Offline Partial Discharge Testing for HV and MV Cables

Offline Cable PD Mapping Service™: Assess the health of MV/HV cables through VLF testing and Tan Delta measurement

Our Cable PD Mapping Service™ is a specialised offline partial discharge testing method designed to accurately assess the health of medium voltage (MV) and high voltage (HV) cables. This service utilises advanced Offline Very Low Frequency (VLF) Testing and Tan Delta Measurement techniques to effectively locate and report issues within HV cables, facilitating timely repair or replacement decisions.

Key Techniques Used in Offline Partial Discharge Testing:

Offline Very Low Frequency (VLF) Testing: Evaluate the condition of HV/MV cables when they are not in operation. This test uses a VLF voltage, typically 0.1Hz, to assess the integrity of electrical insulation in cables and identify the exact location of partial discharge (PD).
Tan Delta Measurement: This supplementary test, performed alongside VLF cable testing, measures the overall health of the cable's insulation. It is vital for partial discharge measurement, revealing early signs of insulation degradation, such as water treeing or impurities, which could suggest the need for repair or replacement.

Offline VLF Testing
Tan Delta Measurement

Offline VLF Testing

Our state-of-the-art VLF Cable PD Mapping test equipment is designed for both new installations and during scheduled downtime, ensuring your electrical equipment's integrity.

In order to measure PD activity, the cable must be energised at a voltage level of at least the normal working voltage. 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 VLF high voltage test supply is used. This allows long lengths of cable to be energised at the required test voltage.

By determining the PD's magnitude and location, stakeholders can manage their assets more effectively, reducing the testing time and the potential for unexpected failures.

VLF testing offline cable testing

Tan Delta Measurement

‟Our system is safe, non-destructive and has a 30-year track record of success globally.”

Advantages of Choosing Our Offline Partial Discharge Testing Service:

Early Detection: Locate PD activity before it results in costly failures, ensuring your electrical equipment remains operational.
Cost-Effective: Minimise the need for extensive excavations and mitigate the risk of expensive unplanned outages by identifying problem areas accurately.
Comprehensive Testing: Our service includes time-of-flight measurement to pinpoint PD activity, applicable to both paper and polymer insulated HV cables, and produces a detailed condition map, highlighting areas in need of attention.

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

Partial discharge activity from along the cable route can be measured and located.
Testing off-line gives us the ability to measure partial discharge and tan delta.
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 33kV. 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	Tests the integrity of cables that have been repaired without the risk of overloading the cable
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

Find out how our Cable PD Mapping Service™ can enhance safety, save costs and extend the lifespan of your cable assets. Get in touch with an expert today!