Unveiling Electrical Transformers: Types, Function, and Essential Applications

Electrical transformers are, without a doubt, crucial components in any power system. They are the silent heroes that ensure electricity safely and efficiently reaches our homes, industries, and businesses, adapting voltage levels for every need. Without them, power distribution as we know it would be unfeasible.

In this post, we'll dive into the world of transformers, exploring how they work, their various types, practical applications, and the factors influencing their viability and sizing.

How Do Electrical Transformers Work? The Principle of Electromagnetic Induction

At the heart of every transformer is the principle of electromagnetic induction, discovered by Michael Faraday. Basically, a transformer consists of two or more coils (windings) of conductive wire, usually copper, which are electrically isolated from each other but magnetically coupled by a ferromagnetic core (made of materials like silicon steel).

1. Primary Winding: This is where the input (primary) voltage is applied. When energized by an alternating current, it creates a varying magnetic field within the core.

   
   

2. Core: It conducts and concentrates this magnetic field, ensuring it "cuts" through the turns of the secondary winding.

   
   

3. Secondary Winding: The varying magnetic field passing through the secondary winding induces a voltage in that winding, whose magnitude is proportional to the number of turns.

   
   

   

The relationship between the voltage in the primary and secondary is directly proportional to the ratio of the number of turns in each winding. This is why a transformer can step up the voltage (step-up transformer) or step down the voltage (step-down transformer), depending on the turn ratio between the secondary and the primary.

It's important to note that transformers only operate with alternating current (AC), as electromagnetic induction requires a varying magnetic field.

Types of Electrical Transformers: An Essential Classification

Transformers can be classified in various ways, whether by their type of insulation, application, or construction. The most common include:

1. Power Transformers

• Technical Description: Designed to operate in high and medium voltage systems (power generation, transmission, and sub-transmission). They are generally large, insulated with mineral oil (which acts as both an insulator and a cooling medium), and feature forced cooling systems (radiators, fans, pumps).

  
  

• Applications: Power substations, generating plants, large industries. Their main function is to step up voltage for long-distance transmission (minimizing losses due to the Joule effect) and then step it down for sub-transmission and distribution levels.

  
  

• Feasibility/Sizing: Sized by electrical engineers in power system projects, considering power (MVA), voltage levels, losses, temperature rise, and characteristics of the installation site.

2. Distribution Transformers

• Technical Description: Used at medium voltage (typically 13.8 kV or 34.5 kV) to step down to low voltage (127V/220V or 220V/380V in Brazil; 120V/240V or 277V/480V in the US), serving end consumers. They can be oil-filled (more common on utility poles and compact substations) or dry-type (for indoor use in buildings).

  
  

• Applications: Utility poles (pole-mounted or pad-mounted transformers), service entrances of residential and and commercial buildings, small to medium-sized industries.

  
  

• Feasibility/Sizing: Sized based on the power demand of the consumers to be served (kVA), number of phases, and input/output voltage levels.

3. Dry-Type Transformers

• Technical Description: Use air or epoxy resin as an insulating and cooling medium, eliminating the need for oil. They are safer in indoor environments as they pose no risk of oil leakage or fire.

  
  

• Applications: Commercial buildings, hospitals, data centers, industries with strict safety requirements and where space is a critical factor.

  
  

• Feasibility/Sizing: Excellent for sensitive environments, but generally more expensive than oil-filled transformers of the same power rating. Projects focus on safety, ventilation, and electrical load.

4. Special Transformers (Instrument, Isolation, etc.)

• Current Transformers (CT):

  
  

  • Technical Description: Designed to reduce high currents to a safe, proportional level that can be measured by instruments like ammeters, energy meters, and protective relays. They are connected in series with the line.

    
    

  • Applications: Measurement and protection in power systems, medium and high voltage switchgear.

    
    

• Potential Transformers (PT) / Voltage Transformers (VT):

  
  

  • Technical Description: Reduce high voltages to a safe, proportional level for measurement and protection (voltmeters, energy meters). Connected in parallel with the line.

    
    

  • Applications: Voltage measurement in power systems, generator synchronization, protection systems.

    
    

• Isolation Transformers:

  
  

  • Technical Description: Have the same turn ratio in the primary and secondary (1:1); they do not change the voltage. Their main function is to electrically isolate one circuit from another, eliminating ground loops and reducing the risk of electric shock.

    
    

  • Applications: Sensitive medical equipment, laboratories, high-humidity locations, high-fidelity audio systems.

    
    

Essential Applications and Project Feasibility

The selection and sizing of a transformer are crucial steps in any electrical project.

• Generation and Transmission: Step-up transformers are used in power plants to raise the generated voltage (e.g., from 20 kV to 500 kV), allowing energy to be transmitted over long distances with minimal losses. Step-down transformers then reduce this voltage in substations to sub-transmission and distribution levels.

  
  

• Distribution: Distribution transformers on poles and at building service entrances are responsible for lowering the voltage to levels usable by homes and businesses (120V/240V or 277V/480V in the US).

  
  

• Industry: Industries use transformers to adapt the grid voltage to their specific machinery, which may operate at various voltages. Dry-type transformers are often preferred for safety reasons.

  
  

• Commercial and Residential Buildings: In larger buildings where the utility delivers medium voltage, an internal transformer is necessary to power the entire low-voltage system of the building.

  
  

Type of Project that Sizes Transformers

Transformer sizing is an electrical engineering task. It's performed by electrical engineers at various stages of an electrical project:

• Feasibility Studies and System Planning: To determine the need for new substations or power delivery points.

  
  

• Substation Projects: Where power transformers are the central component.

  
  

• Distribution Network Projects: To define the location and capacity of pole-mounted transformers.

  
  

• Industrial and Large Building Installation Projects: Where the load demand justifies the installation of a dedicated transformer.

  
  

Sizing considers not only the nominal power (kVA) but also factors such as:

• Load Profile/Curve: The variation in energy demand over time.

• Power Factor: The efficiency with which energy is utilized.

• Operating Voltage Levels: Primary and secondary.

• Transformer Losses: Copper losses (Pcu) and core losses (Pfe).

• Voltage Regulation: The change in secondary voltage as a function of the load.

• Environmental Conditions: Temperature, altitude, humidity.

• Necessary Protections: Overcurrent devices, protective relays.

• Costs: Initial equipment cost vs. cost of losses over the lifetime.

  
  

Electrical transformers are true pillars of power infrastructure. Whether in large substations, on street poles, or within industrial complexes, they ensure electricity is transported and used at the correct voltage, optimizing efficiency and, above all, the safety of everyone. Their understanding and correct sizing are essential for any electrical engineering professional.

Do you need a project or installation that involves the use of electrical transformers?

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