Minimum Clearance in Substation:
Switchin
g
Impulse
Level
(Kvp)
Minimum
Clearance
Voltag
e
Highe
st
Voltag
e
Lighting
Impulse
Level
(Kvp)
11KV
12KV
70
0.178
0.229
2.600
3.700
33KV
36KV
170
0.320
0.320
2.800
3.700
550
1.100
1.100
3.700
4.600
650
1.100
1.100
2.700
4.600
950
1.900
1.900
4.300
5.500
1050
1.900
1.900
4.300
5.500
3.400
4.200
6.400
8.000
132KV 145KV
220KV 245KV
400KV 420KV 1425
1050(PE)
Phase- PhaseEarth Phase
Safety
Ground
Clearance Clearance
(Mt)
(Mt)
Electrical Clearance in Substation:
Height of
II Bay
Bay Width
From
(Mt)
Ground
(Mt)
Phase
Phase
(Mt)
Between
Equipme
nt
Earth Wire
From
Ground
132KV
8.0
(Single)
11.0
3.0
3.0
10.5
220KV
12.5
(Single)
18
4.5
4.5
15.5
220KV
(Double 18.5
)
25
25
4.5
4.5
28.5
400KV
22
22.0
7.0
>6.0
30.0
Voltage
Height
of I Bay
From
Ground
(Mt)
15.6
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
Main Bus
Terminal Elevation
Low
High
(Meter)
Take of
Elevation
(Meter)
11 KV/33KV
2.8 To 4
5.5 To
6.5
6.5To8.5
66KV
2.8 To 4
6 To 8
9To 10.5
9.5
132KV
3.7 To5
8 To
9.5
13.5To14.5
12To12.5
220KV
4.9 To5.5
9To13
18.5
15To18.5
400KV
8.0
15.5
23
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:
No of
Suspension
String
Length
(mm)
No of Disc for Length in
Tension String (mm)
66KV
965
1070
132KV
1255
10
1820
220KV
14
1915
15
2915
400KV
23
3850
2 X 23
5450
Voltage
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
Clearance of Conductor on Tower
Voltage
Tower
Type
Vertical
Space
(Mt)
Horizontal
Space(Mt)
Total Height From
Ground(Mt)
66KV
1.03
4.0
15.91
1.03
4.27
15.42
1.22
4.88
16.24
7.140
2.17
23.14
4.2
6.29
22.06
4.2
7.15
22.68
4.2
8.8
24.06
5.2
8.5
28.55
5.25
10.5
29.08
6.7
12.6
31.68
132KV
220KV
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, OLTCBuchholz, OT,
WT
132/33/11KV
3 O/L relays + 1 dir. E/L
above 8 MVA and
relay
below 31.5 MVA
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, OLTCPRV, OT,
WT
220/33 KV,
31.5MVA &
50MVA
220/132KV, 100
MVA
3 O/L relays + 1 dir. E/L
relay
3 O/L relays + 1 dir.
relay
Differential, Over
flux,Buchholz, OLTCPRV, 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, OLTCPRV, 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
400KV
1425 To 1550
Close To T.C
Minimum Electrical Clearance As Per BS:162.
INDOOR
Voltage in KV
Phase to earth in mm
Phase to phase in
mm
0.415
15.8
19.05
0.600
19.05
19.05
3.3
50.8
50.8
6.6
63.5
88.9
11
76.2
127.0
15
101.6
165.1
22
139.7
241.3
33
222.25
355.6
Minimum Electrical Clearance As Per BS:162.
OUTDOOR
Voltage in KV
Phase to earth in mm
Phase to phase in
mm
6.6
139.7
177.8
11
177.8
228.6
22
279.4
330.2
33
381
431.8
66
685.8
787.4
110
863.6
990.6
132
1066.8
1219.2
220
1778
2057.4
Minimum Working Clearance:
OUTDOOR SWITCHYARD
Voltage in KV
To ground in mm
Between section in
mm
11
2750
2500
33
3700
2800
66
4000
3000
132
4600
3500
220
5500
4500
Minimum Ground Clearance As Per IE-1957 (Rule 77)
Voltage in KV
To ground in mm
132
6.10
220
7.00
400
8.84
800
12.40
Minimum Clearance between Lines Crossing Each Other As Per IE-1957 Rules
System Voltage
132KV
220KV
400KV
800KV
Low & Medium
3.05
4.58
5.49
7.94
11-66KV
3.05
4.58
5.49
7.94
132KV
3.05
4.58
5.49
7.94
220KV
4.58
4.58
5.49
7.94
400KV
5.49
5.49
5.49
7.94
800KV
7.94
7.94
7.94
7.94
Minimum Height above Railway As Per IE-1957
Voltage
Broad Meter & Narrow Gauges
Above 66KV up to 132KV
14.60 Meter
Above 132KV up to 220KV
15.40 Meter
Above 220KV up to 400KV
17.90 Meter
Above 400KV up to 500KV
19.30 Meter
Above 500KV up to 800KV
23.40 Meter
Various Air clearances to be provided as per IE rule 64
Voltage KV
33KV
66KV
110KV
220KV
400KV
BIL (Kvp)
170
325
550
1050
1425
P-E (cm)
30
63
115
240
350
P-P(cm)
40
75
135
210
410
P-G (Meter)
3.7
4.0
4.6
5.5
8.0
Section
Clearance(Mt)
2.8
3.0
3.5
4.3
6.5
Clearances from Buildings of high and extra-high voltage lines IE Rule 80
Vertical Distance
High voltage lines up to 33KV
3.7 Meter
Extra High Voltage
3.7 Meter + Add 0.3 meter for every
additional 33KV
Horizontal clearance between the conductor and Building
High Voltage Up to 11 KV
1.2 Meter
11KV To 33KV
2.0 Meter
Extra High Voltage
2.0 Meter + Add 0.3 meter for every
additional 33KV
Clearance above ground of the lowest conductor As per IE Rule 77
Over head Line Across Street
Low and Medium Voltage
5.8 Meter
High Voltage
6.1 Meter
Over head Line Along Street (Parallel To Street)
Low and Medium Voltage
5.5 Meter
High Voltage
5.8 Meter
Over head Line Without Across or Along Street
Low/Medium /HT line up to
11KV If Bare Conductor
4.6 Meter
Low/Medium /HT line up to
11KV If Insulated Conductor
4.0 Meter
Above 11 KV Line
5.2 Meter
Above 33KV Line
5.8 Meter + Add 0.3 meter for every
additional 33KV
Clearance between conductors and Trolley / Tram wires As per IE Rule 78
Low and Medium Voltage
1.2 Meter
High Voltage Line Up to 11KV
1.8 Meter
High Voltage Line Above to 11KV
2.5 Meter
Extra High Voltage Line
3.0 Meter
Clearances from Buildings of low & medium voltage lines As Per IE Rule 79
For Flat roof, Open Balcony, Verandah Roof and lean to Roof
Line Passes Over Building Vertical Clearance
2.5 Meter
Line Passes Adjustment of Building Horizontal
Clearance
1.2 Meter
For pitched Roof
Line Passes Over Building Vertical Clearance
2.5 Meter
Line Passes Adjustment of Building Horizontal
Clearance
1.2 Meter
