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Once a power swing is detected, if this trajectory enters the inner blinder, it is identified as an unstable swing, whereas, if it leaves the outer blinder without entering the inner blinder, it is identified as a stable swing, as shown in the figure below.

Model Description

Image Added


The mask of the ePHASORSIM Double Blinder OOS Relay model is as shown belowabove. In order to calculate the positive sequence impedance trajectory, the relay requires the voltage and current magnitude as well as angle in p.u.

When an unstable swing is detected the OOS signal becomes TRUE. the Reset pin is 1, it resets the output signals to normal condition.


The out-of-step trip signal OST is made inverse of the OOS signal for this model to make it compatible with the available I/O 'status' pin of Positive Sequence Components. Thus, when an When unstable swing is detected, OST becomes FALSE causing the status pin to make the component out-of-service.

The Reset pin can be used to reset the output values.

Image Removedthe output changes as follows:

Relay Logic

Normal condition01
OOS detected10


The settings for this the OOS relay can be summarized as follows:

Blinder Angle (deg)

The blinder angle of inclination in degrees (refer to relay characteristic figure above).

Inner Blinder (p.u.)

The perpendicular distance of inner blinder from ZTotal (refer to relay characteristic figure above).
Outer Blinder (p.u.)The perpendicular distance of outer blinder from ZTotal (refer to relay characteristic figure above).
PSB Delay (ms)The threshold time delay to distinguish between fault and power swing.
OOS Tripping logicThe OST can be set to '0' for Trip on-the-way-in (TOWI), i.e. when the trajectory enters the inner blinder, or to '1' for Trip on-the-way-out (TOWO), i.e. when the trajectory leaves the inner blinder.
Number of RelaysSpecifies the number of relays to be modeled. This relay model can take vector inputs, and thus, can be used as more than one relay.


See inside the subsystem Power System Protection Relays in demo PHASOR-02.