Delivering efficiency and reliability in every unit - 25 kVA pad mounted transformer
01 General
1.1 Project Description
In 2024, our company delivered 37 single-phase pad-mounted transformers to a customer in Jamaica. This included 2 units of the 25 kVA model, mainly to provide power distribution products for local residential areas. Scotech tailored the optimal transformer solution to meet customer needs. All units were made to IEEE standards, ensuring reliability and long-term performance.
The primary (high) voltage is 24GrdY/13.8 × 12GrdY/6.9 kV, which is a dual-voltage design. Customers can switch between 13.8 kV and 6.9 kV using the dual-voltage selector switch, depending on the distribution line. It has a no-load tap changer (NLTC) ±2×2.5% for voltage adjustment. The secondary voltage is 0.24/0.12 kV, suitable for homes and small businesses. The loop-feed, dead-front design makes installation safe and easy.
The 25 kva pad mounted transformer uses copper windings, ONAN cooling, and mineral oil insulation. It works efficiently and lasts long in tropical conditions. Operating at a frequency of 50Hz, these transformers achieve an outstanding no-load loss of 0.078 kW and on-load loss of 0.165 kW.
Protection and safety are ensured through standard features such as a bayonet fuse, current limiting fuse (CLF), and pressure relief device, with optional surge arrester and internal fault detector (IFD) for enhanced reliability.
Combining high-quality materials, compact design, and advanced protection features, this transformer is suitable for modern distribution networks. It delivers stable, efficient, and safe power to local communities.
1.2 Technical Specification
25kVA single phase pad mounted transformer specification and data sheet
| Delivered to | Jamaica |
| Year | 2024 |
| Type | single phase pad mount transformer |
| Standard | IEEE Std |
| Rated Power | 25kVA |
| Frequency | 50HZ |
| Feed | Loop |
| Front | Dead |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 24GrdY/13.8 12GrdY/6.9 kV |
| Secondary Voltage | 0.24/0.12 KV |
| Vector Group | Ii0 |
| Polarity | Subtractive |
| Winding Material | Copper |
| Impedance | 2.5% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 0.078 KW |
| On Load Loss | 0.165 KW |
| Accessories | Dual-voltage selector switch， IFD ，Surge arrester |
1.3 Drawings
25kVA single phase pad mounted transformer dimensions and weight details
02 Manufacturing
2.1 Core
 | This unit’s cores are made from cold-rolled silicon steel wound using state-of-the-art technology. Compared to traditional laminated cores, wound cores are lightweight, have relatively low no-load losses, and exhibit relatively low noise levels. They are widely used in small-capacity single-phase pad-mounted transformers. Their no-load losses are over 7% lower than those of laminated cores.
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2.2 Winding
What are the advantages of using foil for low-voltage windings? Using a single sheet of copper foil ensures even current distribution, eliminating imbalances caused by “circulating current” or “proximity effect.” Foil windings also offer high mechanical strength and excellent short-circuit electrodynamic resistance. The thinness of the foil allows heat to be easily dissipated by oil or air, resulting in a low temperature rise.
2.3 Tank
 | The switching compartment door can be closed and locked even when the H.V. cable elbows and grounding elbows are inserted into the feed-thru connectors. This design ensures safe operation by preventing exposure of live parts, maintaining the enclosure’s protective rating against rain, dust, and animals, and providing reliable locking to avoid unauthorized access. |
2.4 Elbow Arrester
The 25 kVA Pad Mounted Transformer was equipped with elbow arresters to improve surge protection reliability and ensure long-term stable operation within the underground power distribution network. Installed directly on the transformer’s high-voltage separable connector interface, elbow arresters are specially designed for deadfront underground systems commonly used in local residential areas. |  |
2.5 Final Assembly
03 Testing
Routine Test
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 Dielectric 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: Ii0 | A:0.01 B:0.01 | Pass
|
| 3 | Polarity tests | / | Subtractive | Subtractive | Pass
|
| 4 | No-load losses and excitation current | % kW | I0 :: provide measured value P0: provide measured value the tolerance for no load loss is +10% | 0.58 0.073 | Pass
|
| 5 | Load losses , impedance voltage,total losses and efficiency | / kW kW | t:85℃ Z%: measured value Pk: measured value Pt: measured value the tolerance for impedance is ±7.5% the tolerance for total load loss is +6% | 2.42 0.154 0.227 99.14 | Pass
|
| 6 | Applied Voltage Test | / | LV: 10kV 60s | No collapse of the test voltage occurs | Pass
|
| 7 | Induced Voltage Withstand Test | / | Applied voltage (KV): 40 Duration(s): 40 Frequency (HZ): 150 | No collapse of the test voltage occurs | Pass
|
| 8 | Insulation Resistance Measurement | GΩ | LV-HV to Ground | 46.6 | / |
| 9 | Leakage Test
| / | Applied pressure：20kPA Duration：12h | No leakage and no Damage | Pass
|
| 10 | Oil Dielectric Test
| kV | ≥45 | 49.60 | Pass
|
04 Packing and Shipping
05 Site and Summary
This 25 kva pad mounted transformer is made with strong copper windings and a wound core that gives low loss and low noise. The tank is built to stay safe and locked, even when cables are connected. The unit has a dual-voltage design and a tap changer for easy adjustment. It works well in hot and wet places with ONAN cooling and mineral oil insulation. It is small in size but strong in use. It comes with standard fuses, a pressure relief device, and can add more options like surge arresters and fault detectors.
This transformer is simple, safe, and reliable. It gives steady power to homes and small businesses. It also lasts long and needs little care. It is a good choice for local power use in Jamaica.
