Offline Partial Discharge Cable Mapping

Home
Services
Condition Assessment
Cable Condition Assessment
Offline Partial Discharge Cable Mapping

Our cable condition assessment service offers a thorough review of the status of your cables with two unique offline testing methods. Partial discharge mapping reveals minor insulation failures before they become critical, while Tan Delta to IEEE 400.2 uncovers water tree growth that could otherwise go undetected and reduce the life expectancy of XLPE insulations. Detection through partial discharge alone is not enough; our process ensures thorough safeguarding for peace-of-mind assurance in each test.

Figure 1: Non- destructive VLF testing.

What is Partial Discharge Cable Mapping?
Why choose EA Technology's Cable Mapping Service?
Business Benefits of Cable Mapping
What is Tan Delta testing?

What is Partial Discharge Cable Mapping?

Partial Discharge Mapping is an offline test where the cable system is isolated from the electrical network and energised with a discharge free test supply. This allows the measurement of the magnitude and origin of partial discharge activity within high voltage cable insulation with minimal background noise. By capturing many partial discharge events, a graphical representation of the discharge activity along a length of cable may be generated.

In order to measure partial discharge activity, the cable must be energised at a voltage level of at least the normal working voltage (U₀). Supplying this test voltage for long cables is difficult due to the high-power requirements necessary to provide the charging current to energise the cable capacitance. To reduce the power requirements, a Very Low Frequency (VLF) high voltage test supply is used. This allows long lengths of cable to be energised at the required test voltage from a 230V 13A outlet. The frequency of the test voltage is dependent on the cable length but is typically 0.1Hz.

Each Partial discharge event is detected via a high voltage coupling filter connected at the end of the cable under test. The signals are captured by a digital oscilloscope and transferred to a computer for storage and analysis.

The recorded partial discharge traces are subsequently processed using a software package to determine the origin and the magnitude of each individual partial discharge event. Finally, the processed data is used to produce a graphical representation of the discharge activity along the route length in the form of a partial discharge map.

Why choose EA Technology's Cable Mapping Service?

Testing offline provides many benefits over online cable partial discharge testing, including:

Testing can be conducted on any cable circuit with any termination configuration.
Partial discharge activity from along the cable route can be measured and located, which is often difficult with on-line techniques.
Testing off-line gives us the ability to measure partial discharge and tan delta simultaneously.
We can apply test voltages greater than normal working voltages.
Testing above normal working voltage is recommended by the IEEE 400.2 – 2013 ‘Guide for Field Testing of Shielded Power Cable Systems Using Very Low Frequency (VLF)’.

Multiple applications
The service is effective on all types of HV/MV cable up to 66kV. Paper insulated cables can be tested to approximately 5km in length and polymeric insulated cables up to
approximately 8km in length.

Typical uses include:

Pre-commissioning	Checks the condition of cables and joints before they are put into service
Post-repair	Safely tests the integrity of cables that have been repaired without the risk of overloading the cable, which is inherent in ‘withstand’ tests
Fault detection and diagnosis	Identifies partial discharge in cables and joints at an early stage of their development, before they lead to disruptive failures
Condition data gathering	Collects information on the condition of cable assets, including confirmation that cables are free of partial discharge
Risk analysis	Enables the production of a Health Index for each cable asset, so that the probability and consequences of failure may be calculated
Investment prioritisation	Empowers asset managers to make intelligence-based decisions on cable maintenance and replacement strategies

Valuable condition data
Cables and joints which exhibit deterioration in the form of PD activity are identified by the system as pulses of electrical energy and measured in pico-Coulombs (pC). The magnitude of discharges in each phase is displayed as a function of distance along the cable.
Information from all the PD events can be combined to produce a ‘discharge map’: a comprehensive picture of the condition of the whole cable and its joints. This enables us to provide detailed reports on where partial discharge is present and the likelihood of it developing into a failure.

Tan Delta testing provides additional information on the quality of the insulation.

Business Benefits of Cable Mapping