The burn-in test of three-phase UPS by energy feedback method
In the burn-in test of three-phase online uninterruptible power supply (UPS) system, RLC is usually used as a load in the conventional method. For saving energy and decreasing the test cost of UPS, the energy feedback method is proposed to apply the test of the online UPS. In this method, the utility system is used instead of a load. A voltage regulator is used in parallel operation to turn back the energy, which was dissipated in conventional method, to the utility system. The values of real power and reactive power in the output of UPS can be regulated in the proposed method to imitate various loads. From the experimental results, the efficiency of saving energy is more than 85% near half-load and will be higher while the load increases.<<ETX>>
Inverters for Uninterruptible Power Supplies
The synthesis of the principal types of inverters that are best suited for static uninterruptible power supplies (UPS) is sought. From this synthesis a range of apparatus is evolved that will satisfy present and future needs. For each point of this range new solutions are indicated; their development is tied with the technological evolution of the components. The reliability and redundancy aspects of uninterruptible power supplies are also considered.
Evaluation and Control of Collapsible Soils
Some compacted soils wetted under certain conditions of compaction and loading may exhibit additional settlement (collapse). To investigate the effect of the soil type, compaction water content, initial dry unit weight and applied pressure at wetting on collapse potential, 138 single‐oedometer tests were conducted on eight different soils. The results indicate that well‐graded soils tend to collapse more than poorly graded ones under similar conditions. Furthermore, collapse potential decreases with an increase in (1) The difference between the sand and clay percentages; (2) compaction water content; and (3) initial dry unit weight, while it increases with pressure at wetting. A multiple regression analysis was performed on the laboratory results to provide a collapse‐predictive model that was substantiated by data reported by several researchers. A chart is presented to estimate (1) The collapse potential of soils under various conditions; and (2) the critical water content beyond which no collapse is ex...