Toshiba GR200 Series Instruction Manual page 140

Line differential protection ied

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Common application for ZS and ZG

Applications in ZS and ZG are divided into common features and special features. Each feature

secures this distance protection function.

Power swing block

Operation of power swing block (PSB)

Power swings occur when the output voltages of generators located at different points in the

power system slip relative to one another because of system instabilities. This may be caused

by sudden changes in load magnitude or direction, or by power system faults and their

subsequent clearance. During the course of such a power swing, the impedance locus seen by

the distance protection relay may move (relatively slowly) from the load area into the operating

region of the distance protection. Actually, the relay may see this phenomenon as a three-phase

fault condition and may issue a trip signal if no countermeasure is applied. The majority of

power swings are transient and the power system recovers after a short period. Since a trip

signal from the relay is undesirable in such cases, the function of power swing blocking (PSB)

is provided enabling the operation of the distance protection to be blocked during the power

swing. Figure 2.10-24 illustrates a typical impedance locus as seen by the relay during the

transient power swing.

Figure 2.10-24 Impedance locus during transient power swing

As shown in Figure 2.10-25 (a), for ZS, power swing blocking elements (PSBSOUT and

PSBSIN) are formed as shown in the shaded area. As shown in Figure 2.10-25 (b), for ZG, the

PSBGOUT and PSBGIN elements are provided with the similar characteristic and feature.

Both PSB (PSBS and PSBG) functions do not operate when an earth fault overcurrent (EFL)

element or a negative-sequence phase overcurrent (OCN-PS) element is operating. Note that

the EFL and OCN-PS thresholds are defined with VCT rated value multiplied by 0.2 (i.e.,

secondary rated 1A×0.2 or 5A×0.2).

Distance protection zone (Mho char.)

Impedance locus

during transient

6F2S1914 (0.49)

GRL200 (Soft 033 & 037)

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