Comprehensive specifications for 25 kVA ONAN oil-filled transformer including dimensions, weight, oil volume, and electrical data
Quick Specifications
| Rated Power: | 25 kVA | Phase: | Single-Phase |
| Primary Voltage: | 7200V | Secondary Voltage: | 120/240V |
| Cooling Class: | ONAN | BIL Rating: | 60 kV |
| Weight: | 640 lbs (290 kg) | Oil Volume: | 26 gallons (98 L) |
| Dimensions (H×W×D): | 36″ × 25″ × 18″ (910 × 640 × 460 mm) | ||
A 25 kVA oil-filled transformer is commonly used for Commercial buildings, small industry. This guide provides complete specifications for utility engineers, electrical contractors, and procurement professionals.
25 kVA Oil-Filled Transformer Dimensions
| Dimension | Metric (mm) | Imperial (inches) |
|---|---|---|
| Height (H) | 910 mm | 36″ |
| Width (W) | 640 mm | 25″ |
| Depth (D) | 460 mm | 18″ |
🔧 Installation Note: This 25 kVA oil-filled transformer weighs 640 lbs and contains 26 gallons of insulating oil. Required:
- Concrete pad rated for 960 lbs minimum
- Oil containment per EPA SPCC requirements (110% capacity)
- Minimum 10ft clearance from buildings for outdoor installation
- 4-8 hour settling time before energizing
Weight and Oil Specifications
| Specification | Value | Notes |
|---|---|---|
| Total Weight (with oil) | 640 lbs (290 kg) | Includes all oil and accessories |
| Oil Volume | 26 gallons (98 L) | Mineral Oil |
| Oil Type | Mineral Oil | IEEE C57.106 compliant |
| Containment Required | 28 gallons | 110% per EPA SPCC |
Electrical Specifications
| Parameter | Value | Notes |
|---|---|---|
| Rated kVA | 25 kVA | At rated voltage and ONAN cooling |
| Primary Voltage | 7200V | Standard utility distribution voltage |
| Secondary Voltage | 120/240V | Service voltage |
| Cooling Class | ONAN | Oil Natural, Air Natural |
| BIL Rating | 60 kV | Standard for 2.4kV-7.2kV primary |
| No-Load Loss | 85 W | Core losses |
| Load Loss | 300 W | At rated load |
| Total Losses | 385 W | At 100% load |
| Impedance | 3.5% | Per IEEE C57.12.00 |
| Efficiency | 98.5% | At rated load |
| Sound Level | ~45 dB | Per NEMA TR-1 |
Secondary Full Load Amps
Full load amperage at secondary voltage for 25 kVA single-phase transformer:
| Secondary Voltage | Full Load Amps | Conductor Size |
|---|---|---|
| 120V | 208.3 A | 250 MCM |
| 208V | 120.2 A | 1/0 AWG |
| 240V | 104.2 A | #1 AWG |
| 277V | 90.3 A | #2 AWG |
| 480V | 52.1 A | #6 AWG |
Single-Phase:
Amps = (kVA × 1000) ÷ VoltageExample at 240V:
104.2 A = (25 × 1000) ÷ 240Oil Maintenance Guidelines for 25 kVA Transformer
Proper maintenance of the 26 gallons of Mineral Oil in this transformer is critical for long-term reliability:
| Maintenance Task | Frequency | Purpose |
|---|---|---|
| Visual Oil Level Check | Monthly | Detect leaks, ensure adequate level |
| Oil Sample Analysis | Annually | Dielectric strength, dissolved gas analysis (DGA) |
| Oil Filtration/Reconditioning | Every 3-5 years | Remove moisture and contaminants |
| Silica Gel Breather Check | Quarterly | Ensure moisture protection |
| Bushing Inspection | Annually | Check for cracks, contamination, oil leaks |
⚠️ Oil Handling Safety:
- Always use proper PPE when handling transformer oil
- Dispose of contaminated oil according to EPA regulations
- Never mix different oil types without compatibility testing
- Maintain SPCC containment at all times
When to Choose a 25 kVA Oil-Filled Transformer
A 25 kVA single-phase oil-filled transformer is ideal for:
- Utility distribution in residential neighborhoods
- Rural electrification projects with overhead lines
- Agricultural operations requiring reliable power
- Outdoor installations where dry-type is not suitable
- Applications requiring 7200V or 14.4kV primary voltage
Oil-Filled vs Dry-Type Comparison:
| Factor | Oil-Filled | Dry-Type |
|---|---|---|
| Cost | Lower initial cost | Higher initial cost |
| Efficiency | Higher (less losses) | Slightly lower |
| Maintenance | Oil testing required | Minimal maintenance |
| Location | Outdoor preferred | Indoor or outdoor |
| Fire Risk | Higher (contain oil) | Lower |
Typical Load Distribution for 25 kVA Oil-Filled Transformer
Example utility distribution loads for a 25 kVA oil-filled transformer:
| Load Type | Estimated Demand |
|---|---|
| Residential homes (5-15 homes) | 15 kVA |
| Street lighting | 3 kVA |
| Small commercial loads | 5 kVA |
| Agricultural pumps | 1 kVA |
Note: Utility distribution varies by application. Consult with utility engineer for specific load allocations.
Related Oil-Filled Transformer Sizes
Compare with adjacent kVA ratings:
| kVA Rating | Link |
|---|---|
| 15 kVA Single-Phase | 15 kVA Oil-Filled Specs → |
| 25 kVA Single-Phase | Current Page |
| 37.5 kVA Single-Phase | 37.5 kVA Oil-Filled Specs → |
Frequently Asked Questions
How much oil does a 25 kVA oil-filled transformer contain?
A 25 kVA single-phase oil-filled transformer typically contains 26 gallons (98 liters) of Mineral Oil insulating oil.
What are the dimensions of a 25 kVA oil-filled transformer?
Typical dimensions are 36″ H × 25″ W × 18″ D (910 × 640 × 460 mm).
How much does a 25 kVA oil-filled transformer weigh?
A 25 kVA oil-filled transformer weighs approximately 640 lbs (290 kg) including oil.
What is the BIL rating for a 25 kVA transformer?
The standard BIL (Basic Insulation Level) rating is 60 kV, which is standard for 2.4kv-7.2kv primary.
Related Resources
📊 Complete Reference Charts:
- Transformer Sizing Chart – Compare all kVA ratings
- Transformer Full Load Amps Chart – FLA reference for all voltages
Related Articles
- Transformer Oil: Complete Guide to Types, Testing & Maintenance
- Three Phase Transformer: Complete Guide
- Transformer Protection: Complete Guide
Standards & References
- IEEE C57.12.00 – General Requirements for Liquid-Immersed Distribution Transformers
- IEEE C57.12.90 – Test Code for Liquid-Immersed Distribution Transformers
- IEEE C57.106 – Guide for Acceptance and Maintenance of Insulating Oil
- NEMA TR-1 – Transformers, Regulators and Reactors
- EPA 40 CFR 112 – SPCC Requirements
Disclaimer: Specifications shown are typical reference values. Actual specifications vary by manufacturer, voltage class, and application. Oil-filled transformers require proper containment, maintenance, and environmental compliance. Always consult manufacturer datasheets and local codes. Last updated: January 2026