1. Failure performance and causes of high voltage switchgear

Survey statistics show that the failure of high voltage switchgear mainly has the following categories:

(1) refusal to operate, misoperation failure: this failure is the most important failure of high voltage switchgear, the reasons can be divided into two categories: one is due to the mechanical failure of the operating mechanism and transmission system; The other is caused by electrical control and auxiliary circuits.

(2) breaking and closing failure: This kind of failure is caused by the circuit breaker body, for the less oil circuit breaker, mainly manifested as oil injection short circuit, arc extinguishing chamber burning, lack of breaking capacity, closing explosion, etc. For the vacuum circuit breaker, the performance is arc extinguishing chamber and bellows leakage, vacuum reduction, cutting capacitor bank reignition, ceramic tube rupture.

(3) Insulation failure: the performance of external insulation to ground flashover breakdown, internal insulation to ground flashover breakdown, interphase insulation flashover breakdown, lightning overvoltage flashover breakdown, porcelain sleeve, capacitor sleeve flashover, pollution flashover, breakdown, explosion, lift rod flashover, CT flashover, breakdown, explosion, porcelain bottle fracture, etc.

(4) Current-carrying fault: The main reason for current-carrying fault in 7.2 ~ 12 kV voltage level is the poor contact of the isolation plug of the switch cabinet, resulting in the melting of the contact.

(5) External force and other failures: including foreign body impact, natural disasters, short circuit of small animals, etc.

2. Monitoring and diagnosis methods of high voltage switchgear

For different fault types of high voltage switchgear, there are different fault detection methods:

(1) Mechanical characteristics online detection, the monitoring content is: closing, opening coil loop, closing, opening coil current, voltage, circuit breaker moving contact travel, circuit breaker contact speed, closing spring state, circuit breaker operation process mechanical vibration, circuit breaker operation statistics. At present, the mechanical condition monitoring of circuit breakers mainly includes the monitoring of travel and speed, and the monitoring of vibration signals during operation. The mechanical vibration signal monitoring during circuit breaker operation is to judge the mechanical state of circuit breaker according to the change of the occurrence time of each vibration signal and the change of the peak value, combined with the current waveform of the opening and closing coils. For a circuit breaker with stable mechanical properties, the peak value and the time difference between each peak value of the breaking and closing vibration waveform are relatively stable. The determination of whether the vibration signal has changed is based on the new circuit breaker or the circuit breaker after overhaul for many times, closing test test, record the stable vibration waveform, as the characteristic waveform of the circuit breaker "fingerprint", the vibration waveform measured later, compared with the "fingerprint", to determine whether the mechanical characteristics of the circuit breaker is 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 occurrence time of the shock event are used as the characteristic parameters of circuit breaker fault diagnosis to judge whether the circuit breaker is faulty and the type of fault. Based on the signal singularity detection theory of wavelet transform, the vibration signal of circuit breaker is firstly denoised by wavelet to purify the useful signal. Then the Hilbert transform is used to extract the signal envelope, and the wavelet transform is used to obtain the signal waveform at each scale. Finally, the singularity index of the signal envelope peak is calculated according to the transitivity of the modulus maxima on each scale of the wavelet transform, which is a new and effective method for circuit breaker fault diagnosis.

Travel-time characteristic monitoring is to change the continuously changing displacement into a series of electrical pulse signals by photoelectric sensor. By recording the number of pulses, the measurement of the full stroke parameters of the moving contact can be realized. At the same time, the time value generated by each electrical pulse can be recorded, and the maximum speed and average speed during the motion of the outgoing contact can be calculated. Therefore, the switching and closing characteristics of the connecting rod of the main shaft of the circuit breaker can be measured to reflect the characteristics of the moving contacts. Monitoring the load current and start times of the energy storage motor can reflect the working condition of the load (hydraulic operating mechanism), can also determine whether the motor is normal, and reflect the hydraulic operating mechanism

(2) Electrical performance online monitoring, including circuit breaker breaking current weight, arc extinguishing chamber vacuum degree monitoring. The equivalent wear curve of different on-off currents is used to accumulate the relative electrical wear corresponding to each current breaking. The total allowable electrical wear of each circuit breaker is calibrated by its rated short-circuit breaking current and the number of allowable breaking full capacity. The cumulative wear of contacts is used as the basis for judging its electrical life. This paper describes the factors affecting the life of contacts of vacuum circuit breakers and some SF6 circuit breakers, and puts forward an improved on-line monitoring method for the electrical life of vacuum circuit breakers. The method takes into account the actual breaking process and arc burning time of each phase, and its accuracy is greatly improved, which can more truly reflect the electrical wear of each phase.