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 |
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Excellent information, which will usefull in daily working.
Dear Sir,
the minimum Ground clearances to Ground for the voltages 11kV to 132kV seem to be too small. They should be 5.6 for 11kV and 22kV and 6.5 for 33kV and 6.7 for 66kV and 132kV. The condition should be @ he maximum operating temperature of 75 Deg. C.
Sorry Jignesh, I just found all the past copies, Thanks
Hello Jignesh, thank you for the very interesting info. Where can I find parts 1 ; 2 & 3 ?
Its too useful n knowledgeable thanku
You are a motivation for many of unsuccessful electrical engineers
Hello dear,
you have a grand collection of information, very useful one for the freshers as well as for practicing engineers
Hi mr. Parmar.Please send to me your experiences via my email [email protected] regards.
Excelleng