Sub Station Abstract -(Part-2)

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 / or 800Amp / Sq.inch.
For Phase Bus bar Copper 160 Amp / 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):


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









22KV to 33KV




6.6KV to 11KV












Electrical Quick Reference-Voltage Limits

Economical Voltage for Power Transmission: 

Economic generation voltage (CBIP Manual)

Total Load

Economical Voltage

Up to 750 KVA

415 V

750 KVA to 2500 KVA

3.3 KV

2500 KVA to 5000 KVA

6.6 KV

Above 5000 KVA

11 KV or Higher

  •  Generally terminal voltage of large generators is 11 kV in India. Step up voltage depends upon Length of transmission line for interconnection with the power system and Power to be transmitted.
  • High voltage increases cost of insulation and support structures for increased clearance for air insulation but decreases size and hence Cost of conductors and line losses.
  • Many empirical relations have been evolved to approximately determine economic voltages for power evacuation. An important component in transmission lines is labor costs which are country specific.
  • An empirical relation is given below.
  • Voltage in kV (line to line) = 5.5x√0.62L + kVA/150

  • where kVA is total power to be transmitted;
  • L is length of transmission line in km.
  • American practice for economic line to line voltage kV (based on empirical formulation) is
  • Voltage in kV line to line = 5.5x√0.62L + 3P/100

  • For the purpose of standardization in India transmission lines may be classified for operating at 66 kV and above. 33 kV is sub transmission, 11 kV and below may be classified as distribution.
  • Higher voltage system is used for transmitting higher amounts of power and longer lengths and its protection is important for power system security and requires complex relay systems.

Required Power Transfer (MW)

Distance (KM)

Economical Voltage Level (KM)













 Factor affected on Voltage Level of system:

  • Power carrying capability of transmission lines increases roughly as the square of the voltage. Accordingly disconnection of higher voltage class equipment from bus bars get increasingly less desirable with increase in voltage levels.
  • High structures are not desirable in earthquake prone areas. Therefore in order to obtain lower structures and facilitate maintenance it is important to design such sub-stations preferably with not more than two levels of bus bars.

Voltage Limit (As per CPWD & Kerala Elect.Board):

Voltage Limit (As Per CPWD)

240V < 5 KW
415V <100 KVA
11KV ❤  MVA
22KV <6 MVA
33KV <12 MVA
66KV <20 MVA
110KV <40 MVA
220KV >40 MVA

Voltage Variation

> 33 KV (-) 12.5% to (+) 10%
< 33 KV (-) 9% to (+) 6%
Low Voltage (-) 6% to (+) 6%

 Insulation Class:



Class A


Class E


Class B


Class F


Class H


Class N


 Standard Voltage Limit:

Voltage IEC (60038) IEC (6100:3.6) Indian Elect. Rule
ELV < 50 V    
LV 50 V to 1 KV <=1 KV < 250 V
MV   <= 35 KV 250 V to 650 V
HV > 1KV <= 230 KV 650 V to 33 KV
EHV   > 230 KV > 33 KV

 Standard Electrical Connection (As per GERC):

As per Type of Connection



LT Connection


HT connection

440V to 66KV

EHT connection

>= 66KV

As per Electrical Load Demand

Up 6W Load demand

1 Phase 230V Supply

6W to 100KVA(100KW)

3 Phase 440V Supply

100KVA to 2500KVA


Above 2500KVA


HT Connection Earthing

H.T Connection’s Earthing Strip

20mmX4mm Cu. Strip

CT & PT bodies


PT Secondary


CT Secondary


I/C and O/G Cable+ Cubicle Body


 Standard Meter Room Size (As per GERC):

Meter Box Height Upper level does not beyond 1.7 meter and Lower level should not below 1.2 meter from ground.
Facing of Meter Box Meter Box should be at front area of Building at Ground Floor.
Meter Room / Closed Shade 4 meter square Size



MCB / MCCB / ELCB Quick Reference (Part-1)

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
20A to 63A MCB Max. 35
MCCB Max. 25
6A to 45A ELCB 16
24A to 63A ELCB 35
80A to 100A ELCB 50

 MCB  Class according to Applications:

MCB Class according to Appliances


Capacity / watt

MCB Rating

MCB Class

Air Conditioner

1.0 Tone


C Class

1.5 Tone


C Class

2.0 Tone


C Class


165 Liter

3 A

C Class

350 Liter

4 A

C Class

Oven /Grill

4500 Watt

32 A

B Class

1750 Watt

10 A

B Class

Oven / Hotplate

750 Watt

6 A

B Class

2000 Watt

10 A

B Class

Room Heater

1000 Watt

6 A

B Class

2000 Watt

10 A

B Class

Washing Machine

300 Watt

2 A

C Class

1300 Watt

8 A

C Class

Water Heater

1000 Watt

6 A

B Class

2000 Watt

10 A

B Class

3000 Watt

16 A

B Class

6000 Watt

32 A

B Class


750 Watt

6 A

B Class

1250 Watt

8 A

B Class


1200 Watt

8 A

B Class

1500 Watt

10 A

B Class

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