Electrical Quick Reference-Voltage Limits
August 8, 2013 19 Comments
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 | <3 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 |
JIGNESH PARMAR
excellent ! I have kept electrical thumb rules part 1 to 3 on my desk top ready to refer at any time. Mr. Jignesh is doing a good service to electrical engg. community. Appreciating and all the best.
Regards
kuldip Singh
HI. Can you help me with this harmonic distortion problem? We have THD>30% on 3a, 5a, 15a, 17a, 20a and 22a harmonic . Is it necessary to improve all these levels? Can I only improve the 3a, 5a and 15a harmonics to solve this?
Regards.
very much interesting data
I feel new energy com to my eee cpt and gpt polytechnic thank you yery much
dear sir plz provide me 11KV/415V pole mounted substation and Overhead Line technical Specification including pole erection also
thanks
Hi jignesh,
pl upload some stuff on ups and battery sizing calculation.
Very much informative and useful compilation for the practising Engg, who are not from electrical engg side but have to carry out such work particularly in Govt Deppt. Electrical Notes wonderfull.
Dear sir,
i need the formula of current carrying capacity of LT UG Armoured Aluminium and copper cables.
i view the ur Thump rule calculations but dosn’t mach.
so kindly reply.
There is no any Formula for this..
how can we find out the qty of caacitors required for pf coorrection by measuring current a motor is taking?
Hi Jignesh,
Does the contracted load for High Rise Building includes AC & Heater also OR it includes only Lighting & Small power.
Renjith
it includes everything
Hi,
Can you provide us a Calculator for Annual CO2 Savings ( kg C02) by power factor correction?
Thanks in advance.
Thanks
As long as I need
how many clearance of 220kv line
What is the thumb rule to require kw per sqfeet
Pl send calculation formula for ht cable as per bellow details.
Cable-185*3core ALU
11kV
2.5 MVA transformer
Length-700 mtrs
Under ground
Good and Beautifull stuffs…….Thus helps a lot….YOU ARE DOING A GOOD JOB SIR…
Sir we have 3200KVA Load on dairy plant, Plz suggest transformer selection either one or two transformers ? which capacity ?