Some of the faults are transient and there is no need to operate the distance relays or to trip circuit breakers. These transients are classified as power swing as shown in figure (33). Some conditions must be verified to detect power swing which are listed below:
• No earth fault detection (absence of zero sequence current)
• No phase-phase fault (absence of negative sequence current)
• Change in impedance with time is three-phase and less than some setting value ( R, and X).
