Y-△ started motor automatic mutual switching circuit b

(2) The Y-△ started motor automatic mutual switching circuit
    circuit is shown in Figure 3-66. This circuit can be used when electric contact instruments and other instruments are needed to measure a certain parameter (such as pressure, flow, temperature, etc.) during the transmission process of the substance .
In this circuit , when the electrical contact instrument
KP of the parameter measurement circuit reaches the lower limit (KP contact is disconnected and relay KAI is released), or when the running motor fails and the thermal
relay acts, the backup motor can be automatically put into service. The two motors can serve as backup for each other. The motor uses Y-△
to start.