Method and arrangement for facilitating clearing of a pole fault and isolation of a faulted pole in a power transmission system

A control unit for controlling operation of an interface arrangement configured to couple an alternating current, AC, power system with a direct current, DC, power system, the interface arrangement including:

• a ground electrode,
• at least two poles for coupling-f the DC power system to the AC power system, wherein each of the at least two poles includes:
• a converter for conversion between AC and DC power, including a plurality of controllably switchable switching elements, the converter being configured to selectively be in a blocking mode in which the plurality of switching elements are not switched, the converter including a DC side for coupling of the converter to the DC power system and an AC side for coupling of the converter to the AC power system,
• power transmission line and a power transmission line switching element included in the power transmission line for controllably and selectively electrically coupling the converter with the DC power system, wherein the converter is coupled to the DC power system via the power transmission line, and
• a circuit breaker arranged in a current path between the AC side of the converter and the AC power system and configured to controllably effect discontinuation of flow of current in the current path upon opening of contacts of the circuit breaker and controllably effect flow of current in the current path upon closing of the contacts,
• the interface arrangement further including:
• a neutral bus line for each pole, each neutral bus line geing connected to the respective pole for coupling the converter of the respective pole to the ground electrode, and
• a neutral bus switching element included in each neutral bus line for controllably and selectively electrically coupling the converter of the respective pole to the ground electrode,
• the control comprising an input communicatively connected to a fault sensor,
• the control unit being configured to, if a fault (F) is sensed in one of the poles:
• cause the converter of the pole to enter the blocking mode;
• cause the circuit breaker of the pole to open its contacts so as to effect discontinuation of current flow in the current path;
• cause the neutral bus switching element of the neutral bus line connected to the pole to disconnect the converter from the ground electrode, whereby any transient current generated by the fault is damped out;
• and
• after the transient current has been damped out, cause the power transmission line switching element of the pole to disconnect the converter from the DC power system.

A method of controlling a connection between an alternating current, AC, power system and a direct current, DC, power system, comprising:

• using an interface arrangement which includes:
• a ground electrode,
• at least two poles for coupling the DC power system to the AC power system, wherein each of the at least two poles includes:
• a converter for conversion between AC and DC power including a plurality of controllably switchable switching elements, the converter being configured to selectively be in a blocking mode in which the plurality of switching elements are not switched, the converter including a DC side for coupling of the converter to the DC power system and an AC side for coupling of the converter to the AC power system,
• a power transmission line and a power transmission line switching element included in the power transmission line for controllably and selectively electrically coupling the converter with the DC power system, wherein the converter is coupled to the DC power system via the power transmission line, and
• a circuit breaker arranged in a current path between the AC side of the converter and the AC power system and configured to controllably effect discontinuation of flow of current in the current path upon opening of contacts of the circuit breaker and controllably effect flow of current in the current path upon closing of the contacts,
• a neutral bus line for each pole, each neutral bus line being connected to the respective pole for coupling the converter of the respective pole to the ground electrode, and
• a neutral bus switching element included in each neutral bus line for controllably and selectively electrically coupling the converter of the respective pole to the ground electrode,
• the method further including, if a fault (F) is sensed in one of the poles:
• configuring the converter of the pole to enter the blocking mode;
• opening the contacts of the circuit breaker of the pole so as to effect discontinuation of current flow in the current path;
• using the neutral bus switching element of the neutral bus line connected to the pole to disconnect the converter from the ground electrode, whereby any transient current generated by the fault is damped out;
• after the transient current has been damped out, using the power transmission line switching element of the pole to disconnect the converter from the DC power.

A computer program product configured to, when executed in a control unit, perform a method for use in an interface arrangement configured to couple an alternating current, AC, power system with a direct current, DC, power system, the interface arrangement including:

• a ground electrode, at least two poles for coupling of the DC power system to the AC power system, wherein each of the at least two poles includes:
• a converter for conversion between AC and DC power including a plurality of controllably switchable switching elements, the converter being configured to selectively be in a blocking mode in which the plurality of switching elements are not switched, the converter including a DC side for coupling of the converter to the DC power system and an AC side for coupling of the converter to the AC power system, a power transmission line and a power transmission line switching element included in the power transmission line for controllably and selectively electrically coupling the converter with the DC power system, wherein the converter is coupled to the DC power system via the power transmission line, and a circuit breaker arranged in a current path between the AC side of the converter and the AC power system and configured to controllably effect discontinuation of flow of current in the current path upon opening of contacts of the circuit breaker and controllably effect flow of current in the current path upon closing of the contacts, the interface arrangement further including:
• a neutral bus line for each pode, each neutral bus line being connected to the respective pole for coupling the converter of the respective pole to the ground electrode, and a neutral bus switching element included in each neutral bus line for controllably and selectively electrically coupling the converter of the respective pole to the ground electrode, the method including, if a fault (F) is sensed in one of the poles:
• causing the converter of the pole to enter the blocking mode;
• causing the circuit breaker of the pole to open its contacts so as to effect discontinuation of current flow in the current path;
• and
• causing the neutral bus switching element of the neutral bus line connected to the pole to disconnect the converter from the ground electrode, whereby any transient current generated by the fault is damped out;
• after the transient current has been damped out, causing the power transmission line switching element of the pole to disconnect the converter from the DC power.

A computer-readable storage medium on which there is stored a computer program product configured to, when executed in a control unit, perform a method for use in an interface arrangement configured to couple an alternating current, AC, power system with a direct current, DC, power system, the interface arrangement including:

• a ground electrode, at least two poles for coupling of the DC power system to the AC power system, wherein each of the at least two poles includes:
• a converter for conversion between AC and DC power including a plurality of controllably switchable switching elements, the converter being configured to selectively be in a blocking mode in which the plurality of switching elements are not switched, the converter including a DC side for coupling of the converter to the DC power system and an AC side for coupling of the converter to the AC power system, a power transmission line and a power transmission line switching element included in the power transmission line for controllably and selectively electrically coupling the converter with the DC power system, wherein the converter is coupled to the DC power system via the power transmission line, and a circuit breaker arranged in a current path between the AC side of the converter and the AC power system and configured to controllably effect discontinuation of flow of current in the current path upon opening of contacts of the circuit breaker and controllably effect flow of current in the current path upon closing of the contacts, the interface arrangement further including:
• a neutral bus line for each pole, each neutral bus line being connected to the respective pole for coupling the converter of the respective pole to the ground electrode, and a neutral bus switching element included in each neutral bus line for controllably and selectively electrically coupling the converter of the respective pole to the ground electrode, the method including, if a fault (F) is sensed in one of the poles:
• causing the converter of the pole to enter the blocking mode;
• causing the circuit breaker of the pole to open its contacts so as to effect discontinuation of current flow in the current path;
• and
• causing the neutral bus switching element of the neutral bus line connected to the pole to disconnect the converter from the ground electrode, whereby any transient current generated by the fault is damped out;
• after the transient current has been damped out, causing the power transmission line switching element of the pole to disconnect the converter from the DC power.