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Wire & Cable ASIA – May/June 2017
Highvolt Prüftechnik Dresden GmbH
Marie-Curie-Straße 10
D-01139 Dresden
Germany
Tel: +49 351 8425 700
Email:
Website:
Parameters:
• Cable: 779m
• Capacity: 310nF/km
• Inductivity:
110µH/km
• Voltage: 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 v0 can be
calculated as 171.25m/µs. With that information the cable
length l1 can be determined.
As a cross check the propagation velocity v0 was
calculated from the measurement with the known cable
length l0 .
The maximum deviation from the reference values is < 0.4
per cent.
❍
❍ Figure 11: Measurement equipment
❍
❍ Figure 12: Measurement with broadband attenuator and
negative DC voltage
Voltage kV Cable length l1
with known v0 [m]
Velocity v1, with
known l0 [m/µs]
+ 6.5 778 171.4
- 6.5 776 171.7
+ 11.5 780 170.9
- 11.5 777 171.7
❍
❍ Table 3: Calculated cable lengths and propagation velocity
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