What are the common detection methods for partial discharge detectors

1. Ultrasonic testing

The ultrasonic sensor fixed on the wall of the transformer oil conservator can receive the ultrasonic waves generated by the partial discharge inside the transformer, thereby detecting the size and position of the partial discharge. The detection ultrasonic sensor currently used has poor anti-electromagnetic interference ability and low sensitivity, which increases the difficulty of detection. In recent years, due to the improvement of the efficiency of acoustic-electric transducer elements and the development of electronic amplification technology, the sensitivity of ultrasonic detection has been greatly improved, so the development and application of this method is very promising.

2. Photometry

It is carried out using light radiation generated by partial discharge. In transformer oil, the wavelength of light emitted by various discharges is different. After photoelectric conversion, the identification of partial discharge can be realized by detecting the characteristics of the photocurrent. Although great progress has been made in the laboratory using photometry to analyze the characteristics of partial discharge and the mechanism of insulation degradation, the photometry equipment is complex and expensive, the sensitivity is low, and the substance to be tested needs to be transparent to light. Therefore, it is impossible to be widely used in practice.

3. Chemical detection method

When a partial discharge occurs in a transformer, various insulating materials will be decomposed and destroyed, and new products will be produced. By detecting the composition and concentration of the products, the state of the partial discharge can be judged. At present, this method has been widely used in online fault diagnosis of transformers. The type of fault is different, the degree of the fault is also different, and the composition and concentration of the gas are also different. The pattern recognition system established by this can realize the automatic recognition of the fault. But until now, there is still no unified judgment standard. Because it is more sensitive to early detection of latent failures, but it cannot reflect sudden failures.

4. Pulse current method

The pulse current method is to obtain the actual discharge amount by detecting the impedance, detecting the pulse current caused by the partial discharge in the transformer bushing grounding wire, shell grounding wire, iron core grounding wire and winding. It is the earliest research and the most widely used detection method.

5. Radio frequency detection method

It measures the signal from the neutral point of the transformer. The measured signal frequency can reach 30MHZ, which greatly improves the measurement frequency of partial discharge. At the same time, the test system is easy to install, the test equipment does not change the operation mode of the power system, the sum of the three-phase partial discharge signals cannot be distinguished, and the signals are susceptible to external interference. But with the development of digital filtering technology, radio frequency detection method has been widely used in partial discharge online detection.

6. UHF partial discharge detection

Due to the shortcomings of traditional detection methods, a new detection method, ultra-high frequency detection, emerged. The ultra-high frequency electrical signal generated by the partial discharge of the transformer realizes the detection and positioning of the partial insulation discharge of the power transformer, and realizes the anti-interference. The main advantages of using UHF to detect partial discharge of transformers are as follows: First, the partial discharge pulse energy is almost proportional to the frequency bandwidth. When only the thermal noise of the detection element is considered to affect the sensitivity, the overfrequency broadband detection has higher sensitivity; Studies have shown that at the transformer application site, the frequency of electromagnetic interference generated by the background, noise and corona in the air in the substation is generally very low. Broadband method can be used to effectively suppress it, and the narrowband method can be used to distinguish it from partial discharge signals. It can be seen that the nature and physical process of partial discharge in real transformer insulation can be measured with a suitable UHF sensor.