Introduction
As a critical component in power systems, transformers are widely used for the transmission and distribution of electrical energy. Their performance and quality directly affect the stability and safety of the entire power grid. To ensure efficient operation and long-term reliability, the manufacturing process of transformers must strictly follow standardized procedures. This article provides a brief overview of the transformer manufacturing process, focusing on five key stages: core, winding, tank, assembly, and testing. From material preparation to the final product, it outlines the complete journey of a transformer from start to finish.
Core Processing: Constructing the Main Magnetic Flux Path
1. Definition
A transformer core is a crucial component made of ferromagnetic materials with high magnetic permeability (such as silicon steel sheets), which are laminated or wound to form a magnetic circuit. The core provides a low-reluctance path for magnetic flux and facilitates efficient electromagnetic coupling between the primary and secondary windings.
2. Function
Provides a magnetic flux path: The core offers a closed loop with low magnetic resistance for the magnetic flux to pass through, enhancing the magnetic coupling between coils.
Enhances electromagnetic induction: By concentrating the magnetic field within the core, the efficiency of electromagnetic induction in the transformer is significantly improved.
Reduces energy losses:
High permeability materials reduce magnetic reluctance.
Laminated structures reduce eddy current losses.
Proper core design minimizes hysteresis loss.
Structural support: In certain designs, the core also plays a mechanical role by supporting the transformer windings.
3. Types
Transformer cores can be categorized based on their structural form and material:
(1) By Structural Form:
Core Type
Windings are placed around one or two vertical limbs of the core, and magnetic flux completes the path through the horizontal yoke. Commonly used in power transformers.
Shell Type
The windings are surrounded by the core, and magnetic flux flows through multiple paths. This type offers high capacity and strong short-circuit resistance.
Toroidal Core
A closed ring-shaped core where the magnetic flux flows in a continuous loop. It has low leakage flux and high efficiency, often used in electronic transformers.
(2) By Material Form:
Made of stacked silicon steel sheets, typically used in medium to large power transformers.
Formed by winding silicon steel strips into circular or oval shapes, commonly used in smaller transformers and electronic devices.
Employed in high-frequency and high-efficiency applications such as switch-mode power supplies.
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Winding Production: Enabling Voltage Transformation
| Winding | Layered winding | cylindrical type | Single-layer cylindrical type |
| Double-layer cylindrical type | |||
| Multi-layer cylindrical type | |||
| Segmented cylindrical type | |||
| Foil type | General foil type | ||
| Segmented foil type | |||
| pie winding | Continuous winding | General continuous winding | |
| Semiconductive winding | |||
| Internal shielded continuous winding | |||
| Interleaved Winding | Standard Interleaved Winding | ||
| Staggered Interleaved Winding | |||
| Interleaved Continuous Disc Winding | |||
| Helical Winding | Single Helical Winding | ||
| Single Semi-Helical Winding | |||
| Double Helical Winding | |||
| Double Semi-Helical Winding | |||
| Triple Helical Winding | |||
| Quadruple Helical Winding | |||
| Interlaced winding | Continuously Alternated Helical Arrangement | ||
| Single or Double Disc Winding for Shell-Type Transformers | |||
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Tank: The Protective and Cooling Shell
1. Definition
The transformer tank is the external enclosure of a transformer. Its primary purpose is to contain the transformer core and windings along with insulating oil, while also providing mechanical protection, electrical insulation, and heat dissipation.
2. Main Functions
Sealed Enclosure:
Encapsulates the core and windings, maintaining the cleanliness of the insulating oil and preventing the ingress of moisture and contaminants.
Insulation Medium:
The tank is filled with insulating oil, which enhances dielectric strength between windings and the core.
Cooling System:
Equipped with radiators or cooling devices, the tank helps dissipate heat generated by internal components via oil circulation.
Mechanical Support:
Supports the internal assembly, ensuring structural integrity and safety during transportation and operation.
3. Structural Types of Transformer Tanks
Radiator-Finned Tank
Fitted with welded fins or radiators on the tank wall for natural air convection cooling.
Commonly used in distribution transformers.
Corrugated Wall Tank
Uses corrugated panels that can flex with changes in oil volume due to temperature variations.
Compact design, excellent sealing, ideal for small to medium-sized transformers.
Forced Oil-Circulation Cooling Tank
Includes external oil pumps and coolers for active oil flow and enhanced cooling performance.
Used in large or high-voltage power transformers.
Box-Type or Drum-Type Tank
Simple rectangular or cylindrical structure, robust and easy to manufacture and transport.
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Assembly: Piecing Together the Whole Machine
Final assembly is the critical stage where all major transformer components are integrated into a complete, operational unit. The standard procedure includes:
The pre-manufactured windings are carefully installed onto the designated limbs of the transformer core, ensuring alignment, mechanical stability, and proper insulation clearances.
The upper yoke of the transformer core is assembled and inserted to close the magnetic circuit. Clamping devices are used to secure the core structure and maintain tightness.
The winding leads are connected to the tap changer (on-load or off-load), and other internal electrical connections are made according to design drawings.
Objective: Eliminate internal moisture.
Method: Push the assembled active part into a drying oven for vacuum or hot-air drying.
Key Checks:
Moisture content within acceptable limits.
No insulation deformation or contamination.
After drying, the active part is carefully lifted and lowered into the transformer tank under clean conditions. It is positioned and fixed precisely to prevent mechanical stress or contamination.
All necessary accessories are installed, including the temperature monitor, pressure relief valve, oil level gauge, cooling system, grounding terminals, and other fittings required for safe and efficient operation.
Method: Inject dehydrated and filtered insulating oil after accessories are installed.
Key Checks:
Oil meets purity and dielectric strength standards.
No leaks after filling.
Factory Testing: Verifying Performance and Safety Standards
To verify that the transformer meets design, safety, and performance standards before delivery and commissioning.
Routine tests
1. Measurement of winding direct resistance
2. Measurement of voltage ratio and check of phase displacement
3. Check of Voltage Ratio and Vector Group
4. Measurement of Impedance Voltage and Load Losses
5. Measurement of short-circuit impedance
6. Measurement of no-load loss and no-load current
7. Dielectric routine tests
8.Ratio on all connections and tap positions
9.Angular displacement
10. Applied Voltage Test
11. Induced Voltage Withstand Test With pd Measurement (IVPD)
12. Seal test
13.Magnetic balance test
Type tests
1. Dielectric type tests
2. Temperature-rise test
3. Tests on on-load tap-changers
4. Lightning Impulse Test
5. Oil leakage test
6.Dynamic short circuit test
Special tests
1. Dielectric special tests
2. Determination of capacitances windings-to-earth, and between windings
3. Determination of transient voltage transfer characteristics
4. Measurement of zero-sequence impedance(s)
5. Determination of sound levels
6. Measurement of the harmonics of the no-load current
7. Measurement of the power taken by the fan and oil pump motors
8. Insulation Resistance and absorption Ratio measurement
9. Measurement of dissipation factors and capacitance of bushing
10. Measurement of main body dissipation factor and capacitance
11. Current transformer measurement
12. On-load tap changers-operation test
13. Line terminal AC withstand voltage test (LTAC)
14. Measurement of frequency response
15. Insulation of auxiliary wiring (AuxW)6/4/2025
* Any of the special test can be arranged on special requirement of customer.
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