25 kVA single phase pole transformer – reliable, efficient, and lightning-protected outdoor power
01 General
1.1 Project Description
Three 25 kVA single phase pole transformers were supplied to a Canadian client by Scotech in 2024 as part of a nine-unit order. Completely conform to CSA C2.2-06 standards. Rated for a primary voltage of 25 kV and a secondary voltage of 0.347 kV, offering a total capacity of 25 kVA under continuous load. It uses ONAN natural oil cooling, mineral oil as the insulating medium, additive polarity, and vector group Ii6.
This transformer features aluminum windings, reducing weight and cost, making installation and transportation easier. Its 2.8% impedance helps balance short-circuit currents and voltage regulation in distribution systems, simplifying protection settings. It is equipped with an NLTC (No-Load Tap Changer) with a 2.5% step, allowing output voltage adjustment during operation to keep voltage stable. It also has 33 kV polymer lightning arresters and dual high-voltage bushings for effective lightning and overvoltage protection.
This voltage configuration is common in North American and Canadian distribution systems. This model serves rural communities, residential neighborhoods, and small businesses where stable single-phase power is essential. The 25 kV primary connection makes it a strong choice for feeder or loop systems in outdoor environments with higher lightning activity. Whether used on rural main lines or at the end of a ring network, this transformer provides stable and reliable performance.
1.2 Technical Specification
25 kVA single phase pole transformer specification and data sheet
| Delivered to | Canada |
| Year | 2024 |
| Type | Pole Mounted Transformer |
| Standard | CSA C2.2-06 |
| Rated Power | 25kVA |
| Frequency | 60HZ |
| Polarity | Additive |
| Phase | 1 |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 25 kV |
| Secondary Voltage | 0.347 kV |
| Vector Group | Ii6 |
| Winding Material | Aluminum |
| Impedance | 2.8% |
| Efficiency | 98.63% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 83 kV |
| On Load Loss | 404 kV |
| Accessories | Arrester |
1.3 Drawings
25 kVA single phase pole transformer dimensions and weight details
02 Manufacturing
2.1 Core
The transformer core is a key component forming the magnetic circuit and enabling energy transfer between primary and secondary windings. It uses high-quality grain-oriented silicon steel laminations stacked and insulated to minimize eddy current losses. The core features a core-type design with rectangular columns, optimized for maximum magnetic flux and high efficiency in continuous industrial operation.
2.2 Winding
 | Aluminum windings are produced under strict control of direction, polarity, and tension. The LV coil is wound first, followed by the HV coil, with layer insulation compactly applied and no wrinkles. Turns accuracy is within ±0.3%. Radial oil ducts ≥3 mm and firm compression maintain effective cooling and mechanical strength, preventing deformation during operation. |
2.3 Tank
| The oil tank is built to meet strict arrester installation standards. It has strong flanges and supports, can carry weight and vibration, and features secure mounting holes. Tank material withstands high temperature and pressure. Gaskets ensure no oil leaks. The surface is treated against corrosion. The top provides enough space for easy removal and replacement of arresters without compromising sealing. |  |
2.4 Final Assembly
 | Core and Winding Assembly Install the high-voltage and low-voltage windings onto the core, ensuring insulation and concentricity. Body Installation Place the core and winding assembly into the oil tank. Install leads and insulating bushings, ensuring proper sealing. Filling Transformer Oil Inject filtered transformer oil, ensuring it is clean and free of impurities. Install External Accessories Attach safety valves, oil level gauges, and terminal connections. |
03 Testing
Testing Standard and Routine Test
CSA C2.2-06（R2022） Single-phase and three-phase liquid-filled distribution transformers
CSA C802.1-13（R2022） Minimum efficiency values for liquid-filled distribution transformers
1 Resistance Measurements
2 Ratio Tests
3 Polarity Test
4 No Load Losses and No Load Current
5 Load Losses and Impedance Voltage
6 Applied Voltage Test
7 Induced Voltage Withstand Test
8 Insulation Resistance Measurement
9 Leak Testing with Pressure for Liquid Immersed Transformers
10 Oil Test
Test Results
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | / | / | / | Pass |
| 2 | Ratio Tests | / | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: Ii6 | 0.11~0.12 | Pass |
| 3 | Polarity tests | / | Additive | Additive | Pass |
| 4 | No-load losses and excitation current | % | I0 :: provide measured value（100%） | 0.38 | Pass |
| kW | P0: provide measured value（100%） | 0.0681 | |||
| % | I0 :: provide measured value（105%） | 0.40 | |||
| kW | P0: provide measured value（105%） | 0.0766 | |||
| / | the tolerance for no load loss is +10% | / | |||
| 5 | Load losses , impedance voltage,total losses and efficiency | / | t:85℃ the tolerance for impedance is ±7.5% the tolerance for total load loss is +6% | / | Pass |
| % | Z%: measured value | 2.60 | |||
| kW | Pk: measured value | 0.366 | |||
| kW | Pt: measured value | 0.4341 | |||
| % | Efficiency not less than 98.63% | 98.81 | |||
| 6 | Applied Voltage Test | / | LV: 10kV 60s HV：40kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | / | Applied voltage (KV):2Ur | No collapse of the test voltage occurs | Pass |
| Duration(s):40 | |||||
| Frequency (HZ): 180 | |||||
| 8 | Insulation Resistance Measurement | GΩ | HV-LV·to·Ground | 306 | Pass |
| LV-HV to Ground | 422 | ||||
| HV&LV to Ground | 129 | ||||
| 9 | Leakage Test | / | Applied pressure：20kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 10
| Oil Test
| kV | Dielectric Strength | 61.0 | |
| mg/kg | Moisture Content | 13.6 | |||
| % | Dissipation Factor | 0.158 | |||
| mg/kg | Furan Analysis | ≤0.1 | |||
| / | Gas Chromatography Analysis | / |
04 Packing and Shipping
05 Site and Summary
Reliable and efficient, this 25 kVA single phase pole transformer meets CSA C2.2-06 standards with 25 kV/0.347 kV rating, aluminum windings, and ONAN cooling. Equipped with NLTC tap changer and 33 kV lightning arresters, it ensures stable voltage and protection. Ideal for rural, residential, and small business networks, it delivers safe, durable, and easy-to-install outdoor power.
