When we get calls from clients regarding cable failures there is a general theme that occurs time and time again. “We didn’t realise the cable was in such bad condition” they would say after seeing the destruction caused by the failure. High voltage cables are a common and frequent cause of outages, but how can you determine if they are in good working order? To effectively manage the condition of your cables, owners and operators need to have a good understanding as to the condition of their assets. Eccentricity has over 10 years of experience dealing with high voltage cables throughout a variety of industries and in this article, you will learn how important condition assessments of your HV cables is to ensure the integrity of your electrical system.
Healthy high voltage cables have evident high-performance characteristics. These include no excess heating, no corona buildup, adequate separation, and correctly utilized installation methods. Many cable failures occur at the point of termination or joint within the electrical circuit. Most of these failures could have been prevented if an effective condition assessment was completed at regular intervals throughout the cable’s lifespan. Ultrasonic and partial discharge (PD) measurements using transient earth voltage techniques is the most effective method for determining the health of your HV cables, however, to get a complete guide to the condition of your cables requires some additional techniques.
It is important to consider appropriate testing techniques for detecting the quality of the insulation and if any partial discharge is present. These techniques offer information that can be gathered through the location of PD activity and assessing the dielectric strength of the insulating medium (insulation quality).
There are two ways to gather this data for analysis:
Offline testing is performed on de-energised circuits using an external power supply such as a very low frequency tester (VLF) which can map any PD present which often contains an in-built tan-delta measurement for assessing dielectric strength. This method can detect aging insulation through the presence of water treeing or insulation impurities. One drawback of this method is that it is time consuming and complex to perform and usually only performed on suspect circuits.
Online testing is a great method for determining the condition of your HV cables. It is a non-intrusive method that can be performed on energised circuits by using radio frequency current transformers. These measure the radio frequency current pulses and are generally connected to the earth sheath of the cable. By capturing the waveform data, you can assess the reference signals to determine the level of PD present on the system.
If performed correctly and at frequent intervals, you can trend the data to predict the condition of your cables more accurately. It is a good idea to complete measurements on newly installed cables also which will provide a good baseline for this trend. With the integration of condition assessments, you can ensure peace of mind that the integrity of your electrical system is maintained and make effective plans to replace cabling nearing the end of its lifespan.
If you have aged equipment or are suspicious of your cable’s reliability, contact us for support today.
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Case Study:
“Partial discharge detected on existing paper insulated cable due to incorrect installation method and inadequate clearance between phases”
