MEDIUM VOLTAGE CABLE PARTIAL DISCHARGE DIAGNOSTICS (PDD)
Yes, you can locate weak spots in your cable circuit before breakdown. You will be able to make repairs before breakdown and save money on network components that otherwise might be damaged as a result of breakdown. How? Energize your cable with a Very Low Frequency (VLF) voltage and then measure and locate partial discharges as part of your asset management program. You may call this CBM on power cable networks or for improving “problem circuits”. Convert measurement results into clear recommendations for actions using established expert lines. Plot the partial discharge levels on a discharge map showing the position in the circuit.This technique has been successfully applied to more than 10,000 km of circuit length in Europe, Asia, the Caribbean and the USA.
Principle of PDD
More than ninety percent of the weak spots in MV cables produce partial discharges. In order to measure PD, the cable circuit must be disconnected and measuring equipment connected to the cable terminations (Figure 1). The cable circuit is then energized using a discharge-free VLF generator (0.1 Hz). The partial discharges are detected at one end and located by measuring the time difference between the direct and reflected pulse. The location of each PD is then calculated and plotted on a discharge map (Figure 2).
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Figure 1 
Figure 2 
