No tooling cost process for induction motors energy efficiency improvements

In this paper, the analysis of some possibilities for increasing the induction motor efficiency using production technological process modifications is reported. This approach is known as the "no tooling cost" (NTC) strategy because it does not require a complete redesign of new laminations with a consistent cost in terms of investments. The paper shows the results obtained by a full experimental approach, using "ad hoc" prototypes. The NTC design modification and the technological processes analyzed in this paper have been done on totally enclosed fan-cooled standard induction motors. Obviously, the original motors have been compared from the energetic point of view with these prototypes. The energetic performance has been measured in accordance with the IEEE Std. 112-96 Method B. In particular, the following modifications, for obtaining an increase in efficiency, have been taken into consideration: rotor with copper bar included in the slot before the aluminum die cast, increase of the core axial length, and annealing of the stator core.

I. Introduction

The interest in the energetic problems again rose after the 1997 Tokyo Conference and energy efficiency is a strategic key of the energy policy, in particular, for the European Union, because it improves the efficiency of the economy, increases energy supply security, and decreases harmful emissions due to the electricity generation. Fig. 1. Efficiency limits for four-pole induction motors imposed by CEMEP. Since induction motors can be considered as the larger users of the electrical energy market, an efficiency increase of these motors is very important to obtain a consistent energy saving. For this reason, American and European standards impose upon manufacturers to produce higher efficiency induction motors [1]–[3]. In particular, following the European Standard IEC 34-2, the European Committee of Manufacturers of Electrical Machines and Power Electronics (CEMEP) protocol defines three efficiency classes for the two- and four-poles IP54- and IP55–type industrial motors with a rated power in the range 1.1–90 kW [2]. The proposed efficiency bands for the four-pole motors are shown in Fig. 1 and they are defined as follows: •

EFF3 class—typical motors now in production;

•

EFF2 class—increased-efficiency motors;

•

EFF1 class—high increased-efficiency motors.

The approaches to increase the induction motors efficiency can follow two ways. The first one, known as high tooling cost (HTC), is based on a complete motor redesign with high financial costs, in particular, due to the realization of new punches and the setup of new production lines. Without economical limits, this approach allows for a consistent efficiency increase, as shown in some products available on the market that are produced by the biggest electromechanical companies in the world.