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Why using isolation transformers?

UPS systems have historically had one or more permanently installed internal isolation transformers to provide one or more of the above functions, depending on the design of the data center power system.

Guidelines for using isolation transformers in data center UPS systems
Guidelines for using isolation transformers in data center UPS systems (on photo: Radore Data Center)

Newer UPS systems do not require power transformers as part of their circuits, improving efficiency and reducing weight, size, and cost.

Instead, transformers are added to a transformerless UPS as needed to achieve a desired function!

This paper will show why, in most data center power system designs, transformerless UPSs provide the same function and performance as older UPSs with internal transformers.

Wiring diagram showing input and output connections to a power isolation (“delta-wye”) transformer
Wiring diagram showing input and output connections to a power isolation (“delta-wye”) transformer

Nevertheless, there are many cases where a transformer is required and must be either internal to the UPS or added externally. Even older UPS systems with internal transformers require additional external transformers in many cases.

Most importantly, this paper explains why in almost all cases where a transformer is needed, the transformerless UPS design is superior because it allows the transformer to be installed in a more optimal part of the power path.

First, this paper explains why older UPSs have transformers and the circumstances under which transformerless UPSs behave differently. Second, different transformer arrangements will be reviewed and the preferred arrangements will be described.

This paper focuses on the use of transformers specifically in relation to UPS systems.

It is widely believed that internal transformers were originally provided in UPS systems in order to provide galvanic isolation between the UPS input and output. This is false. The reason internal transformers were used in early UPS systems is because they were inherently required due to the power inverter technology used in the UPS design.

Title:Role of isolation transformers in data center UPS systems – Schneider Electric
Format:PDF
Size:535 KB
Pages:26
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Guidelines for using isolation transformers in data center UPS systems
Guidelines for using isolation transformers in data center UPS systems

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3 Comments


  1. Amol
    Jun 06, 2021

    Will this isolation transformer reduce the voltage between neutral and earth


  2. Sanjay
    May 30, 2020

    If external transformer it located after UPS what shoud be the min or max distance of isolation transformer to ups output panel !


  3. Rolando G. Odones
    Mar 21, 2018

    How the isolation transformer protecting devices when it comes to high voltage.

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