Abstract: A high-voltage d-c transmission system in which one of the converters is operated as a rectifier and the other as an inverter. A first cascade control which sets the rectifier control angle includes a superimposed active power controller and a subordinated d-c controller. A second cascade control which sets the inverter control angle includes a superimposed voltage/active power controller, a superimposed quenching angle control and a subordinated quenching angle controller. The setting signal of each of the two superimposed controllers are controlled in dependence on the control deviation of the other one of the superimposed controllers via a first or second pilot control for decoupling the cascade controls. The gain factors of the pilot control quantities depend on the operating point in such a manner that a small engagement of the pilot control variable exists for small control angles and a large engagement exists for large control angles.

Abstract: A state signal is formed to indicate a transition to a bypass mode of operation. In forming the signal of each winding system of a corresponding converter transformer on a side of the converter transformer are determined, weighted with weighting factors and summed up. The summation current formed in this manner does not have any null zones in the normal operation of the converter. All weighting factors are different if the phase currents between the converter and the converter transformer are used to produce the summation current. In the case of a converter transformer which is connected to the converter via a delta-connected winding system and in which the winding currents are used, certain differences formed by the weighting factors are not to be the same. A DC Hall converter with an insertion hole is particularly well suited for weighting and combining the currents of each individual winding system.

Abstract: If in a high-voltage d-c transmission system (HVDCTS), a resonance frequency of an a-c voltage network (NB) connected to the inverter (1B) is located in the vicinity of a voltage component contained in the a-c voltage network, a resonance frequency which often cannot be compensated by a current regulator controlling the rectifier stage (1A) is coupled into the d-c circuit of the HVDCTS via the inverter. Therefore, resonance phenomena which requires an emergency shutdown of the HVDCTS are generated. Therefore, a pilot quantity (U'.sub.d) is formed with a defined phase shift relative to the resonance oscillation of the HVDCTS voltage and added to the output of the current regulator. Thereby, a constant HVDCTS current can be generated for a given operating point and the resonance in the a-c voltage network (NB) can be damped. If the resonance oscillation is determined by two quantities (U'.sub.d, i'.sub.

Abstract: A circuit for monitoring the voltage stress of a capacitor which produces an over-stress indicator signal responsive to the over-voltage history of the capacitor. If the measured voltage stress of the capacitor exceeds a predetermined over-voltage value, a characteristic-curve generator, having a predetermined transfer function, produces an output signal which is responsive to the measured voltage stress of the capacitor and the transfer function of the characteristic-curve generator. This signal is combined with a further signal which is responsive to a predetermined permissible continuous operation voltage value. The combined signals are conducted to an integrator having a predetermined integration time constant for producing an overload signal. The overload signal at the output of the integrator is a measure of the state of stress of the capacitor. Circuitry may be provided for disconnecting the capacitor from a transmission line in response to the output signal of the integrator.

Abstract: A circuit for monitoring the capacitor battery of a filter circuit connected to a transmission line, the capacitor battery consisting of at least two parallel legs, each with a number of series-connected capacitors. A first signal is produced which corresponds to the total alternating current flowing through the capacitor battery. A second signal is produced which corresponds to the difference between the currents flowing through the respective parallel legs of the capacitor battery. The current difference signal is compared with a respective fraction of the total current signal. A fault indicator signal is produced if the difference between the difference current signal and the fractional total current signal exceeds a predetermined threshold value. Further circuitry is provided for correcting drift in the difference current signal, which may be caused by temperature variations or acceptable capacitor failures.

Abstract: Ignition control signals for a multipulse controlled rectifier are combined in a sequence which is fed through a first time delay stage to a phase control circuit having a voltage-controlled oscillator which generates a phase-locked, gated, highly accurate square-wave oscillation as a trigger pulse series. The ignition control signals and the trigger pulse series of the voltage-controlled oscillator are conjunctively coupled in and gates are then amplified to form firing (ignition) pulses. A second time delay stage is provided for safety, in the event of dynamic control processes, and follows the first time delay stage. The output signals of the second time delay stage are linked to the ignition control signals in additional and gates and are subsequently amplified.

Abstract: A method for the transmission of DC current via a DC network between at least one rectifier station and several inverter stations wherein reference inputs are formed on the basis of a fixed predetermined current-voltage characteristic and a fixed predetermined voltage-current characteristic matched to the aforesaid current-voltage characteristic for the voltage controller of the rectifier of the rectifier station and for the current controller of each inverter station, respectively. The formed reference input for each current controller is released to that current controller when the maximum value of the formed reference input exceeds a value determined for the reference input corresponding to the power demand associated with the inverter station which includes that current controller. When the maximum value of the formed reference input is less than the latter determined value, such value is released as the reference input to the current controller.

Abstract: A circuit arrangement is disclosed comprising a converter for converting a three-phase system of sinusoidal voltages into three trapezoidal control voltages for controlling control units serving three direct cycloconverters. More particularly, in accord with the invention, the converter acts on the sinusoidal control voltages such that during each region from .pi./3 to 2.pi./3 of a half-wave of each particular voltage that voltage is reduced to .sqroot.3/2 times its peak value, while the other two voltages are amplified or increased by an amount equal to the difference between the aforesaid peak value and .sqroot.3/2 times such peak value.

Abstract: A circuit arrangement is disclosed having an odd number of Y-connected frequency converters. The control units of the frequency converters are associated with current regulators, all of which are addressed by an additional common reference value. In accord with the invention, the aforesaid reference value is derived by generating a difference voltage corresponding to the difference of the voltages at the neutral point of the frequency converter circuit and the neutral point of the load. This difference voltage is then passed through a delay member whose time constant corresponds to the time constant of the load to develop the reference value.

Abstract: An improved method and apparatus for operating a converter fed rotating field machine to obtain better utilization of the converter rectifiers in which the stator windings of the machine are fed with non-sinusoidal phase currents with one phase current always limited to a maximum value and the other phase currents increased by the difference between that maximum value and a typical sinusoidal wave current. This is accomplished in such a manner that the power and torque of the rotating field machine are not affected.