Partial discharge measurement principle

  1. What is partial discharge test?   
    The digital partial discharge detection system can sense the high-frequency signals generated by the failure, vibration, leakage and electrical partial discharge of the running equipment. The digital partial discharge tester uses a unique heterodyne method to convert these signals into audio signals, allowing the operator to hear these sounds through headphones and see the intensity indication on the pointer. The principle of heterodyne method is like a radio, which can accurately convert signals into sounds, making it easy for people to identify and understand. The advantage of using ultrasonic technology in the digital partial discharge detection system is that it is easy to understand and convenient. Ultrasonic waves are high-frequency short-wave signals. This sound wave cannot be directly heard by the human ear. When we use ultrasonic full-function detectors, we can fully detect these sounds. Using advanced visual ultrasonic principles and sophisticated sensing technology, it can vividly display the discharge image, and inform the maintenance personnel to perform maintenance in three ways: digital, sound and image, to ensure the safe operation of GIS.   
    The partial discharge detection system is specially used for partial discharge measurement of electrical equipment such as transformers, motors, mutual inductors, cables, GIS, switches, and lightning arresters. Its technical performance fully complies with the requirements of IEC-270 and GB7354 standards, and is an essential test equipment for electrical equipment manufacturers, power generation and operation departments, and power construction, installation and commissioning departments.   
2. What is the measurement principle of partial discharge?   
    The principle used by the digital partial discharge instrument is the pulse current method principle, that is, when a partial discharge occurs, an instantaneous voltage change Δu is generated at both ends of the test piece Cx. At this time, if it is coupled to a detection impedance Zd through an electric Ck, a pulse current I will be generated in the circuit. The pulse voltage information generated by the pulse current through the detection impedance is detected, amplified, and displayed, and some basic parameters of partial discharge (mainly the discharge amount q) can be determined. It should be pointed out here that the actual partial discharge amount inside the test piece cannot be measured, because the transmission path and direction of the partial discharge pulse inside the test piece are extremely complex. Therefore, we can only detect the apparent discharge charge of the test piece through the comparison method, that is, before the test, a certain amount of electricity is injected at both ends of the test piece, and the amplification factor is adjusted to establish a scale. Then, the partial discharge pulse received inside the test piece under the actual voltage is compared with the scale to obtain the apparent discharge charge of the test piece.   
3. Definition of partial discharge   
    Partial discharge, when the field strength generated by the applied voltage in the electrical equipment is sufficient to cause discharge in the insulation area, but no fixed discharge channel is formed in the discharge area, this discharge phenomenon is called partial discharge.   
4. Introduction to partial discharge   
    The partial discharge phenomenon mainly refers to high-voltage electrical equipment.  　　  
    The discharge that occurs in the local range of the insulation of power equipment under the action of a sufficiently strong electric field. This discharge is limited to only causing a local short (bridge) connection between the insulation of the conductors without forming a conductive channel. Each partial discharge will have some impact on the insulating medium. A slight partial discharge has little effect on the insulation of the power equipment, and the insulation strength decreases slowly; while a strong partial discharge will cause the insulation strength to decrease quickly. This is an important factor that causes insulation damage to high-voltage power equipment. Therefore, when designing the insulation of high-voltage power equipment, it is necessary to consider that under the action of long-term working voltage, strong partial discharge is not allowed to occur in the insulation structure. The equipment in operation should be monitored more closely. When the partial discharge exceeds a certain level, the equipment should be withdrawn from operation for inspection or replacement.   
5. Impact of partial discharge on power equipment   
      When the insulation is partially discharged, it will affect the insulation life. Each time a discharge occurs, the impact of high-energy electrons or accelerated electrons, especially long-term local discharge, will cause various forms of physical effects and chemical reactions. For example, when charged particles hit the outer wall of the bubble, they may break the chemical bonds of the insulation and cause cracking, destroying the molecular structure of the insulation, causing insulation degradation and accelerating the insulation damage process.