Method and device for fault location in a multi-terminal transmission system

An Intelligent Electronic Device (IED) configured for protection in response to a fault in a transmission line section of a multi-terminal power transmission system that comprises a first transmission line section connecting a first terminal to a transmission line junction, a second transmission line section connecting a second terminal to the transmission line junction and a third transmission line section connecting a third terminal to the transmission line junction, the IED comprising:

• an interface configured to obtain pre-fault and during-fault measurements of currents for each terminal of the multi-terminal power transmission system;
• a processor;
• and
• a memory storing instructions that, when executed by the processor, cause the processor to:
• calculate pre-fault and during-fault values of positive sequence current phasors from the pre-fault and during-fault measurements of currents for each terminal;
• calculate at least two values of a fault section index for each section, wherein each value of the fault section index for a section is calculated based on:
• an assumed value for fault location;
• a difference between the pre-fault and the during-fault values of the positive sequence current phasors for two terminals of the power transmission system, wherein the two terminals include the terminal that the section is connected at and one of the other terminals of the multi-terminal power transmission system;
• a length of the section;
• source impedances of the two terminals;
• and
• line parameters of the corresponding section;
• wherein each value of the fault section index for a section calculated is not based on voltage measurements or voltage phasors;
• identify the section having the fault based on a comparison of the values of the fault section index estimated for each section;
• and
• generate a signal to control a switching device according to the identification of the section having the fault, wherein auto-reclose is enabled when the section is an overhead line section.

A system comprising:

• a first terminal;
• a second terminal;
• a third terminal;
• a first transmission line section connecting the first terminal to a transmission line junction;
• a second transmission line section connecting the second terminal to the transmission line junction;
• a third transmission line section connecting the third terminal to the transmission line junction;
• and
• an Intelligent Electronic Device (IED) associated with one of the first, second and third terminals and configured to:
• obtain pre-fault and during-fault measurements of currents for each terminal;
• calculate pre-fault and during-fault values of positive sequence current phasors from the pre-fault and during-fault measurements of currents for each terminal;
• calculate a plurality of values of a fault section index for each section, wherein each value of the fault section index for a section is calculated based on
• an assumed value for fault location,
• a difference between the pre-fault and the during-fault values of the positive sequence current phasors for two of the terminals, wherein the two of the terminals include the terminal that the section is connected at and one of the other terminals,
• a length of the section,
• source impedances of the two of the terminals, and
• line parameters of the corresponding section;
• wherein each value of the fault section index for a section calculated is not based on voltage measurements or voltage phasors;
• identify the section having the fault based on a comparison of the values of the fault section index estimated for each section;
• and
• control a switching device according to the identification of the section having the fault.