The PDS800 handheld partial discharge tester developed by our company is a multi-functional handheld instrument that detects partial discharge conditions of equipment based on transient ground voltage, ultrasonic, ultrasonic, and high-frequency current detection methods; it is suitable for cables, Partial discharge detection of electrical equipment such as GIS, switch cabinets and transformers. and its working principle is based on the following;
1. transient ground voltage
When a partial discharge occurs in high-voltage electrical equipment, the discharge electricity first gathers in the grounded metal part adjacent to the discharge point, forming an electromagnetic wave and propagating in all directions. The electromagnetic wave generated by the discharge passes through the seams of the metal box or the gas-insulated switch. The gasket propagates out and at the same time generates a transient ground voltage, which is transmitted to the ground through the surface of the metal box of the equipment.
Transient ground voltage partial discharge monitoring is based on the basic fact that normal power equipment rarely emits transient ground wave signals between 3 and 100MHz. When using this principle to monitor partial discharge, the relationship between the pulse signal and voltage phase does not need to be considered, so it can be used for routine state monitoring of a large number of power grid equipment.
Since the auxiliary equipment of the power station, such as lighting systems with electronic ballasts, charging systems using semiconductor switching elements for voltage regulation, carrier communication equipment, and discharge tubes for main circuit charged display, etc., may produce signals in the above frequency bands, this method should be applied in When developing partial discharge monitoring technology, attention should be paid to eliminating and distinguishing such interference signals. If necessary, other test instruments, such as spectrum analyzers and oscilloscopes, can be used to confirm partial discharge and distinguish interference signals.
2. Ultrasound
Electrical equipment generates sound waves during discharge. The frequency spectrum of the sound wave generated by the discharge is very wide, from tens of Hz to several MHz, in which the signal frequency below 20kHz can be heard by the human ear, and the ultrasonic signal above this frequency must be received by the ultrasonic sensor. According to the relationship between the energy released by the discharge and the sound energy, the change in the sound pressure of the ultrasonic signal represents the change in the energy released by the partial discharge, and the strength of the discharge can be inferred by measuring the sound pressure of the ultrasonic signal, which is the basic principle of the ultrasonic signal detection of partial discharge.
3. UHF
The insulation strength and breakdown field strength of power equipment insulators are very high. When partial discharge occurs in a small range, the breakdown process is very fast and a very steep pulse current will be generated with a rise time of less than 1ns and an excitation frequency of Electromagnetic waves up to several GHz. The basic principle of the ultra-high frequency (UHF) partial discharge detection method is to use UHF sensors to detect the ultra-high frequency electromagnetic wave signals generated during partial discharge in power equipment, thereby obtaining relevant information about partial discharge and realizing partial discharge monitoring and ultra-high frequency detection. The frequency band is 300MHz-1.5GHz. Depending on the conditions of the on-site equipment, built-in UHF sensors and external UHF sensors can be used.
Since the on-site corona interference is mainly concentrated below the 300MHz frequency band, the UHF method can effectively avoid on-site corona and other interference, has high sensitivity and anti-interference ability, and can realize partial discharge charged detection, positioning, and defect type identification. and other advantages.
4. High frequency current
The insulation strength and breakdown field strength of power equipment insulators are very high. When partial discharge occurs in a small range, the breakdown process is very fast and a very steep pulse current will be generated. Partial discharge occurs inside high-voltage electrical equipment, and the discharge current propagates to the earth along the ground wire. The pulse current generated by the partial discharge can be detected on the equipment ground wire. High-frequency current sensors (HFCT) based on this method generally use Rogowski coils. The detection of grounding wires of electrical equipment by using high-frequency current sensors is a non-intrusive detection method. The equipment being detected does not need to be shut down, and it is simple and reliable.