What do street lamps, large motors, data centers, and stadiums have in common? They all rely on ready access to electricity and lots of it.
But getting electricity for a specific purpose isn’t as simple as hooking up directly to the power lines. The high voltage electricity in power lines is only suitable for transmitting power over long distances. To be usable in everyday applications, the electricity must pass through a transformer, which converts the power to a suitable voltage.
Many people know what a transformer looks like. Understanding how they work, though, is a different story. Whether you’re budgeting for a transformer or installing one, knowing what transformers do and how they work provides greater clarity on what you need.
In this article, you’ll find an introduction to transformers, why we need them, how they work, and a run-through of their most important parts.
What is a transformer?
An electrical component known as a transformer is used to move electrical energy between one electrical circuit and another or between several circuits. A changing magnetic flux in the transformer’s core results from a changing current in any of its coils.
As a result, any other coils wound around the same core experience a fluctuating electromotive force (EMF).
AC voltage levels can be changed using transformers, classified as step-up or step-down types depending on whether they increase or decrease the voltage level.
A transformer is composed of several unique components, each of which contributes to the overall performance of the transformer in a different way.
The main components are the core, windings, insulating materials, transformer oil, tap changer, conservator, breather, cooling tubes, Buchholz Relay, and explosion vent.
Nearly all transformers have a core, windings, insulating materials, and transformer oil; transformers with more than 50 KVA have other components. Let’s discuss the working principle of these transformer parts.
Parts of a Transformer
The following are the main parts of a transformer:
- Core
- Winding
- Tank
- Insulation
- Transformer oil
- Terminals and bushings
- Breather
- Tap changer
- Radiators and fans
- Cooling tubes
- Buchholz relay
- Explosion vent
- Oil conservator
- Temperature gauge
#1. Core.
Transformers are constructed using a core, which is the center of the transformer. These are used to support the windings. The primary and secondary windings are supported by the core, which offers an electromagnetic flux path with low reluctance.
It is constructed from thin sheets of premium grain-oriented steel separated by thin insulating materials. The carbon content of the core steel is kept below 0.1% to reduce hysteresis and eddy currents.
Improved core construction methods and highly permeable material help create a desirable, low reluctance flux path and confine flux lines to the core. Core type and shell type are the two different types of core constructions.
#2. Winding.
The windings, divided into several coils, enable voltage lowering between adjacent layers. Several turns of copper or aluminum conductors produce this winding and are insulated from the transformer core and one another.
Transformer winding types and configurations are determined by factors like current rating, short circuit power, temperature rise, impedance, and surge voltages.
Primary and secondary windings are based on supply, which means they apply input and output voltages, respectively.
The primary and secondary windings are divided into two sections: the high voltage (HV) winding and the low voltage (LV) winding.
In contrast, high-voltage and low-voltage windings can be distinguished based on the voltage range. The number of turns and its current carrying capacity determine the winding to use.
#3. Tank.
Transformer tanks are used to hold, protect, and cool the windings and core in an electrical distribution transformer.
It serves as a container for oil and support for all other transformer accessories and protects the core and windings from the outside environment.
Tank bodies are created by shaping rolled steel plates into containers and adding lifting hooks and cooling tubes. Aluminum sheets are also employed rather than steel plates to lighten the product and prevent stray losses.
#4. Insulation.
Most power transformers have cellulose (paper/pressboard) and oil as insulation materials.
Copper is used to make these windings due to their high conductivity and ductility. These components shield the transformer core and the primary and secondary windings from one another.
Insulation is required between the core and the windings, as well as between each winding turn and the tank for all current-carrying components.
The insulators must withstand high temperatures, have good mechanical qualities, and have high dielectric strength.
Transformers can sustain the most severe damage if the insulation fails. Transformer insulation is generally made of synthetic materials, paper, cotton, and other materials. The most fundamental components of a transformer are its core, winding, and insulation.
#5. Transformer Oil.
The core and coil assembly are insulated and cooled using the transformer oil. The transformer’s core and windings must be completely submerged in the oil, which typically contains mineral oils with hydrocarbons.
Transformer oil provides additional insulation between conductor parts, improves heat dissipation, and detects faults, especially in oil-immersed transformers. Transformer oil has a 310°C flashpoint, a 2.7°C relative permeability, and a density of 0.96 kg/cm3.
#6. Terminals and Bushings.
Transformers have terminals that are used for connecting incoming cables and cables leaving the transformer. Normally, they are mounted on the bushings and are connected to the ends of the windings by means of cables.
An insulator bushing is a type of device that forms a barrier between the terminals of the power source and the tank that contains it.
They are positioned above the transformer tanks. The conductors connecting terminals to windings, they provide a secure path. Porcelain or epoxy resins are used to create these devices.
#7. Breather.
A breather is an add-on for liquid-immersed power transformers that are connected to the transformer tank. It is a crucial device for preventing moisture from getting into the oil. The breather is a cylinder filled with silica gel that is used to keep the air entering the tank dry.
This is because moisture can cause internal faults in the insulation when it reacts with the insulating oil, which is why it is essential to maintain dry air. This is why there shouldn’t be any moisture in the air, and the breather accomplishes this.
#8. Tap Changer.
A tap changer’s job is to control a transformer’s output voltage. This is accomplished by changing the number of turns in one winding, which affects the transformer’s turn ratio.
A de-energized tap changer and an on-load tap changer are the two different types of transformer tap changers (DETC).
On-load tap changers can operate while the current is still flowing to the load, whereas off-load tap changers can only operate when the transformer is not supplying any loads. These days, automatic tap changers are also accessible.
#9. Radiators and Fans.
The transformer is made up of exterior radiator tubes, which are cooled by air from fans installed on the tank’s walls. Most of the time, heat is produced as a result of the power that is lost in the transformer. Most dry transformers use natural air cooling.
However, various cooling techniques are used when it comes to oil-immersed transformers. Radiators and cooling fans are mounted on the transformer tank based on the kVA rating, power losses, and level of cooling requirements.
The surrounding transformer oil absorbs the heat produced in the core and winding. At the radiator, this heat is released. Using cooling fans attached to the radiators, forced cooling is accomplished in bigger transformers.
#10. Cooling Tubes.
In order to cool the transformer oil, cooling tubes are used, as their name suggests. It’s possible for oil to circulate naturally or artificially inside the transformer.
When the oil temperature rises, the hot oil naturally rises to the top during natural circulation. In contrast, the cold oil naturally lowers, whereas an eternal pump is used to move the oil between the hot and cold zones in forced circulation.
#11. Buchholz Relay.
Buchholz relays are critical components of oil-immersed transformers rated above 500kVA. Usually, what happens is that transformer oil short circuits produce enough heat to cause the oil to break down into gases like methane, carbon monoxide, and hydrogen.
Buchholz relays are mounted on the pipe connecting the conservator tank to the main tank. They sense these gases and activate the trip and alarm circuits. The trip circuit interrupts the current flow and activates the circuit breaker controlling the primary winding.
#12. Explosion Vent.
An explosion vent, which is a component of the transformer, serves as a means for oil and air gases to escape during an emergency. It typically consists of a metallic pipe that is held just above the conservator tank and has a diaphragm at one end.
When there is an oil leak, the pressure inside the tank can reach dangerous peaks. When this happens, the diaphragm ruptures at a relatively low pressure, releasing the forces inside the transformer into the atmosphere.
#13. Oil Conservator.
The oil conservator tank’s purpose is to offer enough space for transformer oil to expand and contract. It varies in accordance with the fluctuation in the main tank’s ambient temperature for transformer oil.
This cylindrical drum-shaped structure is mounted on top of the transformer’s main tank. It has a Buchholz relay mounted on the pipe connecting it to the main tank. To show how much oil is in the conservator tank, a level indicator is also present on the oil conservator.
#14. Temperature Gauge.
An instrument used to monitor the temperature of a power transformer is called a temperature gauge.
It is placed on top of the tank to measure the temperature of the transformer. There is an alarm or light on this meter that alerts you when the temperature rises.
Types of transformers
Electrical transformers come in all kinds of types depending on their primary function, construction, supply, etc. For example, a residential transformer isn’t going to require the same robust design as an industrial transformer. Here are some of the ways that transformers can differ from one another.
Design
The transformer design depends on how the primary and secondary windings are wound around the transformer’s core.
- Core-type transformers have the windings wound around a magnetic core, much like we discussed in previous sections.
- Shell-type transformers have the windings pass inside the steel magnetic circuit (or the core), which creates a shell around the windings.
Phase/supply
We have mostly referred to transformers that use two windings, but that is not the only way transformers work.
- Single-phase transformers have one primary winding and one secondary winding, giving one main line of power. These are commonly used in residential transformers.
- Three-phase transformers are more commonly used industrially since they have three sets of winding and can therefore generate three-phase power. Three lines of power tend to reduce the amps needed, use smaller wires, and provide more power.
Cooling
Transferring energy creates friction and resistance, which in turn creates heat. Heat can wear down the coils used to build transformers, so there are also cooling mechanisms in transformers to keep coils from overheating and wearing out faster.
- Self-cooled oil-filled transformers are typically used for small transformers and leverage the surrounding airflow to stay cool.
- Water-cooled oil-filled transformers use a heat exchanger to transfer the heat from the oil to the cooling water.
- Air-cooled (air blast) transformers focus on cooling the generated heat by using fans that force the air circulation on the windings and core, not just the naturally surrounding airflow.
Purpose/voltage levels
Depending on whether you want to raise or lower the voltage, there are step-up and step-down transformers.
- Step-up transformers are made to increase the voltage levels, so the transformer is a “step-up” transformer if the secondary winding has a higher number of turns than the primary side.
- Step-down transformers are the opposite and decrease the voltage, so the primary winding needs to have more turns than the secondary side.
Install location/use
Not all transformers are suited for the same level of power or application, so there are multiple types of transformers that vary by use.
- Power transformers are fairly standard and used to transmit electrical power at high ratings.
- Distribution transformers tend to have lower ratings and are used to distribute electricity and convert voltage in transmission lines.
- Measurement/instrument transformers convert voltage proportionately to measuring instruments, such as meters, network analyzers, and other devices.
How Do Transformers Work?
A transformer functions under the law of energy conservation, which states that energy can neither be created nor destroyed, only transformed. Therefore, a transformer does not make electricity; it merely changes the voltage to suit the needs of the user.
Transformers accomplish this change in voltage through the process of electromagnetic induction.
Electromagnetic Induction
When you run an alternating electric current through a wire (conductor), an invisible, moving magnetic field is created around the electrified conductor. When you place a second conductor within this changing magnetic field, the moving flux lines in the field induce a current in the second conductor.
You can use electromagnetic induction to increase or decrease voltage between the two conductors by wrapping the two conductors into coils with one being longer (having more loops in the coil), and the other shorter (having fewer loops in the coil).
If you then electrify the coil having more loops, a current will be induced in the coil with fewer loops at a lower voltage than is present in the first coil.
How Does a Transformer Coil Work?
The first coiled conductor where electricity enters the transformer is called the primary coil, and the other coil where current is induced is called the secondary coil.
Both the primary and secondary coils (also called windings), made of aluminum or copper, are wrapped around an iron core, which strengthens and directs the changing magnetic field for better induction.
As the magnetic field activates, the metal core expands and contracts. This movement creates the transformer humming or buzzing sound.
Each loop in the coil around the iron core is called a “turn”.
How do we get the exact voltage that we need? First, we have to understand one simple rule: the ratio of turns between the primary and secondary coils determines the ratio of voltage between the coils.
If the ratio of turns between the coils is 25:1, then the voltage will be transformed at a ratio of 25:1. To get the precise voltage you need, you would build a transformer with the exact desired ratio of turns in each coil. A transformer with a turns ratio of 25:1 would be used to transform 12,000 volts to 480 volts.
Three-phase transformer coils are connected in either a delta or a wye configuration.
When are transformers used?
Transformers are used in all kinds of industries and environments. For example, a transformer is used to reduce the voltage of standard power circuits so that your household can run low-voltage devices like your small appliances or doorbell.
On the other hand, transformers can also raise the voltage from generators to transmit electricity over huge distances or power industrial machines.
Here are some of the main functions and uses of transformers:
- Transformers raise and lower voltage levels in the circuit of an AC.
- They increase or decrease the value of an inductor or a capacitor in an AC circuit.
- Transformers do not allow DC input to flow through from one circuit to another since DC cannot generate a change in current.
- A transformer can isolate two circuits, both physically and electronically.
You will hear a lot about transformers when it comes to power generation, electric energy consumption, transmission and distribution, lighting, audio systems, and electronic equipment and machinery.