In the modern world, electrical power is the lifeblood of civilization. From the lights in your home to the machinery in manufacturing facilities, electricity powers our daily lives. Yet few people understand the critical role transformers play in making this possible. These essential devices enable the safe and efficient transmission of electrical energy across vast distances, ensuring that power reaches its destination at the right voltage level.
What Is an Electrical Transformer?
An electrical transformer is a static electromagnetic device that transfers electrical energy between two or more circuits through electromagnetic induction. Unlike rotating machines such as motors or generators, transformers have no moving parts, which contributes to their reliability and longevity. The fundamental purpose of a transformer is to change voltage levels—either increasing (stepping up) or decreasing (stepping down)—while maintaining the same frequency and power.
The basic principle behind transformer operation dates back to Michael Faraday’s discovery of electromagnetic induction in 1831. This groundbreaking principle states that a changing magnetic field can induce an electromotive force (EMF) in a conductor. Transformers exploit this phenomenon through mutual induction between two electrically isolated coils.
Faraday and the Law of Electromagnetic Induction
The Essential Components of a Transformer
Understanding how transformers work requires familiarity with their key components:
Core
The transformer core provides a low-reluctance path for magnetic flux. Typically constructed from thin sheets of high-grade silicon steel stacked together, the laminated design minimizes eddy current losses. The core concentrates and directs the magnetic field between the primary and secondary windings, ensuring efficient energy transfer.
Primary Winding
The primary winding connects to the input voltage source. When alternating current flows through this coil, it creates a time-varying magnetic field that penetrates the core. The number of turns in the primary winding, along with the applied voltage, determines the strength of this magnetic field.
Secondary Winding
The secondary winding is where the transformed voltage appears. As the magnetic flux from the primary winding passes through the core and links with the secondary coil, it induces a voltage according to Faraday’s law. The secondary winding delivers power to the load at the desired voltage level.
Insulation and Tank
In liquid-filled transformers, the windings and core are immersed in insulating oil contained within a protective tank. This oil serves dual purposes: it provides electrical insulation and helps dissipate heat generated during operation. Dry-type transformers use air as the cooling medium and rely on solid insulation materials.
Components of a Three-Phase Pad-Mounted Transformer
Recommended Reading:
Top 10 Transformer Suppliers in China
How Transformers Work: The Physics Behind Power Transfer
The operation of a transformer is elegantly simple yet remarkably effective. When an alternating voltage is applied to the primary winding, it causes an alternating current to flow. This current creates a magnetic field that continuously expands and collapses around the primary coil. The soft iron core channels this changing magnetic field, directing it through the secondary winding.
Figure 1 illustrates the principle model of a single-phase transformer. It consists of a magnetic core and two windings mounted on the core. The core is made of materials with high magnetic permeability and low hysteresis loss. The winding connected to the power supply is the primary winding, while the winding connected to the load is the secondary winding.
U₁ denotes the voltage applied to the primary winding, N₁ represents the number of turns of the primary winding, U₂ denotes the output voltage of the secondary winding, and N₂ represents the number of turns of the secondary winding.
Figure 1 — Operating Principle of a Single-Phase Transformer
This is an ideal transformer, meaning that the winding resistance is zero; the magnetic core has very high permeability; the magnetization curve is linear; and there are no hysteresis losses, eddy current losses, or magnetic leakage.
When a sinusoidally varying alternating current is applied to the primary winding, according to the fundamental principle of transformers:
U₁ / U₂ = N₁ / N₂ = k
where k is the voltage ratio (turns ratio).
Thus, the output voltage is given by:
U₂ = U₁ × N₂ / N₁
The waveforms of the input voltage, output voltage, and core magnetic flux are shown in Figure 2. To clearly illustrate the change in magnetic flux direction, the core is depicted as transparent. In the figure, t indicates the direction of waveform progression.
Figure 2 — Waveforms of a Single-Phase Transformer
In practical power systems, three-phase alternating current is commonly used. Figure 3 shows the principle model of a three-phase transformer, which consists of phase A, phase B, and phase C windings, together with a magnetic core.
Figure 3 — Operating Principle of a Three-Phase Transformer
The three pairs of windings are identical. Each pair includes a primary winding and a secondary winding, with a turns ratio of k. The corresponding ends of the three primary windings are connected together, and the corresponding ends of the three secondary windings are also connected together, forming a star (Y) connection.
For an ideal transformer, when a sinusoidally varying three-phase alternating current is applied to the primary windings, the following relationships apply according to the basic transformer principle:
U₁A, U₁B, and U₁C represent the three-phase input voltages, while U₂A, U₂B, and U₂C represent the corresponding three-phase output voltages.
U₁A / U₂A = U₁B / U₂B = U₁C / U₂C = k
The input and output voltage waveforms of the three-phase transformer are shown in Figure 4, where t indicates the direction of waveform progression.
Figure 4 — Waveforms of the Three Pairs of Windings in a Three-Phase Transformer
Types of Transformers and Their Applications in Modern Power Systems
Transformers are essential components in electrical power systems, enabling efficient voltage conversion for power generation, transmission, distribution, and end-use applications. Depending on the insulation method, installation form, cooling technique, and application environment, transformers can be classified into several categories.
Oil-Immersed Transformers
Oil-immersed transformers use insulating oil as both a dielectric medium and a cooling agent. The oil effectively dissipates heat generated by the windings and core while providing excellent electrical insulation.
These transformers are widely used in high-voltage and high-capacity applications such as power substations, transmission networks, heavy industrial plants, and renewable energy projects. Their high efficiency, strong overload capability, and long service life make them a preferred choice for outdoor and utility-scale installations. However, due to fire risk and oil leakage concerns, they require proper safety measures and installation space.
Dry Type Transformers
Dry-type transformers rely on air or solid insulation systems instead of oil. Common designs include cast resin and vacuum pressure impregnated (VPI) transformers. Without flammable liquid insulation, they offer enhanced fire safety and environmental protection.
Dry-type transformers are commonly installed in indoor or densely populated environments such as commercial buildings, hospitals, data centers, airports, and public transportation facilities. Although their capacity is typically lower than that of oil-immersed units, their low maintenance requirements and safe operation make them ideal for sensitive locations.
Pad-Mounted Transformers
Pad-mounted transformers are ground-installed, enclosed distribution transformers designed for underground distribution systems. They are housed in tamper-resistant cabinets and often integrate switching and protection devices.
These transformers are widely used in residential communities, commercial developments, and industrial parks, particularly in urban areas where aesthetics, safety, and space efficiency are critical. Pad-mounted transformers support loop or radial distribution networks and are a key component of modern North American-style power distribution systems.
Pole-Mounted Transformers
Pole-mounted transformers are installed on utility poles and serve as a cost-effective solution for stepping down medium voltage to low voltage in overhead distribution networks.
They are commonly used in rural areas, suburban neighborhoods, and regions with low power demand density. Their simple installation and low infrastructure cost make them ideal for extending electricity access, although their capacity and environmental exposure must be carefully considered.
Additional Transformer Classifications
Beyond these common types, transformers can also be classified as distribution transformers, power transformers, isolation transformers, instrument transformers (CTs and PTs), and special-purpose transformers for traction, marine, or renewable energy systems. Each category is designed to meet specific voltage levels, load characteristics, and regulatory requirements.
VIEW HIITIO TRANSFORMER PRODUCT LINE
Oil Immersed Transformer
Why Transformers Are Essential for Power Distribution
Without transformers, modern electrical grids would be impossible. Here’s why they’re so critical:
Enabling Long-Distance Transmission
Power plants often sit far from population centers due to environmental, safety, and land-use considerations. Transmitting electricity at low voltages over long distances would result in massive energy losses due to resistance in the cables. By stepping up voltage to hundreds of thousands of volts, transformers allow current to decrease dramatically, reducing I²R losses exponentially.
Voltage Regulation
Transformers at distribution substations maintain proper voltage levels throughout the electrical grid. As load conditions change throughout the day, voltage can fluctuate. Distribution transformers help stabilize these variations, ensuring consumers receive consistent voltage regardless of demand patterns.
Safety Enhancement
The high voltages necessary for efficient transmission would be lethal in homes and businesses. Step-down transformers reduce these dangerous voltages to safe levels—typically 120/240 volts for residential use and 208/480 volts for commercial applications. This voltage reduction is essential for protecting people and equipment.
System Flexibility
Transformers enable interconnection between different voltage levels within the power grid. This flexibility allows utilities to optimize system configuration, balance loads across networks, and respond effectively to changing demand patterns.
Transformer Efficiency and Losses
While transformers are highly efficient devices—typically achieving 95-98% efficiency—they do experience some energy losses:
Copper Losses
Also known as I²R losses, these occur due to resistance in the windings. Current flowing through the copper conductors generates heat proportional to the square of the current. Manufacturers minimize these losses by using larger conductor sizes and high-purity copper or aluminum.
Iron Losses
The magnetization and demagnetization of the core material during each AC cycle produces hysteresis losses. Additionally, circulating eddy currents within the core generate heat. Laminating the core with thin, insulated steel sheets dramatically reduces eddy current losses.
Cooling Systems
To maintain efficiency and longevity, transformers employ various cooling methods. Small transformers may use natural air cooling, while larger units incorporate forced air, oil circulation, or water cooling systems. Proper thermal management prevents overheating and extends transformer lifespan.
Effective Strategies for Reducing Transformer Operating Losses
(1) Optimizing Core Design and Material Selection
In terms of core materials, the adoption of new low-loss materials should be actively promoted. Amorphous alloy materials offer distinctive performance advantages: compared with conventional silicon steel sheets, their core losses can be reduced by approximately 70%–80%, making them particularly suitable for distribution transformers with long no-load operating periods. In core design, magnetic flux density must be strictly controlled.
(2) Improving Winding Design and Material Application
Copper conductors should be prioritized as winding materials due to their low resistivity, which helps reduce winding resistance. For high-current windings, resistance can be further reduced by increasing the conductor cross-sectional area. From a structural design perspective, in high-frequency operating scenarios, the use of multi-strand parallel windings can effectively mitigate the skin effect and reduce the increase in resistance.
(3) Rational Selection of Transformer Capacity and Operating Mode
Accurately matching transformer capacity to actual load demand is a critical factor in loss reduction. Studies indicate that the economic operating load factor of a transformer typically falls within the range of 50%–70%, where core losses and copper losses are approximately equal and total losses reach a minimum. Therefore, in practical applications, transformer capacity should be selected based on realistic load conditions. For transformers operating under long-term light-load conditions—where the load factor is below 30%—it is advisable to replace them with smaller-capacity units or adopt parallel operation of multiple transformers, flexibly adjusting the number of units in service according to load variations.
Transform Your Power Infrastructure with HIITIO
When it comes to electrical transformers, quality and reliability aren’t negotiable—they’re essential. HIITIO delivers industry-leading transformer solutions engineered for optimal performance, maximum efficiency, and exceptional longevity. Our comprehensive transformer product line encompasses power transformers, distribution transformers, and specialized units designed for demanding applications. Each HIITIO transformer undergoes rigorous testing to ensure it meets international standards and exceeds performance expectations.
Whether you’re upgrading aging infrastructure, expanding your distribution network, or implementing new power generation facilities, HIITIO provides the expertise and products you need. Call us to request a consultation and receive a customized solution for your project.
