Each data center power system includes a transformer. Isolation transformers have had various roles in the power architecture of data centers throughout history:
- The medium voltage of the main power supply drops to a lower application voltage
- As part of the power conversion circuit within an APC UPS
- Form a neutral wire connected to the local grounding device
- Installed in the distribution unit or UPS to reduce harmonic currents
- Provide taps to accommodate non-standard (high or low) main input voltages
- Eliminate ground loops with multiple generators or main input power sources
- Step down the data center distribution voltage from 480V or 600V to 220V within the distribution unit
- Provide other operating voltages within the distribution power supply
The traditional UPS system has one or more internal blocking transformers to provide one or more of the above functions, depending on the planning of the data center power system. The latest UPS no longer considers blocking transformers as an essential component, which can improve efficiency and reduce weight, scale, and cost. The selection method is based on the requirements for the transformerless type UPS is equipped with a transformer to perform the required functions. This article will explain why in most data center power system planning, transformerless UPS can perform the same functions and functionalities as older UPS systems that use internal transformers. However, in many cases, there is still a need for transformers, which may need to be installed internally or externally within the UPS. Even older UPS systems that use internal transformers often require the installation of external transformers. Most importantly, this article will explain why transformerless UPS planning is better in almost all situations where transformers are needed, as it allows transformers to be installed in more suitable parts of the power path.
Many people believe that the initial inclusion of isolation transformers in APC UPS power supplies was for power isolation between input and output, which is incorrect. The real reason for using internal transformers in early UPS was due to power inverter technology. The initial UPS products were developed over 40 years ago, using a ground based battery system. The grounding circuit and battery configuration require these systems to have two transformers for isolation from the main circuit: one located on the input rectifier and the other located inside the output inverter. Subsequent improvements to these designs involved moving the battery bus to the neutral wire or suspending it electrically, and removing one of the transformers (usually the rectifier transformer). With the development of high-voltage and high-speed power semiconductor technology, the latest UPS design can remove both transformers and become what we call a high-frequency UPS.