Large Induction Motor Starting Time Determination for The Purpose of Protection Coordination

Industrial distribution networks include a wide range of large MV induction motors. In the case of the Direct On-Line (DOL) starting, these motors can cause large transient currents through network branches and failure of the functionality of over current protective relays. So relay manufacturers embed a restricting function called Cold Load Pickup (CLP) into their products. It is very important to set the CLP for minimum cold load time to obtain the minimum disability time of the original setting table of the protective relay. This paper presents a deep evaluation on the performance of starting time calculation of induction motors using analytical method and state variable modeling. These studies are performed on a real case study and the results are compared with site measurements.