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the power swing remains within the shaded area of the rectangle between the outer and inner
elements. A delayed pick-up timer, [TPSBS] is initiated when the locus passes through the
PSBSOUT element and continues until the PSBSIN element operates in order to measure the
time duration for the locus to pass through the shaded area. If this time duration is longer
than the set value of the delayed pick-up timer [TPSBS], the PSBS element will operate to
block the operation of the distance protection trip signal.
Other than the power swing condition, measured impedance locus may stay in the PSBS
zone for a certain time which is much longer than the PSBS detection timer [TPSBS]. In this
case, the PSBS output can be reset forcibly when the locus remains in the PSBS zone for
another timer setting [TPSBSFR] and scheme switch [PSBSFR] is set to On.
If PSB operation is not required when a fault is occurring during the power swing event,
set On for the scheme switch [PSBSRS]; accordingly, PSB operation cannot work when the
fault is detected by the operation of EFL or OCN-PS element (i.e., ZS/ZG element is able to
work even if the PSB operates). It is also possible to remove the PSB operation by utilizing an
external reset signal, which can be injected at PLC connection point ‘PSBS F.RESET’.
Another delayed timer resets the trip block signal that is generated by the PSBS element
when the power swing is detected after the PSBSOUT operation is removed; 500ms is the value
set for the delayed pick-up timer.
Similarly, a PSB element is also provided for ZG and its operation is termed as PSBG
(See Figure 2.10-29). The setting of PSBGs is similar to those of PSBSs.
Figure 2.10-28 PSBS logic
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