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6 F 2 S 0 8 5 0
I d ≥ (1/6)I r + (5/6)DIFGI
where DIFGI is a setting and defines the minimum residual fault current.
2.16.3 Distance Measuring Elements Z1, Z2, Z3, Z4, ZR and PSB
The GRL100 provides eight distance measuring zones with mho-based characteristics or
quadrilateral characteristics.
As shown in Figure 2.16.3.1, mho-based zone characteristics are composed of mho element, offset
mho element, impedance element, reactance element, and blinder element for phase fault
protection and earth fault protection.
Z1 (zone 1) and Z2 (zone 2) are a combination of the reactance element, mho element and blinder
element.
Z3 (zone 3), ZR (reverse zone R) and Z4 use the mho element and blinder element, but Z4 for
phase faults uses the offset mho element instead of mho element. This makes it possible to detect a
reverse close-up fault at high speed if Z4 for phase faults is used for the command protection.
The blinder element is normally used to restrict the resistive reach of the mho or offset mho
element if their operating range encroaches upon the load impedance.
The blinder element (BFR) can be provided for each forward zone. The setting of blinder element
can be set independently or set common to forward zones by the scheme switch [BLZONE].
Z3
Z3
Z2
Z2
Z1
Z1
Z1Sθ1
Z1Gθ1
BRR
BRR
75°
75°
BFR1,2,3
BFR1,2,3
Z3Sθ
Z3Gθ
ZR
ZR
Z4
Z4
(
a) Phase fault element
(b) Earth fault element
Figure 2.16.3.1 Mho-based Characteristics
As shown in Figure 2.16.3.2, quadrilateral zone characteristics are composed of reactance
element, directional element and blinder element. Z4 for phase faults uses the offset directional
element to ensure a reverse close-up fault detection.
The forward offset reach of reverse zone ZR for both mho-based and quadrilateral characteristics
is fixed as 7.5 ohms for 1A rating or 1.5 ohms for 5A rating. However, when they are used for
back-up tripping ([ZRTP]= "ON"), the forward offset reach is limited to the zone 1 reach setting,
as shown in Figure 2.16.3.3. Z4, on the other hand, is normally used to provide blocking in the
command schemes, and its offset is not limited by the zone 1 reach setting. It is fixed at 7.5Ω (or
1.5Ω) in order to give reliable, fast blocking for a close-up reverse fault.
134
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