Arrangement for the rapid compensation of blind currents or spannungsab cases

摘要

1,250,276. Reactive current and volt drop compensation. LICENTIA PATENT-VERWALTUNGS G.m.b.H. 20 Feb., 1969 [21 Feb., 1968], No. 9145/69. Heading H2H. [Also in Division G3] The reactive current or volt drop in an A.C. mains is compensated by capacitors or inductors which are varied step wise by thyristors, the variable total current of a load connected to the mains being used to detect its reactive current component at the beginning of each total current half wave and the compensating current being matched to the reactive current in the same half wave. The reactive current of the inductive load LR may be maintained constant at a desired value (zero or finite) by opposing it with a capacitor current of opposite sign or supplementing it with an inductive current, the respective effects being to remove the reactive current fluctuations above the desired value or to supply the fluctuations below the desired value. If volt drop compensation is desired, the compensating current may be greater than that for reactive current compensation, depending on whether all or only some of the volt drops occurring in the mains are to be compensated. In the described embodiment the inductive load LR is compensated by capacitors Cl, C2, C3 controlled by anti-parallel thyristors whose firing pulses are obtained from a control circuit comprising members Q st , M st and St. From a mathematical analysis of the waveforms of mains voltage U, total load current I, reactive current component and capacitor current, Fig. 1 (not shown), it is explained that the reactive current component is dependent on the product of the phase angle between U and I and the rate of rise of I at the start of each half cycle. Thus in Figure 2 a current transformer W detects the current I and supplies a signal to the member Q st which obtains the angle between U and I, for example by obtaining the time difference between zero passages of U and I using saturable reactors delivering spaced voltage pulses which are counted digitally. The rate of rise of I is obtained by a mutual inductance M and this signal, together with the output signal from member Q st , is fed to member M st which forms the product of the two signals as an ouput signal used to control the member St. The instantaneous value of I just before switch-on of the capacitors may be used to obtain the rate of rise.