GIS Partial Discharge Online Monitoring System
System Monitoring Principles and Features
The GIS online monitoring mode provided by this system is based on the ultra-high-frequency (UHF) method. The UHF partial-discharge detection technology is currently the most advanced condition-monitoring technique widely adopted internationally for GIS equipment. According to the research conducted by CIGRE WG33/23-12, the working group of the International Conference on Large Electric Systems, on GIS partial-discharge detection methods, the UHF method demonstrates the best anti-interference capability, covers a wider detection range, and exhibits high sensitivity toward all types of partial discharges. Our company can simultaneously offer monitoring products supporting multiple monitoring modes tailored to various high-voltage electrical devices, ensuring that these monitoring products can detect defects in monitored equipment at an early stage, thereby making them an effective means of preventing power accidents in GIS equipment.
1.Monitoring Principle
The ultra-high-frequency (UHF) online partial-discharge monitoring system employs the most advanced UHF detection technology currently available internationally. By accessing the casting port of GIS bushing insulators, it can sensitively detect the ultra-high-frequency electromagnetic signals generated by partial discharges, enabling both monitoring and localization of partial-discharge defects while maintaining a high signal-to-noise ratio and sensitivity even under challenging on-site interference conditions.
Traditional partial discharge monitoring techniques operate at relatively low frequencies, and their measurement bandwidth overlaps with the frequency bands of strong interference sources in the surrounding environment. As a result, these techniques are highly susceptible to external interference, making it difficult to isolate and detect partial discharge signals from interfering noise. Consequently, they are challenging to apply to online partial discharge monitoring. In contrast, ultra-high-frequency (UHF) partial discharge detection technology receives the ultra-high-frequency (UHF) electromagnetic pulse signals generated by partial discharges within a broadband range of 300 to 1500 MHz. The cavity structure of GIS and SF6Gaseous transmission media are more conducive to the propagation of ultra-high-frequency electromagnetic signals. Moreover, UHF signals experience rapid attenuation during spatial propagation; therefore, ultra-high-frequency electromagnetic interference signals originating from outside the GIS enclosure—such as corona discharge in the air—have a frequency band that is broader than that of SF.6The narrower the discharge signal in the gas, the more rapidly its intensity decreases as the frequency increases. The basin-type insulators with metal housings are particularly effective at shielding against external interference signals in GIS systems, allowing only a relatively small amount of ultra-high-frequency components to enter the GIS cavity. Consequently, they can effectively avoid most of the interference caused by air discharge pulses. As for fixed-frequency interferences distributed within the UHF monitoring band—such as signals from mobile communications, television, and radar—these can be avoided through built-in filters and background noise sensors, thereby enabling online monitoring.The purpose of partial discharge. Ultra-high-frequency electromagnetic waves in SF6In a gas, spherical waves propagate at the speed of light. According to electromagnetic wave theory, when monitoring electromagnetic wave signals within a metal-enclosed device, if the wavelength is shorter than the dimensions of the enclosure, the signal experiences very little attenuation during propagation—after traveling 10 meters, the signal attenuation is only about 50%. Since the wavelengths of UHF signals are all shorter than 1 meter, they happen to be smaller than the dimensions of GIS cavities. Therefore, UHF electromagnetic waves emitted from the partial discharge source, after undergoing multiple reflections and refractions, will eventually superimpose constructively and reach the sensor location with virtually no attenuation. Moreover, the metallic cavity not only focuses electromagnetic wave energy but also provides electromagnetic shielding, making it difficult for external electromagnetic interference to enter the interior of the enclosure. As a result, when using the UHF method to monitor partial discharges, one can achieve a favorable signal-to-noise ratio and high detection sensitivity. Experimental verification has shown that the ultra-high-frequency method can attain a detection sensitivity of 100 pC in GIS monitoring, enabling it to effectively identify destructive partial discharge defects with discharge quantities exceeding 500 pC. The transmission and reception process of the ultra-high-frequency partial discharge detection technology is illustrated in the monitoring principle diagram.
Ultra-High-Frequency Sensor Monitoring Schematic
2.Characteristics of Ultra-High-Frequency Monitoring Mode
Using ultra-high-frequency sensors, this method detects the electromagnetic pulse signals generated by partial discharges in the UHF band in a non-invasive manner. It demonstrates excellent performance in terms of detection sensitivity and anti-interference capability and has now become the dominant sensing approach for online partial-discharge detection, possessing the following characteristics.
1）It avoids the main electromagnetic interference frequency bands in the power grid, boasts excellent resistance to electromagnetic interference, and is insensitive to vibration and noise.
2）It is highly sensitive to various discharge defects, and even with an external sensing detection method, it can achieve sufficiently high detection sensitivity.
3）Based on the waveform characteristics of discharge pulses and the spectral characteristics of UHF signals, fault diagnosis and localization can be performed.position;
4）Wide effective detection range, few detection points, high detection efficiency, and suitable for online monitoring.
