How to withstand the impulse voltage of transformer

In power system, transformer is one of the key power equipment, which is responsible for voltage conversion and power transmission. However, in the operation process, transformers often suffer from high voltage shocks from inside or outside the system, such as lightning strike and operating overvoltage. These surge voltages may pose a serious threat to the insulation system of the transformer, so it is of great practical significance to study how to withstand the surge voltage of the transformer.

First, the basic concept of impulse voltage

Impulse voltage usually refers to the high voltage acting on electrical equipment in a short time, which mainly includes lightning impulse voltage and operating impulse voltage. Among them, the lightning impulse voltage has a high amplitude (up to hundreds of kilovolts) and a short duration (microsecond level), while the operating impulse voltage is mostly caused by the operation of circuit breakers or system failures, with a slightly longer duration (millisecond level). Both of them will cause different degrees of insulation damage to the transformer.

Second, the ability of transformer to withstand impulse voltage

Whether the transformer can effectively withstand impulse voltage mainly depends on its insulation structure design and manufacturing technology. Modern transformers usually adopt oil-paper insulation system, which has good voltage resistance and long-term stability. In addition, the arrangement of transformer windings, the layout of leads and the selection of insulation materials will also affect its impact resistance.

In order to improve the lightning protection and impact resistance of transformers, the following measures are usually taken in design:

1. Strengthen the design of main insulation and longitudinal insulation: improve the withstand voltage level by increasing the insulation distance between windings and the insulation strength between windings.
2. Use lightning arrester for protection: Installing lightning arrester on high voltage side can effectively absorb lightning impact energy and limit overvoltage amplitude.
3. Adopt neutral grounding mode: Reasonable selection of neutral grounding mode is helpful to reduce the influence of operating overvoltage on transformer.
4. Set shielding layer and electrostatic ring: improve the distribution of electric field and prevent the occurrence of partial discharge and corona.

Third, the test and evaluation

In order to verify whether the transformer has the ability to withstand impulse voltage, strict tests must be carried out. The International Electrotechnical Commission (IEC) and national standards stipulate the items and standards of impulse voltage test, such as lightning impulse test (LI) and operating impulse test (SI). These tests test whether the insulation performance meets the requirements by simulating the waveform of actual impulse voltage and adding it to the transformer.

IV. Matters needing attention in operation and maintenance

Even if the transformer has a good structural design and factory test, the maintenance in operation can not be ignored. Regularly testing the performance of insulating oil, monitoring partial discharge and checking the integrity of bushing and grounding device are all important measures to ensure the long-term safe operation of transformer.

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To sum up, the ability of transformer to withstand impulse voltage is a systematic engineering, involving design, material selection, manufacturing, testing, operation and maintenance and other links. With the development of power system towards high voltage and large capacity, it is of great significance to improve the impact resistance of transformer for ensuring the safe and stable operation of power grid. In the future, with the application of new materials and technologies, the safety performance of transformers under impulse voltage will be continuously improved.