Improvements in electrical inverter stations

摘要

1,174,166. Inverters. ALLMANNA SVENSKA ELEKTRISKA A.B. 19 April, 1967 [20 April, 1966], No. 17927/67. Heading H2F. In an inverter in which the power factor is controlled by an adjustable bank of capacitors 17, a signal is derived indicative of the reactive power and is fed to a control device for the capacitor bank 17 and to the trigger circuits for the inverter 1 in such a way that a reduction in reactive power causes first an increase in the commutation margin of the rectifiers and then a decrease in the capacitance of the capacitor bank the arrangement being such as to ensure a minimum commutation margin. As described, the signal representing reactive power is derived by means of a Hall generator 14 supplied by potential and current transformers 16, 15 and developing a voltage across resistor 20 the polarity of which is dependent on the sign of the effective reactance in the network. When the load is reduced on the network 10, the capacitance of bank 17 tends to be excessive hence the signal from the Hall-generator 14 is such that when fed via control circuits 7, 8 (see Specification 985,674) the delay angle for the rectifiers 2 is decreased. The signal from the Hall-generator is also fed to an electromechanical control device 13 for the capacitor bank so as to reduce the capacitance, correct the power factor and hence cancel the signal from the Hall-generator. The delay angle for the rectifiers 2 is thus restored. When the original load conditions have been re-established, the capacitor bank will be to small and the reactive power in the network will therefore be inductive. A new output signal of opposite polarity will thus be obtained from the Hallgenerator 14 which is fed to control device 13 so as to reset the capacitance. Diode 21, however, prevents the signal from decreasing the commutation margin of the rectifiers 2 beyond a predetermined angle. The trigger circuits for rectifiers 2 include transistors 5 controlled by the combination of signals derived at 8 from the network 10 and at 7 from the current supplied by the D.C. transmission line 90. Fig. 2 (not shown), depicts a simplified arrangement of four inverters 1 connected in series across a three-wire high voltage direct current transmission line and having isolating switches in series with each side of the D.C. line and across each inverter. The Hall-generator 14 is replaced by a potential transformer feeding a rectifier and smoothing capacitor, the output being compared with a D.C. reference voltage.