Minimum Clearance in Substation:
Voltage Highest Lighting Switching Minimum Clearance Safety Ground
Voltage Impulse Impulse Clearance(Mt) Clearance(Mt)
Level Level
(Kvp) (Kvp) Phase- Phase-
Earth Phase
11KV 12KV 70 0.178 0.229 2.600 3.700
33KV 36KV 170 0.320 0.320 2.800 3.700
132KV 145KV 550 1.100 1.100 3.700 4.600
650 1.100 1.100 2.700 4.600
220KV 245KV 950 1.900 1.900 4.300 5.500
1050 1.900 1.900 4.300 5.500
400KV 420KV 1425 1050(P-E) 3.400 4.200 6.400 8.000
Electrical Clearance in Substation:
Voltage Height of Height of Bay Width Phase- BetweenEquipment Earth
I Bay II Bay (Mt) Phase Wire
From From (Mt) From
Ground Ground Ground
(Mt) (Mt)
132KV 8.0 – 11.0 3.0 3.0 10.5
(Single)
220KV 12.5 – 18 4.5 4.5 15.5
(Single)
220KV 18.5 25 25 4.5 4.5 28.5
(Double)
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 Main Bus Take of Elevation
Elevation (Meter) (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
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 Length (mm) No of Disc for Tension Length in (mm)
String String
66KV 5 965 6 1070
132KV 9 1255 10 1820
220KV 14 1915 15 2915
400KV 23 3850 2 X 23 5450
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 Horizontal Total Height From Ground(Mt)
(Mt) Space(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 3 O/L relays + 1 E/L 2 O/L relays + 1 E/L Buchholz, OLTC Buchholz, OT, WT
MVA relay relay
132/33/11KV above 8 3 O/L relays + 1 dir. 3 O/L relays + 1 E/L Differential, Buchholz,
MVA and below 31.5 E/L relay relay OLTCBuchholz, OT, WT
MVA
132/33KV, 31.5 MVA & 3 O/L relays + 1 dir. 3 O/L relays + 1 E/L Differential, Over flux,Buchholz,
above E/L relay relay OLTC PRV, OT, WT
220/33 KV, 31.5MVA & 3 O/L relays + 1 dir. 3 O/L relays + 1 dir. Differential, Over flux,Buchholz,
50MVA 220/132KV, 100 E/L relay relay OLTC PRV, OT, WT
MVA
400/220KV 315MVA 3 directional O/L 3 directional O/L Differential, Over flux,Buchholz,
relays (with dir. relays (with dir. OLTC PRV, OT, WT and overload
High set) +1 High set)+1 (alarm) relay
directional E/L directional E/L
relays. Restricted relays. Restricted
E/F relay + 3 E/F relay
Directional O/L
relays for action
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
