-destructive procedure where the
measured values can be assigned to a
specific location on the cable route. The
following faults can be detected with the
help of the inception voltage (voltage at
which partial discharges occur for the first
time) as well as the measured PD level
during a specified test voltage:
• Permanent damage in the cable sheath
due to external effects, perhaps during
the course of groundwork
• Defects in new and old fittings, for ex-
ample, defective joints or fittings
• Defects affecting the insulation-effect in
the insulation of plastic-insulated ca-
bles, such as electrical trees
• Insufficient paper pulp insulation due to
drying or water penetration
For the purpose of comprehensive cable
diagnostics, it is thus desirable to be able
to carry out both diagnostic procedures -
dissipation factor measurement and partial
discharge measurement - in addition to a
cable or cable sheath test.
3. Voltage sources - requirements and
characteristics
To achieve a successful condition-based
maintenance, the testing and measuring
devices must satisfy a catalogue of re-
quirements. The essential requirements for
the voltage source are:
• Suitability for cable tests / withstand
voltage tests
• High measurement accuracy during
dissipation factor measurement
(see above)
• Significant results during the PD
test (inception and extinction volt-
age, PD level and phase-resolved
PD pattern) and good localisation of
the PD
• High reproducibility of results to
guarantee the comparability of
staggered measurements and vari-
ous cable routes in the network
• Possibility of applying various
methods in parallel and to combine
the results of the test/measurement
automatically so as to save time
• Light in weight, easy to handle,
easy connection, easy operation,
short test duration
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