500 kVA pad mounted transformer-delivering safe, clean, and efficient power with DOE 2016 performance standards
01 General
1.1 Project Description
This project involves the supply of a 500 kVA three-phase pad-mounted distribution transformer, designed for 60 Hz systems with a primary voltage of 13.2 kV GrdY / 7620 V and a secondary voltage of 480 V. The transformer features ONAN (Oil Natural Air Natural) cooling, loop feed configuration, and dead front access, ensuring safe and reliable operation. It is built with a YNd1 vector group and has an impedance of 5.75%.
Manufactured in compliance with DOE 2016 energy efficiency standards, the 500 kva pad mounted transformer delivers high performance with low energy losses-5.75 kW no-load loss and 0.65 kW load loss at rated capacity.
This 500 kVA 13.2 kV / 480 V three-phase pad-mounted transformer is ideal for medium-voltage to low-voltage distribution in urban and suburban areas. Typical applications include:
• Residential communities, supplying power for lighting, HVAC, and household appliances
• Commercial complexes such as offices, supermarkets, and retail parks
• Light industrial facilities, powering small to mid-sized equipment and machinery
• Institutions like schools and hospitals require reliable and safe power
• Underground distribution systems, used in loop feed networks for enhanced reliability and safety
Its pad-mounted, loop-feed, and dead-front design makes it suitable for outdoor or ground-level installations where space, safety, and accessibility are key.
1.2 Technical Specification
500 kva pad mounted transformer specification and data sheet
| Delivered to | America |
| Year | 2025 |
| Type | Three phase pad mount transformer |
| Standard | IEEE Std C57.12.34-2022 |
| Rated Power | 500KVA |
| Frequency | 60HZ |
| Feed | Loop |
| Front | Dead |
| Phase | three |
| Cooling Type | ONAN |
| Primary Voltage | 13.2 Kv |
| Secondary Voltage | 0.48 Kv |
| Vector Group | YNd1 |
| Winding Material | Aluminum |
| Impedance | 5.75% |
| Efficiency and losses | DOE 2016 |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 5.75KW |
| On Load Loss | 0.65KW |
| Accessories | Standard Configuration |
1.3 Drawings
500 kva pad mounted transformer dimensions and weight details
02 Manufacturing
2.1 Core
The five-leg core design ensures balanced magnetic flux paths for all three phases. Even under zero-sequence currents-such as those caused by single-line-to-ground faults-or during unbalanced loading conditions, the magnetic flux can flow smoothly through the two outer legs. This reduces magnetic reluctance, lowers temperature rise, and minimizes vibration.
This core structure is especially advantageous for YNd vector group transformers, as it provides a clear path for zero-sequence flux when the star-connected high-voltage side neutral is grounded, thereby enhancing electrical stability and system reliability.
2.2 Winding
 | The high-voltage winding utilizes a star (Y) connection with a higher number of turns to ensure uniform voltage distribution and excellent insulation performance. The low-voltage winding is connected in a delta (D) configuration, designed for higher current and fewer turns, typically employing a foil winding structure for enhanced mechanical strength and current-carrying capacity. The YNd1 vector group is commonly used in North American power systems requiring high- and low-voltage isolation, harmonic mitigation, and grounding capabilities. |
2.3 Tank
| This 500 kva pad mounted transformer features a sealed mild steel oil tank with a bolted cover, offering strong mechanical integrity and corrosion resistance. It passes pressure leak testing per IEC 60076-1 to ensure oil-tight performance. A set of corrugated radiators is mounted at the rear, seal-welded to the tank to enhance natural air cooling while maintaining leak-free operation. This compact design supports stable thermal performance and long-term reliability in clean energy applications. |  |
2.4 Elbow Type Lightning Arrester
 |
2.5 Final assembly
During final assembly, key components are installed to ensure safe and reliable operation of the 500 kVA pad-mounted transformer. The high-voltage side includes six 200A separable insulated bushings and a dedicated H0 neutral bushing for grounding. The low-voltage side features two resin-cast spade-type bushings with six-hole terminals for secure cable connections. Protection devices include three bayonet fuses and three current-limiting fuses (CLF) for fault isolation, along with three primary surge arresters to guard against overvoltage events. Grounding pads with one-hole connections are provided on both HV and LV sides to support safe site grounding. All components are precisely installed to meet utility and performance standards. |  |
03 Testing
Routine Test and Testing Standard
- Insulation Resistance Measurement： IEEE C57.12.90-2021 Clause 10.11
- Ratio Tests： IEEE C57.12.90-2021 Clause 7；IEEE C57.12.00-2021 Clause 9.1
- Phase Relation Test： IEEE C57.12.90-2021 Clause 6
- Resistance Measurements： IEEE C57.12.90-2021 Clause 5
- No Load Losses and No Load Current： IEEE C57.12.90-2021 Clause 8，IEEE C57.12.00-2021 Clause 9.3
- Induced Voltage Withstand Test： IEEE C57.12.90-2021 Clause 10.7
- Load Losses, Impedance Voltage and efficiency： IEEE C57.12.90-2021 Clause 9； IEEE C57.12.00-2021 Clause 9.2
- Applied Voltage Test： IEEE C57.12.90-2021 Clause 10.6
- Leak Testing With Pressure For Liquid-Immersed Transformers： IEC60076-1
Test Results
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximum resistance unbalance rate | 2.29 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: YNd1 | -0.05% ~ -0.03% | Pass |
| 3 | phase-relation tests | / | YNd1 | YNd1 | Pass |
| 4 | No-load losses and excitation current | / | I0 :: provide measured value | 0.27% | Pass |
| P0: provide measured value（t:20℃） | 0.577kW | ||||
| the tolerance for no load loss is +10% | / | ||||
| 5 | Load losses impedance voltage and efficiency | / | t:85℃ the tolerance for impedance is ±7.5% the tolerance for total load loss is +6% | / | Pass |
| Z%: measured value | 5.67% | ||||
| Pk: measured value | 4.032kW | ||||
| Pt: measured value | 4.609kW | ||||
| Efficiency not less than 99.35% | 99.41% | ||||
| 6 | Applied Voltage Test | kV | HV: 34kV 60s LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | kV | Applied voltage (KV):2Ur | No collapse of the test voltage occurs | Pass |
| Duration(s):48 | |||||
| Frequency (HZ): 150 | |||||
| 8 | Leakage Test | kPa | Applied pressure：20kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 9 | Insulation Resistance Measurement
| GΩ | HV-LV to Ground : | 21.5 | / |
| LV-HV to Ground: | 51.6 | ||||
| HV&LV to Ground | 21.2 |
04 Packing and Shipping
05 Site And Summary
This 500 kVA, 13.2 kV / 480 V three-phase pad-mounted distribution transformer features a YNd1 vector group, offering excellent medium-to-low voltage isolation and grounding capabilities tailored for North American power systems. Its five-leg core design reduces zero-sequence flux, enhancing operational stability and minimizing vibration.
Equipped with a sealed mild steel oil tank and rear-mounted corrugated radiators, it provides efficient natural cooling (ONAN) and long-term reliability. The dead-front design ensures safe and convenient maintenance. The high-voltage side includes six 200A separable insulated bushings and a dedicated H0 neutral bushing, while the low-voltage side uses resin-cast spade-type bushings for secure cable connections. Protection devices such as bayonet fuses, current-limiting fuses (CLF), and primary surge arresters provide reliable fault isolation and overvoltage protection.
Typical applications include medium-to-low voltage distribution in urban and suburban environments such as residential communities, commercial complexes, light industrial facilities, schools, and hospitals, where safety and reliability are critical. It is also well-suited for underground loop-feed distribution systems to enhance supply reliability.
