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2.4 Minimum fault current
The minimum fault current I fmin on a protected transmission line is the current of the phase to
earth fault on the nearest remote terminal.
A s/s
To calculate I fmin , zero sequence earth fault current (I o ), positive sequence earth fault current (I 1 )
and negative earth fault current (I 2 ) are calculated as follows:
I 0 = I 1 = I 2 = (Source voltage)/{(Back impedance of A s/s)
= (150kV/ 3 )/{(0.94 × 75) + 16.8 × (0.4970
= 822.28A
So,
I fmin = I 0 + I 1 + I 2 = 3 × 822.28 = 2.47kA
*Note:
Assuming that positive sequence impedance = negative sequence impedance.
2.5 Scheme setting
Element
CRSCM
DISCR
DEFCR
ZS-C
ZG-C
CHSEL
BOSW
ZONESEL
ECHO
WKIT
CH-DEF
PSB-Z1
PSB-Z2
PSB-Z3
PSB-CR
PSB-ZR
Line length: 16.8km
GRL100
+ (Transmission line zero sequence impedance)
+ (Transmission line positive sequence impedance) × 2*}
+ 2 × 16.8 × (0.0197
Contents
Command protection scheme selection
Distance carrier
DEF carrier
Mho or Quadrilateral characteristic
Mho or Quadrilateral characteristic
Carrier channel configuration
Carrier sending signal
Carrier control element
ECHO carrier send
Weak carrier trip
DEF carrier channel
PSB for Z1 elements
PSB for Z2 elements
PSB for Z3 elements
PSB for carrier trip
PSB for ZR elements
426
B s/s
Earth fault
2
2
+ 1.4387
)
2
2
+ 0.2747
) }
Setting
BOP
ON
OFF
Mho or Quad (Note *1)
Mho or Quad (Note *1)
SINGLE
A
Z2
ON
ON
--
ON
ON
ON
ON
OFF
6 F 2 S 0 8 5 0
M
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