The D90
Plus
Line Protection System and D60 Line Distance
Relay use simple, dedicated control logic for single pole tripping
applications. This control logic uses a Phase Selector, Trip Output
and Open Pole Detector in conjunction with other elements as
shown in the simplified block diagram.
The Trip Output is the central logic of single pole tripping. The Trip
Output combines information from the Open Pole Detector, Phase
Selector, and protection elements to issue a single pole or three
pole trip, and also to initiate automatic reclosing and breaker
failure. The Phase Selector is the key element for maintaining the
security of single pole tripping applications, quickly and accurately
identifying the faulted phase or phases based on measured
currents and voltages, by looking at the phase angles between
the positive sequence, negative-sequence, and zero-sequence
components.
The Open Pole Detector ensures the relay operates correctly during
a single pole trip, placing the relay in an open pole condition when
a single pole trip command is issued, or one pole of the circuit
breaker is open. The Open Pole Detector asserts on a single pole
trip command, before the circuit breaker pole actually opens, to
block protection elements that may misoperate under an open
pole condition, such as negative sequence elements, undervoltage