Electrical Thumb Rules You MUST Follow - part 4 (on photo: distribution substation bus on a clear night in February by Eli Nelson) at Flickr
Continued from: Electrical Thumb Rules You MUST Follow (Part 3)
Eight rules to follow:
- Substation Capacity and Short Circuit Current Capacity (As per GERC)
- Substation Capacity and Short Circuit Current Capacity (As per Central Electricity Authority)
- Minimum Ground Clearance and Fault Clearing Time
- Busbar Ampere Rating
- Busbar Spacing
- Sound Level of Diesel Generator (ANSI 89.2 and NEMA 51.20)
- IR Value of Transformer
- Standard Size of MCB, MCCB, ELCB, RCCB, SFU and Fuse
1. Substation Capacity and Short Circuit Current Capacity
| As per GERC | ||
| Voltage | Sub Station Capacity | Short Circuit Current |
| 400 KV | Up to 1000 MVA | 40 KA (1 to 3 Sec) |
| 220 KV | Up to 320 MVA | 40 KA (1 to 3 Sec) |
| 132 KV | Up to 150 MVA | 32 KA (1 to 3 Sec) |
| 66 KV | Up to 80 MVA | 25 KA (1 to 3 Sec) |
| 33 KV | 1.5 MVA to 5 MVA | 35 KA (Urban) (1 to 3 Sec) |
| 11 KV | 150 KVA to 1.5 MVA | 25 KA (Rural) (1 to 3 Sec) |
| 415 V | 6 KVA to 150 KVA | 10 KA (1 to 3 Sec) |
| 220 V | Up to 6 KVA | 6 KA (1 to 3 Sec) |
2. Substation Capacity and Short Circuit Current Capacity
| As per Central Electricity Authority | ||
| Voltage | Sub Station Capacity | Short Circuit Current |
| 765 KV | 4500 MVA | 31.5 KA for 1 Sec |
| 400 KV | 1500 MVA | 31.5 KA for 1 Sec |
| 220 KV | 500 MVA | 40 KA for 1 Sec |
| 110/132 KV | 150 MVA | 40 KA or 50 KA for 1 Sec |
| 66 KV | 75 MVA | 40 KA or 50 KA for 1 Sec |
3. Minimum Ground Clearance and Fault Clearing Time
| Voltage | Min. Ground Clearance | Fault Clear Time |
| 400 KV | 8.8 Meter | 100 mille second |
| 220 KV | 8.0 Meter | 120 mille second |
| 132 KV | 6.1 Meter | 160 mille second |
| 66 KV | 5.1 Meter | 300 mille second |
| 33 KV | 3.7 Meter | - |
| 11 KV | 2.7 Meter | - |
4. Busbar Ampere Rating
| For Phase Busbar | Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch. |
| For Phase Busbar | Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch |
| For Neutral Busbar | Same as Phase Busbar up to 200 Amp than Size of Neutral Busbar is at least half of Phase Busbar. |
5. Busbar Spacing
| Between Phase and Earth | 26mm (Min) |
| Between Phase and Phase | 32mm (Min) |
| Busbar Support between Two Insulator | 250mm. |
6. Sound Level of Diesel Generator (ANSI 89.2 and NEMA 51.20)
| KVA | Max. Sound Level |
| <9 KVA | 40 DB |
| 10 KVA to 50 KVA | 45 DB |
| 51 KVA to 150 KVA | 50 DB |
| 151 KVA to 300 KVA | 55 DB |
| 301 KVA to 500 KVA | 60 DB |
7. IR Value of Transformer
| IR Value of Transformer | |||
| Voltage | 30°C | 40°C | 50°C |
| >66KV | 600MΩ | 300MΩ | 150MΩ |
| 22KV to 33KV | 500MΩ | 250MΩ | 125MΩ |
| 6.6KV to 11KV | 400MΩ | 200MΩ | 100MΩ |
| <6.6KV | 200MΩ | 100MΩ | 50MΩ |
| 415V | 100MΩ | 50MΩ | 20MΩ |
8. Standard Size of MCB, MCCB, ELCB, RCCB, SFU and Fuse
| MCB, MCCB, ELCB, RCCB, SFU, Fuse – Standard Ratings | |
| MCB | Up to 63 Amp (80Amp and 100 Amp a per Request) |
| MCCB | Up to 1600 Amp (2000 Amp as per Request) |
| ACB | Above 1000 Amp |
| MCB Rating | 6A,10A,16A,20A,32A,40A,50A,63A |
| MCCB Rating | 0.5A,1A,2A,4A,6A,10A,16A,20A,32A,40A,50A,63A,80A,100A (Domestic Max 6A) |
| RCCB/ELCB | 6A,10A,16A,20A,32A,40A,50A,63A,80A,100A |
| Sen. of ELCB | 30ma (Domestic),100ma (Industrial),300ma |
| DPIC (Double Pole Iron Clad) main switch | 5A,15A,30 A for 250V |
| TPIC (Triple Pole Iron Clad) main switch | 30A, 60A, 100A, 200 A For 500 V |
| DPMCB | 5A, 10A, 16A, 32A and 63 A for 250V |
| TPMCCB | 100A,200A, 300Aand 500 A For 660 V |
| TPN main switch | 30A, 60A, 100A, 200A, 300 A For 500 V |
| TPNMCB | 16A, 32A,63A For 500 V, beyond this TPNMCCB: 100A, 200A, 300A, 500 A For 660 V |
| TPN Fuse Unit (Rewirable) | 16A,32A,63A,100A,200A |
| Change over switch (Off Load) | 32A,63A,100A,200A,300A,400A,630A,800A |
| SFU (Switch Fuse Unit) | 32A,63A,100A,125A,160A,200A,250A,315A,400A,630A |
| HRC Fuse TPN (Bakelite) | 125A,160A,200A,250A,400A.630A |
| HRC Fuse DPN (Bakelite) | 16A,32A,63A |
| MCB/MCCB/ELCB Termination Wire / Cable | |
| Up to 20A MCB | Max. 25 Sq.mm |
| 20A to 63A MCB | Max. 35 Sq.mm |
| MCCB | Max. 25 Sq.mm |
| 6A to 45A ELCB | 16 Sq.mm |
| 24A to 63A ELCB | 35 Sq.mm |
| 80A to 100A ELCB | 50 Sq.mm |