Optimal Operation of Variable Speed Pumping System in China’s Eastern Route Project of S-to-N Water Diversion Project

Abstract

A dynamic planning model for optimizing operation of variable speed pumping system, aiming at minimum power consumption, was proposed to achieve economic operation. The No. 4 Jiangdu Pumping Station, a source pumping station in China’s Eastern Route of South‐to‐North Water Diversion Project, is taken as a study case. Since the sump water level of Jiangdu Pumping Station is affected by the tide of Yangtze River, the daily‐average heads of the pumping system varies yearly from 3.8m to 7.8m and the tide level difference in one day up to 1.2m. Comparisons of operation electricity cost between optimized variable speed and fixed speed operations of pumping system were made. When the full load operation mode is adopted, whether or not electricity prices in peak‐valley periods are considered, the benefits of variable speed operation cannot compensate the energy consumption of the VFD. And when the pumping system operates in part load and the peak‐valley electricity prices are considered, the pumping system should cease operation or lower its rotational speed in peak load hours since the electricity price are much higher, and to the contrary the pumping system should raise its rotational speed in valley load hours to pump more water. The computed results show that if the pumping system operates in 80% or 60% loads, the energy consumption cost of specified volume of water will save 14.01% and 26.69% averagely by means of optimal variable speed operation, and the investment on VFD will be paid back in 2 or 3 years. However, if the pumping system operates in 80% or 60% loads and the energy cost is calculated in non peak‐valley electricity price, the repayment will be lengthened up to 18 years. In China’s S‐to‐N Water Diversion Project, when the market operation and peak‐valley electricity prices are taken into effect to supply water and regulate water levels in regulation reservoirs as Hongzehu Lake, Luomahu Lake, etc. the economic operation of water‐diversion pumping stations will be vital, and the adoption of VFDs to achieve optimal operation may be a good choice.