Understanding Transformer Sizing: 25 KVA to 5000 KVA for Industrial Applications

Why Transformer Selection Matters

A transformer is the gateway between the utility grid and your facility's electrical system. Choose too small, and it overheats, trips, and limits your production capacity. Choose too large, and you pay unnecessarily high demand charges, fixed charges, and capital cost. In either case, the financial impact runs into lakhs annually.

Alpha Diesels supplies distribution and power transformers from 25 KVA to 5000 KVA for industrial installations across Rajasthan and Delhi-NCR. This guide helps you understand the sizing process and key specifications.

Distribution vs Power Transformers

Feature	Distribution Transformer	Power Transformer
Capacity range	25 KVA - 2500 KVA	Above 2500 KVA
Voltage levels	11kV/33kV to 415V	33kV/66kV/132kV
Typical use	Factories, commercial buildings	Substations, large industries
Cooling type	ONAN (Oil Natural Air Natural)	ONAF/OFAF (forced cooling)
Efficiency	95-98%	98-99.5%

How to Calculate Required Transformer Capacity

The process is similar to generator sizing but with some key differences:

• Step 1: Calculate total connected load (sum of all equipment kW ratings)
• Step 2: Apply demand factor - typically 0.6-0.8 for most factories, meaning 60-80% of connected load runs simultaneously
• Step 3: Convert kW to kVA using power factor (kVA = kW ÷ power factor). Most industrial loads have a power factor of 0.8-0.85
• Step 4: Add 20-30% margin for future expansion
• Step 5: Select the nearest standard transformer size (25, 63, 100, 160, 250, 315, 500, 630, 1000, 1600, 2000, 2500 KVA)

Transformer Sizing Examples

Facility Type	Connected Load	Demand Factor	Power Factor	Required kVA	Recommended Transformer
Small workshop	50 kW	0.7	0.8	44 kVA	63 KVA
Medium factory	200 kW	0.75	0.85	176 kVA	250 KVA
Large factory	800 kW	0.7	0.8	700 kVA	1000 KVA
Commercial complex	500 kW	0.8	0.85	470 kVA	630 KVA

The Role of APFC Panels

Poor power factor is the silent thief of industrial efficiency. If your factory's power factor drops below 0.9, your DISCOM charges a power factor penalty - up to 2% additional billing for every 0.01 drop below 0.9. An Automatic Power Factor Correction (APFC) panel maintains your power factor at 0.95-0.99 by automatically switching capacitor banks based on load conditions.

Alpha Diesels supplies and installs complete APFC panels, LT panels, HT panels, and synchronizing panels alongside transformers - ensuring your entire electrical system is designed as an integrated unit, not a patchwork of incompatible components.

Key Specifications to Verify Before Purchase

• Voltage ratio: Must match your DISCOM's supply voltage (11kV or 33kV primary) and your distribution voltage (415V secondary)
• Impedance (%): Typically 4-6% for distribution transformers. Higher impedance limits fault current but increases voltage regulation
• Losses: No-load losses (core losses) and full-load losses (copper losses). Lower losses = higher efficiency = lower electricity bills over the transformer's 25-30 year lifespan
• Cooling type: ONAN is standard for up to 2500 KVA. Above that, forced cooling (ONAF) is necessary
• BIS certification: Ensure IS 1180 (for distribution transformers) or IS 2026 (for power transformers) compliance
• Tap changer: Off-circuit tap changer (OCTC) for manual voltage adjustment, or on-load tap changer (OLTC) for automatic voltage regulation under varying load

Get Expert Transformer Advice

Alpha Diesels has supplied and installed transformers for factories, hospitals, malls, and infrastructure projects across Bhiwadi, Neemrana, Gurugram, and Delhi. Our electrical engineers can assess your load profile, recommend the right transformer capacity, and handle complete installation including HT/LT panel supply and APFC integration. Call +91-97993-03700 for a consultation.