## 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:

 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 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 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