Power Transformer Presentation

What does a power transformer do?

A power transformer is a 1 of static electrical equipment that uses alternating magnetic flux to transfer AC energy between two or more windings while changing the voltage, current, or impedance relationship. It does not change the power frequency while transforming the voltage, which is the basic feature of the conventional power frequency transformer.

In the power system, the main task of the transformer is to step up and step down. Raising the voltage can reduce the line current when transmitting the same power, thereby reducing the resistance loss of the line and reducing the requirements for the conductor section. When approaching the load end, the voltage is dropped by a step-down transformer for use by terminal equipment. Large power transformers mainly serve power generation step-up, transmission, system interconnection and large-capacity industrial power supply, while distribution transformers further reduce medium voltage to low voltage that can be directly used by end users.

In addition to changing the voltage, the transformer can also undertake electrical isolation, establish a neutral point, transform impedance, or provide multiple sets of AC input for the rectifier device. Electrical isolation exists only in a double-winding or multi-winding structure where the primary and secondary windings are not conductively connected; autotransformers do not provide complete electrical isolation because the primary and secondary windings share part of the winding.

How does energy get from the primary side to the secondary side?

The work of the transformer is based on electromagnetic induction. After the primary winding is connected to the AC power supply, an alternating magnetomotive force is generated, and the alternating magnetic flux is closed along the magnetic core, and the electromotive force is induced in the secondary winding. Ideally, the voltage ratio is equal to the turns ratio, that is, U1/U2 = N1/N2; the current ratio is the opposite of the turns ratio, I1/I2 = N2/N1. The current is proportionally reduced while boosting, and the current is proportionally increased while stepping down.

After the secondary side is connected to the load, the magnetomotive force generated by the secondary current will change the current taken by the primary side, so that the main magnetic flux in the magnetic core remains approximately stable within the normal range. Therefore, the input power of the transformer varies with the load, and it does not generate additional power by itself. In actual operation, the output active power is equal to the input active power minus the loss of the transformer itself. The loss mainly comes from the hysteresis and eddy current of the magnetic core, as well as the resistance and leakage of the winding.

One thing needs special attention: the transformer cannot rely on stable DC to establish continuous mutual inductance transformation. If DC is added to a winding designed for AC, the limits of the normal inductive reactance are lost and severe overcurrent and overheating may result.

The main components that make up a transformer

A transformer is deployed around the core, windings and main insulation system. The magnetic core provides a low reluctance path for the main flux and is usually stacked with thin electrical steel sheets insulated from each other to limit eddy current losses. The winding is composed of copper or aluminum conductor, and the conductor cross-section, the number of parallel strands and the transposition method are determined by the rated current, loss, magnetic leakage and mechanical strength. The main insulation system is responsible for isolating windings, windings and magnetic cores of different potentials, as well as live parts and ground, inter-turn, inter-layer, inter-segment and main insulation bear different electrical stresses.

Around these 3 parts, there are leads, terminals or bushings, tap windings and tap changers, cooling devices, housings or oil tanks, as well as temperature measuring elements and protective monitoring accessories. The tap changer adjusts the voltage by changing the effective number of turns. The operating conditions, maintenance objects and protection requirements of non-excitation tap and on-load tap are different and cannot be mixed. Bushings provide insulation and mechanical interface for live conductors through the grounded enclosure, where contamination, cracks, leakage or overheating of the connection can affect operational reliability.

According to the insulation and cooling medium, the transformer can be divided into two categories: liquid immersion and dry type. The insulation liquid of the liquid-immersed transformer is also responsible for insulation and heat transfer functions; the dry-type transformer uses solid insulation and air as the main insulation and cooling medium, and the active part is not immersed in the insulation liquid. Poured Resin Dry-type transformers typically have at least the high voltage windings resin-cast into a solid coil to enhance mechanical support and reduce direct exposure of the windings to moisture and contamination.

Common Transformer Types

From the perspective of system location and function, transformers can be divided into generator step-up transformers, transmission or contact transformers, distribution transformers, isolation transformers and voltage regulating transformers. The secondary rated voltage of the step-up transformer is higher than that of the step-down transformer, and the opposite is true; the isolation transformer can be made 1:1, and the voltage conversion can be completed at the same time.

From the perspective of winding structure, there are double winding, 3 winding, multi winding and autotransformer. Double winding is the most basic power transformer structure; 3 winding can be configured on the same magnetic circuit 3 a voltage level; multi winding and double secondary transformer can be isolated from each other load or multiple rectifier bridge power supply.

From the application point of view, there are converter transformers for semiconductor converter devices, phase-shifting rectifier transformers for multi-pulse rectifier systems, traction transformers for rail transit, and special transformers for wind power, photovoltaic, energy storage and data center scenarios. The phase-shifting rectifier transformer supplies power to the rectifier bridge through the secondary windings of different phases, and the phase shift of the windings is used to cooperate with the rectifier bridge to reduce specific low harmonics.

Phase Shifting Rectifier and Dry Products of Shanghai North Transformer

Shanghai Beifan Technology Co., Ltd. focuses on the research and development, design and manufacturing of special transformers and power conversion supporting products. The manufacturing locations are located in Songjiang, Shanghai, Wenzhou, Zhejiang and Jinan, Shandong. The company's products cover medium and high voltage frequency conversion, wind power, photovoltaic, energy storage, charging, power testing, data center, ship and shore power applications, serving steel, cement, petrochemical, thermal power, mining, municipal, data center and marine engineering and other industries.

In terms of phase-shifting rectifier products, Shanghai North Transformer provides general-purpose, Mini-type, air duct heat dissipation structure, upper and lower air duct structure, data center, 22kV and 35kV high voltage levels, four quadrants, triangular iron cores and ultra-large capacity dry products. Among them, the phase-shifting rectifier transformer for data center is used for HVDC, 240V or 336V DC system and high-efficiency UPS front-end rectifier unit, which can supply power to multiple independent rectifier modules. The four-quadrant phase-shifting rectifier transformer is used for drive systems that require bidirectional energy flow and regenerative braking energy feedback.

In terms of dry-type products, the company also provides industrial on-board power dry-type transformers, shore power dry-type isolation transformers, isolation-specific dry-type transformers, epoxy-cast single-phase combined dry-type transformers, new energy-specific dry-type transformers, dry-type transformers for power supply testing and marine dry-type transformers. The company has developed 17000kVA forced oil circulation water-cooled rectifier transformer, 14000kVA air-cooled dry transformer, 35kV dry-type phase-shifting rectifier transformer, 11750kVA fracturing transformer, 21000kVA four-quadrant transformer, 25000kVA water-cooled inverter supporting dry-type phase-shifting rectifier transformer and 27500kVA dry-type products, and can carry out supporting design with inverter, power supply and system equipment customers.

Several issues worth confirming before purchasing

Large power transformers usually need to be designed according to system voltage, capacity, impedance, connection mode, voltage regulation, insulation, cooling, transportation and field interface, and it is difficult to directly replace them with general stock models. Therefore, in addition to the capacity, the primary and secondary rated voltage, frequency, phase number, coupling group, impedance, insulation level, cooling method, enclosure protection level and environmental conditions should be confirmed when purchasing.

From the perspective of supply mode, transformers have different levels such as catalog type, configuration type and engineering customization. Customization does not mean that all components are developed from scratch, but customer-specific parameters cannot replace safety, insulation and performance verification. The manufacturer is the subject of responsibility for product design or manufacturing, and the supplier may be the manufacturer, authorized channel, system integrator or trader, and the legal subject and chain of responsibility must be identified at the time of procurement. The factory name or place of origin can only indicate the place of manufacture, and cannot separately prove the design ownership, quality system, type capability, certification scope or after-sales responsibility.

Clear these conditions, combined with system research and technical specifications to match the product, often than simply compare a capacity number closer to the truly reliable selection results.