engleski

Current Transformer modeling in EMTP-RV for transients studies

During the last decades the demands on current transformers for protection has increased rapidly. Overcurrents in power networks and also time constants for the short-circuit DC offset are increasing. Very short breaker tripping times are stipulated and achieved by fast operating protective relay systems. The relays must perform measurements at a time when the transient (DC offset) is present in short-circuit current. A normal protective core in a current transformer will saturate very rapidly due to high currents and remanent flux. After saturation occurs, the current transformer output will be distorted and the performance of the relay protection system will be affected. For protection relays intended to operate during a fault the core output under transient conditions is of importance. Analysis of CT saturation under transient conditions (AC and DC saturation) was performed in EMTP-RV software. The voltage at the current transformer secondary terminals directly affects the current transformer saturation. This voltage is developed in a loop containing the secondary wires and the burden of all relays in the circuit. The effect of burden on CT saturation was analyzed in EMTP-RV.

current transformer; saturation; relay protection system; EMTP-RV

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