In a transformer, the primary winding is the winding connected to the energy source. It draws in the electrical power, generates an alternating magnetic field in the iron core, and transfers the energy to the secondary winding. Its correct design is decisive for the performance of the entire unit. Designing the primary winding is one of the most demanding tasks in transformer manufacturing and requires deep electrical engineering expertise.
What properties must a primary winding fulfill?
The primary winding must be sized for the input voltage and be electrically and mechanically highly resilient. It is usually made of copper or – in smaller distribution transformers – aluminum, and is carefully insulated. At high voltages, elaborate insulation systems made of paper, pressboard, or epoxy resin are used to prevent partial discharges and voltage breakdowns.
Key Characteristics at a Glance
- Designed for the input voltage (medium, high, or extra-high voltage)
- Material usually copper, though aluminum is also used in smaller units
- Insulation made of a paper-oil system or epoxy resin
- High mechanical strength against short-circuit forces
- Various winding designs (layer, disc, helical winding)
- Various cooling duct concepts between the layers
- Careful clamping prevents movement of the winding during operation
Frequently Asked Questions
Why is copper often preferred over aluminum?
Copper has higher electrical conductivity, requires smaller cross-sections, and thereby enables more compact transformers. Aluminum, however, is lighter and more cost-effective – making it the material of choice for many distribution transformers.
What happens if the primary winding is damaged?
Damage to the primary winding usually results in complete failure of the transformer. An internal insulation breakdown can also decompose the oil and build up pressure. Protective devices such as differential protection and the Buchholz relay detect such faults at an early stage.
Why is clamping the winding so important?
During operation, electromagnetic forces act on the winding that can cause it to move. Consistently high clamping pressure prevents this, avoids friction on insulation parts, and thereby secures electrical strength and mechanical stability over the entire service life.
How is the insulation of a primary winding tested?
Standard tests include insulation measurement with a megohmmeter, an AC voltage test at 2 to 2.5 times the rated voltage, an impulse voltage test, and partial discharge measurement. These tests ensure that the winding safely withstands all electrical stresses occurring during operation.
For custom transformer concepts with highly resilient primary windings, we will develop the right solution together with you. Contact our engineers.