How is the insulation level of a transformer assessed and defined?

How is the insulation level of a transformer assessed and defined?

Today, we will explain how to judge the insulation level of a transformer. This is because the insulation level is a standard for assessing transformer quality, and as a transformer manufacturer, we feel it’s necessary to explain this to facilitate detailed selection in the future. Before introducing the identification methods, we need to understand that the insulation level is generally evaluated by measuring a set of rated withstand voltages.

Below are our manufacturer’s testing methods for this area. We generally have three measurement methods:

① Using a power frequency rated withstand voltage test (including external withstand voltage test and induced withstand voltage test), combined with measuring partial discharge, to assess the insulation reliability under long-term operating voltage;

② Using an impulse voltage generator to simulate lightning overvoltage after lightning protection limitation, conducting a lightning impulse test to assess the transformer’s insulation’s ability to withstand lightning overvoltage;

③ Using an impulse voltage generator to generate a representative operating wave, conducting an operating impulse test to verify the ability of the high-voltage winding insulation of transformers with a voltage level of not less than 330kV to withstand operating overvoltage.

The above are the measurement methods frequently used by transformer manufacturers. In fact, to ensure good quality, transformer manufacturers specify two test voltage levels for transformers of the same voltage rating. The power frequency withstand voltage test at the transformer’s factory is the main method for verifying the insulation condition of the transformer at the time of manufacture.

While consumers generally prefer the higher voltage when purchasing, it’s still advisable to measure from the lower voltage level to ensure stable transformer quality.