Comparison of Efficiency Level for Induction Motor with Dahlander Winding in Direct on Line and via Frequency Converter Drive Connection

One of the main issues with AC machines i.e. induction motors were speed regulation. In general, speed was mainly possible to regulate by changing number of poles or frequency of supply voltage. Also, smaller speed regulation was possible with changing voltage or load but this worked only for smaller ratio of drives so it will not be described here. Until frequency regulators (converters) reached certain level of development, both technical and economical, speed regulation was possible by changing number of poles. It was mainly done in one of two methods: Dahlander winding or separate windings in stator slots. One of deficiencies is that in Dahlander only combination of pole ratio is 2:1 e.g. 8 pole and 4 poles. Other is that speed is still constant depending on which number of poles you choose while when connected via frequency converter you can choose precisely at which speed i.e. frequency should the motor be rotating. In this paper, accent will be at measuring efficiency of the same motor when connected direct on line on a sine wave with different number of poles and using one pole number but driven via frequency converter and with speed regulation by changing frequency of supply voltage.