The selection method of the maximum reactive power

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The selection method of reactive power compensation benefit and compensation capacity

reactive power compensation has been known for a long time in terms of its concept. It is to provide necessary reactive power with the help of reactive power compensation equipment, so as to improve the power factor of the system, reduce energy consumption and improve power and voltage quality. There are many kinds of reactive power compensation equipment. This paper discusses the simplest, most economical and most widely used shunt compensation capacitor. The following analyzes and discusses the benefit of compensation and the selection method of compensation capacity. The benefit of reactive power compensation in modern industrial and mining enterprises, the hydraulic experimental machine controlled manually is connected to the power system with a large number of inductive equipment with different capacities, so that the electric transmission power needs reactive power in addition to active power. Generally, the natural average power factor is between 0.70 and 0.85. The reactive power consumed by the enterprise accounts for about 60% ~ 90% of the active power consumed. If the power factor is increased to about 0.95, the reactive power consumption only accounts for about 30% of the active power consumed [1]. As the input of electric reactive power is reduced, the following benefits will be brought to the enterprise

(1) save electricity expenses of enterprises. The direct economic benefits of improving the power factor for enterprises are obvious, because in the national electricity price system, starting from the rational use of limited electric energy, different values are specified for the power factor of different enterprises. If it is lower than the specified value, it needs to charge more electricity. If it is higher than the specified value, 2.3 interface and program control can reduce the electricity charge accordingly. It can be seen that improving the power factor has important economic significance for enterprises

(2) improve the zero indication of the device without any drift and change utilization. For the original power supply equipment, under the same active power, the load current is reduced due to the increase of power factor. Therefore, the transformer, switch, conductor and other power supply and distribution equipment that transmit power to the load have increased the power reserve, so as to meet the needs of load growth; If the original network tends to be overloaded, due to the increase of power factor and the reduction of transmission reactive current, the system will not be overloaded, so as to give full play to the potential of the original equipment; For newly-built enterprises that are still in the design stage, it can reduce equipment capacity and investment cost. Under certain conditions, the improved power factor can reduce the capacity of the selected transformer. Therefore, the use of reactive power compensation not only reduces the initial investment cost, but also reduces the basic electricity cost after operation

(3) reduce the energy consumption of the system. Let R be the total resistance of the system, cos ψ 1 and COS ψ 2 refers to the power factor before and after compensation, Δ P1 and Δ P2 refers to the line loss before and after compensation, so the line loss is reduced Δ P is: (1) the active power transmitted by the line before and after compensation remains unchanged (i.e., cos ψ The voltage U2 after compensation is slightly greater than the voltage U1 before compensation. For the convenience of analyzing the problem, U2 ≈ U1 can be considered to derive i1cos ψ 1=I2cos ψ 2。 I.e. i1/i2=cos ψ 2/cos ψ 1. In this way, the percentage of line loss P reduction is:? P%=? P/? P1 × 100%=(1-I22/I12) × 100%=(1-cos2?1/cos2?2) × 100% (2) when the power factor is increased from 0.70 ~ 0.85 to 0.95, the active power loss can be reduced by 20% ~ 45% according to equation (2)

(4) improve voltage quality. Taking only one concentrated load at the end of the line as an example, assuming that the line resistance and reactance are R and X, and the active and reactive power are p and Q, the voltage loss Δ U is: Δ U= (pr+qx)/u (3) it can be seen from equation (3) that if the reactive power q is reduced, it is conducive to the stability of line terminal voltage and the starting of large motors. Therefore, reactive power compensation can improve the voltage quality (generally, the voltage stability should not exceed 3%). However, it is not economical to install capacitors only to improve voltage quality. The main purpose of reactive power compensation is to improve power factor and reduce line loss. Voltage quality is only a side effect. 2 selection method of reactive power compensation capacity when the main purpose of reactive power compensation capacity is to improve power factor, the selection of compensation capacity is divided into two categories, namely, the selection of single load local compensation capacity (mainly refers to motor) and the selection of multi load compensation capacity (refers to centralized and local grouping compensation). 2.1 selection of local compensation capacity of motor

(1) select according to the condition that the compensation capacity QC is not greater than the excitation capacity Qo. That is, the compensation capacitance QC is selected as: (4) K1 is the capacitance matching coefficient, generally taken as 0.85 K11; Qo is the no-load excitation reactive power of the motor; Polyurethane accounts for a considerable share in the building insulation material market. K2 is the ratio of no-load current to rated current of motor. K2=0.40 ~ 0.45 is taken for multi small power motor, and k2=0.20 ~ 0.40 is taken for small and large power motor. In this way, equation (4) is changed into: qc=k1k2pe= (0.2 ~ 0.4) pe (5) considering load rate, polar number and other factors, the compensation capacity selected according to equation (5) will not be over compensated under any load, and the power factor can be compensated to more than 0.90. If it is compensated to Cos under rated load? 2=1, the motor must be over compensated under no-load or light load, which will not only affect the voltage, but also make the motor supply motor excitation current due to capacitor discharge after power failure, so that the motor still rotating becomes an asynchronous generator, so that the voltage exceeds the rated voltage, which is unfavorable to the insulation and capacitor of the motor

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