Guideline to Design Electrical Network for Building / Small Area.
October 31, 2011 21 Comments
Guideline to Design Electrical Network for Building / Small Area.
(1) Calculate Electrical Load:
- Find out built up area in Sqft.of per flat per House/Dwelling unit.
- Multiply area in Sqft. by Load/Sqft according to following Table
| Type of Load | Load/Sqft |
| Industrial | 100 Watt/Sqft |
| Commercial | 30 Watt/Sqft |
| Domestic | 15 Watt/Sqft |
- Apply the diversity factor and Compute the load of all dwelling units in the area.
| Type of Load | Diversity Factor |
| Industrial | 0.5 |
| Commercial | 0.8 |
| Domestic | 0.4 |
- Add the load of common services such as Auditorium, Street Lights, Lifts and Water Pumps etc. For simplicity purpose 0.5kW/dwelling units may be considered as common load.
- Compute the “Total Load” of the area by adding load observed at above.
- Apply the power factor of 0.8 to determine the load in kVA.
- Compute the Load in kVA= “Total Load”/0.8
- Take transformer loading of 65% considering the network arrangement Ring Main Circuit.
(2) Decide voltage grade for Electrical Load:
- If load is equal to or more than 2.50MVA, the area shall be fed through 33kV feeder. For such loads, the land space for 33/11kV Sub-station shall have to be allocated by builder / Society/ Authority.
- For load between 1 MVA to 2.5MVA, dedicated 11kV feeder shall be preferred.
- For load below 1 MVA, existing 11kV feed can be tapped through VCB or RMU.
(3) Decide Size of Transformer:
- Select T.C Size of 25 KVA,63 KVA,100 KVA,200 KVA or 400 KVA according to your Load.
- The maximum capacity of distribution transformer acceptable is 400 kVA as a standard capacity.
- Only two-no of transformer at one location shall be acceptable. If there is more number of transformers HT shall be required to extend using underground cables to locate additional transformer.
(4) RMU / LT Panel:
- Either VCB or Ring Main Circuit shall be used to control transformers. There cables should have metering arrangement at 11kV. The protection system at incoming supply shall be using numerical relays.
- On LT side of transformer, LT main feeder pillar shall be provided. The Incoming shall be protected by MCCB/SFU.
- The distribution pillar-box shall be connected into Ring Main Unit.
- The incomer of distribution pillar shall have MCCB / SFU. The outgoing shall have HRC fuses.
(5) The LT cables from T.C to LT panel / Main feeder pillar:
- Decide Size of LT Cable from T.C to LT Panel as per following Table.
|
Transformer Size |
Cable |
| 630kVA transformers | 2 no x 1C x 630 Sq mm, Al, XLPE Cable |
| 400kVA transformers | 1 no x 1C x 630 Sq mm, Al, XLPE |
| 250kVA transformers | 3 ½ C x 400 Sq mm, Al, XLPE |
| 160kVA transformers | 3 ½ C x 300 Sq mm, Al, XLPE |
| 100kVA transformers | 3 ½ C x 150 Sq mm, Al, XLPE |
(6) Considering various Factors & Length of Cable:
- The factors for cable loading shall be taken as 70%.
- The factor for multiplicity of cables from same cable trench shall be 80%.
- The suggested maximum length of LT cable feeder shall be 250 Mtrs.
- The LT cables shall be connected in ring main circuit.
- The load on sub-feeder pillar shall be restricted to 150kW.
(7) LT cables from main feeder pillars to distribution pillar boxes:
| Load on distribution pillar
|
LT Cable Size |
| Up to 50kW | 3 ½ C x 150 sqmm, AL, XLPE |
| Up to 100kW | 3 ½ C x 300 sqmm, AL, XLPE |
| Up to 150 kW | 3 ½ C x 400sqmm, AL, XLPE |
(8) Calculate Voltage Drop and T&D Losses:
- The entire system has to be designed for a voltage drop of 2.0% from11kV Side of transformer to metering equipment at end consumer premises.
- The entire system has to be designed for T&D losses of service maximum 2.0% from 11kV to end consumer meter including of service cable.
Ref:
- NPC Limited.
- Electrical code.
JIGNESH PARMAR
Dear Jignesh
Wonderfull & excellent contribution to the engineering community.
measure the volts and the amps in the outlets read Audels Handy Book of electricity liked the cable information for the transformer in mm thanks
nice article Jignesh, whether this can be used to design a high-rise building.
Dear Jignesh,
First of all excellent work,I would like to leave few comments
1)11kv can feed upto 5MVA load as i read in Rules in Karnataka Electricity Board
2)I did’t understand cablesizes for 630&400kva transformer.
could you explain why 1 core using in 630 & 400 kva transformer..
How can i calculate or determine the number of lighting points in a hall?
Hi Sir ,
I have read your technical blog it’s really informative for who hunger for knowledge .
Do you have any technical guideline on Data Center design ,operation & Maintenance .If you have please send to me .
Regards ,
Ravindra .
good
Can you please guide us the design rules for high rise building also
Dear Jigneshbhai
very useful details given by you.Pl.focus on D.G set selection
Already given in Excel Tool for selection of Size of DG set according to Load
sir how can i calculate the LT cables size (in sqmm)depend on load,plse give details
It is already given in page of EXCEL TOOL of this blog as a”(1) Cable Designing Program”
Refer this sheet.
oh Mr.Parmar i appreciate you greatly for re leafing me from this trouble.
I appreciate you. And would like to be In touch with you. Thanks!
hi thx. plz mention your reference also in all parts….
Mr. Jignesh Parmar,
your work on technical electrical engineering very very good.
First I would like to offer you a sincere thanks and gratitude to you Secondly, I hope that explains the entire example to determine the electrical loads of the residential tower
Dear Jignesh Sir
I really feel proud to belong to this electrical comunity who has such a talented person like you. I wish I get to see you and be under guidance of you.If there is any chance of mine to have your guidance plz information.
Tanx, and Electrical excel tool for this great work
what is the load for sft in Hospitals ( general hospital, super speciality hospital)