Example Data Table
| Project | Connected Load | Demand Factor | Diversity Factor | Growth | Suggested Setup |
|---|---|---|---|---|---|
| Commercial Plaza | 3,200 kW | 85% | 1.20 | 20% | 2 x 2,500 kVA indoor arrangement |
| Industrial Yard | 5,500 kW | 90% | 1.10 | 25% | 3 x 3,150 kVA outdoor arrangement |
| Hospital Block | 2,400 kW | 80% | 1.15 | 15% | 2 x 1,600 kVA GIS arrangement |
Formula Used
- Coincident Demand (kW) = Connected Load × Demand Factor ÷ Diversity Factor
- Future Demand (kW) = Coincident Demand × (1 + Future Growth)
- Required Load (kVA) = Future Demand ÷ Power Factor
- Per Transformer Required (kVA) = Required Load ÷ (Available Transformer Slots × Utilization Limit)
- Primary or Secondary Current (A) = Transformer kVA ÷ (√3 × Voltage kV)
- Main Breaker = Next standard size above 125% of bus demand current
- Estimated Area = Equipment Area + Switchgear Area + Control Room Area + Circulation Allowance
How to Use This Calculator
- Enter the total connected load expected at the project.
- Set demand factor and diversity factor from your load study.
- Add growth margin for future expansion.
- Enter primary and secondary voltages for the selected scheme.
- Choose transformer count and whether N+1 continuity is required.
- Use utilization limit to avoid oversized operating stress.
- Enter average feeder load and spare feeders for outgoing switchgear planning.
- Press the calculate button to view the result, chart, and export options.
Frequently Asked Questions
1. What does this calculator size?
It estimates transformer capacity, switchgear demand, feeder count, and approximate substation site area. It helps early construction planning and budgeting.
2. Why is demand factor important?
Demand factor converts connected load into a more realistic operating demand. It prevents oversizing when every connected device will not run together.
3. Why is diversity factor used?
Diversity factor reflects that separate loads peak at different times. Higher diversity usually lowers coincident demand and can reduce transformer size.
4. When should I choose N+1?
Use N+1 when the project needs supply continuity during one transformer outage. Hospitals, data rooms, and critical process facilities often apply it.
5. Can this replace final utility design?
No. It is a planning calculator for concept design, budgeting, and comparison. Final engineering should still confirm protection, fault level, grounding, and code requirements.
6. Why keep transformer utilization below 100%?
Using a lower operating limit leaves thermal margin, supports load growth, and improves reliability. Many projects prefer an operating band around 70% to 85%.
7. What affects the area estimate most?
Transformer quantity, installed capacity, switchgear count, and station type affect area strongly. GIS and compact arrangements usually need less space than AIS yards.
8. Which voltage values should I enter?
Enter the actual incoming system voltage and the outgoing distribution voltage for the chosen scheme. Common examples include 33/11 kV or 11/0.415 kV.