Transformers are crucial to electrical system infrastructure, function and power. They transfer energy to one or more electrical circuits, increasing or decreasing the voltage without changing the frequency. This is necessary for appliances to function correctly without the risk of an electrical hazard.
A transformer has several parts, each serving a unique purpose to enhance the overall operation of these machines. These include:
- Laminated core
- Windings
- Main tank
- Insulating materials
- Transformer oil
- Cooling tubes or radiators
- Conservator tank
- Dual voltage switch
- Control box and fans
- Pressure relief device (PRD)
- Tap changer
The core, windings, insulating materials and tank are features of almost all transformers, from isolation to distribution transformers. All other components are seen in machines above a certain kilovolt-amp (kVA). Let’s look at each part in more detail.
1. Laminated Core
A transformer’s core allows electromagnetic flux to pass easily via a low-reluctance path and supports primary and secondary windings. It is typically made with stacked sheets of either silicone steel or soft iron separated by a thin insulating material. These sheets help reduce eddy current loss, prevent hysteresis loss and allow for magnetic path continuity.
The exact design of a unit’s core will depend on its current, voltage and frequency. However, its diameter is often directly proportional to the loss of copper and inversely proportional to the loss of iron.
2. Windings
There are always two sets of windings — the primary and the secondary. These are made from several turns of copper or aluminum bundled together. Copper is most commonly used as it is one of the most conductive metals, whereas aluminum is only around 60% as conductive. Both are insulated from each other and are wound around the core.
Windings are classified based on either the supply’s input and output or on the supply’s voltage level. When classifying based on input or output, the windings are:
- Primary: This winding is connected to the input supply.
- Secondary: This winding takes the output load.
The primary winding is connected to the electrical source, which generates the magnetic flux. The magnetic flux passes through the core to the secondary winding, completing the movement and creating a magnetic circuit.
However, windings are also classified based on the voltage level:
- High voltage: This winding is connected to the higher voltage and can either be the primary or the secondary. It is generally made from a thin copper conductor with a larger number of turns.
- Low voltage: This winding is connected to a lower voltage. It can also be primary or secondary. Unlike their high-voltage counterparts, low-voltage windings are usually made from a thicker conductor with fewer turns.
3. Main Tank
Also known as the casing, the main tank is one of the most sturdy parts of a transformer. It houses the windings, core and all other components and protects them from the external environment.
These tanks are typically made from steel, yet aluminum is becoming increasingly popular to help reduce the weight of these parts. Aluminum is a lighter metal, only weighing one-third as much as steel.
4. Insulating Materials
Every transformer requires insulation to isolate both sets of windings from each other, the core and other parts made from conducting materials such as the tank. As 70% to 80% of all transformation failures result from internal winding insulation faults, the insulating materials are considered the most important electrical transformer parts.
Ideal insulating materials have excellent dielectric strength, beneficial mechanical properties and high temperature resistance. Paper, cardboard and cotton are often used as insulation, and transformer oil is also an insulating material.
5. Transformer Oil
Transformer oils are usually hydro-carbon mineral oils that are either paraffin- or naphtha-based. Along with providing additional insulation between the windings in oil-immersed transformers, this oil also cools the core and coil.
Due to its chemical properties and dielectric capabilities, transformer oil transfers the heat created by the core and windings to the external environment. Once the windings heat up due to the current’s flow, the oil cools these parts as it circulates inside the machines and displaces this heat via cooling tubes.
6. Cooling Tubes or Radiators
Cooling tubes or radiators cool the transformer oil. Oil circulation in the transformer can either be forced or natural.
With forced circulation, an external pump is necessary. If the circulation is natural, the hot oil moves upwards when the temperature rises, and the cold oil moves downwards, naturally circulating in the tubes.
7. Conservator Tank
The conservator tank is a metallic, airtight, drum-like structure that sits on top of the main tank. The primary function of the conservator is to allow the oil to expand and contract according to changes in the ambient temperature inside the tank. When the transformer heats up, the oil expands and flows into the conservator tank. As it cools, the oil contracts and moves back into the main tank, helping to ensure a balanced oil level.
This process is vital for the transformer’s operation, as it allows other components to be constantly submerged in oil, keeping air out of the system and protecting insulation and cooling properties. As a result, there is a much lower risk of that machine overheating, which could result in suboptimal performance, unnecessary wear and tear, and even failure. The conservator tank controls oil levels and temperatures, promoting a transformer’s longevity and efficiency.
8. Dual Voltage Switch
Dual voltage transformers can supply power at two different voltages. If the two windings have a series connection, the output will be the sum of both voltages. The total voltage will be lower if they have a parallel connection.
A dual voltage switch is essential to alternate between the different voltages according to the necessary output. This switch is typically located outside the main tank.
9. Control Box and Fans
The control box and fan are two indispensable components of a transformer. Control boxes manage the voltage and current that moves through these machines, helping to balance the load on the grid and ensure an even and efficient distribution of electricity. Transformer control boxes also shield the grid from failures and faults using fuses, surge arresters and circuit breakers to avoid overloads, short circuits and other issues.
However, control fans have a multifaceted role:
- They can reduce the amount of noise a transformer generates.
- They dissipate the heat in the transformer, helping to maintain an ideal temperature and improve the stability of these machines.
- Transformer fans can also boost insulation, helping to properly disperse static electricity and lower the risk of electrical accidents.
10. PRD
In the case of a severe internal fault, the tank’s pressure may rise to dangerous levels. Mounted on top of the transformer, PRDs protect transformers from sudden increases in pressure by ensuring this pressure can be released, preventing a potential rupture or explosion.
The way these devices work is simple — if pressure levels exceed a safe limit, a valve cap opens to expel oil and hot air gases, depressurizing the tank. Once the levels return to normal, this cap returns to its leak-tight, closed position.
11. Tap Changer
Tap changers change the transformer’s output voltage, also known as its secondary voltage, by adjusting its turn ratio. There are two types:
- On-load: With this tap changer, tapping can be adjusted without disconnecting the transformer from the supply. As a result, it can function without interrupting the power supply.
- Off-load: Conversely, with this changer, the transformer must be disconnected from the supply to change its turn ratio.
Some transformers have automatic tap changers.
Contact Sunbelt Solomon for Your Transformer Needs
If you understand the various parts of a transformer, you’ll likely understand these machines and how they work much better. With so many key components, regular maintenance and timely repairs are nonnegotiable to help ensure your transformer functions at its prime. With 100 years of combined experience, Sunbelt Solomon is here to be your trusted partner.
We are the nation’s leading field service and maintenance specialist and offer comprehensive repair and replacement services. With our engineering capabilities, commitment to safety and various environmental qualifications, we will keep your equipment working as it should. We know experiencing issues with your transformer can be highly disruptive, so we also provide high-quality rentals to help you minimize downtime.
To learn more about our services, contact us today.
