3MVA Custom Power Transformers – Reliable IEC-Certified Solutions for Stable Urban Distribution and Superior Voltage Control
01 General
1.1 Project Description
3MVA-33/11kV distribution step down transformer belongs to the medium voltage distribution system voltage level, used for urban distribution network – power distribution from the regional substation to users. Ordered by customers in Zimbabwe, South Africa in 2025. Produced and tested according to IEC 60076-1:2011standard.From raw material inspection to final testing, we use advanced monitoring systems and strict QC procedures to ensure every transformer meets international standards.
It is equipped with OLTC + Tapping Range ±6*1.8%+ independent voltage regulation oil conservator, which can cope with fluctuating grid voltage and ensure stable power supply output. Equipped with gas relay, pressure relief valve, oil temperature/oil level monitoring, with a comprehensive protection mechanism. The vector group is Dyn11 and uses copper winding, with good conductivity, low loss and high efficiency.
1.2 Technical Specification
3000 kVA custom power transformers specification and data sheet
| Delivered to | South Africa |
| Year | 2025 |
| Type | Oil immersed transformer |
| Standard | IEC 60076-1:2011 |
| Rated Power | 3MVA |
| Frequency | 50HZ |
| Phase | 3 |
| Cooling Type | ONAN |
| Primary Voltage | 33 KV |
| Secondary Voltage | 11 KV |
| Winding Material | copper |
| Angular displacement | Dyn11 |
| Tap Changer | OLTC |
| Tapping Range | ±6*1.8% |
| No Load Loss | 3.1 KW |
| On Load Loss | 27.6 KW |
| Accessories | Standard Configuration |
1.3 Drawings
3000 kVA custom power transformers dimensions and weight details
02 Manufacturing
2.1 Core
The 3000 kVA power transformers core is now laminated. The lamination reduces eddy current losses that occur when magnetic fields induce circulating currents in the core material. By using thin sheets of material, each layer is more resistant to eddy currents, which reduces energy losses and improves the overall efficiency of the transformer. The lamination also reduces the core’s hysteresis losses, which occur when the core’s magnetic material is repeatedly magnetized and demagnetized. |  |
2.2 Winding
 | This power transformer winding adopts a cylindrical winding structure with copper flat conductors, ensuring excellent electrical performance and mechanical strength. The high-voltage and low-voltage windings are concentrically arranged, with insulating paper wrapped between layers. Designed with Dyn11 vector group, it is one of the most common designs for small and medium capacity three-phase transformers. It provides reliable phase displacement and is suitable for various distribution and substation applications. |
2.3 OLTC Conservator
This 3000 kVA custom power transformers has two oil conservators, one is the oil tank conservator and the other is the on load tap changer oil conservator. OLTC oil is easily contaminated by arcing and needs to be circulated and filtered independently to avoid the effects of temperature, oxidation and moisture, thereby extending the life of OLTC and ensuring the safe operation of the transformer. |  |
2.4 Final Assembly
 | 1. The core and winding have been assembled. In the picture, the worker is about to weld the lead wire and install the tap changer. 2. The active part is being lifted into the tank. 3. Install other parts: oil temperature indicator, pressure relief valve, oil level indicator, gas relay, breather, earthing terminal, marshalling box, radiators. 4. Pour insulating oil into the transformer tank to fill the internal space of the transformer and ensure that the oil level meets the requirements. |
03 Testing
Routine Test and Testing Standard
IEC 60076-1-2011, Power transformers – Part 1: General
IEC 60076-3-2013, Power Transformers-Part 3: Insulation levels, dielectric tests and external clearances in air
IEC 60076-7-2018, Power transformers- Part 7 Loading guide for mineral-oil-immersed power transformers
1. Measurement of dissolved gasses in dielectric liquid from each separate oil compartment except diverter switch compartment
2. Measurement of Voltage Ratio and Check of Phase Displacement
3. Measurement of Winding Resistance
4. Measurement of D.C Insulation Resistance Between Each Winding To Earth And Between Windings
5. Applied Voltage Test
6. Measurement of No-Load Loss and Current
7. Induced Voltage Test
8. Measurement of Short-circuit Impedance and Load Loss
9. Leak Testing with Pressure For Liquid-Immersed Transformers
04 Packing and Shipping
4.1 Packing
1. After the transformer has completed the factory test, the oil will be drained (or a small amount of oil will be retained), the interior will be thoroughly dried, and then filled with dry air or nitrogen, and a slight positive pressure will be maintained.
2. Pressure monitoring and maintenance: Install a pressure gauge and a pressure relief valve to prevent overpressure.
3. Remove the radiators, oil conservator, gas relay, oil connecting pipe and other accessories. Packed separately from the transformer body.
4. Flange sealing: All flange interfaces are secondary sealed and tightened with bolts to prevent sealing failure due to transportation vibration.
5. Add corner protectors around the transformer, and then wrap the entire unit with protective film.
Corner protection material: foam, plastic, or cardboard corner protectors (special corner guards made of pressed cardboard).
6. Finally, pack the unit in a steel frame wooden crate. Shock monitoring devices will be mounted on the wooden crate if required by the customer
7. The wooden crates should be marked with forklift handling symbols and center of gravity indicators.
8. Cover the top of the wooden crate with a moisture-proof tarp.
4.2 Shipping
Before loading, measure the transformer’s size and weight, and plan a route that avoids height, width, and weight restrictions. Use low-bed or specialized trucks with adequate capacity.
Align the transformer’s center of gravity with the vehicle. Use channel steel and proper fastening methods to secure the base to the truck, if permitted. Secure the transformer with slings or chains through designated transport holes, avoiding fragile components such as radiators and bushings. Lock internal components and seal all doors.
Keep speed ≤60 km/h and tilt ≤15° during transport. Avoid sudden moves and strong vibrations. Assign escorts to check binding and stop transport in severe weather.
When lifting, keep rope angles ≤60°. Use spreader bars if needed. Always lift upright, and for units without top lugs, use bottom lifting rods.
05 Site and Summary
3MVA-33/11kV distribution step down transformer can be used for urban power distribution and renewable energy, such as connecting medium voltage to the grid and stepping down the voltage in wind power or solar power sites. It can also be adapted to skid-mounted and container-mounted mobile power stations as temporary power stations for emergency use.
In addition to distribution step down transformer, we manufacture a complete range of transformers, including pad mounted, pole mounted, dry type, power, furnace, and special application transformers, meeting diverse industrial needs.
