The power factor automatic compensator is a fully automated electronic device that improves the power factor in the power grid system. Through its regulation, the reactive power consumption in the power grid is minimized, and the purpose of fully utilizing electric energy and saving electricity is achieved. The GBK4-1C type controller used in our station automatically detects and reduces the power factor of the load in the system to make the system power factor operate within the specified range.
The idea of ​​detecting the power factor throwing and cutting method is to input the compensation capacitor when the power factor of a system drops below the lower limit setting value, and cut off the compensation capacitor when the power factor exceeds the upper limit setting value. Figure 1 illustrates the principle of this control method.
In the figure, OA is the power factor lower limit setting value COSj A line, OB is the power factor upper limit setting value COSj B line, assuming that the load line increases along the OD line, its power factor is COSj, when the load increases to the critical regulation power point M1, the capacitor When C1 is input, the reactive power compensated is M1K1, and the apparent power is OK1, so that the power factor is within the range defined by the two lines of OA and OB. If the load continues to increase to the M2 point, the capacitor C2 is put into operation again, and the power factor is controlled within the specified range. When the load is further increased to the M3 point, the capacitor C3 is input to maintain the power factor within the prescribed range. When the load is reduced, the capacitor C1 is cut off when the K3 point is reduced to the N1 point. When the load is reduced to the N2 point, the capacitor C2 is cut off again, and when the load is reduced to the left side of the critical adjustment power line, the capacitor is completely cut off. The position of the critical adjustment line here depends on the capacity of the minimum compensation capacitor bank, the nature of the load and the range of adjustment of the specified power factor. Figure 2 shows the schematic diagram of the automatic compensation controller.


In the figure, the controller is divided into: a measuring part by a broken line; a DC amplifying part; an executing part; and a power supply part. The work is as follows: first convert the phase difference between the AC voltage and the current into a DC voltage signal, and then amplify the DC signal to drive the execution part of the action, and input or cut off the compensation capacitor.
The AC signal of the measuring part is taken from the bus line A, C phase line voltage uAC and B phase current iB in the grid system. In the three-phase AC system of Figure 3, when the B phase current iB is in phase with the B phase voltage uB, ie COSj =1 When the phase current iB differs from the line voltage uAC by p /2, when iB leads or lags uB, the phase difference of iB and uAC is less than or greater than p /2. In order to measure the change of the phase relationship, the measurement part is adopted. The half-wave phase-sensitive differential amplifier line, u1 and u2 respectively reflect the two AC voltage values ​​of the ACAC and iB phases on the AC side. It can be seen from the figure that the conduction junction of T1 and T2 is forward biased only when u2 is in the negative half cycle, and it is possible to conduct. Whether or not the collector currents i1, i2 are generated is determined according to the polarity of u1. Figure 4, Figure 5, and Figure 6 show the phase relationship between u1 and u2 and the current flow of the T1 and T2 collectors in the detection circuit. Figure 4 shows that u1 and u2 are in phase only T1 is turned on in one week. Since the average values ​​of the voltages u1 and u2 applied by the emitter and the collector are the largest, the collector current i1 is the largest and T2 is not turned on. The DC output voltage U between b is equal to i1R1>0 and is maximum. Figure 5 shows u1 lead and u2 phase p /2. As can be seen from the figure, when 0~p /2, u1 is in positive half cycle, u2 is in negative half cycle, T2 emitter junction is forward biased and turned on, and collector current i2 passes. Diode D2 flows to resistor R2. During 3p /2~2p, u1 and u2 are both in the negative half cycle. The T1 emitter junction is forward biased and the collector current i1 flows through resistor D1 through diode D1. , T1, T2 are both turned on p /2, and the average voltage of the two triode base voltages and the collector voltage are the same during the conduction period, so i1=i2, select R1=R2, then the DC output voltage Uab= in one week i1R1-i2R2=0. Figure 6 shows that the difference between u1 and u2 is less than p /2. Obviously, the T2 conduction time is shorter than the T1 conduction time. At this time, the average value of i1 is greater than the average value of i2 in one week, so Uab=i1R1-i2R2>0, Uab is smaller than this time. When the phase difference between u1 and u2 is in phase, if the phase difference between u1 and u2 is greater than p /2, Uab=i1R1-i2R2<0 can also be obtained. Therefore, the phase difference amplification can be made according to the phase difference between the AC side voltage uAC and the current iB. The line outputs different DC voltages to control the DC amplification part. When Uab<0, Uab is added to the emission junctions of T3 and T5 via D4 and R4, and then the relay J1 is driven by the amplification of T3 and T5. Otherwise, when Uab>0, Uab is added to the T4 and T6 emission junctions via D3 and R3, and is amplified by T4 and T6 to drive J2 action. When J1 is activated, J1 normally closed contact opens, C5 is charged by negative power supply via R7, so that the base potential of T7 keeps decreasing. After a period of time (delay), T7 and T9 are turned on, and relay J3 acts to make the first group. The capacitor is put into operation of the system, and the normally closed contact of J3 that controls the input of the second group of capacitors is turned on, and the second group starts to delay. If the power factor of the system is still not met after the first group of capacitors is put into operation, the DC of the measuring circuit is The output Uab is still less than zero, then after the delay of the second group ends, the relay J5 acts to put the second group of capacitors into operation; if the Uab is greater than zero, the T4 and T6 conduct the J2 action, and after the delay, the J4 action, The first set of capacitors are cut off from the system. If the Uab is still greater than zero, the second set of capacitors is removed after a delay, thereby achieving the effect of automatically regulating the power factor of the system.

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