WCA May 2017

Field Tests, Conclusions The experimental tests have shown the practical feasibility of the proposed method for fault location on AC and DC cables. They also have shown that damping and dispersion of the measured signal depend strongly on the monitored cable. Nevertheless, the experiments have been limited to a relatively low voltage and to a short cable length. There has been no further knowledge about the behaviour of cables which are laid in the soil or in the sea. It is assumed that the much higher voltage during test or operation will have a positive effect on the measured signal. It is also presumed that the dispersion and damping on a laid cable is lower than on the drum or turntable. Furthermore, the reflection losses as seen in the measurements should not play a big role in a real situation. All of these assumptions are not proven so far. Therefore, the results of the described tests can be taken as a first step, which has to be continued with field tests on laid cables. The proposed method might be helpful as a monitoring tool during commissioning or routine tests on long cables, but also as an always-online tool to monitor the cable under service conditions. In case of a fatal breakdown the monitored signal shall help to find the location of the fault in a very short time and without further investigations. References [1] CIGRÉ 490. Recommendations for Testing of Long AC Submarine Cables with Extruded Insulation for System Voltage above 30 (36) to 500 (550)kV [2] CIGRÉ 496. Recommendations for Testing DC Extruded Cable Systems for Power Transmission at a Rated Voltage up to 500kV [3] IEC 62067. Power cables with extruded insulation and their accessories for rated voltages above 150kV (Um = 170kV) up to 500kV (Um = 550kV) – Test methods and requirements [4] CIGRÉ 297. Practical aspects of the detection and location of partial discharges in power cables [5] Leißner, Sebastian, Untersuchungen zur Fehlerortung an langen HVDC-Kabeln, Diplomarbeit, 2013 [6] Highvolt data sheet 1.31/4, AC Capacitor, Type WC

❍ ❍ Figure 11 : Measurement equipment

Parameters: • Cable: • Capacity: • Inductivity: 110µH/km • Voltage:

779m

310nF/km

up to 12 kV, DC, both polarities

• Measurement equipment: transient recorder for fault location, broad- band divider (resistive- capacitive attenuator) ( Figure 10 , Figure 11 ) The same measurements as with the AC cable were performed.

From Equation 1 the propagation velocity v 0 can be calculated as 171.25m/µs. With that information the cable length l 1 can be determined. As a cross check the propagation velocity v 0 was calculated from the measurement with the known cable length l 0 . ❍ ❍ Figure 12 : Measurement with broadband attenuator and negative DC voltage

Voltage kV

Cable length l 1 with known v 0

, with [m/µs]

Velocity v 1 known l 0

[m]

+ 6.5 - 6.5

778 776 780 777

171.4 171.7 170.9

Highvolt Prüftechnik Dresden GmbH Marie-Curie-Straße 10 D-01139 Dresden Germany Tel : +49 351 8425 700

+ 11.5 - 11.5

The maximum deviation from the reference values is < 0.4 per cent. 171.7 ❍ ❍ Table 3 : Calculated cable lengths and propagation velocity

Email : sales@highvolt.de Website : www.highvolt.de

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Wire & Cable ASIA – May/June 2017