PD Testing and Monitoring of HV XLPE Cable Systems Authors Wojciech Koltunowicz, OMICRON Energy Solutions GmbH Michael Krüger, OMICRON Electronics GmbH -------------------------------------------------------------------------------------------------------------------------- The correct design and the quality of production of XLPE cable and its accessories, terminations and joints, is checked by various routine tests at the manufacturer’s plant according to relevant standards. However, installation work on site poses a possible risk of introducing faults, which could negatively impact reliable operation over time. Small particles, dust, and moisture might lead to defects in electrically critical locations of the accessories. Dielectric tests performed on site are therefore highly recommended. These supplementary tests are aimed at checking the dielectric integrity of the fully assembled cable line in order to eliminate defects caused by damages during transportation and lay-out or incorrect assembly of the accessories. The preferred voltage for on-site tests is ac voltage of industrial frequency, although voltage testing only delivers binary results (withstand or breakdown). Therefore, it is recommended to combine ac voltage testing with sensitive on-site partial discharge (PD) measurements. Why PD? A major part of all in-service failures in HV XLPE cables can be attributed to the insulation system of accessories, joints and terminations. These failures will normally develop over time. In order to detect these changes at an early stage, detailed information about the actual insulation condition is necessary. With suitable sensors, this information can be derived by monitoring PD activity during the operating life of the equipment. This article describes the best practice for performing after installation testing and continuous PD monitoring to assess the quality and extend the life of the HV XLPE cable system. PD Measurements During After-Installation Testing High-voltage (HV) tests are executed on site for all extruded HV cables. On-site test procedures usually have to be negotiated between the manufacturer and the user on the basis of international and national standards. Two IEC standards cover after installation tests of extruded cable systems: IEC 60840:2004 for cables of rated voltages from 30 kV (U m = 36 kV) up to 150 kV (U m =170 kV) and IEC 62067:2001 for rated voltages above 150 kV up to 500 kV (U m = 550 kV). High test power, especially required for long cable lines testing, can only be effeciently generated by
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PD Testing and Monitoring of HV XLPE Cable Systems
Authors
Wojciech Koltunowicz, OMICRON Energy Solutions GmbH
Michael Krüger, OMICRON Electronics GmbH
-------------------------------------------------------------------------------------------------------------------------- The correct design and the quality of production of XLPE cable and its accessories,
terminations and joints, is checked by various routine tests at the manufacturer’s plant
according to relevant standards.
However, installation work on site poses a possible risk of introducing faults, which could
negatively impact reliable operation over time. Small particles, dust, and moisture might lead
to defects in electrically critical locations of the accessories. Dielectric tests performed on
site are therefore highly recommended. These supplementary tests are aimed at checking
the dielectric integrity of the fully assembled cable line in order to eliminate defects caused
by damages during transportation and lay-out or incorrect assembly of the accessories.
The preferred voltage for on-site tests is ac voltage of industrial frequency, although voltage
testing only delivers binary results (withstand or breakdown). Therefore, it is recommended
to combine ac voltage testing with sensitive on-site partial discharge (PD) measurements.
Why PD? A major part of all in-service failures in HV XLPE cables can be attributed to the
insulation system of accessories, joints and terminations. These failures will normally
develop over time. In order to detect these changes at an early stage, detailed information
about the actual insulation condition is necessary. With suitable sensors, this information can
be derived by monitoring PD activity during the operating life of the equipment.
This article describes the best practice for performing after installation testing and
continuous PD monitoring to assess the quality and extend the life of the HV XLPE cable
system.
PD Measurements During After-Installation Testing
High-voltage (HV) tests are executed on site for all extruded HV cables. On-site test
procedures usually have to be negotiated between the manufacturer and the user on the
basis of international and national standards.
Two IEC standards cover after installation tests of extruded cable systems: IEC 60840:2004
for cables of rated voltages from 30 kV (Um = 36 kV) up to 150 kV (Um =170 kV) and
IEC 62067:2001 for rated voltages above 150 kV up to 500 kV (Um = 550 kV). High test
power, especially required for long cable lines testing, can only be effeciently generated by
mobile resonant test systems, where the weight-to-power ratio and feeding power demand is
relatively low and the transport volume is acceptable (See Figure 1).
One MPD 600 unit from OMICRON was connected to the coupling capacitor and calibration
was performed according to the IEC 60270 and IEC 60885 standards. A performance check
was performed on the other fifteen PD acquisition units, which were mounted into the link
boxes close to the terminations and connected in a daisy chain with fiber optics. (See Figure 3). A real calibration is not possible here because impulses cannot be injected directly into
The monitoring server receives data for analysis, display, and storage. The acquisition units
are configured and remote-controlled by the monitoring system software. The software
supports remote access over TCP/IP. This allows operators to quickly react to detected
problems and access the stored data from any remote location. The software is a highly
modular, scalable distributed system. Its system architecture consists of the Windows-based
core part and the web-based control part. The core part of the monitoring software is realized
as windows services and runs continuously without any direct user interactions. The core
system implements: Collection and persistence of measurement; data post-processing and
analysis; security tasks for data access and system operations; and external interfaces for
data exchange over Ethernet or field bus.
E. Trend Analysis
The monitoring system provides data from each of the acquisition units and oil pressure
sensors in permanent and periodic time intervals (See Table I). ----------------------------------------------------------------------------------------------------------------------
Table I: Default time scheduling for different measured values
Mode
Value Permanent Periodic
Partial Discharge every 2-3 sec for 1 every 1 h
Oil pressure at terminations every 2- 3 sec once every 1 h