Motor protection device selection purposes, give full play to both the motor overload, but also from damage, but also improve the continuity of the electric drive system reliability and production. In the case meets the protection requirements Consider the simplest protection devices, when simple protective device does not meet the requirements, or to protect the functions and features of higher demands, before considering the use of complex protective devices, so that economic and reliability unity. Specific function selection should be based on comprehensive consideration of the value of the motor itself, load conditions, the quality of the environment, the importance of the motor out of operation if a serious impact on production systems and other factors, and strive to achieve economic rationality.