I.L. 40-386.3
(10/94) 3-3
• Zero sequence impedance: /
Z
0L
(pri) = 50∠73° ohms
• Current Transformer Ratio (CTR):
RC = 1200/5 = 240 (Set CTR = 240)
• Voltage Transformer Ratio (VTR):
RV = 600/1 = 600(Set VTR = 600)
Relay secondary ohmic impedances are:
Z= Z
pri
x R
C
/R
V
Z
1L
= Z
2L
= 15
∠
77
°
x 240/600 = 6
∠
77
°
ohms
Z
0L
= 50∠73° x 240/600 = 20∠73° ohms
3.2.1 Ratio of Zero and Positive Sequence Impedances (ZR)
ZR = Z
0L
/Z
1L
= 20/6 = 3.33
Then REL 301/302 will automatically calculate the zero sequence current compensa-
tion factor (k
0
) by using the value of Z
OL
/Z
IL
, i.e.,
NOTE: The setting range of ZOL/ZIL has been expanded 0.1 - 7.0 to 0.1 - 10.
Also the setting ranges of Ang Pos. (Positive sequence line impedance
angle) and Ang Zero (Zero sequence line impedance angle) have been ex-
panded from 40° -90° to 10° -90° as well. These changes were made to
accommodate a wide variety of system components and configurations.
However, the selection of each setting has to be carefully considered if
the maximum fault current is 200 Amperes (secondary or above).
If the maximum fault current is 200 Amperes (secondary) the following
restrictions must be observed:
ZOL/ZIL less than or equal to 7.5
The setting difference of |Ang Pos| - |Ang Zero| = 50 or less
If the maximum fault current is less than 200 Amperes (secondary)
these restrictions do not apply.
3.2.2 Zone1 Distance Settings
A setting of 80% of the line impedance for Zone1 reach is recommended, thus the
Zone1 phase and ground reach should be
Zone1 Ø = 6 x 0.8 = 4.8 and
Zone1 G = 6 x 0.8 = 4.8
NOTE: Zone1 Ø and Zone1 G can be set for different values if the applica-
tion is required.
As stated above, start with a setting of 80% of the line impedance for the Zone1 reach
setting. Adjustment of the Zone1 reach (line percentage) should be considered if any
of the following are true:
k
0
= Z
0L
Z
1L
–()/3Z
1L
= ZR GANG PANG–1–()∠[]/3
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