When to choose an Isolation Transformer?

Last Updated on: 27-02-2023

This article refers to the basic knowledge of isolation transformers and their applications.

Let us first understand what an isolation transformer is.

A typical transformer with a 1:1 primary to the secondary winding ratio transfers alternating voltage from one electrical circuit to another via electromagnetic induction.

Usually, this device isolates the powered device from the power source for safety reasons and helps supply clean power.

Isolation Transformer

Based on the market demands, most of the digital UPS battery systems are being manufactured as transformerless designs to reduce the size of the modem UPS to make it sleek, stylish, improved efficiency and cost-effective.

But still, the demands for a UPS battery system with isolation transformers have not been reduced.

It should be noted that the isolation transformers shall play two different roles when connected to the input of the UPS system and the output of the UPS.

Let us understand some insights about the isolation transformer when connected to the UPS input side.

Isolation Transformer @ UPS Input:

Isolation Transformer


  1. The transformer provides perfect galvanic isolation to the secondary circuit and recreation of a fixed TN-S System (grounding system) without reducing operating efficiency.
  2. It blocks the DC components, if any present in the utility supply.
  3. It effectively reduces power surges.
  4. Electrical isolation transformer blocks interference due to ground loops.
  5. The transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.
  6. Reduce harmonic content.
  7. The transformer can reduce common-mode noise with proper grounded faraday’s shield between primary and secondary winding.

Isolation Transformer @ UPS Output:

Isolation Transformer


  1. It prevents the DC components from flowing towards the load during the static bypass short circuit.
  2. Improves the power factor of non-linear loads (SMPS, Lazer printers etc.,) and prevents DC bus unbalance in digital UPS systems.
  3. Match impedance between a source (secondary of isolation transformer) to load and ensure maximum power transformation.

Isolation Transformer

Hence if the utility condition and its parameters are well within the designer’s spec, then the need for an isolation transformer at modem UPS input is not mandated. Similarly, the connected load’s power factor and measured crest factor do not meet the specification, and usage of isolation transformer output becomes a mandate.

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