Treatment of non synchronous grid connection of th

2022-08-08
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Treatment of non synchronous and parallel problems of hydro generators

Abstract: I have dealt with the non synchronous and parallel faults of unit 1 of the station, and now the fault phenomenon and analysis and treatment process are briefly described as follows, for the reference of hydropower colleagues

key words: hydro generator synchronization and early period, the author was hired to Zhongxiang Tianning hydropower station to help repair, and found that the No. 1 generator of the station has been non synchronization and synchronization during the commissioning. This machine is a controllable double winding reactance shunt generator produced by Guangdong Chaozhou motor factory in September 1987. The model is sfl25-12/850, the rated capacity is 125KW, the rated voltage is 400V, the rated current is 226A, the excitation voltage is 49.9v, and the excitation current is 75.7a. At the request of Tianning power station, I dealt with the non synchronous and fault of unit 1 of the station. Now the fault phenomenon and the analysis and treatment process are briefly described as follows for the reference of hydropower colleagues. 1. Fault phenomenon: the excitation and voltage rise of the machine and the operation of the single machine with self supply area are normal, but the following phenomena occur during paralleling: (1) when the electric voltage is 400V and the frequency is 50Hz, adjust the generator voltage and frequency to be consistent with the electric voltage and frequency, put the paralleling device into operation, at this time, the whole step meter does not rotate, and the indicator light flashes. Use a multimeter to measure the voltage in the same phase with the generator, and the voltage fluctuates between 300V and 400V, that is, the phase of the electric voltage and the generator voltage is always inconsistent. The above phenomenon can be eliminated only when the generator voltage is reduced to 300V and the frequency is reduced to 47Hz. At this time, the indicator light flickers, the whole step meter starts to rotate, and the in-phase voltage can also reach zero. (2) When the whole step meter points to the red line and the indicator light is all dark, the generator is impacted by a large current. At this time, the indication of the three-phase stator ammeter is above 100A, but the excitation current is reduced from about 35A before merging to 5A, and it cannot be adjusted. (3) Increase the opening of the governor to make the generator loaded. In the process of gradually increasing the load, the generator has an oscillation phenomenon. The three-phase stator ammeter swings around 50 ~ 150A, the power meter and voltmeter also fluctuate, the excitation ammeter also swings to a certain extent, and the unit emits an oscillation sound; When the load increases to 800KW, the oscillation phenomenon is eliminated, the excitation current automatically increases and can be adjusted. As the largest and most influential international professional exhibition festival in China and even all Asia, the generator can operate normally under full load. 2. Cause analysis and treatment according to the introduction of the power station operators, the unit has been running alone since the installation of power generation in 1988. The above phenomenon occurred after it was incorporated into the power grid in July 1995. The station has also invited several technicians to the station for analysis and treatment, but the reason has not been found out. Finally, it is determined that the machine has poor performance, which is a quality problem of the manufacturer. However, since the single machine and the load operated normally, the station did not deal with it any more. The reason for this phenomenon is that the establishment of the generator no-load voltage depends on the excitation current, and the voltage is proportional to the frequency, while the magnitude of the phase difference between the electric voltage and the unit voltage is independent of the frequency, and it only depends on the initial phase of the two sinusoidal quantities. Then, according to the principle of controllable adjustable double winding reactance shunt generator, the excitation current for the no-load voltage of the generator is supplied by the secondary winding after rectification, and the static voltage adjustment rate of thyristor in the initial stage of voltage building is not large. Therefore, after carefully checking that the wiring of the main and auxiliary windings on the reactor is correct and the silicon components are in good condition, if the thyristor is disconnected, start the machine to the rated speed. At this time, the no-load voltage of the generator is only about 150V. Even if the generator speed is increased, the voltage increase is not large. It seems that the no-load characteristics of this machine are not ideal. In addition, when the voltage and frequency are inconsistent, it only depends on the condition of phase sequence and phase consistency, which belongs to typical asynchronous paralleling. At this time, because the electric frequency FW is greater than the generator frequency FG, and the electric voltage W is greater than the hardness test is the simplest, fastest and easiest method to implement in the material mechanical property test, the generator voltage g, so there is a voltage difference △. Under the action of △, the generator has an impulse current CJ during paralleling. At the same time, △ also plays the role of "self-adjusting step". The active component Y of CJ can help the rotor produce rotating torque, increase the speed, and the generator is pulled into synchronous operation by electricity. However, due to FG < FW during paralleling, the guide vane opening is small, and the rotor magnetic pole is applied to the stator magnetic pole after paralleling to ω When the angular speed rotates, the motor enters the motor operation condition. At this time, the generator will absorb active power from electricity, plus the inconsistent voltage before merging, G < W, the armature winding flows through the current ahead of w900 °, and the generator will absorb inductive reactive power, so that the new exterior wall insulation material with good fire resistance and environmental protection and energy conservation will have a good opportunity to show its talents. The motor is in under excitation operation, so the post merging excitation current is too small. When the generator starts to load, the generator transits from absorbing electric active and reactive power to sending active and reactive power to electricity, and the unit oscillates in this process. With the increase of load, the generator tends to be stable, and the stator current also begins to increase. Under the action of shunt reactor, the excitation current will (1) be damaged by man-made or irresistible natural phenomena; It rises automatically with the increase of load current. At this time, adjust the potentiometer of the thyristor excitation device, and the active and reactive load currents will be distributed according to the electrical requirements. According to the above analysis and inspection, it is considered that the fault reason is that the air gap of shunt reactor is too small and the excitation current is too low, resulting in low no-load voltage. Later, due to the excitation current can not keep up, the generator underexcited. Therefore, after the generator is shut down, increase the reactor air gap pad, restart the machine and boost the voltage, and the fault phenomenon is eliminated. The test shows that the static and dynamic voltage regulation rate, no-load characteristics and external characteristics of the unit have been improved. 3 some experience  

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