Power Transformer Parts And Their Functions

Power Transformer Structure

A power transformer may appear to be a quiet unit, but structurally, its typical components include a magnetic core, primary and secondary windings, main insulation, leads and terminals, tap-in components, housing or fuel tank, cooling structure, and protective accessories. The primary function of the transformer body, housing, or fuel tank is to support and protect the magnetic core, windings, and insulation system, while also meeting the requirements for protection, heat dissipation, grounding, and mechanical strength. Dry transformers use solid insulation and air as the main insulation and cooling media, and the active part is not immersed in the insulating liquid; liquid-immersed transformers rely on the insulating liquid to perform both insulation and heat transfer functions.

The core provides a low magnetoresistance path for the main magnetic flux

The magnetic core is the skeleton of the transformer’s magnetic circuit, providing a closed path with low magnetoresistance for the main magnetic flux. It is typically made of thin, insulated electrical steel sheets stacked together to limit eddy current losses. Magnetic core materials are usually cold-rolled oriented electrical steel or other low-loss magnetic materials. The grade, sheet thickness, magnetic flux density and joint structure of the material will directly affect the no-load loss and noise. During manufacturing, the magnetic core undergoes processes such as shearing or slitting of electrical steel sheets, lamination or winding, joint control, clamping and grounding. The stepped joint structure can improve the magnetic flux distribution at the joint, thereby reducing joint loss and no-load noise.

The winding is responsible for the conversion of voltage and current

The winding is the part of the transformer that actually converts electrical energy and is made of copper or aluminum conductors. The conductor cross section, number of parallel strands and transposition method are determined by the rated current, loss, magnetic leakage and mechanical strength. You cannot just choose a random wire diameter based on the current. Depending on the voltage, current, short-circuit force and cooling requirements, the winding can be made into various forms such as layered, cylindrical, continuous, pancake, spiral or foil. High-current windings also employ multi-strand parallel connection and conductor transposition to improve current distribution and reduce additional losses caused by eddy currents and circulation. The axial and radial cooling channels reserved inside the winding not only bear the responsibility of heat dissipation, but also affect leakage magnetism and mechanical support. They are parts that need to be considered simultaneously in design and manufacturing.

Insulation systems define safe boundaries

Insulation systems are needed between windings, between windings and cores, and between live parts and ground to isolate parts with different potentials. The electrical stresses experienced by the turns, layers, segments, and main insulation are not the same, and the insulation material must match the highest electric field, temperature level, cooling medium, partial discharge, mechanical load, and expected environment. In dry products, NOMEX paper is often used for the turn insulation of H-grade non-encapsulated coils, which is combined with solid insulation and air to complete insulation and heat dissipation.

Power Transformer Parts And Functions

In addition to the three core components of magnetic core, winding and insulation, there is also a group of auxiliary components on the transformer, each responsible for a specific function. The sleeve provides insulation and mechanical interface for the live conductor to pass through the grounded housing or structure; the tap changer adjusts the voltage by changing the effective number of turns. The operating conditions of unexcited tap and loaded tap are different and cannot be mixed. Radiators, fans, oil pumps or water coolers are responsible for taking away the heat generated by losses; oil storage cabinets provide a buffer space for the thermal expansion and contraction of insulation liquid for some liquid-immersed transformers; respirators are used to reduce the moisture entering the interior when the equipment is ventilated with the outside world. Accessories such as temperature indication, liquid level, pressure release, and gas or burst pressure protection are used to monitor or mitigate specific abnormal conditions. Built-in current transformers, terminal boxes, and monitoring interfaces are part of the protection and measurement chain, and their ratio, polarity, accuracy level, and wiring must be consistent with the protection design. From a cost perspective, copper or aluminum conductors, electrical steel, insulation materials, resins, insulating fluids, sleeves, tap changers, and cooling equipment are also the main sources of costs for transformer materials and components.

After sorting out these components and functions, looking at a transformer again will not make it a black box. Whether it’s verifying the completeness of a specification, understanding the significance of a test, or initially locating the problem in the event of a fault, comparing the core, windings, insulation, and various auxiliary components item by item is a reliable approach. Whether a transformer can operate stably ultimately depends on whether the components are properly coordinated.