Sub Station Abstracts
Sub Station Equipments and Safety Clearance
Rating of Lighting Arrestor:
- Size of L.A = 1.5 X Phase to Earth Voltage OR
- Size of L.A =1.5 X system Voltage/1.732 OR
- Size of L.A = 0.81 X highest System Voltage
Lighting Arrestor Protection Radius:
- Protection Radius (Rp) = Sqrt (H X (2D-H)+L(2D+L))
- H= Actual Height of L.A
- D= 20 meter, 40 meter or 60 meter
- L= V X T (T=Discharge Time & V= 1m/ms)
Creepage Distance:
- 18 mm to 22 mm /KV for Moderate Polluted Air.
- 25 mm to 33 mm /KV for Heavily Polluted Air.
- In HVDC System The value is double from above value.
Lighting Arrestor Rating:
Rated Voltage | Highest Voltage | L.A Rating |
132kv | 145kv | 120kv To 132kv |
220kv | 245kv | 198kv To 216kv |
400kv | 420kv | 336kv |
Location of Lighting Arrestor:
Rated Voltage | Max Distance from Equipment |
132kv | 35 meter To 45 meter |
220kv | Closed To Transformer |
400kv | Closed To Transformer |
Size of Corona Ring:
Rated Voltage | Size of Corona Ring |
Less than 170 KV | 160mm Ring Put on HV end |
170KV To 275KV | 350mm Ring Put on HV end |
More than 275KV | 450mm Ring Put on HV end |
More than 275KV | 350mm Ring Put on HV end |
Capacity of Sub Station as per GERC:
Size of S/S | Electrical Load |
66 KV | 80 MVA |
132 KV | 150 MVA |
220 KV | 320 MVA |
400 KV | 1000 MVA |
Breaking / Short Circuit Capacity of Sub Station:
Size of S/S | Short Circuit Current |
66 KV | 25 KAmp for 1 or 3 sec |
132 KV | 31.5 KAmp for 1 or 3 sec |
220 KV | 40 KAmp for 1 or 3 sec |
400 KV | 40 KAmp for 1 or 3 sec |
Fault Clear Time:
Size of S/S | Fault Clear Time |
66 KV | 300 mili Sec |
132 KV | 160 mili Sec |
220 KV | 120 mili Sec |
400 KV | 100 mili Sec |
Normal Type of Conductors:
Voltage | Main Bus | Auxiliary Bus |
11KV | Twin ACSR Zebra | ACSR Zebra |
33KV | ACSR Zebra | ACSR Zebra |
132KV | ACSR Zebra | ACSR Panthers |
220KV | Twin ACSR Zebra | ACSR Zebra |
400KV | 1/14.2 mm Dia Alu Pipe | Twin ACSR Moose |
Number of Disc Insulator:
System | Number | Strength (KN) |
11KV | 4 | 120KN |
33KV | 4 | 120KN |
132KV | 10 | 120KN |
220KV | 14 | 70KN |
220KV (Anti Fog) | 2 X 15 | 120KN |
400KV (Anti Fog) | 2 X 25 | 120KN |
Minimum Clearance:
Voltage | Phase to Earth Wire | Phase to Phase | Section Clearance |
2.2KV | 28cm | 33cm | 27.45cm |
33KV | 380cm | 43cm | 27.7cm |
132KV | 107cm | 12cm | 25cm |
220KV | 178cm | 20.6cm | 42.8cm |
400KV | 350cm | 40cm | 65cm |
Ground Clearance:
Voltage | Meter |
33KV | 3.7meter |
66 KV | 6.1meter |
132 KV | 6.1meter |
220 KV | 7.0meter |
400 KV | 8.8meter |
Conductor Spacing:
Voltage | Highest Voltage | Lighting Impulse Level (Kvp) | Min Clearance | Ground Clearance | Safety working Clearance | |
Phase to Earth | Phase to Phase | |||||
11KV | 12kv | 70 | 178mm | 229mm | 3700mm | 2600mm |
33KV | 36kv | 170 | 320mm | 320mm | 3700mm | 2800mm |
132 KV | 145kv | 550 | 1300mm | 1300mm | 4600mm | 3700mm |
220 KV | 245kv | 950 | 2100mm | 2100mm | 5500mm | 4300mm |
400 KV | 420kv | 1425 | 3400mm | 4200mm | 8000mm | 6400mm |
Earthing Resistance Value:
Particular | Max Earthing Resistance |
Power Station | 0.5Ω |
EHT Sub Station | 1Ω |
33KV Sub Station | 2Ω |
Double Pole Structure | 5Ω |
Tower foot Resistance | 10Ω |
Distribution Transformer | 5Ω |
220KV Sub Station | 1Ω To 2Ω |
400KV Sub Station | 0.5Ω |
Losses in 11 kv Transformer at 75c (As per CBIP):
Transformer | No Load Loss(kw) | Load Loss (kw) | % Impedance |
3.15MVA | 2.9 | 20 | 6.25 |
4MVA | 3.2 | 27 | 7.15 |
5.3MVA | 3.9 | 31 | 7.15 |
6.3MVA | 4.5 | 37 | 7.15 |
Losses in 66 kv Transformer at 75c (As per CBIP):
Transformer | No Load Loss(kw) | Load Loss (kw) | % Impedance |
6.3MVA | 6 | 40 | 8.35 |
8MVA | 7.1 | 48 | 8.35 |
10MVA | 8.4 | 57 | 8.35 |
12.5MVA | 9.7 | 70 | 8.35 |
20MVA | 13 | 102 | 10.0 |
Standard Rating of 66KV Transformer (As per CBIP):
Transformer | KV | Type of Cooling |
6.3MVA | 66KV/11KV | ONAN |
8MVA | 66KV/11KV | ONAN |
10MVA | 66KV/11KV | ONAN |
12.5MVA | 66KV/11KV | ONAN / ONAF |
20MVA | 66KV/11KV | ONAN / ONAF |
% Impedance for Transformer (As per IS 2026):
33KV Transformer | 66KV Transformer | ||
MVA | %Impedance | MVA | %Impedance |
1MVA | 5% | 6.3MVA | 8.35% |
1.6MVA | 6.25% | 8MVA | 8.35% |
3.15MVA | 6.25% | 10MVA | 8.35% |
4MVA | 7.15% | 12.5MVA | 8.35% |
5MVA | 7.15% | 20MVA | 10% |
6.3MVA | 7.15% | 16MVA | 10% |
8MVA | 8.35% | 25MVA | 10% |
10MVA | 8.35% | 31.5MVA | 12.5% |
MVA | %impedance |
Less Than 1MVA | 5% |
1MVA To 2.5MVA | 6% |
2.5MVA To 5MVA | 7% |
5MVA To 7MVA | 8% |
7MVA To 12MVA | 9% |
12MVA To 30MVA | 10% |
More Than 30MVA | 12.5% |
Bus Bar Materials:
| Description | Bus Bar and Jumper Material |
| 400 kV Main Bus | 114.2 mm dia. Aluminium pipe |
| 400 kV equipment interconnection | 114.2 mm dia. Aluminium pipe |
| 400 kV overhead bus & droppers in all bays. | Twin ACSR Moose |
| 220 kV Main Bus | Quadruple / Twin ACSR Zebra / Twin AAC Tarantulla |
| 220 kV Auxiliary Bus | ACSR Zebra |
| 220 kV equipment interconnection | Twin ACSR Zebra / Single ACSR Zebra |
| 220 kV overhead bus & droppers in all bays. | Twin ACSR Zebra / Single ACSR Zebra |
| 132 kV Main Bus | ACSR Zebra |
| 132 kV Auxiliary Bus | ACSR Panther |
| 132 kV equipment interconnection | ACSR Zebra / ACSR Panther |
| 132 kV overhead bus & droppers in all bays. | ACSR Panther |
| 33 kV Main Bus | ACSR Zebra |
| 33 kV Auxiliary Bus | ACSR Zebra |
| 33 kV equipment interconnection, overhead bus and droppers: | |
| (i) Bus coupler & transformer bay | ACSR Zebra |
| (ii) Feeder bay. | ACSR Panther |
| 11 kV Main Bus | Twin ACSR Zebra |
| 11 kV Auxiliary Bus | ACSR Zebra |
| 11 kV equipment interconnection, overhead bus and droppers: | |
| (i) Transformer bay | Twin ACSR Zebra / Single ACSR Zebra |
| (ii) Bus coupler | ACSR Zebra |