Clearences

1. Electrical Clearance in Substation
APRIL 6, 2011 23 COMMENTS
Minimum Clearance in Substation:
Volta
ge
High
est
Volta
ge
Lighti
ng
Impul
se
Level
(Kvp)
Switchi
ng
Impuls
e Level
(Kvp)
Minimum
Clearance
Safety
Clearance(
Mt)
Ground
Clearance(
Mt)
Phas
e-
Eart
h
Phas
e-
Phas
e
11KV 12KV 70 0.17
8
0.22
9
2.600 3.700
33KV 36KV 170 0.32
0
0.32
0
2.800 3.700
132K
V
145K
V
550 1.10
0
1.10
0
3.700 4.600
650 1.10
0
1.10
0
2.700 4.600
220K
V
245K
V
950 1.90
0
1.90
0
4.300 5.500
1050 1.90
0
1.90
0
4.300 5.500
400K
V
420K
V
1425 1050(P
-E)
3.40
0
4.20
0
6.400 8.000
Electrical Clearance in Substation:
Voltage Height
of I
Bay
From
Groun
d (Mt)
Height
of II
Bay
From
Groun
d (Mt)
Bay
Widt
h
(Mt)
Phase
-
Phase
(Mt)
BetweenEquipme
nt
Earth
Wire
From
Groun
d
132KV
(Single)
8.0 - 11.0 3.0 3.0 10.5

2. 220KV
(Single)
12.5 - 18 4.5 4.5 15.5
220KV
(Double
)
18.5 25 25 4.5 4.5 28.5
400KV 15.6 22 22.0 7.0 >6.0 30.0
Standard Bay Widths in Meters:
Voltage Bay Width (Meter)
11KV 4.7 Meter
33KV 4.7 Meter
66KV 7.6 Meter
132KV 12.2 Meter
220KV 17 Meter
400KV 27 Meter
Standard Bus and Equipment Elevation
Voltage Equipment live
Terminal
Elevation (Meter)
Main Bus Take of
Elevation
(Meter)Low High
11 KV/33KV 2.8To 4 5.5 To6.5 9 6.5To8.5
66KV 2.8To 4 6To8 9To 10.5 9.5
132KV 3.7To5 8To9.5 13.5To14.5 12To12.5
220KV 4.9To5.5 9To13 18.5 15To18.5
400KV 8.0 15.5 - 23

3. Phase spacing for strung Bus:
Voltage Clearance
11KV 1300 mm
33KV 1300 mm
66KV 2200 mm
132KV 3000 mm
220KV 4500 mm
400KV 7000 mm
Minimum Clearance of Live Parts from Ground:
Voltage Minimum Clearance to
Ground (Mt)
Section Clearance (Mt)
11KV 3.700 2.600
33KV 3.700 2.800
66KV 4.600 3.000
132KV 4.600 3.500
220KV 5.500 4.300
400KV 8.000 7.000
Insulator String:
Voltage No of Suspension
String
Length
(mm)
No of Disc for
Tension String
Length in
(mm)
66KV 5 965 6 1070
132KV 9 1255 10 1820
220KV 14 1915 15 2915
400KV 23 3850 2 X 23 5450

4. Nominal Span:
Voltage Normal Span (Meter)
66KV 240-250-275
132KV 315-325-335
220KV 315-325-335
400KV 315-325-335
Minimum Ground Clearance:
Voltage Ground (Meter)
66KV 5.5
132KV 6.1
220KV 7.0
400KV 8.0
800KV 12.4
Indoor Substation Minimum Clearances
Distance Descriptions
0.9 Meter Horizontally between any item of equipment and thesubstation wall
0.6 Meter Horizontally between any Two items of equipment
1.2 Meter Horizontally in front of any HV switchgear

5. Clearance of Conductor on Tower
Voltage Tower
Type
Vertical
Space (Mt)
Horizontal
Space(Mt)
Total Height From
Ground(Mt)
66KV A 1.03 4.0 15.91
B 1.03 4.27 15.42
C 1.22 4.88 16.24
132KV A 7.140 2.17 23.14
B 4.2 6.29 22.06
C 4.2 7.15 22.68
D 4.2 8.8 24.06
220KV A 5.2 8.5 28.55
B 5.25 10.5 29.08
C 6.7 12.6 31.68
D
NORMS OF PROTECTION FOR EHV CLASS POWER TRANSFORMERS
Voltage ratio &
capacity
HV Side LV Side Common relays
132/33/11KV up
to 8 MVA
3 O/L relays +
1 E/L relay
2 O/L relays +
1 E/L relay
Buchholz, OLTC Buchholz,
OT, WT
132/33/11KV
above 8 MVA and
below 31.5 MVA
3 O/L relays +
1 dir. E/L relay
3 O/L relays +
1 E/L relay
Differential, Buchholz,
OLTCBuchholz, OT, WT
132/33KV, 31.5
MVA & above
3 O/L relays +
1 dir. E/L relay
3 O/L relays +
1 E/L relay
Differential, Over
flux,Buchholz, OLTC PRV,
OT, WT
220/33 KV, 3 O/L relays + 3 O/L relays + Differential, Over

6. 31.5MVA &
50MVA
220/132KV, 100
MVA
1 dir. E/L relay 1 dir. relay flux,Buchholz, OLTC PRV,
OT, WT
400/220KV
315MVA
3 directional
O/L relays
(with dir. High
set) +1
directional E/L
relays.
Restricted E/F
relay + 3
Directional
O/L relays for
action
3 directional
O/L relays
(with dir. High
set)+1
directional
E/L relays.
Restricted E/F
relay
Differential, Over
flux,Buchholz, OLTC PRV,
OT, WT and overload
(alarm) relay
The bottom most portion of any insulator or bushing in service should be at a minimum
height of 2500 mm above ground level.
Location of L.A (From T.C Bushing):
Voltage BIL KV Peak Distance (Mt)
11KV 75 12
33KV 200 15
66KV 325 24
132KV 550 35
220KV 900 To 1050 Close To T.C
400KV 1425 To 1550
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