Cables are exposed to the elements like moisture, dirt and other contaminants. They are also subjected to mechanical and electrical stress during operation. This is the importance of regular testing of cables. Predictive maintenance often employs diagnostic type tests which will provide the test data necessary to prioritize the replacement of those cables before they become faulted and the source of unscheduled down time.
Here are some of the cable testing equipment used in preventive maintenance.
This device can find faults that are several miles away. A TDR allows easy and fast troubleshooting of cable defects. It works by sending out a low voltage traveling wave through the central conductor and surveying the impedance of the insulation between that conductor and another one such as a concentric neutral or shield. If a cable has a localized defect, the impedance between these two conductors at that specific place will not be homogeneous with the rest of the cable. This causes the test pulse to reflect back to the source. The speed at which the pulse travels along the cable, and the time that it takes for the pulse to reflect back to its source can be used in localizing the point at which the cable insulation is compromised.
This tester helps assess the reliability of the insulator. Microscopic voids as well as other defects that lead to the insulation being compromised can be detected by using this tester. Ideally, we look at insulation as being an impenetrable electrical boundary. However, we also know that there is no perfect insulator, and that even a very good insulator can have a very small amount of leakage current flow through it when it is under stress. A high potential test set finds faults by applying a high voltage that is 2-3 times higher than the cable's rating, and monitoring the leakage current through the insulator. Ideally, a cable's insulation should be able to handle voltages 3-4 times higher than its rated line to neutral voltage without allowing an excessive amount of leakage current to flow.
Related electrical test equipment available for rent from Protec:
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Editor’s Note: This post was originally published April, 2012 and has been updated freshness, accuracy and comprehensiveness.