What Is Power Transformer?

The power transformers are types of transformers used to transmit electrical energy between a primary distribution circuit and a generator to any component of an electronic or electrical circuit.

These transformers are used for interfacing step-down and step-up voltages in the distribution network. The general form of power transformers is liquid-immersed, and the life cycle of this equipment is about 30 years.

Power transformers can be divided into three types according to categories. They are large power transformers, medium power transformers, & small power transformers.

1. The range of larges powers transformers can be 100MVA and above
2. The range of medium power transformer -100MVA. can be from
3. The ranges of lows powers transformers can be up to 500-7500kVA

These transformers transmit voltage. It holds the low voltage, the high current circuit in one section of the transformer, and the high-voltage low current circuit on the other side of the transformer.

A power transformer works on the basis of Faraday’s law of induction. This explains the power network in areas where every gear connected to the system is designed according to the rates set by the power transformer.

Power Transformer Definition

A power transformer is a stationary device used to convert power from one circuit to another without changing the frequency. These are the very simple definition of transformers.

Because there are no moving or rotating components, a transformer is modeled as a stationary device. Power transformers perform based on AC supply. A transformer works on the laws of mutual induction.

Power Transformer Theory:

The most common purpose of power electronic transformers is to convert alternating current (A.C) power from one AC voltage (or current) to another AC voltage (or current). Other common purposes are to provide electrical isolation between electricals circuits.

Power is the product of voltages times currents. Powers transformers do not change power levels except for parasitics losses. Inputs power minus parasitics power loss equals output power. The ideal power transformer has no losses, so the output power is equal to the inputs power.

Increasing the output voltages will decrease the output current. Electrics utilities prefer to transmit power at low current values ​​to reduce resistive losses in power transmission lines. Lower currents allow even smaller-sized transmission cables.

Power transformers are used between the generating equipment & the power line(s) to raise the transmission voltage to a higher voltage and reduce the transmission currents.

Distributions transformers, which are power transformers, are used to reduce the voltage to the required voltage level for industrial and domestic use.

Power electronic transformers can be classified by their power rating, fractional VA to mega-VA, by their type of construction, &/or by their intended applications.

The same basics power transformer may be suitable for multiples applications; hence the same power transformer may be classified under several overlapping range types.

Common man connects the power transformer with the power utility, so they think of pole transformer and distribution transformer. The power transformers used inside their equipment and electronic equipment do not easily come to mind.

The two most broad categories of power transformers are electric utility power transformers and electronic power transformers (1 and 3 phase).

Utility transformers are almost entirely AC sine wave transformers. Electronic power transformers are essentially any electronic transformer that supplies power to an electronic circuit.

There are several sub-categories: pulse, inverting, switching flyback, forward converter, toroidal, square wave, isolation, and others. Instrument Transformer Example Current transformers are not considered power transformers.

They measure voltage or current rather than a power supply. Electronics transformers/power transformers range in sizes from one cubic centimeter to several cubic meters. Weight can range from fractions of an ounce to several tons.

The size and weight of the transformers of power depend on many factors. A non-exhaustive lists include desired power rating, maximum ambient temperature, allowable temperature rise, cooling method (air or liquid-cooled, natural convection or forced), transformer size, voltage dielectric requirements, required voltage regulation, operating frequency, operating waveform, and main ingredients.

Of these, the two most limitings parameters are the allowed temperature rise and the required voltage regulation.

Operating frequency is a key parameter in the selection of core material. Low-frequency applications typically use either tape wound or laminated silicon steel cores. Medium frequency applications use tape wound or laminated nickel-iron cores.

High-frequency applications typically use ferrite cores. Power transformers are manufactured in different sizes. Toroidal power transformers are high performers. They offer the smallest size (by volume & weight), low leakage inductance, and low electromagnetic interference. (EMI).

Their windings cool better due to the proportionally larger surface area. Bobbin or tube wound transformers are generally more economical to manufacture.

Long thin cores are more suitable for low-frequency high Q transformers. Certain sizes, pot cores, for example, self-shielding reduces EMI.

Power Transformer Working Principle:

Power transformer works on the principle of “Faraday’s law of induction.” This is the main law of electromagnetism that explains the working principle of motors, inductors, generators, and power transformers.

The law indicates, “once a closed-loop or small component is brought near a fluctuating magnetic field, a current will flow in that closed-loop.” To describe the law betters, let us explains it in more detail. Firsts, let’s consider the schemas below.

Consider a conductor & a permanent magnet are initially brought near each other. Then the conductor is short-circuited in both the sections carrying a wire, as shown in the figure.

In this case, no currents will flow through the conductor or loop because the magnetic field cutting the loops is constants, & as stated in the law, just a varying magnetic field can force current into the network.

So, in the first phase of the static magnetic field, the loop or conductor will have zero momentum. Now consider if the magnets are moving back and forth, like pendulums, then the magnetic field cutting the conductor resumes the variations.

Because a modified magnetic field is available in this phase, Faraday’s law will result, and thus we can see currents moving in the loops. As presented in the figures, after the magnets move back and forth, and we can see the current “I” moving in the closed-loop and the conductor.

Let us now end to recover the permanent battery with other modified magnetic field sources such as the one below. Now an alternatives voltages supply & conductors are employed to generate a varying magnetic field.

After the loops are brought closes to the magnetics field limit, an emf generated through the conductor can be observed. Because of this exciting emf, we can have a current flow “I.”

The magnitude of the simulated voltage is related to the field strengths experienced by the secondary loop, so the greater the magnetic field strengths, the greater the current flowing in the closed-loop.

Although it is possible to apply a simple conductor configuration knowing Faraday’s law, for more practicals operations, using a coil on both sections is preferred. Here, an alternating current flows through the first primary coil, which produces a modified magnetic field near the conducting coil.

And when the second coil enters the rating of the magnetic field produced by the first coil, an emf is created in the second coil due to Faraday’s law of induction. And due to the voltage produced in the second coil, a current “I” flows within the closed secondary network.

Now we must remember that both the coils are hanging in the air, so the mediums of conductions applied by the magnetic environment are air.

Air has a higher resistance than metals in terms of magnetic field conditions, so if we use ferrite or metalcore to perform as a medium for an electromagnetic network, we can more appropriately use an electromagnet.

Magnetic induction can be obtained. So, let’s now replace the surrounding air with an iron gap for further development. As presented in the figures, we can apply ferrite or irons cores to drops the magnetic flux wastes during energy transmissions from one coil to another.

During this time, the wasted magnetic flux in the atmosphere would be much less than if we employed the air medium because the gap is a suitable conductor of the magnetic field.

While the fields are produced by the first coils, they will travel across the iron core, reaching the second coils, & due to Faraday’s law, the second coil generates an emf, which will be detected by a galvanometer attached to the second coil.

Now, if we trace that precisely, we will find this configuration similar to a single-phase transformer. And yes, every device that exists today works on the same principle. Go here to know the fundamentals of Power Transformer completely.

Use of Power Transformers:

The production of electrical energy at low-voltage ratings is much more cost-effective. This low voltage rating power can theoretically be transferred to the receiving section. This low-voltage power, if transferred, causes more current in the lines, which actually results in more line waste.

But if the power voltage rate is improved, the power current is reduced, resulting in a reduction in ohmic or I2R waste in the network, a reduction in the cross-sectional side of the loop, i.e., a reduction in the total network cost. , and it also enhances the voltage adjustment of the system.

Because of this, lower-rated power must be increased for effective electrical power applications. This is done by the step-up device in the transmit section of the power network.

Since this large voltage power cannot be distributed directly to the users, it must be moved at a suitable rate to the receiving side with the help of step-down devices.

As a result, electrical power transformers play important roles in powers transmission matters. Two winding transformers are usually employed where the high voltage & low voltage levels are greater than 2. It is cost-effective to implement autotransformers where the level between high voltage and low voltage is less than 2.

Again, the transformer unit is more efficient than a bank of three single-phase devices in a simple three-phase, three-phase network. Buts there are a few problems with using a simple three-phase set, and if one of the phase sections breaks, it should stop working completely.

Power Transformer Design:

The structure of the power transformer is fabricated with metal which is covered with sheets. It is fixed either in shell type or core type. Transformer structures are wound and connected, employing conductors to produce three 1-phase or one 3-phase transformer.

Three 1-phase transformers are required to isolate each bank from additional parts and thus provide continuity of service when one bank flops. A single 3-phase transformer, whether it is core or shell type, will not perform even when one bank is out of service.

The 3-phase transformers are cost-effective to produce, and have a low footprint, & operate comparably with high efficiency. The structure of the transformer is covered with a fire retardant special fluid inside a tank.

The conservatory at the top of the liquid tank allows the rising oil to cover it completely. The load’s charger is moved to the side of the tank, varying the number of turns on the low current-high voltage section for better voltage adjustment.

Tank bushings allow parts to enter and exit the system properly without damaging the outer cover. The power transformers can be operated beyond its lows rating as long as it remains within 65ºC rise of temperature.

Transformers are fitted with special fans that cool the center of the transformer to operate to a point below the certified temperature at the above standard operation.

Power Loss in Transmission Lines:

There are many reasons to employ power transformers in electrical power networks. But one of the essential reasons to use this device is to reduce power loss during power transmission applications.

Now let us see how the wastage of electricity is reduced by employing power transformers: First, the equation for wastage of electricity is

P = {I}^{2} RP=I2R

Here I is the currents across the conductors, and R is the resistance of the part. So, the power wastage is directly related to the class of current going across the conductor or transmission line.

So, the smaller the magnitude of the current flowing within the conductor, the lesser the power wastage. How we will take advantage of these phenomenons is discussed below:

Take the starting voltage is 100V, the load draw is 5A, and the power delivered is 500 watts. Then here, the transmission system should draw a current of magnitude 5A from the supply to the load.

But if we increase the voltage in the first section to 1000V, the transmission system should only take 0.5A to deliver the same power of 500W.

Therefore, we will increase the voltage at the primary stage of the transmission system by using a power transformer and employ a second power transformer to reduce the output at the end of the transmission network.

With this configuration, the magnitude of the current flowing through the +100 km transmission system is significantly reduced, thereby reducing power wastage during transmission.

Difference Between Power Transformer and Distribution Transformer:

The power transformer is usually used at full load as it is designed for high efficiency at 100% load. Otherwise, the distribution transformer has a high efficiency when the load is between 50% and 70%. Therefore, distribution transformers are not desirable to operate at 100% load continuously.

Because power transformers lead to larger voltages during step-down and step-up, the windings have much better insulation than distribution type or instruments transformers. Since applying high-level insulations, they are very large in size and also very heavy.

Since power transformers are generally not directly connected to homes, they experience little load fluctuations, whereas distribution types, on the other hand, experience heavy load variations.

These are fully loaded 24 hours a day, so the iron and copper waste remains piled up throughout the day. The flux density in power transformers is also higher than the distribution type.

Types of Power Transformer:

Transformers can be classified in several ways on the basis of their purpose, application, production, etc. Consider that these classifications sometimes overlap – e.g., A transformer can be both a three-phase form & a step-up form at the same time.

For more clarification, some important electrical engineering books discuss the operation of a transformer in more detail. Types of transformers include the following:

#1. Step-up Transformer and Step-down Transformer

Step-up transformers convert low voltage (LV) and high-current inputs from the primary section of the transformer to high-voltage (HV) and low current values ​​on the secondary section of the device.

Step down type converts high voltage (HV) and low current values ​​from the primary section of the device into low voltage (LV) and high current outputs on the secondary section of the type.

#2. Three Phase Transformer and Single Phase Transformer

A three-phase transformer is commonly employed in three-phase power networks because it is more efficient than single-phase types.

But when size is imported, it is recommended to employ a bank of three single-phase versus three-phase transformers, as it is easier to transmit than a single three-phase set.

#3. Electrical Transformers, Distribution Transformers, and Instrument Transformers

Power transformers are commonly employed in transmission applications to step down or up the voltages rating.

It performs mostly during peaks or high loads & has maximum efficiencies at or near full load. Distribution transformers reduce the output for distribution cases to commercial or domestic consumers.

It has suitable voltage regulation and performs 24 hours a day with maximum efficiency at 50% of the full load. Instrument transformers consist of both a current transformer and a power transformer, which are employed to drop high voltages and currents into low outputs that can be controlled by conventional instruments.

#4. Two-winding transformer and autotransformer

Two-winding transformers are especially used where the difference between the low voltage and high voltage sides is greater than 2. It is more efficient for autotransformers in situations where the ratio between the different sides is less than 2.

#5. Outdoor Transformer and Indoor Transformer

As the name implies, outdoor types are designed to be installed outside. At the same time, indoor forms are made to be installed indoors.

#6. Oil Cooled And Dry Type Transformer

This type is related to the transformers cooling configurations used within the transformers. In oil-cooled types, the cooling method is transformers oils. Whereas in dry types, air cooling is applied instead.

#7. Types of Power Transformer Based on Windings

Power transformers have two main types of windings, shell and core types. There are also Berry-type transformers built into special applications.

#8. Core Type Transformer

A core type transformer consists of two vertical limbs or legs with two horizontal sides projected into a yoke. The main shape is rectangular with a typical magnetics circuit. Cylindrical coils (HV & LV) are installed on both legs.

#9. Shell Type Transformer

A shell-type transformer is comprised of two outer limbs and a central limb. Both HV & LV coils are installed in the central section. A double magnetic circuit is available.

#10. Berry Type Transformer

Cores look like they spoke of a wheel in Berrys-type transformers. The metal sheet tanks are tightly fitted, and oil is fed inside the transformer to the transformer housing.

Power Transformer Specifications:

Powers transformers can be designed as either a three-phase or a single-phase design. There are several important specifications to find out when searching for a power transformer.

Specifications of a power transformer include maximum power rating, maximum voltage rating, maximum secondary current rating, and O/P type. Power transformer specifications mostly include:

1. The primary Voltage is 22.9 kV
2. Frequency if 60Hz,50Hz
3. Secondary Voltages is 6.6/3.3 kV
4. Vector Dd0, Dyn11, etc.
5. Phase is 3Ø
6. Tap Voltages 23.9-R22.9-21.9-20.9-19.9kV

Power Transformer Applications:

These transformers are used as step-up devices for transmission to reduce I2r losses to a specified power current. Power transformers can be used to switch from one voltage type to another at higher power ratings.

These transformers are employed in various electronics networks & are also present in different types and applications.

Applications of power transformers are the transmission and distribution of electrical energy. These devices are widely used by industrial plants, power plants, and conventional electric utility companies.

Power transformers are installed in high-voltage transmission lines to step down and increase the voltage.

These transformers are generally used for the transmission purpose of heavy loads. These devices are large in size compared to the distribution types employed in production stations and transmission networks.

Powers transformers are used in transmissions networks, so they are not directly employed by consumers. So, the load variations among them are less. These devices are used as step-up systems for transmission to reduce I2R waste to a specified power flow.

Power transformers are mostly used at power generation and distribution stations. They are also used in isolations systems, six pulse and twelves pulse rectifier transformers, earthing transformers, wind farm transformers, solars PV farm transformers, & autotransformer starters.

Some other applications of power transformers include:

1. Reducing wastage of electricity during power transmission
2. High voltage step-down and high voltage step-up
3. During long-distance consumer applications
4. In cases where the load runs at full capacity 24×7

Custom Power Transformers

Transformers are electromagnetic devices that convert energy from an electrical circuit into energy in a magnetic circuit and then back into electrical energy.

Using this process, transformers can efficiently transfer power between two or more electrically isolated circuits or convert voltages and currents to desired levels.

There is no off-the-shelf transformer in general transformers. All of our products are customs designed & manufactured to meet your individual design needs.

Whether you require a specific temperature rating, size, or mounting configuration, we work closely with you to design and manufacture transformers with the appropriate magnetic topology for your application.

What Does an Electric Transformer Do?

Transformers are machines that work using the principle of electromagnetic inductions. Basically, this device allows you to increases or decreases the voltage and intensity of an electric current alternating but keeping the power constants.

These machines contribute greatly to the safety and efficiency of power distribution systems over long distances as the best way to move the electric current from the power plant to the high voltage.

The problem is that these high-voltage currents cannot reach homes this way, as it will damage the entire electrical installation and equipment connected to it, so it must be reduced to a tolerable limit for use in homes and businesses.

Wind Turbine Transformer:

Hitachi ABB Power Grid wind turbine transformers & reactors are designed for installations on the nacelle platform, inside the tower base, or outside the tower adjacents to the base.

Transformers for nacelle & in-towers applications have a compact construction design that allows them to easily pass through tower doors without disassembly.

They are designed to minimize losses and operate in environments with high vibration, such as nacelles, as well as in harsh ambient conditions where salt, sand, specks of dust, & 100 percent relative humidity are common.

All transformers dry-type and liquid-filled and reactors designed & rated according to the size of the wind turbines generator and collection array voltage class to meet international standards, environmental standards, as well as climate and fire behavior standards Is.

They are suitable for both onshore & offshore wind turbine applications.

Why Hitachi ABB Power Grid?

1. Transformer technology leader with extensive experience in wind farm applications
2. Leading Technology – Best short-circuit record in the industry
3. Global manufacturing facilities provide production close to the points of delivery.
4. Transformers are suitable for installation & operation in all environments & locations.
5. Transformers are designed for high efficiency, environmental friendliness, & superior operational reliability.

FAQ: Power Transformers

What Is a Power Transformer?

A power transformer is a stationary electrical device used to transfer electrical energy between two or more circuits through electromagnetic induction. It adjusts voltage levels between a primary distribution circuit and a generator or load, typically without changing the frequency.

What Are the Different Types of Power Transformers?

Power transformers are categorized into:

1. Large Power Transformers: Rated at 100 MVA and above.
2. Medium Power Transformers: Rated from 1 MVA to 100 MVA.
3. Small Power Transformers: Rated up to 500-7500 kVA.

How Does a Power Transformer Work?

A power transformer operates based on Faraday’s law of induction. It uses alternating current to create a fluctuating magnetic field in the primary coil, which induces a voltage in the secondary coil. This process allows the transformer to step up or step down voltage levels while transferring power between circuits.

What Are the Main Applications of Power Transformers?

Power transformers are used in:

1. High-Voltage Transmission: To step up or step down voltage for efficient power transmission over long distances.
2. Distribution Networks: To reduce voltage levels for industrial and domestic use.
3. Industrial Plants and Power Stations: For voltage regulation and isolation.

What Is the Difference Between a Power Transformer and a Distribution Transformer?

Power transformers are designed for high efficiency at full load and are used in transmission systems. They handle larger voltage changes and are built to operate with minimal load fluctuations. Distribution transformers are used to deliver electricity to end-users and are optimized for partial load conditions, often experiencing more load variations.

What Are the Common Types of Power Transformers Based on Their Construction?

Common types include:

1. Step-Up Transformers: Increase voltage from the primary to secondary side.
2. Step-Down Transformers: Decrease voltage from the primary to secondary side.
3. Three-Phase Transformers: Used in three-phase power systems.
4. Single-Phase Transformers: Used in single-phase power systems.

What Are the Key Specifications of a Power Transformer?

Key specifications include:

1. Primary Voltage: e.g., 22.9 kV
2. Secondary Voltage: e.g., 6.6/3.3 kV
3. Frequency: 50 Hz or 60 Hz
4. Power Rating: Ranges from fractional VA to mega-VA
5. Cooling Method: Oil-cooled or air-cooled

How Does a Power Transformer Reduce Power Loss in Transmission Lines?

By stepping up the voltage, a power transformer reduces the current required for the same amount of power transmission. Lower current reduces resistive losses (I²R losses) in transmission lines, which enhances the efficiency of power distribution.

What Is the Principle Behind the Operation of a Power Transformer?

The operation of a power transformer is based on Faraday’s law of electromagnetic induction, which states that a changing magnetic field in the primary coil induces a voltage in the secondary coil, allowing for voltage transformation between the circuits.

What Are the Different Cooling Methods for Power Transformers?

Power transformers can be cooled using:

1. Oil Cooling: Uses transformer oil to dissipate heat.
2. Air Cooling: Uses air, either natural or forced, for cooling.
3. Hybrid Systems: Combines oil and air cooling methods for efficient temperature management.