Abstract:
A method and an arrangement are provided for determining values of impedance parameters related to a transformer configuration including three single pole voltage transformers each respectively having at least a primary winding, a secondary winding and a tertiary winding. The primary windings are connected to phases of a three phase electric system. The arrangement is configured to conduct an earth fault in the three phase electric system, measure a primary voltage from the faulted phase, measure secondary voltages from the secondary windings, and determine values of one or more impedance parameters related to the transformer configuration on the basis of the measured primary voltage, the measured secondary voltages and an equation relating the primary voltage to the secondary voltages and the one or more impedance parameters.
Abstract:
A method and an arrangement for voltage measurement with a transformer configuration comprising three single pole voltage transformers having tertiary windings open-delta connected with each other. The arrangement is configured to apply a correction to measured secondary voltages on the basis of one or more parameters of the voltage transformers and/or one or more quantities in a known relation to one or more parameters of the voltage transformers, one or more parameters of a circuit connected to the secondary windings and/or one or more quantities in a known relation to one or more parameters of the circuit connected to the secondary windings, and one or more parameters of a circuit connected to the tertiary windings and/or one or more quantities in a known relation to one or more parameters of the circuit connected to the tertiary windings.
Abstract:
A method and apparatus are provided for differential protection of a three phase electric connection of an electric system. The apparatus includes means for determining a value of an operate quantity, which operate quantity is based on a difference between current quantities at a first point and a second point of the electric connection, and means for detecting a fault 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. The operate quantity is based on a difference of residual currents at the first point and the second point, or a quantity indicative thereof, and a coefficient indicative of an angle between a residual voltage of the electric connection and the difference of residual currents at the first point and the second point.