This paper will elaborate electrical performance test procedure for uninterruptible power supplies (UPS). The focus will be pointed to on - line one-phase UPS up to 3000 VA nominal output power that are mostly used for protection computer equipment. But the test procedure can be applied to three - phase UPS or off - line and line interactive UPS and also for more powerful UPS. Test procedures are based on relevant standards (IEC 62040-3 31-Mar-1999: Uninterruptible power systems (UPS) - Part 3: "Method of specifying the performance and test requirements"; CSA C813.1-01: "Performance Test Method for Uninterruptible Power Supplies";..), but all those mentioned standards have international restrictions and they are applicable only for domestic use in some countries. This paper will propose unique test procedure only for electrical performances of UPS that can be applicable worldwide. In this paper it is excluded other UPS performances like noise, heating, weight, and other. Electrical performances that are observed are: - Input current total harmonic distortion (THDI), - Output voltage total harmonic distortion (THDU), - Input efficiency, - Output efficiency and - Autonomy time. It will be given electrical schema for testing each performance. Total harmonic distortion of current and efficiency will be distinguished for linear and nonlinear load. It will be given simple electrical schema for simulation nonlinear load. Total harmonic distortion of voltage will be distinguished for case when AC power is present and case when there is no AC power and battery starts to provide power for load. In the paper will be described possible power problems (also power quality) in the electrical network and from which problems each UPS protect its load. Paper will present test results for almost twenty different UPS (power range form 500 VA to 3000 VA; and from different manufacturers).
