Most Important Parts of a Transformer and Their Functions

Learning parts of a transformer will help us greatly to understand what is the capability of a transformer in supplying electrical energy to a lot of households and industries.

Electrical Transformer Parts

If we are asked “what is a transformer?”

The easiest explanation:

A transformer is an electrical device to deliver electrical power with minimum power losses. For a small and basic transformer, we can find three main parts to build it:

  • A core
  • Primary windings
  • Secondary windings

But, in reality, a transformer is built from many more components that we may never know before. It is what makes it an important task for us to learn every part that builds a transformer.

Knowing all of its parts will help us to troubleshoot, analyze, and repair them when something happens in the future.

The bigger the transformer, the more components it has to function properly, and of course provide better functional and purpose.

Transformers are essential in electrical power transfer from higher power rating to lower rating or vice versa. Thus, it is wise to learn about the parts of a transformer.

Transformers can be divided into step-up transformers and step-down transformers. We will not learn about them at the moment, let us spare them for another time. Now we will learn about the important parts of a transformer.

Working Principle of a Transformer

A transformer is an electrical device that uses the principle of electromagnetic induction. This static device produces an electromagnetic field when an alternating current flows through its primary winding.

From this phenomenon, an electromotive force (EMF) is induced to the secondary winding where its magnitude is proportional to the turns ratio.

Parts of a Transformer

Transformers are essential in electrical power transfer from higher power rating to lower rating or vice versa. Thus, it is wise to learn about the parts of a transformer.

Transformers can be divided into step-up transformers and step-down transformers. We will not learn about them at the moment, let us spare them for another time. Now we will learn about the important parts of a transformer.

  1. Core
  2. Winding (primary and secondary)
  3. Insulation
  4. Tank
  5. Transformer oil
  6. Oil conservator
  7. Tap changer
  8. Breather
  9. Explosion vent
  10. Terminals and bushings
  11. Buchholz relay
  12. Radiator and fan

Now let us learn them one by one.

Transformer Core

This is the one of the most basic parts of a transformer.

A transformer core should have a low reluctance path for electromagnetic flux. Not only that, our transformer core will be the support base for primary and secondary windings. A transformer core is commonly made by stacking  many thin sheets of high-grade grain-oriented steel.

The core is separated from the direct contact with the windings using a thin insulating material. This sheet of steel has carbon content maintained below 0.1% to make the eddy currents and hysteresis losses as minimum as possible.

parts of a transformer 1

The illustration above is the common three-phase transformer core. We install our primary and secondary windings around the limbs. The limbs are coupled by the yokes magnetically.

There are two types of core construction:

  • Core type
  • Shell type

parts of a transformer 2

Source: LEARNENGINEERING

Core type transformer is a transformer where its primary and secondary windings are wound around the core’s limbs.

Shell type transformer is a transformer where its primary and secondary windings are wound around the middle core’s limb.

We assemble the laminated sheets in series to make the laminated core. The thickness needs to be calculated thoroughly. The core is the part where we place the copper windings. It is usually made from iron to reduce current loss and Hysteresis loss.

The iron material has low reluctance against the flow of magnetic flux. From the mathematical analysis, the core’s diameter is proportional to copper loss and inversely proportional to iron loss.

Transformer Windings

Every transformer has two sets of winding per phase, the primary winding and secondary winding. These windings are made from a copper or aluminium conductor wound around the transformer core. Each winding is insulated from other windings and the core.

The arrangement and type of our windings will affect the current rating, temperature rise, surge voltages, impedance, and short circuit strength.

Windings can be made from copper wire formed in a coil and bundled together. The bundle is connected to each other to form a winding. Windings will be divided into primary winding and secondary winding.

parts of a transformer 3

Source: LearnEngg

The primary winding is connected to the supply circuit (input) while the secondary winding is connected to the load circuit (output). It is also different between high voltage winding and low voltage winding. We place the primary windings and secondary windings on the limbs and separate each other using insulating sheets.

When doing the calculation, primary and secondary windings can be replaced with the terms of Low Voltage (LV) and High Voltage (HV) windings.

Both low voltage and high voltage windings are wound together around a limb. The lower voltage winding is placed closer to the core while the higher voltage winding is placed around the lower voltage winding.

The shell type transformer has its winding split into several turns of a conductor. The HV windings are sandwiched between the LV windings.

The core type transformer are classified into:

  • Helical windings
  • Foil windings
  • Disc windings
  • Multi-layer windings

After learning what is the function of the winding, we can say that windings are very important parts of a transformer.

Transformer Insulation

Insulation is also the most important parts of a transformer, to build an electrical power device. It is very important to design insulation features to make sure our electrical device doesn’t get caught on fault.

For a transformer, an insulation can protect it from the failures caused by the windings and core, windings and windings, the conductor’s turns of a winding, and every conductor part such as the tank.

Make sure that the insulator has high dielectric strength, can withstand high temperature, and good mechanical strength. For the insulator between core limbs and windings we can use paper, cotton, synthetic material, etc.

parts of a transformer 4

Source: HUBPAGES

The insulating sheets will protect the windings from each other along with the core. The windings are made from copper wire formed in a coil. The copper itself has high conductivity and ductility.

High conductivity means less needed copper and losses. High ductility means easier bending for conductors to become a tight winding around the core and reduces the needed copper and winding volume.

Transformer Tank

The tank will protect all the parts inside it, the cores and windings from the atmospheric effect. The windings will be placed inside it.

The transformer tank has main purposes to the transformer:

  1. As a container of every parts of a transformer inside it,
  2. Container for oil, and
  3. Protect the core and windings from any external effects.   

Tank structure is made from the steel plates fabricated into the container. We can find the lifting hooks and cooling tubes on it.

parts of a transformer 5

Source: FEROKOTAO

Instead of steel plates, it is better to use aluminium plates to minimize the losses and weight.

Of course every benefit will make us pay more. Yes, the aluminium sheets are more expensive than the steel sheets.

Transformer Oil

A transformer oil gives insulation between the conductor elements inside it, produces better heat dissipation, and increases detection against faults. It is common to use hydro-carbon mineral oil that is formed from olefins, paraffin, naphthenes, and aromatics.

Transformer oil has a density of 0.96 kg/cm3, a flashpoint of 310 degrees Celsius, and a relative permeability of 2.7.

parts of a transformer 6

Source: POWERTRANSFORMERSBLOG

This oil is mainly used for cooling and insulating purposes. What parts of a transformer need to be cooled down and insulated? Of course the core and coils. This oil usually contains hydrocarbon mineral oils.

Transformer Oil Conservator

The oil conservator is positioned far above the tank and bushings and is moved onto the top of the transformers. Certain oil conservators commonly have a rubber bladder. As the temperature rises and falls, the transformer oil expands and shrinks.

The oil conservator has enough room to accommodate oil expansion. It has a conduit leading to the main tank. The conservator has a level indicator installed to show the oil level within.

parts of a transformer 7

Source: STDTRANSFORMER

Conservator is usually made from metallic material with the shape of a drum and placed on top of a transformer. It is half-filled with oil for expansion and contraction when temperature changing happens.

Conservator in the transformer contains the insulation oil. It has a level indicator and silica gel to absorb water content. Oil in the transformer covers all parts of a transformer, thus high voltage and low voltage coils are immersed in oil.

There are two types of insulation: solid (cellulose paper) and liquid (oil).The purpose of insulation is to prevent contact between coils which can cause short-circuit and fault, along with spark. Conservator is mounted on the top of a transformer.

Transformer Tap Changer

Why is the tap changer one of the important parts of a transformer?

Transformers’ secondary voltage can be changed using tap changers. They are made to adjust the transformer’s turn ratio as needed. On-load tap changers and Off-load tap changers are the two different categories of tap changers.

On-load tap changers can function while the current is still flowing to the load, whereas off-load tap changers can only function when the transformer is not supplying any loads. There are also automatic tap changers available.

parts of a transformer 8

Source: PROJECTSUPPLIERS

Tap changer is used for changing the transformation ratio to produce secondary operating voltage which is better than changing the primary operating voltage. It is essential for the power grid to meet the quality of service voltage by changing the transformation ratio so it can produce desired output voltage.

When the tap changer is used it will be either on-load or off-load. For an on-load changer we don’t need to disconnect the transformer from the input while for the off-load changer we need to disconnect the transformer from the input.

Transformer Breather

Breathers or silica gel breathers are commonly used or even mostly used to fit inside the conservator of the oil filled transformers. Silica gel breather is used to absorb the moisture in the air sucked in by the transformer during the transformer breathing activity.

The moisture sucked in inside the transformer can cause faulty because the insulation is affected. The silica crystals absorb the moisture inside the air when it passes through the silica gel.

parts of a transformer 9

Source: Electrical Engineering Portal

All oil-immersed transformers with a conservator tank have a breather. The oil must be kept dry and free of moisture. Air moves in and out of the conservator tank as a result of temperature changes that cause the transformer oil to expand and come into contact. There should be no moisture in this air. This parts of a transformer, the breather accomplishes this.

The air pipe’s end has a breather attached to it so that it serves as both the conservator’s entrance and escape. By removing moisture from the air and delivering moisture-free air to the conservator, the silica gel found in the breathers.

Transformer Explosion Vent

Within a transformer, an explosion vent serves as an emergency outlet for air and oil gases. It is 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 might reach deadly heights. Under these conditions, the transformer’s diaphragm ruptures at a relatively low pressure, releasing internal forces into the atmosphere.

parts of a transformer 10

Source: LearnEngg

Explosion vent is installed above the conservator tank. It is used to expel boiling hot oil from the transformer when internal faults occur to prevent the transformer from exploding.

Transformer Terminals

Since a transformer is an electrical device, it has input and output terminals. These are where we connect the transformer with the power grid and our house electrical circuit.

Transformer Bushings

Bushing is used as an insulation between generated voltage from windings inside the transformer to deliver it to the power grid. This will minimize the contact risk with the atmosphere and cause a short circuit. Bushing is usually made from ceramic. Bushing also gives insulation between conductor and earthed tank.

parts of a transformer 11

Source: LearnEngg

The transformer’s terminals are mounted to the bushings. Bushings are the insulator that isolate the terminals from the tank. This porcelain or epoxy resin part is the safe path for the conductor that connects the terminal to the winding.

Transformer Buchholz Relay

One of the most crucial components of oil-immersed transformers rated over 500kVA is the Buchholz relay. A relay that is triggered by oil and gas is used to detect flaws in parts that are submerged in oil.

Transformer oil short circuits provide enough heat to cause the oil to break down into gases like methane, carbon monoxide, and hydrogen. Through the connecting pipe, these gases progressively migrate in the direction of the conservator tank.

The trip and warning circuits are activated when these gases are detected by the Buchholz relay, which is located on the pipe that connects the conservator tank and the main tank. The trip circuit interrupts the current flow and opens the circuit breaker controlling the primary winding.

parts of a transformer 12

Source: LearnEngg

Large transformers contain a variety of additional components, including heat exchangers (for effective cooling), valves, indicators, protective relays, and additional sensing devices (temperature sensors, pressure sensors, etc.). They are found in large transformers and are application-specific.

The name already implies its function as a part of a transformer. What does a cooling tube cool? The cooling tube cools the transformer oil used in the conservator. The cooling protocol is divided into natural and forced. The natural cooling will make the cold oil move down when the hot oil moves up. For the forced cooling we will use an eternal pump.

Transformer Radiator and Fan (Cooling Tubes)

The name already implies its function as a part of a transformer. What does a cooling tube cool? The cooling tube cools the transformer oil used in the conservator. The cooling protocol is divided into natural and forced.

The natural cooling will make the cold oil move down when the hot oil moves up. For the forced cooling we will use an eternal pump.

parts of a transformer 13

Source: ELECTRICALBABA

Heat is produced as a result of the power that is lost in the transformer. The majority of dry transformers are naturally air-cooled. Yet there are numerous cooling techniques used for transformers submerged in oil. Radiators and cooling fans are positioned on the transformer tank depending on the kVA rating, power losses, and level of cooling requirements.

The transformer oil surrounding the core and winding absorbs the heat produced there. The radiator is where this heat is expelled. Forced cooling is accomplished in larger transformers with the use of cooling fans mounted on the radiators.

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