Development of a specialised test rig for assessing the efficiency of large industrial induction machines

Kinyua, Jamlick Murimi

Development of a specialised test rig for assessing the efficiency of large industrial induction machines

Thesis / Dissertation

2017

Publisher

University of Cape Town

Department

Department of Electrical Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

This thesis critically scrutinizes the application of international testing standards for estimation of induction machine efficiency in South Africa (SA) and across the globe. Approximately 60% of the electrical consumption in SA is utilised by motorised systems. The need for optimization of efficiency is on the rise due to the crisis not only in South Africa but in the whole world. Minimum energy performance standards (MEPS) applications are emphasised to increase machine efficiency. Most of the industries use induction machines without clear knowledge of how efficient they are. Eskom Demand Side management (DSM) embarked on strategies that would reduce the demand on electrical energy through optimization of electrical machines. Since most of the low voltage (LV) motors in the country are imported from different countries/nations, there is a clear need to quantify the efficiency of these machines. However, few facilities exist to test the efficiency of the machines in respect of the high use of IM in the mining industries. This has raised the need to develop a flexible specialised test rig that conforms to the requirements of international testing standards. Furthermore; there are different methods of assessing the efficiency of induction machines, for example, the IEEE 112-B method which requires the use of a dynamometer as the load machine. Numerous tests need to be performed to assess the efficiency of induction machines. In most cases, the manufacturer of the machines quotes the efficiency, but in some instances, the difference between the laboratory results and the efficiency on the nameplate is observed. The proposed test bed can evaluate various industrial loads. Various induction machines (IMs) ranging from 37kW to 75kW were analyzed and therefore the test bed developed is very flexible to accommodate a wide range of industrial IMs. The Active Front End (AFE) which has regenerative capability was utilized. When the quasi equilibrium state is reached, the AFE draws only the inherent losses in the entire system from the supply. Consequently, the excess energy generated by the system is fed back to the utility supply. After the process of developing and implementation of a test bed for evaluating the efficiency of motor drives, the test begins with a steady state analysis of efficiency over a wide range of output torque, speed and loading. Together, the dynamic and steady state provide a realistic assessment of the performance of the industrial motor drive. In addition to the estimation of efficiency, the error analysis due to the instrumentation used was also investigated. This study also included the quantification of error and the analysis of uncertainty associated with the methods of estimating the efficiency of induction machines. This rig was designed economically for a continuous and reliable operation. Safety to equipment and personnel conducting the tests was emphasized. The ease of operation and maintenance with minimum power loss, mechanical protection of the equipment, interchangeability of the motors and load variation was critically observed.