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X
θ 2
(a) Z1 and Z1X
The setting of θ1(Z1θ1) and θ2(Z1θ2) are set to the following:
-1
Z1θ2 < tan
( X / R
F
Where,
X = reactance component
R
= fault resistance
F
-1
Z1θ1 < tan
{I
/ (I
Lmax
I
= maximum load current
Lmax
I
= minimum fault current
Fmin
Blinder element
The blinder element is commonly applicable to Z1, Z2, Z3, ZR and Z4. As shown in Figure
2.16.3.9, the blinder element provides the forward blinder and the reverse blinder. The operating
area of the forward blinder is the zone enclosed by the lines BFR and BFL, and that of the reverse
blinder is the zone enclosed by the lines BRR and BRL. The BFR has an angle θ of 75° to the
R-axis and BFL 90° to 135°. The angle of BRL is linked with that of BFL.
X
BFL
X
θ
(a) Forward blinder
The characteristic of the BFR is obtained by the following equation.
X ≥ (R − Rs) tan 75°
where,
θ 1
R
Figure 2.16.3.8 Reactance Element
)
+ I
)}
Lmax
Fmin
BFR
75°
R
Rs
R
BRR
Figure 2.16.3.9 Blinder element
139
X
90 °
(b) Z2 and ZF
X
-Rs
75°
(b)
Reverse blinder
6 F 2 S 0 8 5 0
R
Rs
R
θ
BRL
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