Y-△ main circuit adapted to motors with long starting time

For loads with long startup time, such as centrifugal fans, circulating compressors, ball mills, etc., the Y-△ main circuit should be wired as shown in the figure. The current setting value IFT of the thermal relay FT is approximately 0.58IN. Since the thermal relay is in the starting circuit, the starting current is very large at startup (such as a 37kW motor, rated current IN = 70.2A, starting current up to 163A, thermal relay setting value IFT is 40A), so the FT will act instantly and start fail. If IFT is increased, the thermal relay will lose its overheating and overload protection function in the normal operation of the motor M. Using the connection method shown in the diagram can avoid the above situation.