Method of regulating high voltage direct current transmission system operating with several converter stations connected in a multipoint network

Claim 2

In the method of regulating a high voltage d-c transmission system having more than two converter stations for providing a multipoint power supply, and wherein the converter stations working in rectifier and inverter operation are provided with current, voltage and extinction angle regulators, the improvement wherein the station regulators are switched, in the event of a short-circuit in the d-c mains to a characteristic curve with reduced nominal current and voltage values as compared to the values utilized during normal operation, thereby to effect a support of the cut-off process of d-c switches.

Claim 3

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system wherein said current and voltage regulators are designed for a regulation according to the limiting voltage method.

Claim 4

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system and which includes the step of changing the nominal values of all rectifier current regulators from the original value to a lower value, such as 0.2 IdN in the event of a short circuit.

Claim 5

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system wherein said current and voltage regulators are designed for a regulation according to the limiting voltage method and which includes the step of changing the nominal values of all rectifier voltage regulators from the originAl value to a lower value, such as 0.1 UdN in the event of a short circuit.

Claim 6

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system and which includes the step of changing the current regulators of the inverter stations from their nominal value to a lower value, such as 0.1 IdN, and the voltage regulators of the inverter stations from their nominal value to a value U*d 0 so that they already resume their operation at reduced power during the cut-off process.

Claim 7

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system wherein in the event of failure of one inverter station the further step is provided for protecting the remaining inverters of the same station against overload by deliberately causing a short-circuit in the faulty inverter station such as by zero modulation of the inverter or sequential ignition of two valves which are connected to a common phase.

Claim 8

The method of regulation, as defined in claim 1, for a high voltage d-c transmission system where, in order to avoid overloading of a high voltage d-c transmission switch in the event of a fault in the automatic switching system of a rectifier, the further step is provided of changing the characteristic of the inverter in the case of short circuit by inserting an additional maximum voltage regulator to prevent the voltage from rising above a certain value, such as 0.15 UdN.

Claim 9

Arrangement for regulating a high voltage d-c transmission system comprising more than two converter stations interconnected by transmission links for providing a multipoint power supply, each said station comprising controllable valves controlled by the output of a firing pulse generator, a d-c current regulator, a d-c voltage regulator, each said d-c regulator being controlled respectively by the output of a corresponding comparison device which functions to effect comparisons respectively between actual and reference values of the d-c current and between actual and reference values of the d-c voltage, switching means for alternatively connecting the respective outputs of said d-c current and voltage regulators to the input of said firing pulse generator for controlling the latter and hence also the operation of the controllable valves of said converter station, said switching means normally connecting the output of said d-c voltage regulator to the input of said firing pulse generator under normal d-c current conditions at the converter station but being responsive upon an abnormal increase in said station current to switch the input of said firing pulse generator to the output of said d-c current regulator, means providing dual sources of reference values of the d-c current and voltage, each said dual source providing a normal reference value and a substantially lower-than-normal reference value, and switching means normally connecting said normal reference values of said d-c current and voltage as inputs respectively to said d-c current and voltage comparison devices but being responsive upon an abnormal increase in said station current to substitute said lower-than-normal reference values of said d-c current and voltage as the inputs to said d-c current and voltage comparison devices.

Claim 10

Arrangement for regulating a high voltage d-c transmission system comprising more than two converter stations interconnected by transmission links for providing a multipoint power supply, each said station comprising controllable valves controlled by the output of a firing pulse generator, a d-c current regulator, a d-c voltage regulator, each said d-c regulator being controlled respectively by the output of a corresponding comparison device which functions to effect comparisons respectively between actual and reference values of the d-c current and between actual and reference values of the d-c voltage, switching means for alternatively connecting the respective outputs of said d-c current and voltage regulators to the input of said firing pulse generator for controlling the latter and hence also the operation of the controllable valves of said converter station, said switching means normally connecting the output of said d-c voltage regulator to the input of said firing pulse generator under normal d-c current conditions at the converter station but being responsive upon an abnormal increase in said station current to switch the input of said firing pulse generator to the output of said d-c current regulator, means providing dual sources of reference values of the d-c current and voltage, each said dual source providing a normal reference value and a substantially lower-than-normal reference value, and switching means normally connecting said normal reference values of said d-c current and voltage as inputs respectively to said d-c current and voltage comparison devices but being responsive upon an abnormal increase in said station current to substitute said lower-than-normal reference values of said d-c current and voltage as the inputs to said d-c current and voltage comparison devices.

Claim 11

Arrangement as defined in claim 8 for regulating a high-voltage d-c transmission system wherein the actual value of the d-c current is produced by a current transformer inserted in the corresponding transmission link, and wherein the actual value of the d-c voltage is produced by a voltage transformer inserted in the corresponding transmission link.

Claim 12

Arrangement as defined in claim 8 for regulating a high voltage d-c transmission system wherein said switching means at each station for alternatively connecting the respective outputs of said d-c current and voltage regulators to the firing pulse generator of the station includes control means therefor comprising the output of a diode, said diode being conNected to the input terminal for the d-c current regulator of the station and being rendered conductive so as to establish an output therefrom when said station current rises to an abnormal value resulting in an input to the d-c current regulator having a positive polarity.

Claim 13

Arrangement as defined in claim 9 for regulating a high voltage d-c transmission system and which includes switching means common to the d-c current and voltage reference value inputs to said comparison devices for simultaneously switching the d-c current and voltage reference values between their higher and lower levels, said switching means being controlled by the output of said d-c voltage transformer.