An Intelligent Motor-Pump System

Abstract

Process industries are energy intensive in nature and are one of the largest consumers of electrical energy that is commercially generated for utilization. Motor driven systems consume more than two-thirds of the total energy consumed by the industrial sector; among which, centrifugal pumps are the most widely used equipment mainly for the purpose of fluid transportation. The efficiency of pumping units is around 40 to 50%, hence they offer tremendous opportunities of not only improving the efficiency of the process, but also ensure effective energy utilisation and management. With the increasing use of power electronics equipment, power quality (PQ) has become a very serious issue of consideration. On account of the random switching of single-phase loads in addition to time varying operations of industrial loads, PQ problem of voltage variation and unbalance is inevitable across three-phase systems. Application of varying or unbalanced voltages across the three-phase motor terminals results in performance variations leading to inefficient operation. For the purpose of study, the performance of a motor-pump system can be separately analyzed from the motor and pump points of view. The motor efficiency may vary in a very narrow band, pump efficiency depends upon the system head and flow rate but the system efficiency is a combination of the two; hence, necessary to analyze separately. As centrifugal pumps are classified under variable torque-variable speed load category, variation on the input side has a significant effect on the output side. Therefore the system efficiency now becomes an important index for ensuring efficient energy utilisation and efficiency. The main objective of the chapter is to put forward a methodology to analyze the working performance of a three-phase induction motor driven centrifugal pump under conditions of voltage and load variations by, defining additional factors for correct interpretation about the nature and extent of voltage unbalance that can exist in a power system network; define induction motor derating factors for safe and efficient operation based on operational requirements and devise energy management strategies for efficient utilization of electrical energy by the motor-pump system considering the voltage and load conditions.