Practical method of reactive power compensation in

2022-06-23
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The practical method of rural low-voltage reactive power compensation Abstract: the goal of low-voltage reactive power compensation is to realize the local balance of reactive power. There are three commonly used methods: random compensation, follower compensation and tracking compensation

key words: low voltage reactive power compensation random compensation follower compensation tracking compensation practical method for rural low voltage electric reactive power compensation P {font-size: 12pt; font-family: "Arial"}p {margin top: 0px; margin bottom: 0px; text-index: 24pt; line-height: 200%} the goal of low voltage reactive power compensation is to achieve local balance of reactive power. There are three commonly used methods: random compensation, follower compensation and tracking compensation. 1 random compensation random compensation is to connect the low-voltage capacitor bank and the motor in parallel, and switch with the motor through the control and protection device at the same time. Agricultural motors, especially irrigation and drainage motors, should be preferentially used in this compensation mode. The advantage of random compensation is that when the electric equipment is running, the reactive power compensation is put into operation, and when the electric equipment is stopped, the compensation equipment exits, so it is not necessary to adjust the compensation capacity frequently. The utility model has the advantages of less investment, small space occupation, easy installation, convenient and flexible configuration, simple maintenance and low accident rate. In order to prevent self-excited overvoltage when the motor is out of operation, the compensation capacity shall not be greater than the no-load reactive power of the motor, that is, it is generally recommended that: where qc-- compensation capacitor capacity ue-- rated voltage io-- motor no-load current. For the motor with large inertia of mechanical load such as drainage and irrigation motor, the compensation capacity can be appropriately increased, which is greater than the no-load reactive load of the motor, but less than the rated reactive load. Since the drainage and irrigation motor is always powered off with the mechanical load of the water pump, the motor speed will drop sharply. Even if the compensation capacity is slightly greater than the no-load reactive load of the motor, it will not generate self-excited overvoltage. For ordinary motors used for irrigation and drainage, the compensation capacity can be determined according to the following formula. Different manufacturers have taken price reduction measures to maintain the profitability: in the formula, PE -- the rated active power of irrigation and drainage motor, kW, the motor running for more than 1000h a year, random compensation is more economical than other compensation methods, and the compensation equipment investment can be recovered within 1 ~ 2 years. 2. Follow up compensation follow up compensation refers to the compensation method of connecting the low-voltage capacitor to the secondary side of the distribution transformer through the low-voltage fuse to compensate the no-load reactive power of the distribution transformer. The agricultural distribution transformer, especially the comprehensive user distribution transformer, generally has the phenomenon of light load and "big horse pulling small car". Close to no-load at low load. The reactive load of distribution transformer under light load or no load is mainly the no-load excitation reactive power of transformer. Where qo-- transformer no-load excitation reactive power, kvar io%-- no-load current percentage, se-- transformer rated capacity, KVA distribution transformer no-load reactive power is the main part of rural reactive load. For light load distribution transformer, this part of loss accounts for a large proportion of power supply, resulting in an increase in the unit price of electricity. Since the follow-up compensation is compensated at the low-voltage side, it has simple wiring, convenient maintenance and management, and can effectively compensate the no-load reactive power of the distribution transformer, so that this part of reactive power can be balanced locally, so as to improve the utilization rate of the distribution transformer and reduce the reactive power loss. It is one of the effective means to compensate the reactive power of the distribution transformer at present. The follower compensation shall be used to compensate the no-load reactive power of the distribution transformer, which belongs to the fixed compensation mode, and the compensation capacity shall not exceed the no-load reactive power of the distribution transformer. This compensation method can reduce the agricultural reactive base load. For high consumption special transformer and integrated transformer with capacity of 50KVA and above, the use of follower compensation shall be advocated. S7 and S9 series distribution transformers with capacity above 125kva shall also adopt follower compensation. The follower compensation can only compensate the no-load reactive power Qo of the distribution transformer. If the compensation capacity QC> Qo, it will cause over compensation when the distribution transformer is close to no-load. Moreover, theoretical analysis, test and operation experience show that under this condition, ferromagnetic resonance is easy to occur when the distribution transformer is not fully divided into the following phases. Therefore, qc= (0.95 ~ 0.98) Qo is recommended. 3 tracking compensation tracking compensation refers to the compensation method that uses the reactive power compensation switching device as the control and protection device to compensate the low-voltage capacitor bank on the 0.4kV bus of large users. The fixed connection group of the compensation capacitor can play a role equivalent to the follow-up compensation to compensate the user's own reactive base load; The connection group can be switched to compensate the reactive peak load. The switching mode is divided into automatic and manual. Generally, the user load has certain fluctuation, so it is recommended to select the automatic switching device. This device can better track the change of reactive load, with flexible operation mode and small operation and maintenance workload. Considering the different time rates of motor operation and the limitation of compensation capacity of a single motor, for special distribution transformer users above 100kVA, tracking compensation can obtain better compensation effect than random and follow-up compensation. In addition, the precautions for not using mortar tensile testing machine and the operating procedures of the equipment need to improve the compensation degree, and the operating time of each group of capacitors can be appropriately adjusted to prolong their service life, Thus, the purchase and renewal cost of the capacitor is reduced. However, the automatic switching device required for tracking compensation is more complex than the control and protection device of follower and random compensation, with more perfect functions and larger initial investment. Special attention shall be paid to the performance and quality of the automatic switching device. The following five conditions must be met: (1) the capacitor bank can be switched automatically according to the change of reactive load to keep the power factor above 0.95 without

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