Pumping performance in Distribution Systems is dependent on many factors. This paper highlights the most important factors and discusses their evaluation in the context of the interaction between the pumping system and the distribution system. High efficiency not necessarily the outcome of good hydraulic performance, but good hydraulic system performance is a prerequisite to high pumping station efficiency. Factors that influence hydraulic performance and those that lead to high pumping station efficiency, as well as the interdependency of factors are summarized. Several issues are detailed particularly the key topic of connections to reservoirs: an overview of system changes associated with adding pumping stations to the system, reservoir inlet and outlet configuration and, in addition, suction conditions for the pumping units, including Net Positive Suction Head required (NPSHr) and Net Positive Suction Head available (NPSHa). A proven reservoir sump illustrates the key design parameters used in the choice of sump layout. The Hydraulic System Performance Envelope is considered by reviewing how the system operational envelope is developed for current and future system demands. Two example system curves illustrate first a system where the pumping station is located (hydraulically) near the receiving balancing reservoir and, second, a system where the pumping station is located (hydraulically) far from the receiving balancing reservoir. For both case studies, a duty point is defined, and the impact of adding additional future demands on the system is considered as well as the resulting impact on the pumping system performance. Speed variation of pumping units, to meet the resulting changes in duty points is evaluated in detail. A strategy is provided to deal with possible but unexpected variations in the overall system envelope, to allow for easy correction (within limits). Variable Speed Drives (VSD) are reviewed including the influence of VSD's on the overall system performance, both from a hydraulic perspective as well as from an efficiency perspective. This topic is illustrated based on the above noted sample curves, taking the various likely operational conditions into account. A strategy is proposed on when the use of VSD's is suggested and when not, and some reasons to support the selection. In addition, a strategy is proposed to allow the future upgrading to VSD's with minimal changes to the pumping units.
展开▼
