Alstom SHPM 101 - 19.17 Selecting Zone 3 Reach; 19.18 Ground fault compensation settings

SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 23 of 27
19.17 Selecting Zone 3 Reach
Blocking scheme is to be used so reverse Zone 3 reach should be set to Zone 2
reach of remote end relay (at MARCH 132 substation).
Zone 2 reach of remote end relay would be:
= MARCH – FEB line impedance + 50% (FEB – JAN line impedance)
= 60 x 0.44
/69° + 0.5 x 20 x 0.44 /69°
= 30.8
/69° ohms primary
Thus required Zone 3 reverse reach = 30.8
/69° ohms primary
= 12.84
/69° ohms secondary
Required Zone 3 reverse reach multiplier
=
required reverse reach
|Z
Ph
|
=
12.84 = 2.68
4.8
Select K35 = 2
K36 = 0.7
K33 = 1
K37 = 1.0
Actual Zone 3 reverse reach = (K35 + K36) K33 x K37 x Z
Ph
= 2.7 x 1 x 1 x 4.8 /70°
= 12.96
/70° ohms secondary
Required Zone 3 forward reach= minimum possible if power swing blocking is
not required
Select K31 = 1
K32 = 0.0
Actual Zone 3 forward reach = (K31 + K32) x K33 x Z
Ph
= 1.0 x 1 x 4.8 /70°
= 4.8
/70° ohms secondary
Alternatively if power swing blocking is required, the required Zone 3 forward
reach ≥120% of Zone 2 forward reach. Use of the Zone 3 lenticular settings may
be required to prevent load impedance encroaching on the Zone 3 and power
swing blocking impedance characteristics.
19.18 Ground fault compensation settings
Ground loop impedance of line Z
LE
= (1+K
N)
Z
L1
where K
N
=
Z
L0
– Z
L1
3Z
L1
Neutral impedance coarse setting = Z
N
= K
N
Z
Ph
Z
LO
– Z
L1
= (0.34 + j1.03) – (0.16 + j0.41)
= (0.18 + j0.62) = 0.65
/73.8°
K
N
= 0.65 /73.8° = 0.492 /4.8° (49% compensation)
3 x 0.44
/69°