Galvanic isolation completely separates the input and output supplies to a device so that energy flows through a field rather than via electrical connections. It enables power transfer between two circuits that must not be connected.
In a UPS system, isolation transformers transfer AC current to connected equipment while isolating them from the power source. This protects against electric shock and suppresses harmful electrical noise. It also protects the inverter from load interruptions.
Typically, transformer-based uninterruptible power supplies are the choice for industrial environments and medical applications that tend to demand galvanic isolation.
However, it is possible to add two isolation transformers to the input supplies of a transformerless UPS, which helps ensure complete neutral separation. (Learn more about the differences between transformer-based and transformer-free UPS).
The image below outlines the simplest installation for a UPS with a single power supply and input:
- Figure 1 shows how an isolation transformer can be installed at point A, point B, or both (NB if point A, the transformer must be oversized in accordance with the UPS input supply rating).
- Figure 2 highlights a more complex installation where the UPS has a dual input supply. In this case, the isolation transformer can be installed at point C, point D, or both.
Installing a transformer on the input side of the UPS can deliver a secondary benefit too. It also provides a fixed earth-to-neutral connection that assists with fault clearance if the mains supply is interrupted.