Brugg Kabel AG uses silicone insulation for high voltage cable accessories up to 400kV. Routine partial discharge (PD) testing is done on prefabricated joints to ensure quality and detect defects. On-site PD measurements after installation can accurately detect PD above 5pC and localize faults. Directional coupler sensors allow sensitive PD detection and localization in unscreened environments. PD testing is important for ensuring reliability of joints and avoiding premature failures during operation.

1. Workshop 2001, Alexandria, Virginia, December 3 & 4, 2001
Partial Discharge Measurement in HV Joints: Brugg Solutions
W. Weissenberg, Brugg Kabel AG, Switzerland
1. Introduction
At Brugg Kabel AG silicones are used as the insulation material for high voltage accessories in
conjunction with polymeric-insulated power cables. Silicones are characterised by a long electrical service
life /1/. When subjected to electrical stress brought about by high voltage, a life expectancy far in excess
of 50 years can be assumed. If, however, as a result of partial discharges (PD), the ageing process is
accelerated, premature breakdown may be observed (Fig. 1).
Figure 1: Aging in Silicone
It is, therefore, of considerable importance that the accessories are free from partial discharge. In the
standards, which reflect the current state of the art technology, a PD level of ≤ 10 pC for a test voltage of
1,5 Uo is specified /2 ,3 /. As far as electrical tests, which are undertaken after a cable system has been
installed, are concerned no general PD testing is specified in the standards. A CIGRE TF 21-05 working
group has conducted a survey regarding practices, techniques, experiences and results of electrical tests
following the installation of polymeric extra high voltage (EHV) cable systems /4/. The results of the survey
carried out in 15 countries have come to the conclusion that for EHV cable systems, selective PD testing,
in particular, is extremely effective following the installation of joints. When undertaking the PD
measurement to ensure that the joints are free from partial discharge a lower test voltage can be used for
the a.c. voltage test. This rules out the possibility of causing any premature damage to the newly installed
cable by the electrical test. The general technical tendency towards assessing the state of joints in EHV
cable systems is the diagnostic appraisal of being free from partial discharge.
2. Practical experience at Brugg Kabel AG
2.1 Routine tests in the factory
The PD measurement, as a routine test for prefabricated HV and EHV cable accessories is the first
important step for demonstrating the quality of the electrical long term robustness of the high voltage cable
accessories. Brugg Kabel AG uses special test equipment to carry out routine testing of all prefabricated
stress-cone and slip-on joints to establish freedom from partial discharge. A typical test system for this

2. operation comprises a short length of cable which has a water terminator at one end and a closed metal
housing on the other for mounting the stress-cone to be tested (Fig. 2).
Figure 2 : Routine test on prefabricated stress- cones
The partial discharge test for slip-on joints is carried out using two short lengths of cable equipped at one
end with water terminators. The other two ends of the cable are inserted into the slip-on joint and also
encased with a metal housing (Fig. 3)
Figure 3 : Routine test on prefabricated joints
So-called directional coupler sensors ( DCS ) /9/ have proven extremely suitable for carrying out partial
discharge measurements as a routine test for prefabricated slip-on joints in unscreened test rooms /6/.
They are also ideal for carrying out tests and monitoring /7, 8/ following installation. In principle, a
directional coupler can be understood as a mixed capacitive and inductive PD sensor with two outputs
(Fig. 4).

3. Figure 4 : Setup and signals of directional couplings
Two directional couplers are mounted to the left and right of the joint adjoining the outer semiconducting
layer of the high voltage cable. An impulse propagating from left to right is coupled at outputs A and C
whilst an impulse propagating from right to left is coupled at outputs D and B. This output coupling
configuration is typical for external noise or partial discharge of other successive accessories. PD from the
joints is coupled at outputs B and C. This method is used to accurately measure and localise PD in joints.
2.2 AC test after installation
Initial findings have been gathered in respect of on site electrical tests to establish the presence of partial
discharge following installation and monitoring of long-time 110 kV, 220 kV and 400 kV test installations in
Switzerland, Singapore and Germany. This method of PD testing was successful for tests carried out
following the installation of cable systems up to a nominal voltage of 400 kV. Monitoring of PD can also be
undertaken using the same test configuration. The sensitivity for assessing the presence or not of partial
discharge of the accessories was better than 5 pC. During testing, accessories were observed which
displayed a PD in excess of the specified noise level and the fault positions could be localised down to an
accuracy of a few centimetres. Following repairs to the accessory testing was resumed.
The next on site PD measurements to be conducted on a 400 kV high voltage slip-on joint following
installation will be carried out in Switzerland in September of this year. (Fig. 5). The slip-on joint has been
in operation for 2 1/2 years and the findings will be published.

4. Figure 5 : Test set-up for on-site-pd-measurement on 380- kV-joint in UW Bonaduz/Switzerland
3. Conclusions
At Brugg Kabel AG, accessories for polymeric insulated (E)HV cable systems up to 400 kV are
manufactured from silicone. Silicone accessories are extremely reliable and have an electrical life span in
excess of 50 years if they are not destroyed prematurely by PD. The prefabricated accessories, therefore,
are consistently subjected to routine tests to determine the presence or not of partial discharge. The
progress of PD measurement technology has reached the stage whereby methods such as the direction
coupler method are able to detect, measure and localise a PD of less than 5 pC, even in unscreened test
rooms. This ensures that possible defects in joints can be accurately identified and localised by the on site
tests even after installation. The accessories can then be repaired and a breakdown during operation
subsequently avoided. Due to the considerable effort involved for on site PD measurements these are
generally only undertaken for extra-high voltage systems and for networks, such as power supply
systems, where high priority has to be given to ensure that operational failures are kept to a minimum.
4. References
/1/ Oesterheld, J.: Dielektrisches Verhalten von Silikonelastomer-Isolierungen bei hohen elektrischen
Feldstärken. Diss. TU Dresden 1995
/2/ IEC 62067, Ed. 1: Power cable systems – Cables with extruded insulation and their accessories
for rated voltages above 150 kV (Um = 170 kV) up to 500 kV (Um = 550 kV) – Test methods and
requirements
/3/ IEC 60840/Rev3: Power cables with extruded insulation and their accessories for rated voltages
above 30 kV (Um = 36 kV) up to 150 kV (Um = 170 kV) – Test methods and requirements
/4/ CIGRE SC 21,TF21-05: Experiences with ac tests after installation
/5/ CIGRE SC 21, DOC 00/06, Report by WG21-16: Partial discharge detection in installed extruded
cable systems
/6/ Schmidt F., Weissenberg W.: Stück- und Inbetriebnahmeprüfungen an Garnituren für VPE-
isolierte Hochspannungskabel, Elektrizitätswirtschaft, Jg. 97 (1998), Heft 26, Seite 26-29
/7/ Craatz P., Plath R., Heinrich R., Kalkner W.,: Sensitive On-Site PD Measurement and Location
th
using Directional Coupler Sensors in 110 kV Prefabricated Joints, 11 ISH99, London, paper
5.317 P5
/8/ Weissenberg W., Heinrich R., Kalkner W.,: Sensitive pd measurements at varios 110 kV
th
accessories in an unscreened laboratory using directional coupler sensors, 12 ISH01, Bombey,
paper 6.55
/9/ Pommerenke D., Strehl T., Heinrich R., Kalkner W., Schmidt F., Weissenberg W.: Discrimination
between Internal PD and other Pulses using Directional Coupling Sensors on High Voltage Cable
Systems, IEEE Transactions and Dielectrics and Electrical Insulation, Vol6, December 99, pp 814-
824