Ang Nagkalab-ot nga Pagtukod sa Teknolohiya ug Metodo sa Analisis sa Parcial nga Discharge sa SF6 Floor Tank Circuit Breaker

Ang floor-mounted tank-type circuit breaker usa ka importante nga butang sa kontrol ug proteksyon sa mga substation ug sistema sa kuryente. Ginagamit kini para mobati, mopasabot, ug mobayad sa normal nga load current sa mga linya, ug mobati sa short-circuit current sa panahon sa mga sayop sa sistema. Gisangpotan kini sa mga komponente sama sa interrupting elements, insulating bushings, bushing-type current transformers, arc-extinguishing chambers, operating mechanisms, ug grounding casings, ang arc-extinguishing chamber sa floor-mounted tank-type circuit breaker gisangpotan sa usa ka grounded metal casing.

Ang SF₆ mibutang isip insulating ug arc-extinguishing medium alang sa tank-type circuit breakers. Sa uniform nga electric field, ang iyang insulation strength mahimong tulo ka beses mas taas kay sa hangin, ug ang iyang arc-extinguishing capacity mahimong usa ka raan ka beses mas taas kay sa hangin. Taliwala niini, ang SF₆ circuit breakers naka-characterize ngadto sa compact nga structure ug gamay nga footprint. Padulong, ang floor-mounted tank-type circuit breakers may adlawon sama sa gamay nga equipment center of gravity, stable nga structure, maayo nga seismic performance, built-in current transformers, matigas nga resistance sa dirt, ug convenient nga maintenance.

Gaynonman, sa panahon sa pagbuhat, pag-assembli, pagtransport, ug operasyon sa tank-type circuit breakers, matabangan usab ang insulation defects tungod sa mga factor sama sa dili maayo nga processing, collision, impact, ug switching operations. Ang typical nga insulation defects kasagaran naglakip og protruding metal objects sa conductors o casings, floating electrodes, ug free metal particles. Kon ang electric field strength na concentrated sa insulation defect nakaabot sa breakdown field strength sa area sa test voltage o rated voltage, mooccur ang partial discharge (PD). Ang partial discharge mao ang primary nga cause sa insulation degradation sa circuit breakers ug precursor sa insulation failures. Taliwala niini, ang online monitoring sa partial discharge signals makakita sa insulation defects human sa magkamalos, nga usa ka vital nga means aron sigurado ug stable ang operasyon sa floor-mounted tank-type circuit breakers ug sistema sa kuryente.

Batasan sa physical signals nga giproduktso sa panahon sa discharge, ang main partial discharge detection methods alang sa circuit breakers mao ang pulsed current method, ultrasonic method (AE), transient earth voltage method (TEV), ug ultra-high frequency method (UHF) [2 - 3]. Kini nga artikulo gi-combine ang experimental ug on-site experience aron review sa iba't ibang partial discharge detection ug analysis techniques alang sa SF₆ floor-mounted tank-type circuit breakers ug summarize ang characteristics sa bawg method.

Pulsed Current Method

Kon mooccur ang partial discharge, ang movement sa charges mogenera og pulsed current, nga makakita sa usa ka coupling device o current sensor nga giconnect sa test circuit. Ang pulsed current method mao ang unang method nga gitukoy sa IEC 60270 ug relevant standards para sa quantitative measurement sa partial discharge. Ang uban pa nga methods mainly gamiton sa detection o location sa partial discharge. Ang pulsed current method high sensitivity, pero labi ka susceptible sa on-site electromagnetic interference. Taliwala niini, kinahanglan nga extract ang faint discharge signals gikan sa detected signals. Ang physical quantity nga represent sa magnitude sa partial discharge mao ang apparent charge q, nga makakuha pinaagi sa mosunod nga formula.

Sa formula, i(t ) represents the pulsed current of partial discharge, Um(t) is the pulsed voltage, Rm is the detection impedance value, and q is the apparent charge, with the unit of pC (picocoulomb).

Ang pulsed current method batasan sa current sensors suitable for online partial discharge detection. Ang high-frequency current sensors typically operate within a frequency range of 16 kHz to 30 MHz and are designed in a clamp-on structure, facilitating their installation at the grounding end of floor-mounted tank-type circuit breakers.

Ultrasonic Method

Ang partial discharge mokausa og intense molecular collisions, generating ultrasonic waves nga mapapadaog sa circuit breaker. Ang ultrasonic sensors nga gisangpot sa circuit breaker casing makakita sa partial discharge signals. Ang piezoelectric elements sa loob sa ultrasonic sensors convert ang ultrasonic signals nga giproduktso sa partial discharge sa voltage signals, nga pagkatapos transmittable sa detection circuit. Ang detection circuit sa ultrasonic method mainly consists of a decoupler (used to separate power supply signals from ultrasonic signals), a signal amplifier, and a filter.

Ang time-domain ug frequency-domain signals sa ultrasonic waves gikan sa partial discharge sa floor-mounted tank-type circuit breakers gihatagan sa Figure 2, ang frequency range mainly distributed between 50 ug 250 kHz. Ang ultrasonic method may adlawon sama sa low cost, easy installation, strong resistance sa electromagnetic interference, ug suitable for partial discharge location. Gaynonman, ang internal insulation structure sa circuit breakers complex, ug ang ultrasonic waves molihok langgam ug experience significant attenuation sa SF₆ gas, requiring the identification of an optimal detection position.

Ultra-High Frequency (UHF) Method

Ang rise time ug duration sa current pulses nga giproduktso sa partial discharge sa nanosecond scale, exciting electromagnetic waves sa equivalent frequencies sa ultra-high frequency range of 300 MHz to 3 GHz. Karon, ang detection frequency range sa most UHF sensors sa market 300 MHz to 1.5 GHz. Tungod sa weak ug high-frequency nature sa signals, ang UHF method requires conditioning the input signals through filtering circuits, amplifying circuits, ug integrating circuits before transmitting them to a data acquisition card for subsequent analysis.

Meanwhile, when using the UHF method, it is necessary to eliminate noises such as communication signals and lighting power supply signals from both software and hardware aspects. The UHF method features high sensitivity, strong anti-interference ability, and is suitable for partial discharge location. The phase-resolved partial discharge (PRPD) pattern of UHF signals from partial discharge at floating potential is shown in Figure 3, which contains information about the discharge amplitude, phase, and number of occurrences.

Transient Earth Voltage (TEV) Method

When the electromagnetic waves generated by partial discharge propagate to the metal enclosure of a floor-mounted tank-type circuit breaker, an induced current is generated on the surface of the enclosure, resulting in a transient earth voltage across the wave impedance of the grounding body. The working principle of a TEV sensor can be equivalent to that of a capacitive voltage divider. It determines the occurrence of partial discharge by detecting the voltage across the equivalent capacitor between the sensor electrode and the insulating layer. The transient earth voltage signals of partial discharge inside an SF₆ circuit breaker are shown in Figure 4, with the main frequency range being 1 - 100 MHz. The TEV method is characterized by its ease of use and the absence of a need for an additional detection circuit.

Partial Discharge Analysis Methods

Ang partial discharge analysis methods gigamit aron assess ang risk level sa discharges, denoise signals, ug extract discharge characteristics for fault type classification. Kini nga methods mainly include the pulse waveform method, phase-resolved partial discharge (PRPD) pattern method, three-phase amplitude relationship pattern method, time-frequency pattern method, ug time-based statistical characteristic method.

Ang pulse waveform method analyzes a single discharge waveform based on parameters such as rise time, fall time, pulse width, kurtosis, and skewness. The PRPD pattern method accumulates partial discharge signals under AC power-frequency voltage to obtain the phase, amplitude, and occurrence number distribution characteristics of the discharges. Hence, it is also known as the \(\varphi -q -n\) pattern method. The three-phase amplitude relationship pattern method is used for analyzing partial discharges under three-phase AC voltage.

It acquires the discharge distribution characteristics by collecting the discharge amplitudes of a unified discharge signal under different phase voltages. The time-frequency pattern method collects discharge pulses, calculates their equivalent time and equivalent frequency, and plots the discharge distribution pattern in the equivalent time-equivalent frequency domain. The time-based statistical characteristic method is applicable to the analysis of partial discharges under high-voltage direct current. It statistically analyzes the discharge distribution characteristics based on the magnitude of the discharge quantity and the time difference between discharge pulses.

For the location of partial discharges inside SF₆ floor-mounted tank-type circuit breakers, the absolute time-difference method or the relative time-difference method can be adopted. The absolute time-difference method uses the discharge current pulse signal or the ultra-high frequency (UHF) signal as the starting time of the discharge. After calculating the time difference between the ultrasonic signal and the discharge starting signal, it locates the discharge source. The relative time-difference method only uses multiple ultrasonic sensors installed at different positions on the circuit breaker tank. It determines the location of insulation defects by calculating the time difference between each ultrasonic signal and the reference ultrasonic signal.

Conclusion

The online monitoring of partial discharges can effectively assess the insulation performance of SF₆ floor-mounted tank-type circuit breakers before a fault occurs, and it is one of the important means to ensure their safe and stable operation. This article reviews the detection and analysis methods of partial discharges in floor-mounted tank-type circuit breakers, combining experimental and on-site experience.

During on-site applications, multiple detection means and analysis methods should be used to improve the accuracy and reliability of online monitoring. Meanwhile, in line with the requirements of the construction of the ubiquitous power Internet of Things, implementing key technologies such as wireless passive sensing, low-power-consumption wireless communication networks, edge computing, and big data represents the future development trend of partial discharge detection for floor-mounted tank-type circuit breakers.