Comprehensive Analysis of Principal Slot Harmonics as Reliable Indicators for Early Detection of Interturn Faults in Induction Motors of Deep-Well Submersible Pumps

Early detection of interturn faults is one of the most important issues in electrical machines, as the fault severity evolves very fast to a catastrophic failure due to the high thermal stress. However, as this article shows, in submersible induction motors for deep-well pumps, it evolves slower. These motors are highly water-cooled, which significantly reduces the thermal stress caused by the fault, increasing the possibility of early detection. Among fault detection methods, only those based on line current/voltage measurements can be used, as motors are at great depths. This article investigates the principal slot harmonics as reliable indicators for early detection of interturn faults in this application. To this end, a comprehensive analysis is conducted using finite-element analysis where the behavior of these harmonics is studied under different fault severities, both alone and coexisting with other asymmetries, such as unbalanced voltages, eccentricity, or rotor faults. The findings are used to develop a reliable diagnostic scheme based on the monitoring of the most fault-sensitive harmonics along with the voltage and current unbalance indexes. Finally, the scheme is applied, for the first time, in the context of continuous monitoring of a 230-HP induction motor showing its efficacy.