Toshiba GRL100-701B Instruction Manual page 426

2. Distance protection
2.1 Power System Data
[Example system]
• Line impedance of A s/s - Bs/s
- Positive sequence impedance: 0.0197 + j0.2747 (ohms/km)
- Zero sequence impedance:
- Mutual impedance:
• Back impedance
- A s/s: 0.94 (%pu) at 100MVA base
- B s/s: 0.94 (%pu) at 100MVA base
• Normal load current:
• Minimum fault current: 2.05kA
2.2 Relay Setting
- Relay application:
Relay type:
Protection scheme: BOP (Blocking overreach protection), 3 zone time-stepped distance
Autoreclose mode:
2.3 Setting Calculation
Normal load current
To calculate load current, back impedance is converted from a percent unit value to an impedance
value.
Base impedance Zbase = (Vbase)
Therefore, load current I L is:
I L = (Source voltage)/(A s/s back impedance + Line impedance + B s/s impedance)
= (150kV/ 3 )/(0.94 × 75 + 16.8 × (0.0197
= 594.7A
A s/s
Line length: 16.8km
CT: 600/5A
VT: 150kV/ 3 : 110V/ 3
0.4970 + j1.4387 (ohms/km)
0.0212 + j0.3729 (ohms/km)
594.7A
GRL100-701
protection
1 + 3
2
/VAbase
2
= (150kV/ 3 ) /100MVA
= 75 ohms
 425 
B s/s
CT: 600/5A
VT: 150kV/ 3 : 110V/ 3
2 2
) + 0.94 × 75)
+ 0.2747
6 F 2 S 0 8 5 0