Choosing the right transformer

A transformer is an electrical element that changes the voltage and current of a circuit. The voltages and currents obtained have different values from the original current, but they keep the same frequency and form. The current is transformed with an efficiency close to 1.

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  • What are the different types of transformers?

    SANERGRID power transformer

    There are 5 main types of transformers. The differences between each transformer are related to the types of applications possible.

    • Current transformers: these are transformers in which the secondary current is proportional to the primary current. They can be used with all low-frequency alternating currents.
    • Power transformers: these are distribution transformers with a voltage of one phase higher than 1,000V. They are used to transport electricity over long distances.
    • Instrument transformers: these supply measuring devices and meters which allow the latter to measure the current. They transform the current without phase shift.
    • Pulse transformers: these produce electrical pulses at high frequencies. They are often used to control electronic components such as transistors and thyristors. They can provide a significant current.
    • Isolation transformers: these create a galvanic isolation between the primary and secondary current, which makes it possible, for example, to protect installations from electrocution risks. They are often used in operating rooms.
  • What are the different kinds of transformer technology?

    HARTING voltage transformer

    HARTING voltage transformer

    There are 5 main types of technology for transformers.

    Voltage transformer

    The voltage transformer makes it possible to modify the voltage and current delivered by an alternative electrical source while maintaining the same frequency. This transformation is carried out efficiently.

    Three-phase transformer

    The three-phase transformer allows the transformation of the voltage and current of three phases at the same time. This means you don’t have to use one transformer per phase, i.e. three transformers. Here a single device combines all three phases. This system has the advantage of being less expensive and taking up less space than using a  separate transformer per phase.

    Toroidal transformer

    The toroidal transformer contains a magnetic core manufactured in a toric shape. It is therefore distinguished from other transformers by its toric shape. It is lightweight, uses less space on the circuit and is easy to assemble. It generates little noise and electromagnetic interference compared to conventional transformers. Toric cores also have the advantage of consuming less energy to maintain the magnetic field so they use less electricity. Toroidal transformers are also generally good value for the price. 

    Rectifier transformer

    It is a low power transformer whose purpose is to rectify voltage in everyday applications. It is used in particular for telephones and portable computers.
    The rectifier transformer is rather expensive compared to a conventional transformer.

    Auto-transformer

    The auto-transformer, also called a step-down transformer, contains only one winding transformer with 3 inputs/outputs to make the electrical connections. It can raise or lower voltages so that equipment manufactured in the United States can be powered by a higher voltage. The advantage of auto-transformers is that they are  small, light and inexpensive compared to double-wound transformers. They are also used to start induction motors or in the railway industry in Great Britain.

  • What are the different transformer configurations?

    EREA dry power transformer

    EREA dry power transformer

    There are two types of transformer configurations:

    • Dry transformers
    • Immersed or oil-filled transformers

    Dry transformers

    These transformers are composed of coils wrapped in an epoxy resin without intermediate liquid, which allows them to withstand thermal shocks well. The presence of epoxy resin prevents dielectric leakage and the risk of fire or explosion. The coating allows them to be resistant to external agents such as dust and humidity. 

    These transformers require little to no maintenance. They are also more environmentally friendly than immersed transformers.

    These transformers are designed for indoor installations. For example in shopping malls, hotels, industry or high-rise buildings. Some countries make the installation of this type of transformer mandatory for all high-rise buildings. 

    Immersed transformers

    Immersed transformers, also called oil-filled transformers, are immersed in a liquid which is either mineral oil from petroleum or, as a more ecological alternative, vegetable oil from plants. This liquid is used as a dielectric. 

    These liquids are flammable, so a number of safety devices such as a DMCR or DGPT2 protective relay must be used when operating them.

    These transformers are suitable for indoor and outdoor installations. Unlike dry transformers, due to the presence of flammable liquids this type of transformer requires protection against fire risks. There are therefore installation constraints. For example, they are not permitted in high-rise buildings.

    Transformer configurations

    Dry transformer
    Immersed transformer

  • What are the important characteristics for a transformer?

    Power, primary voltage and secondary voltage are the most important characteristics of a transformer.

    Power

    This must for your circuit and the devices it’s composed of. Oversizing a transformer can result in significant no-load losses. Undersizing a transformer can reduce efficiency, cause windings to heat up or even accelerate the aging of the insulation, which can put the transformer out of service.

    This means you will have to determine the optimal power for the transformer. To do so, you will have to:

    • Determine the installation’s cycle and duration of the load or overload
    • Compensate reactive energy if necessary
    • Ensure operational safety
    • Take cooling the room where the transformer is located into account.

    The primary current 

    This is the voltage at the input of the transformer. This determines what circuit you can connect your transformer to.

    The secondary current 

    This voltage determines the supply voltage of the devices in your circuit.

    Transformer characteristics

    Power
    Primary current
    Secondary current

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