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5.1
CALCULATION OF MDAR SETTINGS
The following MDAR setting calculations correspond
to the setting categories in the Installation Section
(4). Assume that the protected line has the following
data:
• 18.27 miles
• Line reactance 0.8 ohms/mile
• 69 kV, 60 cycles
• Positive and negative sequence impedances:
ZIL(Pri) = Z2L(Pri) = 15∠77° ohms
• Zero sequence impedance: /
Z
(pri) = 50∠73° ohms
0L
• Current Transformer Ratio (CTR):
RC = 1200/5 = 240 (Set CTR = 240)
• Voltage Transformer Ratio (VTR):
RV = 600/1 = 600
• Relay secondary ohmic impedances are:
Z = Z
x R
/R
pri
C
V
= 15 ∠ 77 ° x 240/600 = 6 ∠ 77 ° ohms
Z
= Z
1L
2L
Z
= 50∠73° x 240/600 = 20∠73° ohms
0L
5.1.1 Ratio of Zero and Positive Sequence
Impedances
ZR = Z
/Z
= 20/6 = 3.33
0L
1L
then MDAR will automatically calculate the zero se-
quence current compensation factor (k
the value of ZR, i.e.,
(
)/3Z
[
k
Z
Z
=
–
=
0
oL
1L
1L
5.1.2
Zone 1 Distance Unit Settings
A setting of 80% of the line impedance for zone-1
reach is recommended, thus the Zone-1 phase and
ground reach should be:
Z1P = 6 x 0.8 = 4.8 and
Z1G = 6 x 0.8 = 4.8
NOTE: Z1P and Z1G can be set for different val-
ues if the application is required. Refer
to Section H, Step 10 for calculation and
example.
(5/92)
Section 5. SETTING CALCULATIONS
(Set VTR = 600)
) by using
0
∠
(
) -1
]/3
ZR
GANG PANG
–
5.1.3 Zone 2 Distance Unit Settings
Generally, Zone-2 reach is set for 100% of the pro-
tected line plus 50% of the shortest adjacent line. If
the shortest (or only) adjacent line primary imped-
ance is 20 ohms, then the Zone-2 reach setting
would be:
Z2P = 6 + (20 x 0.5) x 240/600 = 10 and
Z2G = 10
NOTE: Z2P and Z2G can be set for different
values if the application is required.
5.1.4 Zone 3 Distance Unit Settings
Generally, Zone-3 reach is set for 100% of the pro-
tected line plus 100% of the longest adjacent line
emanating from the remote bus, while accounting for
the infeed from the same remote bus.
If the longest (or only) adjacent line from the remote
bus is 25 ohms primary, and the infeed effect may in-
crease its impedance by 30%, then the Zone-3
reach setting should be:
Z3P = 6 + (25 x 1.3) x 240/600 = 19 and
Z3G = 19
NOTE: Z3P and Z3G can be set for different val-
ues if the application is required.
5.1.5 Overcurrent Unit Setting
a. The low set phase overcurrent unit is used for su-
pervising the OSB, the load-loss-trip and CIF func-
tions. It should be set higher than the line charging
current and below the minimum load current.
NOTE: It should be set above the maximum
tapped load current if applicable.
Assume that the line charging current is negligible
for this line section, and the minimum load current is
2.0 A secondary, then the low set phase overcurrent
unit setting should be:
IL = 1
b. The low-set ground overcurrent unit is used for
supervising the reverse directional overcurrent
ground unit (RDOG). It should be set as sensitive as
possible. A setting of 0.5 amperes is recommended:
IOS = 0.5
I.L. 40-385.1B
5-1
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