Single-Phase Pad-Mounted Transformer – Compact & Silent, Perfect for Urban Grids!
01 General
1.1 Project Description
50 kVA single phase pad mounted distribution transformers was delivered to Jamaica in 2025. The rated power of the padmount transformer is 50 kVA with ONAN cooling. The primary voltage is 24GrdY/13.8*12GrdY/6.9 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.24/0.12 kV, they formed a vector group of YNyn0.
This 50 kVA single-phase pad-mounted transformer is designed for versatile and reliable operation in dual high-voltage distribution systems, featuring a 24GrdY/13.8 kV and 12GrdY/6.9 kV primary configuration with a 0.24/0.12 kV secondary output. Its robust protection system includes bayonet fuses and current-limiting fuses for enhanced fault interruption, along with surge arresters to safeguard against voltage transients. An Internal Fault Detector (IFD) provides real-time monitoring, while the dual-voltage selector switch enables seamless transition between primary voltages. For operational flexibility, an off-circuit tap changer allows precise voltage adjustment, and a load break switch ensures safe isolation during maintenance.
Additional safety features include a pressure relief device to mitigate internal overpressure risks and an oil level gauge for dielectric fluid monitoring. Built for durability and ease of maintenance, this transformer is ideal for utility, commercial, and industrial applications requiring a resilient and adaptable power distribution solution.
1.2 Technical Specification
50 kVA single phase pad mounted distribution transformers specifications type and data sheet
| Delivered to | Jamaica |
| Year | 2024 |
| Type | Pad mounted transformer |
| Standard | IEEE StdC57.12.34-2022 |
| Rated Power | 50 kVA |
| Frequency | 50HZ |
| Phase | 1 |
| Feed | Loop |
| Front | Dead |
| Cooling Type | ONAN |
| Primary Voltage | 24GrdY/13.8*12GrdY/6.9 kV |
| Secondary Voltage | 0.24/0.12kV |
| Winding Material | Copper |
| Angular displacement | Ii0 |
| Impedance | 4% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 0.116 kW |
| On Load Loss | 0.445 kW |
| Accessories | Standard Configuration |
1.3 Drawings
50kVA single phase pad mounted distribution transformers diagram drawing and size.
02 Manufacturing
2.1 Core
| Transformer features an advanced toroidal wound core design, constructed from continuously wound, high-permeability, low-loss grain-oriented silicon steel strips to form a seamless closed-loop structure. The wound core fully utilizes the grain orientation characteristics of the silicon steel, aligning the magnetic flux direction with the rolling direction, while an insulated coating on the surface minimizes eddy current losses. It offers significant advantages, including low no-load loss (20-30% reduction compared to traditional laminated cores), quiet operation, high efficiency (core fill factor exceeding 95%), and excellent mechanical strength. |  |
2.2 Winding
 | This transformer features a hybrid winding design combining low-voltage foil and high-voltage wire construction for optimal performance. The 0.24/0.12kV low-voltage winding utilizes flat copper foil layered with insulating paper, providing excellent short-circuit strength, efficient heat dissipation, and compact design. The 24kV/12kV high-voltage winding employs round/rectangular copper wire with interleaved insulation, ensuring superior voltage distribution, dual-primary configuration flexibility, and partial discharge resistance. This combination of copper foil (LV) and copper wire (HV) delivers high efficiency with minimized eddy current losses, robust mechanical stability to withstand thermal and short-circuit stresses, and a space-efficient package ideal for pad-mounted distribution applications. |
2.3 Tank
| The transformer tank features a fully sealed welded structure constructed from 4-6mm high-quality mild steel plates, processed through sandblasting (Sa2.5 grade), CNC cutting (±0.5mm tolerance), and automated MAG welding. It passes a 20kPa/30min pressure test, with double sealing (rubber gasket + sealant) and stainless steel flanges to ensure leak-proof performance. The surface is treated with hot-dip zinc coating (≥80μm) and dual-layer anti-corrosion paint. With 100kPa pressure resistance and C5-M corrosion rating (ISO9001 certified), it meets all outdoor hermetic operation requirements. |  |
2.4 Final Assembly
 | 1. Winding Assembly: Precisely mount the HV/LV windings onto the wound core, ensuring proper insulation alignment and mechanical fastening. 2. Electrical Connections: Solder or bolt winding leads to tap changers, bushings, and other conductors, then verify contact resistance. 3. Core-Coil Drying: Place the assembled active part into a drying oven, applying vacuum and heat to remove moisture until insulation resistance meets standards. 4. Tank Insertion: Use lifting equipment to carefully lower the dried active part into the tank, securing it to avoid collisions. 5. Accessory Installation: Install bushings, pressure relief valves, IFD, surge arrester, etc., applying sealant to gasket surfaces for leak-proofing. 6. Oil Filling & Standing: Fill with oil under vacuum to the specified level, degas, and let stand for 24+ hours before final dielectric and DGA tests. |
03 Testing
| 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:-0.03 B:-0.05 | 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% | 0.35 0.095 | 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% | 4.28 0.432 0.527 99.23 | 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 | 28.2 | / |
| 9 | Leakage Test | / | Applied pressure：20kPA Duration：12h | No leakage and no Damage | Pass |
| 10 | Oil Dielectric Test | kV | ≥45 | 59.40 | Pass |
04 Packing and Shipping
4.1 Packing
| The packaging process for a single-phase pad-mounted transformer involves cleaning, internal protection, external reinforcement, and labeling. First, the transformer is thoroughly cleaned, with oil levels and seals checked; for transport, oil may be drained and replaced with dry nitrogen (0.02–0.03 MPa) to prevent moisture ingress, or retained with all openings sealed. Externally, anti-vibration measures (straps or bolted base fixation) are applied, while critical components (bushings, IFD and etc.) are protected with impact-resistant covers, and metal surfaces are treated with anti-rust spray. The unit is then wrapped in waterproof plastic film with sealed seams (enhanced for maritime shipping). The goods are packed in wooden cases (with shock-absorbing materials inside) in accordance with the transportation requirements. Clear markings (weight, lifting points, hazards) and documents (packing list, test reports) are attached, ensuring compliance with moisture-proof, shockproof, and IP56 standards for maritime transport. |  |
4.2 Shipping
 | The single phase pad mounted distribution transformers is shipped via containerized sea transport aboard vessel ZIM SAMMY OFER (Voyage 8E) under Bill of Lading 177PNBNBNL8580A, departing from Ningbo Chuanshan Port to Jamaica. Secured in a 40’HC container with steel-wood anti-vibration base and foam-padded critical components, the unit is filled with 0.02-0.03MPa dry nitrogen for moisture prevention and coated with anti-rust oil. The shipment features sealed-container management, real-time GPS tracking, and nitrogen pressure monitoring (≥0.01MPa). Upon arrival, inspections include seal integrity verification, visual examination, and insulation tests, accompanied by submission of B/L and packing photos to ensure compliance with international maritime standards for moisture and shock protection. |
05 Site And Summary
As a cornerstone of power distribution networks, this single-phase pad-mounted transformer combines innovative design with superior craftsmanship to deliver unmatched reliability for diverse power supply scenarios. With its compact structure, high energy efficiency, and optional smart monitoring features, it perfectly meets modern grids’ stringent demands for safety, economy, and environmental sustainability. From urban communities to remote areas, from conventional distribution to renewable energy integration, we are committed to providing simpler, safer, and more sustainable electrical solutions through this meticulously engineered product. Choosing our transformer means investing in a dependable energy future.
