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Assessment of the condition of cable terminations (HV and MV)
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The condition of your MV and HV polymeric cable terminations may be assessed while on-line. Partial discharges may be measured locally using sensors located in the low voltage area of the termination. Based on the level and trend of the discharges over time, recommendations for action can be made so that defective terminations can be replaced before breakdown occurs, thereby preventing unexpected outages.
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Measurement method
Discharges may be measured using a VHF transient recorder and
sensor. The sensor is connected between the cable shield and the
grounded bottom flange of the termination, and can be installed
without removing the existing ground connection. Local discharges
are measured by using the VHF frequency part of the power spectrum
of the partial discharge. By selecting the proper part of the power
spectrum, background noise can be reduced.
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Experiences and benefits
Using this measuring technique, critical defects in cable terminations have been detected and unexpected outages prevented in Europe and the USA. Several of the defective terminations were then dissected and visually inspected, and in each case traces of severe discharges were found. By comparison, in cases where defective terminations were not replaced as recommended, breakdowns occurred, resulting in service outages.
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KEMA services
KEMA offers cable-consulting services for CBM on power cables
including the following:- Diagnostic measurements such as partial discharge diagnostics
on all types of MV cable circuits
- Water tree diagnostics on MV polymeric circuits
- Partial discharge diagnostics on MV and HV
cable accessories
- Outer sheath testing and voltage withstand testing of the cable
insulation
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