Thermal Protection of Biopower Plant Electric Drives

Electrical power equipment of biopower plant electric drives is usually based on asynchronous electric drives and the specific character of their operating conditions makes it necessary to apply thermal protectors. A comparative analysis of well-known methods of asynchronous motor thermal protection was carried out. A new method providing a measurement of the winding resistance right during the asynchronous motor operation was proposed to monitor the temperature. This method is based upon the measurement of the alternating phase voltages and currents and further algorithmic processing of this information in order to extract from it the components of direct voltage and current by calculating the stator winding resistance and making use of its value to estimate the winding thermal state. The hardware implementation of this method includes making use of a current-sensing device in the form of an instrument shunt and two independent asymmetric instrument channels designed on the basis of amplitude detectors and switch analog to digital converters. Experimental investigations confirmed the high accuracy of the winding temperature control. It was shown that the developed system could be used to provide thermal control and winding protection of any electric devices supplied from AC mains and used in different industrial electric installations and electric drives.