Electrical Thumb Rules-(Part 4)

Sub Station Capacity & 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)

 Sub Station Capacity & 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

 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

 Bus bar Ampere Rating:

For Phase Bus bar	Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.
For Phase Bus bar	Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch
For Neutral Bus bar	Same as Phase Bus bar up to 200 Amp than Size of Neutral Bus bar is at least half of Phase Bus bar.

 Bus bar Spacing:

Between Phase and Earth	26mm (Min)
Between Phase and Phase	32mm (Min)
Bus bar Support between Two Insulator	250mm.

 Sound Level of Diesel Generator (ANSI 89.2&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

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

Standard Size of MCB/MCCB/ELCB/RCCB/SFU/Fuse:

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