1 Overview Synchronous generator brushless excitation completely solves a series of collector ring brush problems caused by high excitation current of large capacity or super large capacity synchronous generator, eliminates sparks and noise, and reduces maintenance, generator set Can run continuously for a long time. Rotary rectifiers in synchronous generator sets are the most important part of a brushless excitation system and must be operated in a normal state. When the rotary rectifier power diode fails (open or short), it should be immediately detected and quickly alerted. However, due to the elimination of slip rings and brushes, it is difficult to directly monitor rotor fault conditions.
The key to solving this problem is how to obtain the signal with the rotor fault information and how to use it to identify it effectively and accurately. It is a common method to install the detecting coil between the stator poles of the AC exciter, but in practical applications, the inter-pole detecting coil is difficult to install and causes the loosening of the detecting coil during transportation, and the inter-pole detecting coil is obtained. The signal is weak, and the number of turns required for the detection coil is large, as shown in Figure 1. Another way to obtain the signal is to directly use the stator excitation winding of the AC exciter as the detection coil. The advantage is that the design, installation and maintenance of the detection coil are omitted, and the signal data is convenient to be collected on site, and the signal quantity is strong. The amount of rotor fault information is large, but due to the influence of the saturation of the excitation pole core, the signal has a certain degree of distortion, that is, the blur phenomenon occurs, and it is difficult to realize the fault classification and recognition of the rotary rectifier. Therefore, this method has been rarely used. In this paper, the fuzzy pattern recognition technology is used to establish a computer digital diagnosis model. The signals induced in the stator excitation circuit of the AC exciter are preprocessed by spectrum analysis, and then the fault classification of the rotary rectifier is identified. The method expands the identification of the fault type range and improves the accuracy of the fault identification, thereby realizing the microcomputer monitoring of the synchronous generator set rectifier fault.
2 Fault monitoring method In this paper, the method of obtaining the fault information of the synchronous generator rotor rectifier is to connect the capacitor and C 2 on the stator excitation winding of the AC exciter, as shown in Fig. 2. The armature magnetic field generated by the armature AC excitation electromechanical current must cut its stator excitation winding and induce the potential, and then divide the voltage through the capacitors C and C. It only needs to collect the voltage waveform across the capacitor C with the rotor fault information. The frequency domain analysis is performed to decompose the harmonic components of different amplitudes, and then the fuzzy pattern recognition technology is used to perform fault classification and recognition processing.
Let the period of the induced potential signal wave e = E be T, and expand from the Fourier series to f -- the fundamental frequency of the AC excitation electromechanical current? Research and development?
Moreover, there is E k, so the integral calculation in the above formula can be calculated by numerical integration. Since the Fourier series decomposition calculation requires a large number of addition, subtraction, multiplication and division operations, a complex trapezoidal integral formula with a certain precision is used. The above Fourier series coefficient expression is where N is the number of sampling points in one signal period. When the A/D conversion uses the chip ADC0809, its analog-to-digital conversion rate is 100μs/time, so the sampling interval time h = when the signal data is preprocessed, the fault diagnosis is performed by the fuzzy diagnosis mode in the computer. Set the set of operating conditions reflecting the synchronous rectifier of the synchronous generator as the domain U in the domain U of the operating condition of the rotating rectifier, take n = 8, then the elements in the domain are defined as "- normal operation" arm open circuit fault ) Two arm open circuit fault) Arm short circuit fault) Two arm short circuit fault --- A phase positive and negative group (A) Two arm short circuit fault phase negative group (C) Three arm open circuit fault phase negative group (C) Three arm short circuit fault When the element P in the domain U has r eigenvalues, it can be represented by a vector P. Each such vector is referred to as a model sample, and each element in the model sample has a feature quantity that characterizes the operating conditions of the synchronous generator rotating rectifier. The voltage signal u in the parallel capacitor on the stator excitation winding of the AC exciter is preprocessed by the spectral analysis numerical method, and the relative value of each harmonic amplitude is extracted as the information characteristic value. Therefore, P 4 , 5 , 6 , 7 , 8) constitute a set of fuzzy cluster sample models. The following table shows the fuzzy pattern recognition sample set of a 360 kW brushless excitation synchronous generator rotary rectifier.
Table Rotary Rectifier Fuzzy Pattern Recognition Sample Set Sample Model Vector Stator Signal E Harmonic Component Relative Value Fundamental Wave 2 Harmonic 3rd Harmonic 4th Harmonic 5th Harmonic 6th Harmonic In actual operation, the above The set of identification samples obtained by the test is stored in the computer memory. When the generator set is monitored online in real time, the feature vector P(U) of the sampled signal u should be calculated close to the vector P in the fault sample set, using Hamming Proximity To correctly diagnose which of the fuzzy sets P the vector P belongs to, it is necessary to compare H) the closeness in the mapping domain F (ω), and the two fuzzy sets with the closest proximity are It is regarded as the same type of working condition, that is, P is diagnosed as the synchronous generator operating condition of the type fault of the vector P.
3 fault monitoring system design The hardware part of the rotary rectifier fault monitoring system is mainly composed of two parts: LCU measurement and control unit and system host.
The core of the LCU measurement and control unit is the 8751 microcontroller, which has a strong data storage processing function, I/O port control function and a new method for data brushless synchronous generator rotary rectifier fault monitoring. The signal acquisition channel of the LCU unit is composed of an input limiting circuit, a low-pass filtering circuit, a rectifying circuit, and an analog-to-digital (A/D) conversion circuit, and the monitoring alarm channel is composed of a power amplifying circuit, an early warning circuit, and a circuit breaker control circuit. They are all controlled by the I/O port of the 8751 microcontroller, which completes the monitoring signal acquisition, early warning and control of the circuit breaker task. Under the control of the program, the serial port of the 8751 MCU can work in four ways. It can use the asynchronous communication port to realize the dual-machine or multi-machine communication as needed. The sampling data is transmitted to the upper-layer system microcomputer, and all the data are preprocessed by the microcomputer. , fault fuzzy diagnosis and database maintenance functions, and control commands are transmitted back to the LCU unit to form a synchronous generator distributed monitoring system. The system design principle is shown in Figure 3.
In the system software design, the following application software design must be carried out: 1 signal acquisition program design. 2 data processing program design. 3 fault diagnosis program design. 4 alarm monitoring program design.
5 data communication program design.
Because the main function of the 8751 MCU in the LCU measurement and control unit is to collect signals, the digital signal is transmitted to the system host, and the system host performs data processing and fault diagnosis, and then receives the command signal from the system host for real-time alarm and control. Therefore, the program compiled by the assembly language of the microcontroller should include signal acquisition, data transmission and transmission and alarm monitoring functions.
The data processing, fault diagnosis and system host operation interface programs of this system are all written in Visual Basic language. When using the system host communication program designed with Visual Basic 5.0, you should first initialize the serial port in the form loader (set the baud rate and working mode of the serial port), and add two commands to the form. Button: Enable data transmission and reception function to close the serial port and release control.
4 Conclusion When the synchronous generator rotary rectifier fails, the magnitude and waveform of the AC excitation armature current changes, causing the change of the armature magnetic field, and induce a series of harmonic potentials in the stator excitation winding. The harmonic potential waveform Reflects the operation of the rotor rotating rectifier. Therefore, this paper deals with the harmonic potential waveform by fuzzy diagnosis technology, and uses the fuzzy pattern recognition method to diagnose the fault type of the rotary rectifier.
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