The change in the efficiency factor of the pumping unit with a frequency converter

This paper gives the results of the investigation of the operation of a pumping unit equipped with a frequency converter. As a rule, it is widely assumed that when changing the speed up to 50 %, the pump efficiency almost does not change, and the possibility of decrease of its efficiency is not taken into consideration when calculating the economic efficiency of the operation of the pumping unit equipped with a frequency converter. However, failure to take account the efficiency decrease may cause inaccurate assessment of the economic efficiency of the use of the frequency converter and, consequently, improper selection of the method of control of the operation of the pumping units. This is particularly important for irrigation pumping plants the operation of which is characterized by large volume of the pumpable volume and less severe requirements for provision of the water pressure required for the consumer. The purpose of this paper is to carry out experiments on a test-bed equipped with a pumping unit, parameter measuring instrument, and a frequency converter, and detection of the pattern of efficiency variation with speed. The paper presents the results of the carried out experiments, the obtained characteristic curves of the variation of different types of the efficiency at variation of the pump shaft speed, as well as their analysis