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(iv) Element equations for blinder characteristic
The characteristics about the forward and the reverse blinders are provided as shown in Figure
2.10-8. The operating area (Figure 2.10-8.a) is enclosed with forward blinders (BFR and BFL
lines); the BFL line is placed as the mirror image of the BFR line. Similarly, the operating area
(Figure 2.10-8.b) is enclosed with the reverse blinders (BRR and BRL lines).
Figure 2.10-8 Blinder elements
The characteristics about the BFR and BRR lines are obtained by Equations (2.10-25)
and Equation (2.10-26), respectively:
where,
R = resistance component of measured impedance
X = reactance component of measured impedance
Rs = reach setting
If the minimum load impedance (Z
Lmin
) is predictable, we can take the Rs setting for
the worst case such that the load angle is of 30° and the margin is of 80% in case of θ=75°;
Equation (2.10-27) can be applied to obtain the resistive setting for the blinder element:
(v) Element equations for directional characteristic
Figure 2.10-9 illustrates that a directional element used for the element in Quadrilateral
characteristic. The characteristic of the directional element is obtained using Equation
(2.10-28); the polarizing voltage (Vp) is the same one as employed in the Mho characteristic.
where,
I = fault current
Vp = polarizing voltage
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