Principal cable diagnostic tests include partial discharge (PD), Tan Delta (and variations of Tan Delta), return voltage method (RVM), and isothermal relaxation current (IRC) tests. Tan Delta tests and their variants can be categorised as tests sensitive to global or local problems, whereas PD is a measurement sensitive to local problems only. It should be noted that PD is not detectable in the field as a result of water trees directly. However, “Water trees cause electrical trees, which are detectable as a result of system voltage impulses and operational switching surges occurring, or when excessive test voltage levels are applied.” (IEEE 400.2 – 2013)
Tan Delta testing, also known as Power Factor and Dissipation Factor testing, involves the use of state-of-the-art instruments that give the user a wide range of results for qualitative cable assessments, such as degradation and lifetime estimations on MV and HV systems.
Partial discharge activity is an indication of incipient insulation faults and is widely regarded as one of the best ‘early warning’ indicators of deterioration in medium and high voltage insulation. PD diagnostics has therefore become a well-established method of quality control for new assets, as well as the condition assessment of service-aged systems.
Megger has an extensive history of manufacturing and supplying PD test equipment to many top industrial organisations for transformer, switchgear and cable testing. These partial discharge testers can take the role of quality assurance for product manufacturing or off-site plant analysis and mapping at almost any voltage the customer requires.
Partial discharge test and monitoring systems can be supplied in the form of handheld tools, as well as bigger, transportable diagnostic products. Megger’s broad range of equipment provides solutions for almost all types of MV and HV assets, from battery operated online PD handheld units, to full, extra high voltage (EHV) on-site testing systems.
Megger employs some of the world’s greatest experts in cable testing and diagnostics. With such a variety of possible testing and diagnostic methods, Megger can help you determine the appropriate techniques and equipment for your cable assessment needs.