1 Basic situation of the generator set of the Cocoto seawater power station The Cocoto seawater power station is located in the Cocotohai mining area of â€‹â€‹Fuyun County, Altay Prefecture. It is a self-contained power station of the enterprise. It is affiliated to the non-ferrous metal company Cocoa Sea Rare Co., Ltd., and has 4 power stations. The unit has a total installed capacity of 19,000 kW, the actual output is about 14,000 kW, and the annual power generation is 90 million kWh. At present, the power supply situation is: in winter, due to limited reservoir storage, the actual power generation can only reach 50% of the design capacity. Left and right, this is caused by objective factors. The peak of power consumption of power stations is mainly concentrated in the summer. Because of the abundant water in summer, the crew can use the maximum capacity to generate electricity. However, because the summer weather is high, the insulation equipment of the existing units has mostly aged, and the unit is generally running. The problem of too high temperature, coupled with some subjective and objective factors in the hydro-generator unit, has made the output of each unit not reach the ideal state in summer. According to the regulations of the unit operation chart, the hot air temperature (connected to the generator stator coil) of the generator should not exceed 75 Â°C during normal operation, and the cold air temperature (connected to the generator rotor cooler) should not exceed 50 Â°C. Below 5 Â° C, as much as possible, the surface of the unit cooler does not condense water droplets. If the cold air temperature is increased by 1C within 40 Â°, the stator rated current value should be reduced by 1.5%. For every 1C added in 45 ~ 50C, the stator rated current value should be reduced by 2%, and when the temperature exceeds 50C, the cold air temperature should be increased by 1C. To reduce the stator rated current value of 3%. The mathematical relationship expression of the generator output is: P = U.:! It can be seen from the above formula that when the voltage U = 6.0kV is constant, if the stator current value I of the generator is lowered, the power P of the generator is unintentionally reduced. Therefore, the key to improving the output of the generator set is how to It can better reduce the operating temperature of the generator set stator and rotor and improve the operating efficiency of the turbine.
2 reduce the operating temperature of the stator and rotor of the generator set. The following methods can be adopted to reduce the underground temperature of the generator house. The air flow and ventilation are much worse than the ground power station itself. The summer temperature of the main building is relatively low. In winter, the temperature is about 20C, and the temperature is above 35C. Due to the influence of the ambient temperature, the temperature of each part of the generator set is generally increased, and the heat dissipation condition is poor. Therefore, lowering the ambient temperature can effectively reduce the temperature of the generator set. The specific methods are as follows: (1) Install a large fan at the existing ventilation duct of the main plant in the underground, and use the wind generated by the fan to force the convection of the air in the main building to reduce the main plant. The temperature thus reduces the temperature of the generator set. (2) In the case of high load demand and high temperature in summer, the tailgate can be properly raised to allow more cold air to enter the turbine layer to reduce the temperature of the generator set. (3) Open the top cover of the main building to discharge the hot air of the main building.
2.2 Improvement of the cooling system of the generator set The cooling methods of the stator and rotor of the generator set of the Cocoa Seawater Power Station are as follows: the stator part is cooled by the additional cooler, and the rotor part is cooled by the fan that is carried by itself, so the cooler The cooling effect is essential for the cooling and cooling of the generator set. It should be improved in the past when the genset cooler is unreasonable: (1) The number of installations of each unit cooler can be added. For example, only 4 of the original 4 generator stators are installed. The cooler is added to the rear, and the cooling effect is obviously improved. (2) Increase the water pressure of the cooler. All the cooling water of the generator set of the Cocoto Seawater Power Station comes from the water of the pressure pipe of the pump house of the power station. The water pressure is generally 0.8MPa, and the pressure is reduced to 0.3MPa after the pressure reducing valve, and then supplied to the stator cooler of each generator set. If the water pressure of the cooler is increased from the original 0.3MPa to 0.5MPa, not only can the temperature of the generator set be better, but also because the water pressure increases, the circulation speed of the water flow is increased, and the stator heat of the generator that has been cooled can be reduced. Take it faster, which not only improves the output of the generator set, but also does not change the temperature rise of the generator. (3) Strengthen the cleaning degree of the cooler. Because of the water quality factor, the cooler is easy to scale on the pipe wall after long-term use. Therefore, the mud is washed with water first, then washed with 10% dilute hydrochloric acid solution for 2 hours, then rinsed with water, and then alkali solution ( Rinse with trisodium phosphate) and rinse thoroughly with water. This ensures that the maximum capacity of the cooler passes through the cooling water to reduce the temperature of the generator set. (4) Perform a wire transformation on the rotor portion of the generator set to reduce the rotor temperature. The working principle is to increase the number of turns of the rotor winding, thereby increasing the number of ampere turns of the rotor to establish the main magnetic potential. If the main magnetic potential of the generator rotor is kept constant, according to the theorem that the number of turns is inversely proportional to the current, the rotor current will decrease as the number of windings of the rotor increases, thus reducing the temperature of the generator rotor. At the same temperature, the generator set can carry more reactive load.
3Re-replace the large-capacity unit excitation equipment to improve the output of the generator set. The original excitation equipment of the Cocoa Hydropower Station has never been replaced after the normal power generation. The service life has exceeded 30 years, and the existing excitation equipment is insulated. The aging phenomenon is serious, and it is unable to meet the requirement of providing sufficient excitation current to the generator rotor, thus limiting the reactive power generated by the generator, thereby affecting the stator voltage and the output of the entire unit. There are many ways to improve the excitation equipment: (1) The number of turns of the exciter and the excitation coil can be increased to increase the voltage of the exciter. (2) The rotor current of the generator can be met by replacing the advanced thyristor excitation device.
At present, our factory adopts the second method, replacing the old-fashioned excitation equipment with a new type of thyristor excitation device, ensuring that the excitation voltage and current can reach the required rated value at any time, so that the load demand is high and the water head In the case of lower unfavorable factors, it can also generate electricity better and ensure the output of the generator set.
4 Through the transformation of the turbine unit, to improve the output of the generator, the output of the unit should be increased under the condition of the head of the existing generator set. Only increase the water receiving area of â€‹â€‹the turbine water worm gear and increase the governor adjustment force distance to increase the opening of the water guide vane to reduce the loss of the water head. The specific measures are as follows: (1) In the case of the water worm gear diameter unchanged, the water is raised. The lower ring of the worm wheel is 40mm, and the water worm wheel blade is reduced from the original 16 pieces to 14 pieces, which increases the cross section of the water worm wheel blade from 0.925m2 to 1.05m2, which increases the generator output by 1025%. (2) Renovation and modification of the large shaft earrings of the governor, so that the large axial force distance from the original R= to 260mm, increase the adjustment force distance to meet the output requirements of the new water worm gear, and ensure the normal unit opening. The adjustment of the governor's adjustment force can also increase the adjustment angle of the speed control ring from the previous 14Â°30' to 1750', and the opening of the guide vane is increased from the previous 72mm to 88mm, within the designed water head range. The increase in the amount of water from the original 5.92m3/s to 7.68m3/s also indirectly increases the output of the generator.
5 Conclusion Although the Cocoa Hydropower Station is a small hydroelectric power station, it is the "heart" of the rare company of Cocoa, and its operation directly affects the survival and economic benefits of the company. Through the simple transformation of the generator set, not only the cost is not used much, but also the unit that can not achieve the brand-name output can reach the brand name as much as possible.
Wire cross section mm2 3 Conclusion In the cable selection design, in addition to considering the safe operation of the cable, the allowable current carrying capacity must be selected to select the core cross section. At the same time, the core cross section should be selected from the principle of the smallest sum of power loss and initial investment. This is science. And economical. Generally, the economic current is used to select the cable core cross section, which can reduce a large amount of line loss and save a lot of investment.
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