1. Failure manifestations and causes of high-voltage switchgear
Survey statistics show that the faults of high-voltage switchgear mainly fall into the following categories:
1. Refusal to operate and malfunction: This type of failure is the most important failure of high-voltage switchgear. Its causes can be divided into two categories: one is caused by mechanical failure of the operating mechanism and transmission system; the other is caused by electrical failure. Caused by control and auxiliary loops.
2. Breaking and closing faults: This type of fault is caused by the circuit breaker body. For circuit breakers with less oil, the main manifestations are fuel injection short circuit, arc extinguishing chamber burning, insufficient breaking capacity, and explosion when closing. wait. For vacuum circuit breakers, the symptoms include air leakage in the arc extinguishing chamber and bellows, reduced vacuum, re-ignition of the cut capacitor bank, rupture of the ceramic tube, etc.
3. Insulation fault: manifested as external insulation to ground flashover breakdown, internal insulation to ground flashover breakdown, interphase insulation flashover breakdown, lightning overvoltage flashover breakdown, porcelain bottle bushing, capacitor bushing flashover, Pollution flashover, breakdown, explosion, lift rod flashover, CT flashover, breakdown, explosion, porcelain bottle breakage, etc.
4. Current-carrying fault: The main cause of current-carrying fault at 7.2 to 12 kV voltage level is poor contact of the isolation plug of the switch cabinet, resulting in melted contacts.
5. External forces and other failures: including foreign object impact, natural disasters, small animal short circuits, etc.
2. Monitoring and diagnosis methods of high-voltage switchgear
According to different fault types of high-voltage switchgear, there are different fault detection methods:
1. Online detection of mechanical characteristics. The monitored contents include: closing and opening coil circuits, closing and opening coil currents and voltages, circuit breaker moving contact stroke, circuit breaker contact speed, closing spring status, and circuit breaker action. Mechanical vibration during the process, statistics on the number of circuit breaker operations, etc. At present, the mechanical status monitoring of circuit breakers mainly includes the monitoring of stroke and speed, the monitoring of vibration signals during operation, etc. The mechanical vibration signal monitoring during circuit breaker operation is based on the changes in the occurrence time and peak value of each vibration signal, combined with the current waveforms of the opening and closing coils, to determine the mechanical status of the circuit breaker. For a circuit breaker with stable mechanical properties, the peak sizes of its opening and closing vibration waveforms and the time difference between each peak are relatively stable. The basis for judging whether the vibration signal has changed is to conduct multiple opening and closing tests on a new circuit breaker or a circuit breaker after overhaul, and record the stable vibration waveform, which will be used as the characteristic waveform "fingerprint" of the circuit breaker and will be measured in the future. The vibration waveform is compared with the "fingerprint" to determine whether the mechanical characteristics of the circuit breaker are normal. According to the radial basis function network theory (RBF network), the residual formed by the difference between the healthy vibration signal and the actual vibration signal peak amplitude of the circuit breaker and the time of the impact event are used as characteristic parameters for circuit breaker fault diagnosis to judge the circuit breaker. Whether there is a fault and the type of fault. Based on the signal singularity detection theory of wavelet transform, the vibration signal when the circuit breaker is closed is first subjected to wavelet denoising processing to purify the useful signal. Then the Hilbert transform is used to extract the signal envelope, and the wavelet transform is performed on the envelope to obtain the signal waveforms at each scale. Finally, the singularity index of the signal envelope peak is calculated based on the transitivity of the modulus maximum at each scale of the wavelet transform, and is used as a characteristic parameter for circuit breaker fault diagnosis. It is a novel and relatively effective method.
Stroke-time characteristic monitoring refers to converting the continuously changing displacement amount into a series of electrical pulse signals through a photoelectric sensor. By recording the number of pulses, the full stroke parameters of the movable contact can be measured; at the same time, by recording the moment when each electrical pulse is generated, the maximum speed and average speed during the movement of the movable contact can be calculated. Therefore, measuring the opening and closing characteristics of the main shaft linkage rod of the circuit breaker can reflect the characteristics of the moving contacts. Monitoring the load current and number of starts of the energy storage motor can reflect the working status of the load (hydraulic operating mechanism), and can also determine whether the motor is normal and reflect the secrets of the hydraulic operating mechanism.
2. Online monitoring of electrical performance includes monitoring of circuit breaker breaking current weighted value, arc extinguishing chamber vacuum degree, etc. Using equivalent wear curves under different breaking currents, the relative electrical wear corresponding to each current breaking is accumulated. The total allowable electrical wear of each circuit breaker is determined by its rated short-circuit breaking current and the number of times allowed to break at full capacity. For calibration, the accumulated wear amount of the contacts is used as the basis for judging its electrical life. This paper expounds the factors that affect the contact life of vacuum circuit breakers and some SF6 circuit breakers, and proposes an improved online monitoring method for the electrical life of vacuum circuit breakers. This method takes into account the actual breaking process and arcing time of each phase, and is accurate The performance has been greatly improved and can more truly reflect the electrical wear of each phase.