Lecture 26 :
Power Swing Detection, Blocking and Out-of-Step Relays
Introduction (contd..)
Out-of-Step Blocking Relays (contd..)
If the transit time, from point A to B is larger than a preset interval of the order of few cycles, the out of step blocking unit will operate auxiliary relays to block tripping of phase relays.
In case, only blocking of reclosing is required, the blocking unit will restrain automatic reclosing equipment. An out of step blocking scheme with an impedance starting relay having similar principle as described above is shown in fig 26.3.
Out-of-Step Tripping Relay
Out-of-Step tripping relay is required for controlled separation of the system into multiple islands. Out of step condition is detected by out of step tripping relay which detects presence of an unstable power swing. It then proceeds to either trip the local breaker or issue a transfer trip signal to remote breaker to separate the system at a more convenient point.
