I.L. 40-385.5
13-1
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:
Z
1L(Pri)
= Z
2L(Pri)
= 15
∠
77˚ ohms
Zero sequence impedance: Z
oL(pri)
= 50
∠
73˚ ohms.
Current transformer ratio: R
C
= 1200/5 = 240,
Set MDAR (REL-300) CTR = 240
Voltage transformer ratio: R
V
= 600/1 = 600,
Set MDAR (REL-300) 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.
13.1 Calculations and settings:
(a)
The ratio of zero and positive sequence imped-
ances
ZR = Z
0L
/ Z
1L
= 20/6 = 3.33,
Set MDAR (REL-300) ZR = 3.3,
PANG = 77,
GANG = 73.
then, MDAR (REL-300) will automatically cal-
culate the zero sequence current compensa-
tion factor k
o
by using the value of ZR, PANG
and GANG, i.e.
k
o
= (Z
0L
- Z
1L
)/Z
1L
= (ZR/PANG-GANG - 1)
(b)
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
Set MDAR (REL-300) Z1P = Z1G = 4.80
Note:
Z1P and Z1G can be set for different val-
ues as the application requires. Refer to
section H, step 10 for calculation and ex-
ample. Either Z1P or Z1G can be disabled
independently by setting it to OUT posi-
tion if this function is not needed.
(c)
Zone-2 distance units settings:
Generally, Zone-2 reach is set to underreach
the shortest adjacent line off the remote bus. A
practical setting is set for 100% of the pro-
tected line plus 50% of the shortest adjacent
line off the remote bus. For this example, if the
shortest adjacent line primary impedance is 20
ohms, then the Zone-2 reach setting would be:
Z2P = 6 + (20 x 0.5) x 240/600 = 10 and
Z2G = 10
Set MDAR (REL-300) Z2P = Z2G = 10.00
Note:
Z2P and Z2G can be set for different val-
ues as the application requires. Either Z2P
or Z2G can be disabled independently by
setting it to OUT position if this function is
not needed.
(d)
Zone-3 distance unit settings:
Generally, Zone-3 reach is set to underreach of
the shortest zone-2 reach of the adjacent line
off the remote bus. A practical setting is set for
100% of the protected line plus 100% of the
shortest adjacent line off the remote bus. For
example, if the shortest zone-2 reach off the
remote bus is 25 ohms primary, and infeed
effect may increase its impedance by 30%,
then the Zone-3 reach setting should be:
Z3P = 6 + (25 x 1.3) x240/600 = 19 and
Z3G = 19
Set MDAR (REL-300) Z3P = Z3G = 19.00
Note:
Z3P and Z3G can be set for different val-
ues as the application requires. Either Z3P
or Z3G can be disabled independently by
setting it to OUT position if this function is
not needed.
(e)
Pilot distance unit settings:
The pilot zone distance phase and ground
Section 13. MDAR (REL-300) SETTING CALCULATIONS
AND SELECTIONS
