Energy absorption capacity of de-excitation resistors of auxiliary machines and other synchronous generators LI Zi-zhen, PENG Hui, FU Zhong-en, XIA Ju-xi (College of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China) The calculation and selection method of the energy capacity of the demagnetization resistance.

Generator; de-excitation resistance; energy absorption capacity 1 Overview At present, the rapid de-excitation of large and medium-sized synchronous generators generally uses displacement energy to eliminate magnetism, so the de-excitation resistor must quickly absorb the magnetic field energy under various working conditions. According to analysis: the most serious working condition is the generator's no-load out-of-control mis-excitation and sudden short-circuit at the stator outlet end. The rotor current of these two conditions can reach 3~4.5 times of the rated excitation current, and the magnetic field energy of the rotor also reaches the maximum. The following is an example of the largest three-gorge hydropower generator in China, and the magnetic field energy under these two conditions is discussed separately. Because the transient transition process of the motor is very complicated, and because the electromagnetic parameters of the generator are incomplete, it can only be based on the basic theory of "Electrical Science" 111, ignoring some minor factors, and making some simplifying assumptions. The rough analysis of the working conditions is based on the basic parameters of some generators provided by the Yangtze River Water Resources Commission (hereinafter referred to as the “Changing Committee”) (see Table 1), and a preliminary calculation is made for the purpose. For the calculation, the generator of ABB is taken as an example. The saturation value parameter of the maximum capacity is used as the calculation raw data, and the excitation mode is self-excitation of the machine end and three-phase full control bridge type rectification.

2 Generator no-load out of control Magnetic field energy 21 excitation current calculation This working condition means that the generator is not connected to the grid, but due to the breakdown of the power rectifier cabinet pulse transformer, etc., the excitation adjustment is out of control, the control angle a = 0 * generator is forced to strong excitation, the stator voltage rises, so that the excitation secondary voltage also rises, assuming that it rises to 1.3 times the rated value (considering the excitation voltage drop factor due to the large excitation current), At this time, the excitation current can be reached: because the stator winding and the damper winding are open circuit, the time constant of the field winding = Rf (w is the electrical angle frequency, for a 50 Hz motor, w = =1.16H (unsaturated value). Here R / take " The long-term committee provides the resistance value of 130 * C. This temperature should be consistent with the corresponding temperature taken at 2d.' of the motor design. The domestic motor factory generally takes 75ABB and does not know how much it takes.

Since there is no X. and Xad data, it is only subjectively assumed that the rotor leaks 1.16 = 0.116H (unsaturated value). Since most of the magnetic circuit of the leakage flux passes through the air, if the saturation of the magnetic circuit is not considered, then L/> is constant, and the magnetic flux leakage energy is taken as 0.5X0.116X. Actually, the magnetic circuit of the leakage flux is partially in the core. In the large table 1 serial number numerical unit remarks parameter name Sun rated capacity maximum capacity rated voltage rated power factor rated speed stator winding connection straight shaft synchronous reactance standard value unsaturated / saturated, rated capacity is not saturated / saturated, maximum capacity straight Axis transient reactance standard value is not saturated/saturated, unsaturated/saturated at rated capacity, direct axis ultra-transient reactance at maximum capacity Xd standard value is unsaturated/saturated, unsaturated/saturated at rated capacity, maximum capacity Straight-axis transient open time constant r'd* Straight-axis transient short-circuit time constant r: Stator winding short-circuit time constant: When the rotor winding resistance is excited, the secondary side voltage is Shunde contact point to determine the no-load excitation voltage no-load excitation current Load excitation voltage rated capacity / maximum capacity when load excitation current rated capacity / maximum capacity when excitation top value voltage excitation top value current allows strong excitation time excitation top value current under rotor overvoltage Let the saturation coefficient be 0... then do =0. 2.3 The energy of the rotor main flux The rotor magnetizing inductance (the inter-chain stator winding produces an induced potential e. (unsaturated value).

According to the theory of Electrical Engineering 121, the energy of the main magnetic flux W0=K. Analysis, due to the principle of conservation of the closed-loop flux linkage, after the stator is short-circuited, the short-circuit current of the periodic component and the non-periodic component is immediately induced in the three-phase winding of the armature. Its role is to keep the magnetic flux in the closed armature winding unchanged. However, the magnetic field generated by the short-circuit current passes through the rotor, causing the flux linkage of the rotor to change. Therefore, the excitation coil is short-circuited (as long as the excitation current is not equal to zero, the power rectifier bridge is in the on state, which can be regarded as a short circuit) and the rotor excitation winding itself. Periodic and aperiodic currents are also induced immediately in the short-circuited damper winding to keep their flux linkage constant. The current amplitude is large, and if the magnetic switch is de-excited at this time, the rotor will release a large amount of energy. Since the time constant of the damper winding is small, and the relay protection action time is generally above 0.1 s, the damper winding current has been substantially attenuated, so when the annihilation energy is analyzed, the damper winding can be regarded as an open circuit. The maximum rotor current / / * at 0.1 s after stator short circuit can be calculated by two methods: the rotor equivalent reactance X' = Xy + Xq is the sum of rotor and stator leakage reactance, and the leakage flux is mostly passed through the air. If the magnetic circuit saturation is not considered, L/ is regarded as a constant, then the magnetic field energy = 0.5X. Actually, the magnetic circuit of the leakage flux is partially in the core, so the influence of the saturation of the magnetic circuit should be considered. Here, the magnetic line passes through the rotor. Our company will resume normal operation after replacing the demagnetization resistor (or magnetic field breaker). From a comprehensive perspective of security and economics, such a choice should be appropriate. However, there are contradictions between safety and economy. The specific choice is determined by the importance of generator safety and the economic ability of users.

The energy absorption capacity of the degenerative resistance of other hydroelectric generators can be determined by referring to the above calculation method and selection principle. Due to the strong eddy current damping effect in the whole core of the rotor, most of the magnetic field energy is transferred into the eddy current of the rotor core, so that the energy absorption of the de-excitation resistor is greatly reduced. According to the experimental analysis|61, the ZnO demagnetizing resistance energy absorption is less than 10% of the magnetic field energy storage when no-load demagnetization. For the safety meter, the energy dissipation of the degenerative resistance of the turbo generator (generally also serving as the rotor over-voltage protection) can be taken. The capacity is 30%~50% of the stored energy of the magnetic field. The magnetic gap between the magnetic circuit and the stator leakage magnetic circuit is small, so the saturation depth is small, and the saturation coefficient is 0.6 (the above section is taken as 0... because only the rotor is considered) Leakage magnetic circuit, air gap is small, so the saturation is deep, the saturation coefficient is small) Wf=0. 4 summed up the calculation of the rotor magnetic field energy storage under extreme conditions, also made a lot of partial safety assumptions, so the calculation The result should be too large. In addition, during the demagnetization process, the rotor winding resistance, the excitation loop resistance and the magnetic field circuit breaker also absorb part of the energy, so the actual energy absorption of the de-excitation resistor is smaller than the above calculation result, and according to the Chinese electric power industry standard DL/T5834995. ASEA factory. Demagnetization of large generators. Technical requirements for static rectification excitation system and device of low-voltage DL/T58H995 large and medium-sized hydro-generators.

Institute of Plasma Physics, Chinese Academy of Sciences, Dongfang Electric Machinery Factory, Huangtai Power Plant. Report on the demagnetization test of 300MW steam turbine generator Li Zizhen (943-) Suzhou, Jiangsu Province, graduated from the Electric Power Department of Anshui University in 1965, engaged in the development of ZW varistor application, and is currently the company of the Institute of Plasma Physics, Chinese Academy of Sciences. Chief engineer, researcher. Peng Hui (1962-) An Ying, a graduated from the Department of Electrical Engineering of Xi'an Jiaotong University in 1983, is engaged in varistor and application research. He is currently the deputy general manager and senior engineer of the Institute of Plasma Physics, Chinese Academy of Sciences. .

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