Efficient and durable 300 kVA pad-mounted transformer for reliable outdoor power distribution.
01 General
1.1 Project Description
In 2024, a Canadian client received a 300 kVA three-phase pad-mounted transformer, designed and manufactured in full compliance with CSA Standard C227.4:21. The unit is intended for outdoor pad-mounting on concrete foundations and is suitable for use on effectively grounded systems.
This transformer features a dead-front design for safety and reliability in outdoor installations. It uses ONAN cooling and mineral oil for insulation. The aluminum windings give a good balance of efficiency, weight, and cost. The transformer is rated 300 kVA, 60 Hz. The primary voltage is 12.47(4.16) kV. The secondary voltage is 0.208 kV. The vector group is YNyn0.
The 300 kVA pad mounted transformer residential has a no-load tap changer (NLTC). The tap changer is of the cap and wrench type, providing a ±2×2.5% tapping range, in accordance with CSA C227.4 Clause 5.1.9, ensuring easy operation and reliable performance.
The unit also incorporates a 5-legged core construction for stability and reduced magnetic losses in GrdY–GrdY connected systems. Grounding is provided via a copper grounding bracket bolted to the ground bar, complying with CSA C227.4, and allowing safe attachment of working ground clamps.
Designed for high efficiency, this transformer achieves 98.94% efficiency, with no-load losses ≤705 W and load losses ≤4000 W. Built to withstand outdoor conditions, it comes with standard CSA-compliant accessories and represents a reliable, durable solution for Canadian distribution networks.
1.2 Technical Specification
300kVA three phase pad mounted transformer specification and data sheet
| Delivered to | Canada |
| Year | 2024 |
| Type | Three phase pad mount transformer |
| Standard | CSA C227.4:21 |
| Rated Power | 300KVA |
| Frequency | 60HZ |
| Feed | Radial |
| Front | Dead |
| Phase | three |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 12.47 kV |
| Secondary Voltage | 0.208 kV |
| Vector Group | YNyn0 |
| Winding Material | Aluminum |
| Impedance | 4 % |
| Efficiency | 98.94 % |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | ≤705 W |
| On Load Loss | ≤4000 W |
| Accessories | Standard Configuration |
1.3 Drawings
300kVA three phase pad mounted transformer drawing and nameplate
02 Manufacturing
2.1 Core
The five-limb core gives good magnetic balance in a small size. It is perfect for pad-mounted transformers. The compact shape saves space and cost. The efficient magnetic path lowers power loss and helps the transformer work better in tight areas. Each layer of steel is stacked with care. The sheets are 0.30–0.35 mm thick and have 2–4.8% silicon. This material helps cut down eddy current and hysteresis losses.
2.2 Winding
 | All coils are carefully wound with aluminum foil and wire. They spread heat well and keep losses low. With controlled impedance and high efficiency, these transformers run reliably and are ready for pad-mounted installations. Featuring a YNyn0 three-phase layout, each phase is hand-wound by skilled technicians to ensure proper neutral connection and balanced magnetic flow. |
2.3 Tank
The 300 kVA pad mounted transformer residential enclosures shall be mild-steel sealed tanks with bolted covers. The design shall ensure mechanical integrity under a 50 kPa pressure test, without leakage or permanent distortion exceeding 0.25 % of the surface diagonal. Tanks shall be weather- and tamper-resistant, equipped with captive pentahead bolts per CSA C227.4 requirements. |  |
2.4 Final assembly
During the transformer assembly process, we not only operate in a cleanroom with constant temperature and humidity, but also have established a comprehensive standardised operating system. From transformer assembly to lead connection, each step is guided by clear, standardised procedures, ensuring precise and accurate execution within a lean environment. This dual focus on both the environment and processes ensures our products consistently maintain a high level of craftsmanship quality.
2.5 Transformer Accessories
03 Testing
Testing Standard and Routine Test
| CSA C227.4-21 | Three-phase, pad-mounted distribution transformers with separable insulated high-voltage connectors |
| CSA-C802.1-13 (R2022) | Minimum Efficiency Values for Liquid-Filled Distribution Transformers |
1. Resistance Measurements
2. Ratio Tests
3. Phase Relation Test
4. No Load Losses and No Load Current
5. Load Losses Impedance Voltage and Efficiency
6. Applied Voltage Test
7. Induced Voltage Withstand Test
8. Leak Testing with Pressure for Liquid Immersed Transformers
9. Insulation Resistance Measurement
10. Oil Dielectric Test
Test Results
DC resistance was measured to verify winding integrity and phase balance. | 10 kV applied to LV winding for 60 seconds. |
| 2. Ratio Test The voltage ratio was tested on the principal tapping to confirm accuracy. | 2Ur applied at 240 Hz for 30 seconds. |
The vector group was verified as YNyn0, consistent with the nameplate specification. | 20 kPa pressure maintained for 12 hours. |
Measured at rated voltage to determine core performance. Excitation current (I₀): 0.26% No-load loss (P₀): 0.4693 kW | LV-HV to ground: 17.9 GΩ HV & LV to ground: 10.3 GΩ |
Test conducted at 85°C equivalent temperature. Impedance voltage (Z%): 4.25% Load loss (Pk): 3.419 kW Total loss (Pt): 3.909 kW Efficiency: 99.17% (≥ 98.94% required) All values meet specified tolerances. | Dielectric strength: 54.0 kV Moisture content: 11.2 mg/kg Dissipation factor: 0.00199% Furan content: ≤ 0.1 DGA: Normal Oil quality is in good condition. |
04 Packing and Shipping
05 Site And Summary
This 300 kVA three-phase pad-mounted transformer is made for Canada. It follows CSA C227.4:21. It uses ONAN cooling and mineral oil insulation. The aluminum windings make it efficient and light. The five-limb core keeps the transformer stable and reduces noise. The sealed tank is strong and can handle outdoor weather. It is also tamperproof and easy to maintain. Every transformer is made in a clean workshop with strict steps to make sure the quality is high. It works at 98.94% efficiency and has low losses. It gives steady power for commercial, residential, and small industrial users.
