Power Transformer Parts And Functions Explained

What are the components of a transformer?

A power transformer uses alternating magnetic flux to transfer alternating electrical energy between two or more windings while changing the voltage, current, or impedance relationship. To really understand it, the more intuitive way is to take a transformer apart and see which power transformer parts it consists.

Functionally, the core components of a typical transformer include the magnetic core, windings and main insulation system, around which there are also leads, terminals or bushings, tap windings and tap-switches, cooling devices, housings or oil tanks, as well as temperature measuring elements and protection monitoring accessories. These parts perform their respective duties and cooperate closely with each other to determine whether a transformer can operate stably and safely.

Core and Winding: Accomplishing the Main Role of Energy Transfer

The magnetic core provides a closed path of low reluctance for the main flux and is usually stacked with thin electrical steel sheets insulated from each other, so that the eddy current loss can be pressed to a relatively low level. The winding is made of copper or aluminum conductor, and the conductor cross-section, the number of parallel strands and the transposition method are determined according to the rated current, loss, magnetic leakage and mechanical strength. Together, the core and windings form the active part of the transformer, that is, the part that actually performs energy transfer.

The voltage ratio of a transformer is equal to the turns ratio of the primary and secondary windings. During boost operation, the number of secondary turns is more and the current is smaller, while during buck operation, the opposite is true. Ideally, the input apparent power is equal to the output apparent power, and the actual operation of the output power will be less than the input power, the difference mainly comes from the core loss, winding resistance loss and additional loss caused by magnetic leakage.

Main insulation system: determine safety and life

The main insulation system is responsible for isolating windings of different potentials, windings and cores, and live parts from ground. The inter-turn, inter-layer, inter-section and main insulation each bear different electrical stresses. The insulating material needs to be compatible with the highest electric field, temperature class, cooling medium, partial discharge, mechanical load and expected environment. The state of the insulation system directly determines the voltage resistance and long-term life of the transformer.

Liquid immersed transformer with insulation liquid at the same time to assume the insulation and heat transfer function, dry-type transformer with solid insulation and air as the main insulation and cooling medium, the active part is not immersed in the insulation liquid. Cast resin dry-type transformers also encapsulate at least the high voltage windings in a cured resin to enhance mechanical support and reduce direct exposure of the windings to moisture and contamination.

Bushings, Terminals and Tap-Switches

The bushing provides insulation and mechanical interface for live conductors through the grounded enclosure, and its contamination, cracks, leakage or overheating of the connection may affect the reliability of operation. The lead wire and terminal are responsible for leading out the winding current and connecting it to the external circuit.

The tap changer adjusts the voltage by changing the effective number of turns, which is divided into two types: no excitation tap and on-load tap. The operating conditions, maintenance objects and protection requirements of the two are different, and the operating procedures cannot be mixed. With the tap, the transformer can maintain a relatively stable output voltage when the system voltage fluctuates.

Cooling device and housing

Transformer operation will produce losses, these losses eventually become heat. Radiators, fans, oil pumps or water coolers take heat away. Dry-type transformers can be used for natural air cooling or forced air cooling, while liquid-immersed products may rely on the natural circulation of oil and air, and may also be equipped with fans, oil pumps or water coolers to form forced cooling. It is important to note that after the forced cooling accessory is shut down, the equipment cannot continue to be used according to the corresponding forced cooling capacity.

The shell or oil tank is used to support and protect the iron core, winding and insulation system. Its protection, heat dissipation, grounding and mechanical strength must match the installation environment. Some liquid-immersed products will also be equipped with oil storage tanks to provide buffer space for the thermal expansion and contraction of insulating liquid, and cooperate with respirators to reduce the risk of moisture brought in when ventilating with the outside world.

Protection and Monitoring Annex

Accessories such as temperature indication, level, pressure relief, and gas or sudden pressure protection are used to monitor or mitigate specific abnormal conditions, but no single accessory can cover all internal failures. The current transformer, terminal box and monitoring interface built in the transformer are part of the protection and measurement chain, and its transformation ratio, polarity, accuracy level and wiring must be consistent with the protection design.

If the above components are put together, the overall logic of the power transformer structure can be understood: the magnetic core and winding are responsible for energy transmission, the insulation system ensures electrical safety, the bushing, terminal and tap changer are responsible for electrical connection and voltage regulation, the cooling device and shell control heat dissipation and mechanical protection, and the protection and monitoring accessories are for long-term safe operation. Parts transformer each type of power are not isolated. Their materials, sizes and processes must match each other. Any short board may become a hidden danger to the entire equipment.