Method and apparatus for differential protection of an electric connection

A non-transitory computer-readable recording medium having a computer program recorded thereon that causes a processor of a computer processing device to carry out operations for differential protection of a three phase electric connection of an electric system, the operations comprising:

• detecting current quantities at a first point and a second point of the three phase electric connection of the electric system;
• determining a value of an operate quantity, the operate quantity being based on a difference between the detected current quantities at the first point and the second point of the electric connection;
• determining that a fault is present in the electric connection between the first point and the second point if the value of the operate quantity exceeds a value of a predetermined threshold quantity;
• and
• controlling, by at least one protective relay, a switching element of the electric system to activate a fault protection when a fault in the electric connection is determined to be present,
• wherein the operate quantity IOP is defined by the following equation:
• IOP=|d3Ī0|·gain=|3Ī0L+3Ī0R|·gain,
• where
• d3Ī0=residual differential current phasor,
• 3Ī0L=residual current phasor at the first point such that a positive current flow is towards the second point,
• 3Ī0R=residual current phasor at the second point such that a positive current flow is towards the first point, and
• gain=cos(angle(−Ū0/d3Ī0)−□□b),
• where
• φb=characteristic angle setting, and
• Ū0=residual voltage phasor of the electric connection.

An apparatus for differential protection of a three phase electric connection of an electric system, the apparatus comprising:

• means for detecting current quantities at a first point and a second point of the three phase electric connection of the electric system;
• means for determining a value of an operate quantity, the operate quantity being based on a difference between the detected current quantities at the first point and the second point of the electric connection;
• and
• means for determining that a fault is present in the electric connection between the first point and the second point if the value of the operate quantity exceeds a value of a predetermined threshold quantity;
• and
• means for controlling, by at least one protective relay, a switching element of the electric system to activate a fault protection when a fault in the electric connection is determined to be present,
• wherein the operate quantity IOP is defined by the following equation:
• IOP=|d3Ī0|·gain=|3Ī0L+3Ī0R|·gain,
• where
• d3Ī0=residual differential current phasor,
• 3Ī0L=residual current phasor at the first point such that a positive current flow is towards the second point,
• 3Ī0R=residual current phasor at the second point such that a positive current flow is towards the first point, and
• gain=cos(angle(−Ū0/d3Ī0)−□□b),
• where
• φb=characteristic angle setting, and
• Ū0=residual voltage phasor of the electric connection.