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)

3500

500

765

500

400

400

120

150

220

80

50

132

 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:

Insulation

Temperature

Class A

               105°C

Class E

120°C

Class B

130°C

Class F

155°C

Class H

180°C

Class N

200°C

 Standard Voltage Limit:

VoltageIEC (60038)IEC (6100:3.6)Indian Elect. Rule
ELV< 50 V  
LV50 V to 1 KV<=1 KV< 250 V
MV <= 35 KV250 V to 650 V
HV> 1KV<= 230 KV650 V to 33 KV
EHV > 230 KV> 33 KV

 Standard Electrical Connection (As per GERC):

As per Type of Connection

Connection

Voltage

LT Connection

<=440V

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

11KV,22KV,33KV

Above 2500KVA

66KV

HT Connection Earthing

H.T Connection’s Earthing Strip

20mmX4mm Cu. Strip

CT & PT bodies

2Nos

PT Secondary

1Nos

CT Secondary

1Nos

I/C and O/G Cable+ Cubicle Body

2Nos

 Standard Meter Room Size (As per GERC):

Meter Box HeightUpper level does not beyond 1.7 meter and Lower level should not below 1.2 meter from ground.
Facing of Meter BoxMeter Box should be at front area of Building at Ground Floor.
Meter Room / Closed Shade4 meter square Size