Field testing of medium- and high-voltage cables may performed for various reasons, such as acceptance after installation, charting the gradual deterioration of insulation over time, verification of splices and joints, and for special repairs. This assessment applies to both the cable itself, as well as the associated accessories (splices and terminations) — referred to as the "cable system."

In accordance with ICEA, IEC, IEEE and other consensus standards, testing can be performed by means of direct current, power frequency alternating current, or very low frequency alternating current. These sources may be used to perform insulation-withstand tests, baseline diagnostic tests such as partial discharge analysis, and power factor or dissipation factor.

This article provides an overview of some commonly used maintenance and diagnostic techniques that are commercially available for performing tests in the field on medium- and high-voltage power cables. Due to the various cable testing methods available, a test method selection should only be made after an evaluation of each test method and a thorough review of the installed cable system by a certified testing agency and the cable owner.

Safety Considerations

When testing cables, personnel safety is most important. All cable and equipment tests should only be performed by qualified persons on isolated and de-energized systems, except where otherwise specifically required and authorized. There are cases in which switches may be connected to a cable end and serve to isolate the cable from the rest of the system. Exercise extreme caution after de-energizing power cables as they are capable of holding large capacitive charges, use the correct PPE and electrical safety tools to properly discharge cables before and after testing.