Adjustment of generator power factor in zhehuo Hyd

Adjustment of generator power factor of hydropower station

Abstract: it is an important work for the operation of power station to reasonably adjust the motor power factor and ensure the reactive power demand of the system. This paper mainly describes how to adjust the power factor of the generator under various operating conditions, so that the power station can not only generate more active power, but also meet the reactive power demand of the system, so as to improve the economic benefits of the power station

key words: power factor adjustment of hydropower station in the operation of hydropower station, the power factor of generator is a parameter that is often adjusted. How to reasonably adjust the power factor of generator according to the characteristics of large seasonal water volume change and uneven generator load of hydropower station, meet the demand of system reactive load, and solve the problem of high generator terminal voltage during full load operation. It is of great significance to the safe operation of hydropower stations and to improve the economic benefits of hydropower stations. Dandong hydropower station in Boai County is a diversion hydropower station developed in steps in the Danhe River Basin, with a total installed capacity of 3130kw, including two 1250KW and one 630kw water turbine generator unit. The rated voltage of the generator is 6.3kV, the power factor of the generator is 0.8, and the three generators are synchronous generators. The annual generating capacity of the power station is 14million kW · H. 1995: green, reduced, recyclable, with obvious results, combined with large power, and at the same time, the power station has an independent self supply area. The ratio of the annual load to the self supplied load is three to one. Since the power supply system of the power station consists of two parts, the power factor of the generator must be adjusted reasonably to meet the reactive power demand of the two systems. In the self supply area of the power station, a total of 3000kva transformers and nearly 40 transformers are installed, most of which are old-fashioned high energy consuming transformers, with large changes in power load and large demand for reactive load. Capacitors are not installed on 10kV lines and 400V low-voltage users. For example, installing capacitors to compensate reactive power and improve the power factor of the lines in the self supply area will result in large one-time investment, and the transportation price of capacitors is also about 2000 yuan/ton. The maintenance cost is high, and the phenomenon of "over compensation" often occurs. Therefore, it is reasonable to timely adjust the power factor of the generator in the power station, supplement the reactive load of the line in the self supply area, and improve the economic operation of the line. The power factor of the parallel load is also very strict with the requirements of the power department, which stipulates that the power factor must be 0.8. In case of less reactive power punishment and more reactive power reward, the reward and punishment shall be based on the standard of 0.8, with 0.1% of the electricity charge in the month of the low 0.01 award and 0.5% of the electricity charge in the month of the high 0.01 award, that is, the regulation of one award and five penalties. Although the regulations of the power sector are very strict, our power station reasonably adjusts the power factor of the generator in different seasons according to the characteristics of water volume and load changes, which not only ensures the need of reactive load in the self supply area, but also receives the reward of multiple reactive power. To reasonably adjust the power factor of the generator, we must pay attention to several problems, that is, to correctly adjust it according to the characteristics of different operating seasons. For the runoff type small hydropower station without regulation capacity, when the water volume is sufficient in the rainy season, many units in the station can operate at full load. At this time, the power factor of the generator should be adjusted to about 0.85 ~ 0.9, so that the generator can generate more active power and less reactive power. The "generator operation specification" stipulates that the power factor should be 0.8 and should not exceed 0.95. If necessary, it can be operated with the power factor of 1. It indicates that the power factor adjustment is slightly higher, which meets the requirements of the specification. On the other hand, the power factor should not be adjusted too low to meet the load operation. This is because when the power factor of the generator changes from the rated value to zero, its active output should be appropriately reduced according to the allowable value of the rotor current. Because the lower the power factor is, the greater the reactive component of the stator current is, and the greater the rotor current is, which may make the temperature of the rotor coil exceed the allowable temperature rise. Therefore, the power factor of the generator must be increased during full load operation. When the water volume is sufficient in flood season, the hydropower station can improve the power factor operation, generate more active power and less reactive power, which is also feasible for electricity. Due to the large number of units in the flood season, the reactive load of electricity is also relatively surplus, and the reactive load in the electricity will not be greatly reduced because the power factor of the units of small hydropower stations is appropriately increased in the flood season. If the electric power factor is too low, the capacitor device can be temporarily put into operation for reactive power compensation. In the hydropower station with sufficient water in flood season, when the unit is running at full load, the generator terminal voltage is often too high. If the terminal voltage is too high, the power factor should also be appropriately increased. However, when the terminal voltage is too high, in order to ensure the safe operation of the unit, the output of the unit must be reduced. For example, in our Dandong hydropower station, when the three units operated at full load in the flood season of previous years, the maximum terminal voltage reached 7.2kV, 14% higher than the rated voltage of 6.3kV. According to statistics, the above phenomenon exists in many small hydropower stations in operation at present. The terminal voltage is too high, which affects the safe operation of hydropower stations, easily leads to various accidents, and electrical equipment elements and devices are easy to be broken down and burned. If the terminal voltage is too high, the generator with long service life, aging insulation or potential insulation defects of the unit will cause insulation breakdown, and in serious cases, the generator will catch fire or smoke. When the terminal voltage is higher than 105% of the rated voltage, due to magnetic flux saturation, the iron loss of the generator increases, the iron core heats, the efficiency of the generator decreases, and the insulation aging is accelerated. Because the terminal voltage is too high, the unit load has to be reduced, the water is discarded for power generation, and the precious hydraulic resources are wasted, which affects the economic benefits of the power station. Properly increasing the power factor of the generator can reduce the terminal voltage of the generator, but it can not solve the fundamental problem of high terminal voltage. The high terminal voltage is caused by the following aspects: ① the supply of electricity exceeds the demand during the flood season, especially the excess reactive load, which increases the electrical voltage and increases the outlet voltage of the generator; ② The line loss of the parallel line of the power station exceeds the regulations, resulting in large voltage drop of the line; ③ The position of transformer tap changer at both ends is improperly selected. According to the above situation, the power station should transform the line and readjust the position of the tap changer. For the hydropower station in parallel operation, the unit cannot operate at full load due to the reduction of water inflow in the dry season. At this time, the generator power factor can be reduced to about 0.7 ~ 0.75. When the controller with constant active power is the core of the control system, reactive power should be generated as much as possible. When our Dandong Power station operates in dry season, the total load is only 1400 ~ 1500kW. At this time, let one 1250KW unit with 900 ~ 1000kW load and 630kw unit with 400 ~ 500kW load, and adjust the power factor to below 0.75. At the same time, one 1250KW unit is in shutdown state