The Role of Isolation Transformers in Data Center UPS Systems Most modern UPS systems do not include the internal transformers that were present in earlier designs. This evolution has increased efficiency while decreasing the weight, size, and raw materials consumption of UPS systems. In the new transformerless UPS designs, the transformers are optional and can be placed in the best location to achieve a required purpose. In older designs, transformers were typically installed in permanent positions where they provided no benefit, reduced system efficiency, or were not optimally located. This paper considers the function of transformers in UPS systems, when and how transformers should be used, and how the absence of internal transformers in newer UPS designs frequently improves data center design and performance.