Condition-based Maintenance on HV Cable Networks by Using

Condition-based Maintenance on HV Cable Networks by Using
Condition-based Maintenance on HV Cable Networks by Using DAC Technique
The HV cable lines have been in operation for 30 – 40 years. The condition of
these cable lines is of utmost importance to reach the main goals:
to sustain and improve network reliability
to reduce the cost of maintenance and the annual time of outages
To fulfil these two goals DAC technology was introduced on HV areas
some years ago. To energize the cable section DAC technique uses damped
alternating current by switching capacitance (cable line) and inductance in
cascade. The test object can be tested up to 150 kVpeak. During the DAC stress
partial discharge (PD) activity can occur. The PD measurement pinpoints the
weak point(s) of the whole system (failure of termination(s), joint(s) or cable
part(s) [IEC 60270:2000; TDR]. Besides the PD measurement it is possible to
estimate the dielectric losses from the damping of the sinusoidal wave.
Measurement results
Partial discharge and tan delta measurement, furthermore voltage withstand test have been carried out recently on service aged XLPE insulated
power cable.
Cable data:
3129 m; 76/132 kV; installation year: 2000; number of joints: 5 pcs.; termination: porcelain insulated outdoor
Measurement data:
Ground noise: 230 pC; PD level at Uo: 58000 pC; capacity: 0.53 μF; frequency: 72.5 Hz; dielectric losses at Uo: 0.1%; dielectric losses at 1.4Uo: 0.1%
partial discharge inception voltage (PDIV): >1.4Uo (L1); > 1.4Uo (L2); 0.11Uo (L3) ; partial discharge extinction voltage (PDEV): 0.068Uo (L3 )
Intensity and amplitude of PDs at PDIV (damped wave, L3)
Phase identified location of PDs along the sinusoidal wave (L3)
Intensity and amplitude of PD-s at 1.4Uo (damped wave)
PD map up to Uo; (amplitude: Y axis; location: X axis)
PD map up to Uo; (cardinality: Y axis; location: X axis)
Increment of dielectric losses during 1.4Uo; 20 min.
PDIV: extremely low; PD intensity: increasing in function of elevating voltage level; PD amplitude: extremely high on Uo and does not change significantly
up to 1.4Uo; PD mapping: PD contrentation on both terminations; PD cardinality: considerably higher on near end
The cases of concentrated PDs on near end could either be caused by connection problem or floating point or small cavity inside of termination;
PD concentration can exist on far end termination too;
DAC technique is able to indicate early insulation degradation locally (PD) or in general (dielectric losses), before it becomes a breakdown failure in both of paper-
oil and XLPE insulated cables;
DAC technology is able to support asset management either to plan maintenance more effectively or reduce risk of investment decision on HV cable circuits;
Site acceptance tests carried out by the using of DAC technology has become more and more popular all around the world.
GA Hungary Ltd.  Budapest University of Technology and Economics, (Hungary)
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