5 generator set loss-free asynchronous operation Niu Xize, Qiu Jiajun, Tana, Lang Zuogui, School of Mechanical Engineering, Tianjin University, Tianjin 372 manifold theory analysis of the dynamic characteristics near the junction point; numerical simulation analysis of the unit shafting system during the loss of magnetic asynchronous operation The variation of the torsional vibration and the oscillation of the power angle, etc.; finally, the experimental research was carried out using the laboratory generator set, which is in good agreement with the theoretical analysis. Synchronous generator's magnetics, including total loss of magnetism and underexcitation, are common faults in power systems. The history of large-scale units has increased the chance of loss of magnetism. The main causes of demagnetization are regulator failure, auxiliary exciter failure and open or short circuit of generator excitation circuit. (1) After asynchronous operation of generator de-magnetism, the rotor slips out of step, and the generator emits less power. Suction, a large amount of reactive power, between the load and the power supply, the balance will be destroyed. The lack of reactive power reserve may also cause system oscillation or even voltage collapse. After the loss of magnetism, if the generator can continue to work in the asynchronous operation mode for a period of time until the river is eliminated to avoid the full load unloading and stoppage caused by the loss of magnetism, or even damage the equipment and large-area power failure, improve the reliability of the generator set operation. Sex, reduce economic losses and energy consumption, reduce the sudden removal of load and the number of shutdowns, thereby reducing the impact on the operating life of the generator rotor. Therefore, the impact of the asynchronous operation of the loss of magnetism on the grid and the unit is an engineering concern, to ask. The research results of the effects of asynchronous operation on the torsional vibration of the shafting after the loss of magnetism are not much. Mu Wen has established a transient nonlinear equation system with the synchronous generator Shifangke coupled with the mechanical torsional vibration equation. The fork and central manifold theorem gives the dynamic interpretation of the unit's underexcited to asynchronous operation. The variation of torsional vibration during the asynchronous operation of the unit is analyzed, and the theoretical analysis results are verified by the laboratory generator set. The establishment of the 1 unit model uses the laboratory generator set to simulate the actual generator set. The experimental model 1. The DC motor is driven by the shaft system to drive the synchronous generator. According to the method of electromechanical analysis dynamics 4, the transient mathematical model feeding of the unit can be established. What needs to be explained is that the generator equation is taken as. 1 equation, do 1 transformation, each physical quantity is standardized according to the system; 屯 motive 〃 generator rotor rotation angle is 1 and the relative generator set is connected to the grid, the reference speed is the power frequency power angle. The hairpin machine turns to a wide rotation and satisfies so dry kiki=ll, b=it; the generator has no damper winding, the rotor damping equation is omitted, and the mathematical model of the unit is the received date 213. Fund Project 973 National Key Basic Research Planning Project, 1998020319. One pull balance, 6 saddle knot bifurcation point stable balance 焱 generator excitation current æ² is DC motor armature current is DC motor excitation current, taken as a constant. In the model analysis, the torsional vibration angle and power angle of two important variables in mechanical vibration analysis and circuit analysis are taken as independent variables, which is convenient for understanding ± also understanding the variation law of machine power. The specific values ​​of the electromechanical parameters in the equation can be measured by the no-load experimental short-circuit test and the zero-power factor load test. It is worth noting in the experiment and calculation that some electrical parameters such as generator synchronous reactance 1 will change with different operating conditions, so the parameter value should be determined according to the corresponding working conditions during analysis and calculation, and the obtained result can be more reliable. . 2 The central manifold analysis at the saddle junction point is easily derived from Equation 1, and there are an infinite number of equilibrium points in the steady-state operating system. In the rated working condition, the power angle is corresponding to the two equilibrium points in the range, and although there is a strong nonlinear indium combination in the model equation, the characteristics of the system linearization matrix at the equilibrium point can still be adopted. Value to determine its stability. For example, the characteristic roots of the matrix have a negative real part, which is a stable equilibrium point node, and the inch is required. The 1 matrix has a characteristic root with a positive real part, which is an unstable equilibrium point saddle point. When the excitation current is reduced or the active load is reduced, the saddle node, the node, the saddle point decreases with the force or the household increases, the stable equilibrium point and the unstable equilibrium point are close to each other, and eventually the convergence disappears, and the meeting point is The saddle knot bifurcation point power angle of the system, the vertical line in the bifurcation 9 divides the bifurcation into two areas, namely, the solution area and the asynchronous operation area. After the system is disturbed by small disturbances, in the solution zone, the operation tends to stabilize the equilibrium point, while in the sweat step operation area, the system is unstable and runs asynchronously. The saddle knot bifurcation point is the boundary point between the two regions. Near the saddle junction, the central manifold can be used to reduce the system to a central equation to analyze the motion characteristics of the system. The rest of the special roots have a negative real part + a saddle knot bifurcation point. The corresponding feature matrix 7 takes 7 = Guangyou, so especially = hit, substituting into the formula 2, the central manifold is separated by 1 and substituted into the equation 4, eliminating the derivative term, and comparing the same power terms of the two sides of the equation, 14 linearities are obtained. Algebraic equations, from which milk and machine generation can be solved, Equation 4. Formula, the square on the central manifold, for the comparison of the obtained torsional vibration angle curve, the step-running domain, the generator speed change, the illusion phase current waveform 3, the loss-of-magnet asynchronous operation numerical simulation and the experiment 3.1 numerical simulation in the asynchronous running domain. The numerical calculation can be used to analyze the electromechanical, and the underexcited oscillation curve is the same as the median value. The maximum value of the single-phase current fluctuation is 1. 5 times the generator speed cycle fluctuates. After the mean value is greater than the out-of-step step, the generator emits active power reduction and absorbs large reactive power from the grid; 56 and is the change of power angle and torsional vibration angle. The maximum amplitude of the vibration angle is 0.7, which is smaller than the maximum torsional angle 20 when the same generator no-load rated operating phase is short-circuited. The physical mechanism can be explained as the loss of synchronization between the rotor speed of the generator and the rotational magnetic potential of the stator phase when the underexcited or demagnetized asynchronous operation occurs, and the slip pole is asynchronous. In each cycle, the conditions of the stator and rotor magnetic potentials are close to each other and leave, and the polarity and strength of the air gap magnetic field occur. + Oscillation reactive power oscillation 0 power angle oscillation, the torsional vibration waveform is abrupt, causing a sudden change in the induced current of the stator winding of the generator, so the electromagnetic torque also undergoes a corresponding mutation. This transient electromagnetic moment causes a torsional vibration of the shafting and a sudden change in the rotational speed of the rotor. The stator has been cut off by 5 strokes. The starting boundary is slowly increased by a value slightly smaller than å…€2, and a sudden change occurs when it reaches 7 and rapidly increases. After the sliding pole is about a week, the torsional vibration signal outputted by the dynamic strain gauge needs to be pointed out when the estimated number is recorded. Avoid DC offset is too large, use AC gear; 6, for generator speed; 61 for power angle fluctuations. The variation characteristics of the oscillating waveform are also caused, and the theoretical results agree well with the experimental results. 笮 slightly less than 2 怙. Complete the change of 1 cycle period. The sudden change of the magnetic field caused by the sudden change of the sliding pole causes the shock oscillation phenomenon to occur at the same time for all the electric machines, so the oscillation periods of the respective quantities are completely the same. The amplitude and frequency of each physical quantity change with changes in excitation current and work power. 3.2 Experimental research When the experiment is carried out, the generator is connected to the grid, first, the large excitation current, the fixed active power output is adjusted, the excitation current is gradually reduced, and the unstable oscillation waveform of different excitations is recorded. The phase current signal is taken out with a transformer. The power angle is obtained by comparing the phase difference between the voltage signal output by the generator shaft end AC signal generator and the standard voltage signal of the in-phase grid. Dressing torsional vibration waveform, generator speed change (1) Power angle oscillation In addition, the effects of excitation current on the unstable oscillation frequency and torsional vibration impact at different powers were calculated and tested. Results 7 and 6.3, the experimental flow curve can be When the active power is the same, the frequency of the instability increases as the frequency decreases. In the case of the same field current, the greater the active power, the higher the instability frequency. When the rated power loss is completely demagnetized, the frequency of the unstable oscillation is about 1.2. When force, overtime, the oscillation frequency is reduced until the system is restored to a stable distance. With the change of the excitation current. By the same excitation current, the greater the active power before demagnetization, the larger the torsional vibration, and the same kind of active power, 4 conclusion that the under-excited asynchronous operation of the generator set is the system through the saddle knot bifurcation, after the equilibrium point disappears The kind of unstable operation state. The central manifold theorem can be used to analyze the dynamic characteristics near the bifurcation point. In the asynchronous operation region, the law of unstable oscillation can only be sought through numerical calculation and corresponding experiments. After the generator loses magnetism or underexcited asynchronous operation, the oscillation frequency of the torsional vibration angle increases with the decrease of the excitation current, and the maximum is about 22, which is quite different from the natural frequency and the rotational speed of the torsional vibration of the unit shafting. . If there is no relevant nonlinear coupling term in the model, the possibility of resonance is small, but the maximum torsional vibration amplitude of the asynchronous operation is close to twice the rated value. Long-term asynchronous operation will also cause fatigue damage to the shafting system and affect the life of the shafting. When the generator loses its asynchronous operation, it must absorb large reactive power from the grid. Flash this system should have enough reactive power. At the same time, the generator stator inrush current makes the stator end windings warmer and faster. When operating asynchronously, the active output should be reduced to reduce the stator current. Yao Qinglin. Synchronous generator loss of magnetism and its protection. Beijing Mechanical Industry Press, 1978. Gao Chongbin, Chen Ban. Transient digital simulation of synchronous generator demagnetization and study of the effects of rectifier unidirectional conduction characteristics. Power System Automation, Li Weiqing, Mao Guoguang. Experimental research on the asynchronous operation of domestic large-scale steam turbine generators. Automation of Power Systems, 1986, 1022635. 41 Qiu Jiajun. Electromechanical coupling and vibration of the non-line 1 of the system 1. Beijing Science Press, 1996, the editor of this article, Yu Yumei
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