Industrial variable speed drives for induction motor practical failures and their solutions

Variable speed drives (VSD) is rapidly replacing the conventional electromechanical contactors. Earlier engineers have shown hesitation to except the change of conventional starting method to soft starting using solid-state switches as the cost relatively high. But now the condition has changed as industrialist prefers this power electronics based inverters for both soft starting and speed control, this in fact getting more attention as price of solid states semiconductors has gradually reduced and eventually the VSD is cost effective as compare to electromechanical switches especially when the questions of efficiency, energy saving and reliability arise. However, as VSD is not a stand-alone device hence, there are many practical problems and failures confront by design engineers, project engineers as well as maintenance engineers. For this reason, this paper includes practical failures or problems faced by engineers during design, selection, installation and operation of VSD for induction motor in particular. Failures and problems in each stage will be elaborated in the simple manner from industrial point of view. Their appropriate solutions or preventions will be introduced to minimize breakdown and possible severe damages of VSD.