The Role of Power Transformers in Electrical Grids

It is important for machine design engineers to understand how transformers work so they can design machinery that operates optimally within the proper voltage ranges, as well as select the right transformer types and ratings for specific applications.

Because the equipment that these engineers design will interface with electrical systems, they also need to know the correct voltage and current levels to prevent malfunctions or damage. Most important, the placement of transformers within power grids maximizes effectiveness and safety, preventing loss of life and valuable resources.

Power transformers are essential components in electrical grids, ensuring the reliable transmission and distribution of electricity across vast distances. Their strategic positioning within the grid is designed to optimize the efficiency of power delivery.

These transformers play a critical role in adjusting voltage levels, either stepping them up or down to suitable levels. This is necessary for both the long-distance transmission of power at high voltages and for reducing voltage to safe levels for residential and industrial use.

Deep Dive into a Power Transformer

A power transformer is a static electrical device that transfers electrical energy between circuits without any moving parts. It operates based on the principle of electromagnetic induction, efficiently adjusting voltage levels for power distribution and transmission. A typical power transformer consists of two or more coils of wire connected by a shared magnetic core.

The device commonly contains two wire coils: the primary winding and the secondary winding. These coils are wrapped around a central laminated iron core made of stacked silicon steel sheets. The iron core serves to concentrate and direct the magnetic flux generated by the current passing through the coils. The transformer’s active part consisting of core and coils is housed in a steel tank filled with insulating oil, which cools and insulates the device during operation.

Regular components, such as bushing, tap changer, measurement and protection gauges are essential for proper functioning, reliability and safety of most small and mid-size units. Other than this, enhanced monitoring, cooling and protection systems may be required for large size power transformers based on customer needs and system requirements.

The 525kV 525MVA oil-immersed power transformer is a super high voltage class, large capacity 3-phase autotransformer in deployment in the United States to keep the power grid up and running.

Inner Workings of a Power Transformer

Power transformers operate based on the principle of electromagnetic induction: A changing magnetic field in one coil induces a voltage in another coil located near it. Specifically, when alternating current flows through the primary coil, it creates a fluctuating magnetic field within the iron core, which induces a voltage in the secondary coil wrapped around the same core.

Here’s a breakdown of the process inside a power transformer:

Current flow. An alternating current flows through the primary coil, generating a changing magnetic field around the transformer’s iron core.
Magnetic field variation. As the alternating current cycles, the magnetic field inside the core expands and collapses, following the AC’s rhythm.
Induced electromotive force. This fluctuating magnetic flux passes through the secondary coil, inducing an electromotive force (EMF) in the coil due to the changing magnetic field, as per Faraday’s law of induction.
Voltage adjustment. The induced voltage in the secondary coil depends on factors such as the rate of magnetic flux change and the number of turns in the coils. By varying the number of turns in the coils, the voltage can be stepped up or down according to the transformer’s turn ratio.
Transmission. The transformed voltage is then ready for distribution or further transmission after passing through the secondary winding.

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Powerful Applications

Power transformers are used in various scenarios depending on the voltage requirements. They play an important role in ensuring efficient electricity delivery over long distances. Some common applications include:

Substations. Transformers in substations are crucial for voltage regulation. Step-up transformers increase voltage for long-distance transmission, while step-down transformers, located in Primary-to-Secondary substations, reduce it for local distribution to homes and businesses. Additionally, they provide electrical isolation between different voltage levels to enhance system reliability.
Copper mines. Specialized transformers are used in copper mines to prevent explosions in hazardous underground environments. They are typically robust and designed to operate in harsh environmental conditions such as high humidity, dust and temperature variations. These transformers have protective enclosures to prevent electrical arcing from igniting potentially explosive gases.
Power plants. In thermal and hydroelectric plants, power is generated at a voltage that may not match transmission standards. Generator step-up transformers adjust these voltages to proper levels for efficient transmission through power lines. These large size units are sophisticated equipments to handle large loads and ensure the generated power is transferred to the transmission grid without overloading or voltage instability.

Puerto Penasco’s photovoltaic power station in Mexico’s National Power Electric Utility delivers supporting power equipment for new energy with 115 KV transformers, 158 MW PV modules and 12MW/24MWh ESS.

Voltage Ranges

Power transformers come in a range of voltage levels, from medium to extra-high voltage, based on the specific needs of the power system they serve.

36kV ~ 750kV, up to 1,000MVA natural ester oil-filled power transformers. For high-capacity, long-distance transmission lines, often spanning countries or continents for efficient power delivery.
36kV ~ 1000kV, up to 1,200MVA mineral oil-filled power transformers. For ultra-high capacity, ideal for power generation plants, substations, industrial facilities and renewable energy installations.

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Power transformers are necessary for the efficient and safe transmission of electricity worldwide. Their ability to step up or step down voltage enables long-distance power delivery and ensures that electrical power reaches end users at appropriate levels. Understanding their operation, applications and specifications is essential for professionals in the energy sector.