Directional ground relay system

A directional ground relay system comprising:

• a directional ground relay configured to calculate a zero-phase sequential current and a zero-phase sequential voltage based upon electric values relating to voltage and current detected from a three-phase electric power transmission line to be protected, the directional ground relay being configured to decide a direction of a ground fault in the power transmission line based upon a phase relation of the zero-phase sequential current and a zero-phase sequential voltage;
• an sudden current-change relay configured to be activated when a phase current has changed at a rate more rapid than a pre-determined rate;
• and
• a faulty phase decision unit configured to decide that a phase corresponding to the activated sudden current-change relay is a phase in which the fault has occurred, when the ground fault is decided to be a forward fault by the directional ground relay.

A directional ground relay system comprising:

• a first directional ground relay configured to receive a plurality of electric values relating to voltage and current from a three-phase electric power transmission line to be protected, the directional ground relay being configured to decide a direction of a fault in the power transmission line based upon the plurality of electric values, the directional ground relay comprising:
• a zero-phase sequential current calculation unit configured to calculate a zero-phase sequential current based upon the current detected from the power transmission line;
• and a phase-comparison unit configured to compare a phase of the zero-phase sequential current to a phase of voltage corresponding to the voltage in the power transmission line, to decide whether the zero-phase sequential current is within a pre-determined range, and to output the phase of the voltage as a faulty phase of voltage in which a forward ground fault has occurred, when the zero-phase sequential current is within the pre-determined range;
• a second directional ground relay configured to calculate a zero-phase sequential current and a zero-phase sequential voltage based upon electric values relating to voltage and current detected from the power transmission line, the directional ground relay being configured to decide a direction of a ground fault in the power transmission line based upon a phase relation of the zero-phase sequential current and a zero-phase sequential voltage;
• and
• a faulty phase decision unit configured to decide that a phase in which the first ground directional relay is activated is a faulty phase, when the second directional ground relay decides a forward fault.

A directional ground relay system comprising:

• a directional ground relay configured to calculate a zero-phase sequential current and a zero-phase sequential voltage based upon electric values relating to voltage and current detected from a three-phase electric power transmission line to be protected, the directional ground relay being configured to decide a direction of a ground fault in the power transmission line based upon a phase relation of the zero-phase sequential current and a zero-phase sequential voltage;
• a transmitter and a receiver configured to exchange signals between a local terminal and a remote terminal;
• and
• an sudden current-change relay configured to be activated when a phase current has changed at a rate more rapid than a pre-determined rate;
• wherein the system is configured to output a trip signal of a local terminal to the output phase of the sudden current-change relay and to transmit a permission signal to the remote terminal, if a permission signal is received from a relay of the remote terminal, and if the directional ground relay has not detected a reverse fault.