Direction impedance relay why there is a dead zone?
The characteristic circuit of the direction impedance relay passes through the origin, and when the short circuit occurs on the protection outlet, the residual voltage on the line is 0, and the amplitude and phase can not be compared. Therefore, the protection can not be performed.
Solution:
The elimination method uses a memory circuit or introduces a third phase voltage.
Get the polarization voltage
(1) the use of R, L, C circuit constitutes a memory circuit
(2) the introduction of non-fault phase voltage
Full impedance relay without voltage dead zone, because the impedance of the origin of the coordinates contained in the action impedance circle, even if the protection of the installation near the three-phase short-circuit residual voltage is zero, the measured impedance is zero in the coordinates of the origin, also belong to the action area, to protect the correct action The
Directional impedance relay causes dead zone:
The residual voltage on the faulty line bus will be reduced to zero when a phase short circuit occurs at the outlet in the positive direction of the protection installation site. At this point, the direction of the impedance relay will be added to the voltage can not be zero, resulting in the protection device dead zone.
