8 MVA Small Power Transformer-33/33 kV | Zimbabwe 2024

The Heart of the Grid, Built to Last.

01 General

1.1 Project Description

The 8 MVA auto power transformer was delivered to South Africa in 2022.

The rated power of the oil Immersed transformer is 8000 KVA with ONAF cooling, the primary voltage is 33 kV with ±10*1.5% tapping range (OLTC), the secondary voltage is 33 kV, they formed a vector group of YNa0. The high-voltage (HV) winding is star-connected with a neutral (Y). here is no phase displacement between the HV and LV windings (denoted by “0”). Allows for voltage adjustment on the high-voltage side without interrupting the load. Compensates for voltage variations in the grid or load side. High mechanical and electrical strength ensures long-term operation with minimal downtime. In natural cooling mode (ONAN), the transformer can operate at a fraction of its full rated capacity. In ONAF mode, forced air cooling enables the transformer to reach full load capacity (8MVA).

1.2 Technical Specification

8 MVA power transformer specification and data sheet

1.3 Drawings

8 MVA power transformer diagram drawing and size.

02 Manufacturing

2.1 Core

The core is composed of multiple stacked silicon steel sheets, held together with fasteners and straps to maintain structural stability. The red frame provides support and fixation, with reinforced connecting parts at the top and bottom. The central part of the core uses multiple layers of insulating material to reduce eddy current losses. The overall structure is solid, with surface protection treatment, making it suitable for industrial environments that require a stable magnetic field.

2.2 Winding

Windings are key components of the transformer, they are made of high-quality oxygen free copper, with our advanced technology and experience, our windings have the following features: 1. The windings are able to withstand lighting overvoltage, transient overvoltage, longtime overvoltage. 2. High heat resistant strength, it’s able to continuous working over 20 years under the heat generate by current. 3. The windings are able to withstand the short-circuit current. 4. High mechanical strength.

2.3 Tank

Transformer tanks produced by our company have many advantages: High quality materials: We use high quality steel to make our fuel tanks durable and strong. Anti-corrosion and explosion-proof design: Our fuel tanks are specially treated to have excellent anti-corrosion properties and are designed according to relevant standards to prevent fire or explosion. Precision machining: We use advanced processing equipment and technology to ensure the precision machining of the fuel tank to ensure its dimensional accuracy and assembly quality. Appearance design: We pay attention to the appearance design of the fuel tank, so that its appearance is beautiful and generous, while meeting industry standards. Customization capability: We can provide customized tank solutions according to the specific requirements of customers to meet the needs of different transformers.

2.4 Final Assembly

Core and coil assembly: The core and winding coils, which are the essential components of the auto transformer, are assembled together. This involves careful placement and securing of the winding coils around the core to create the magnetic circuit essential for voltage transformation. Insulation and protection: Insulation materials are applied to protect the winding coils from damage and to ensure electrical safety and reliability. This may involve the use of insulating tapes, varnishes, or other protective coatings. Connection of terminals: The terminals of the winding coils are connected to the appropriate connectors or terminals on the auto transformer, ensuring a complete electrical circuit for power transmission.

03 Testing

1. Insulation resistance test: Test the insulation resistance to ensure that the insulation performance meets the requirements.

2. Interturn resistance test: test the interturn resistance to ensure good insulation and connectivity between windings.

3. Interturn voltage test: Test the interturn voltage to ensure that the insulation performance between the windings meets the requirements.

4. Voltage test: Apply a certain AC or DC high voltage to test the insulation performance of the equipment under high pressure.

5. Rectifier test: Test the performance and efficiency of the rectifier.

6. Load test: Test the performance of the transformer under rated load.

7. Short circuit test: test the performance of the transformer under short circuit conditions.

8. Overtemperature test: test the working performance and insulation performance of the transformer under high temperature environment.

04 Packing and Shipping

4.1 Packing

We choose wooden box as packing material because it can bear the weight and size of the transformer. The transformer is then securely secured to the package with straps or brackets to prevent movement during transport.

4.2 Shipping

During handling and transportation, we always take care to protect the transformer from dust, moisture and physical damage. The packaging is also marked with proper handling instructions and warning signs to ensure safe transport. During transportation, we constantly monitor transformers for signs of damage or displacement and take additional precautions as needed to ensure the safety of the cargo. Upon arrival at the destination, the packaging is carefully removed and the transformer is checked for any potential damage before installation.

05 Site And Summary

Preparation: Inspect the transformer foundation and equipment status, perform insulation checks, and prepare appropriate lifting and rigging tools.

Hoisting: Lift the transformer using specified lifting points, ensure it is properly aligned and leveled, then fasten it securely to the foundation.

Accessory Assembly: Mount bushings, cooling radiators, and other auxiliary components, ensuring all connections are sealed and tightened according to specifications.

Oil Injection: Carry out vacuum oil filling using a high-efficiency oil purification system. Monitor the oil level and confirm all seals are intact to prevent leakage.

Testing: Conduct insulation, ratio, no-load, and short-circuit tests.

Grounding: Set up the grounding system and measure earth resistance to ensure safe and reliable operation.

Commissioning: Double-check all installation steps, conduct step-by-step load testing, and officially energize the transformer once all performance parameters are within acceptable limits.