Manufacturing
How a power transformer is built.
Scroll to assemble a three-phase oil-immersed power transformer, from the bare core to a tested unit. Scroll back up to take it apart.
Scroll to build it
- 01 / 08
Core
Grain-oriented silicon-steel laminations are cut to length and stacked with step-lap joints to keep no-load loss and noise low. The top yoke is then unlaced so the windings can be lowered onto the limbs.
- Material
- Grain-oriented silicon steel
- Joints
- Step-lap, mitred
- Equipment
- Soenen cut-to-length line
- 02 / 08
Windings
Each limb takes a low-voltage winding next to the core and a high-voltage winding outside it, separated by pressboard cylinders and spacers. The top yoke is re-laced and the active part is clamped.
- Arrangement
- Concentric: LV inner, HV outer
- HV coils
- 20 t horizontal winding machine
- LV coils
- Foil winding machine
- 03 / 08
Leads and tap changer
Winding ends are connected to the bushing leads, and tapping leads run to the tap changer: on-load (OLTC) for regulation in service, or off-circuit (OCTC) for settings chosen at commissioning.
- HV leads
- To HV bushings
- LV leads
- Copper bar, incl. neutral
- Tap changer
- OLTC or OCTC
- 04 / 08
Vacuum drying
The active part is heated under vacuum to draw moisture out of the cellulose insulation. It is re-clamped afterwards, because the insulation shrinks as it dries.
- Removes
- Moisture from paper and pressboard
- Then
- Re-clamping of the windings
- 05 / 08
Tank, cover and bushings
The dried active part goes into the welded tank without delay, the cover is bolted on and the high- and low-voltage bushings are mounted on it.
- Tank
- Robot-welded steel
- HV bushings
- 3 phases
- LV bushings
- 3 phases + neutral
- 06 / 08
Oil filling
Filtered, degassed insulating liquid is filled under vacuum so that no air stays trapped in the insulation, followed by a standing time before testing.
- Liquid
- Mineral oil or natural ester
- Method
- Filling under vacuum
- 07 / 08
Cooling and conservator
Radiators carry heat away by natural oil and air circulation (ONAN); fans add forced air (ONAF). The conservator takes up oil expansion, with a Buchholz relay and breather on its pipework.
- Cooling
- ONAN, ONAF with fans
- Protection
- Buchholz relay
- Breathing
- Silica-gel breather
- 08 / 08
Tests and release
Routine tests confirm every unit before shipment: ratio and vector group, winding resistance, no-load and load loss, impedance, applied and induced voltage, and partial discharge. Lightning impulse and temperature rise are added when specified.
- Lightning impulse
- 2,400 kV test system
- Power frequency
- 300 kV test system
- Partial discharge
- 8-channel detector
Where each step happens at Tianyu.
The same sequence runs through the Fuzhou manufacturing base, from core cutting and winding lines to the test laboratory.
Review the build of your transformer.
Ask for a factory visit or the inspection and test plan for your specification.