According to statistics, the vast majority of overhead line faults are "transient", with permanent faults generally accounting for less than 10%. Currently, for 10kV distribution network lines, the combined use of automatic reclosers and sectionalizers can quickly restore power supply after a transient fault and isolate the faulty line section in case of a permanent fault. It is necessary to monitor the operating status of the automatic reclosing controller to enhance its operational reliability.
1. Domestic and Foreign Technological Research
1.1 Classification of Automatic Reclosers
Automatic reclosers are classified into current - type reclosers and voltage - type reclosers. A current - type recloser is one that can reclose after tripping in response to a fault current. This type of recloser serves both as a protective tripping device and can perform one to three reclosing operations. It eliminates the faulty sections one by one starting from the last section until the faulty section is identified. Since it requires multiple reclosing operations with fault current, it has a relatively large impact on the power grid. Moreover, the more sections there are, the more reclosing operations are needed and the longer the time required. Therefore, the number of sections is generally not advisable to exceed three. It is suitable for branch lines and radial - type lines.
The other type of recloser, the voltage - type recloser, trips when the line loses voltage and recloses after a time delay when power is restored. The outgoing circuit breaker in the substation needs to reclose twice to complete the fault isolation and power supply restoration. The first reclosure is for identifying the faulty section. Based on the number of open switches in each section, the faulty section is determined, and the switches on both sides of the faulty section are locked to isolate the fault. The second reclosure is for restoring power supply to the non - faulty sections.
The entire feeder only experiences the fault current once during the reclosing process, but it takes a relatively long time to complete the fault isolation and power supply restoration. Since the over - current quick - break protection needs to be accomplished by the feeder circuit breaker in the substation, it is not suitable for long lines. However, with the increase in system capacity, this contradiction has been gradually alleviated. It is applicable to radial - type or loop - type short lines to achieve primary automation.
1.2 Problems with Traditional Detection
Due to factors such as manufacturing processes and wear - and - tear from long - term use, automatic reclosers may malfunction or operate erroneously. Currently, the detection of automatic reclosers mainly relies on manual detection devices, which incur high investment costs.
1.3 Research Status and Development Trends at Home and Abroad
Regarding the state - detection technology for automatic reclosers, in China, off - line periodic maintenance methods are mainly adopted, including insulation resistance tests, insulation resistance tests of the control circuit, AC withstand voltage tests, etc.
Its main drawbacks are that the detection equipment is bulky and heavy, inconvenient to transport. During the testing process of the detection equipment, it needs to be elevated, posing certain safety risks. Meanwhile, detection requires a large amount of manpower and material resources. Currently, relatively complete detection and diagnosis systems are still very rarely applied in actual production.
The detection and analysis of automatic recloser controllers have seen certain developments. Currently, automatic analyzers have been successfully and widely adopted. It only requires a simple interface connection and can be connected to various automatic reclosers from different manufacturers in a "plug - and - play" manner. By injecting current signals into the automatic recloser, relevant information such as the TCC (Time - Current Characteristic) curve and control sequence can be measured.
It enables comprehensive control over parameters such as the waveform, time, and amplitude of the current signal. At the same time, it can accurately record the response information of the current controller, with the response time accurate to microseconds. It can completely control and execute a complete test in sequence and instantaneously display the text test results, such as displaying the commands generated by the current input response together with the measurement and recording events, including tripping, reclosing, and reset blocking.
Research on intelligent fault diagnosis mainly focuses on the following aspects:
- Research on integrated intelligent fault diagnosis technology;
- Research on networked intelligent fault diagnosis systems;
- Research on adaptive intelligent fault diagnosis structures.
2. Fault Diagnosis Technology for Automatic Reclosers
The fault diagnosis system for automatic reclosers is applicable to the fault diagnosis of controllers of automatic reclosers for 10kV overhead lines. After the "circuit breaker part" of the line is connected to the recloser controller, different types of simulated fault currents are injected into the recloser controller through software control, and "opening and closing" operations are carried out according to the commands of the controller. The action response of the recloser controller to current changes is recorded. Through software analysis, it is determined whether the controller can correctly respond to the fault situation and whether the response meets the requirements. Various fault test analyses can be performed, enabling the automatic detection of recloser controller faults.
The fault diagnosis system for automatic reclosers connects to different models of automatic reclosers through universal or specially - made interfaces. The relevant performance of automatic reclosers can be detected through professional analysis software, and all control and testing are achieved through software. The system characteristics of the fault diagnosis for automatic reclosers are as follows:
- The system uses a high - precision current source, which has the advantages of high precision, high resolution, and reliable performance, improving the accuracy of simulated current output. Through software, parameters such as the waveform, amplitude, rise time, duration, and fall time of the current can be comprehensively controlled, enhancing the authenticity of fault current simulation. At the same time, information such as the current waveform and amplitude can be displayed in real - time, enabling more effective analysis.
- The system is designed with a universal interface, which enables "plug - and - play" on - site operation through the universal interface, realizing the transmission of signals and data.
- Database establishment: The ampere - second characteristic is the inverse - time relationship curve between the opening time and the interrupting current of a recloser, including fast TCC (Time - Current Characteristic) and slow TCC. Currently, for automatic reclosing。
- Database establishment: The ampere - second characteristic is an inverse - time curve for recloser opening time vs. interrupting current, covering fast and slow TCC. Currently, automatic reclosing controller ampere - second curves mainly are Cooper, IEEE (US), and IEC standards. The system's analysis software has built - in databases for easy analysis.
3. Conclusion
Automatic recloser fault diagnosis technology can analyze various abnormal conditions, including abnormal instantaneous reclosing function, abnormal TCC (Time - Current Characteristic) curve, abnormal over - current protection function, abnormal reclosing interval test, and abnormal closing interlock. This technology represents the development trend of transitioning automatic recloser maintenance from traditional scheduled maintenance to advanced condition - based maintenance. It enables comprehensive analysis and diagnosis of the control part of reclosers, significantly enhancing the technical level of recloser condition - based maintenance. It plays a crucial role in preventing distribution network transmission line accidents.
