Introduction to partial discharge test

Definition of partial discharge:

1. Partial discharge refers to an electrical discharge that partially bridges the insulation between conductors. This discharge may or may not occur near the conductor.

2. The so-called bridge refers to short circuit or breakdown of insulation. The characteristic of partial discharge is that "partial bridge" is a discharge phenomenon that occurs in the weak area of insulation, that is, the local area of insulation.

3. Under the action of the electric field, only part of the insulation system is discharged, that is, there is no breakdown between the applied conductors. This phenomenon is called partial discharge.

According to the location of partial discharge, partial discharge can be divided into three categories

1. Internal partial discharge: partial discharge occurred inside the insulator.

2. Surface partial discharge: partial discharge occurs on the surface of insulator.

3. Corona discharge: refers to partial discharge near the conductor surrounded by gas.

Causes of partial discharge

1. Uneven electric field

2. Uneven dielectric (mainly caused by uneven electric field)

3 During the manufacturing process, due to the problems of technology and processing materials and the operation of some equipment, thermal expansion and cold contraction will occur, resulting in cracks in the insulation material gradually, which will lead to partial discharge.

Detection impedance

The main function of impedance detection is to extract the high-frequency pulse signal generated by partial discharge, and suppress the power frequency of test voltage and the low-frequency signal of harmonic. Detection impedance is a key component connecting the test object and the main part of the instrument, which has a direct relationship with the frequency characteristics and sensitivity of the instrument. Some foreign companies call it input unit. four-terminal network.

Coupling capacitor (CK)

Coupling capacitor (CK) is an important link in the direct detection of partial discharge circuit. The coupling capacitor (CK) couples the partial discharge pulse information to the detection impedance. At the same time, it separates the test high voltage from the detection impedance, so that the detection impedance can safely and sensitively detect the partial discharge information. Ensure the safety of instruments and test operators.

In the partial discharge test, the capacitance value of the coupling capacitor is required to have sufficient value, and there is no partial discharge (or the partial discharge value is less than a given index) under the action of the test voltage

Transformer without partial discharge test

To detect the partial discharge of the test object, especially when the detection sensitivity is high, the parts of the whole partial discharge test circuit are required to be free of partial discharge, which is actually less than a certain allowable given value. The test transformer is used to supply the test voltage of the test object. It is required that the test transformer itself should not have partial discharge exceeding the given value, otherwise the test will not be carried out effectively.

Filter control power supply

In order to prevent the interference caused by the intrusion of the test power supply during the partial discharge test, the method of isolating and filtering the partial discharge test voltage is adopted. In addition, the gradual increase of partial discharge test voltage from zero to the required voltage, and the application of protection and emergency shutdown of test voltage.

Test photos: