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2.8 Zero sequence compensation
In the GRZ100, vector type zero sequence compensation is applied to Zone 1 and Zone 2, and the
compensation factor is given in the resistive and reactive components independently.
Step 1
Calculate the positive, zero sequence impedance and mutual impedance:
Z 1 = [R 1 : 0.0197] + j[X 1 : 0.2747] (ohms)
Z 0 = [R 0 : 0.497] + j[X 0 : 1.4287] (ohms)
Z m = [R m : 0.0212] + j[X m : 0.3729] (ohms)
Step 2
Calculate the zero and mutual sequence compensation factor setting according to the following
equations:
K RS = R 0 /R 1 × 100 = 0.497/0.0197 = 2523*
K XS = X 0 /X 1 × 100 = 1.4387/0.2747 = 524
K Rm = R m /R 1 × 100 = 0.0212/0.0197 = 108
K Xm = X m /X 1 × 100 = 0.3729/0.2747 = 136
*Note:
If the calculated value exceeds 1000, then a setting of 1000 should be applied, this being
considered to be the maximum practical value.
2.9 Current setting
a.
Definite time earth fault protection (EF)
The EF element may be used either to provide back-up earth fault protection or, alternatively,
open circuit protection. For example, to detect open faults of the CT circuit, the operating
value of the detector should be lower than the normal load current on the line:
EF ≤ (normal load current/CT ratio) × 0.5
= (594.7 × 5/600) × 0.5
= 2.48A
b.
Directional earth fault element (DEF)
The DEF element should not be operated by the unbalance current or voltage present in
normal conditions. It is recommended to set the current and voltage after measuring the actual
unbalance residual current and voltage on the site.
DEFFI, DEFRI > Max. zero sequence current (3I o ) in normal conditions
Element
Setting
K RS
1000
K XS
524
K Rm
108
K Xm
136
Element
Setting (A)
EF
2.4
430
6 F 2 S 0 8 5 0
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