Verifying suspected insulation faults in power transformers

TEIAS, an electrical transmission utility in Türkiye, relies on MONTESTO 200 as part of its holistic approach to assessing the insulation condition of power transformers in its repair workshop and the field.

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Power transformers are one of the power grid's most important high-voltage (HV) assets. They are the key elements in generation, transmission, distribution networks and industrial sites. With the advancing age of power transformers worldwide, it is vital to check their insulation condition by continuously assessing the health of various components to ensure reliability.

A power transformer is exposed to many stress factors during its life cycle due to environment and load conditions, high electrical field stress, mechanical vibrations, and chemical contamination. A lack of a regular diagnostic testing and maintenance plan can result in eventual undetected insulation faults that can shorten the expected service life of a power transformer.

Assessing insulation condition in power transformers

A holistic approach is generally adopted for the overall check of insulation condition in power transformers based on Dissolved Gas Analysis (DGA), various electrical tests, monitoring, and visual inspections.

DGA results from the insulating oil are used as a first alarm for any evidence of problems that can occur inside oil-filled power transformers. Abnormal levels of certain gasses can indicate potential problems, triggering additional investigations to identify and localise developing faults using electrical testing, monitoring, and a direct visual inspection inside the transformer.

Advanced electrical testing and diagnostic tools, such as Dielectric Frequency Response (DFR) testing, Sweep Frequency Response Analysis (SFRA) testing and Partial Discharge (PD) testing and monitoring are now widely used to assess and diagnose the insulation condition of power transformers by detecting certain faults that conventional testing methods are unable to detect. In this article, we will focus on PD testing and monitoring.

Partial discharge testing on power transformers