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2.6 Impedance setting
Element
Z1S
Z2S
Z3S
Z3Sθ
Z4S
Z1G
Z2G
Z3G
Z3Gθ
Z4G
PSBSZ
PSBGZ
Step 1
Calculate the setting impedance from the given recommended reach point table.
Step 2
Multiply the actual impedance by the factor "k" to calculate the relay impedance:
Relay impedance = k × Actual impedance
Factor "k" is calculated as follows:
K = (CT ratio)/(VT ratio) = (600/5A)/((150kV/ 3 )/(110V)/ 3 )) = 0.088
Note *1: Z3Sθ and Z3Gθ line angle settings are applicable if [ZS-C] and [ZG-C] are set to
"Mho".
Line angle θ = tan
-1
The line angle setting is set to 85°. Alternatively set to a smaller angle (e.g. 80°) in consideration
of higher levels of fault resistance.
<Z1S, Z2S, Z3S, Z4S, Z1G, Z2G element>
Z1S, Z2S, Z3S, Z4S, Z1G, Z2G element settings are calculated as shown in the following table.
<Z3G, Z4G element>
Zero sequence current compensation is not applied to Z3 or Z4. Z3G and Z4G settings should be
larger than the calculated values because of the underreaching effect without zero sequence
current compensation.
a.
Setting condition of Z3G element:
The Z3G element must operate on all faults for which the Z2G element operates.
(lower setting limit: Z3G > Z2G)
The Z3G element must not operate on load current. (upper setting limit), so:
X3G setting = [Zline × 130%](Z2G setting) × 2.6(operating margin for no zero phase
Standard setting (Recommended)
80% of protected line reactance
120% or more of protected line reactance
100% of protected line impedance plus 150%
of next line section
Line angle setting (Note *1)
120% of Z3S
75% - 80% of protected line reactance
120% or more of protected line reactance
400% - 600% of protected line impedance
Line angle setting (Note *1)
120% of Z3G
2 ohms (5A rating)
2 ohms (5A rating)
(0.2747/0.0197) = 85.9°
428
6 F 2 S 0 8 5 0
Setting
80%
130%
300%
120% of Z3S setting
75%
130%
500%
120% of Z3G setting
2 ohms
2 ohms
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