Reliable Operation of UPS in Respect of EMI: EMC Design Specifications and Test Results

This paper presents the EMC specifications for the supplying of UPS (uninterruptible power supply) for district energy distribution control centres and the proper immunity test procedures developed by the ENEL (Italian Electricity Board) to qualify the UPS electromagnetically, by type tests that reproduce the different types of interference, caused by different possible sources. A UPS designed to fulfill the above specifications is then described with regard to particular features of power and control circuits, component lay-out and cabinet design. The scope was to reach the immunity "severity level" 3 and not to exceed the emission limit C of the reference standard. Laboratory tests performed on a 10 KVA UPS in accordance with the ENEL standard and procedures demonstrated the validity of the chosen solutions. The test results are presented and discussed.