Fuse protection circuit one a

After the fuse is blown, a voltage
must be generated at both ends of the fuse, which is caused by the vector difference between the induced potential generated by breaking one phase winding and the power supply phase voltage. The size of the broken wire voltage is related to the motor load (speed). The broken wire protection circuit is to connect a relay
in parallel at both ends of the three-phase fuse , and the broken wire voltage is used to make the relay close. The relay pull-in voltage is generally set to less than 60V. The circuit is shown in Figure 4-15. The two circuits in the figure operate on the same principle. The relay in the picture adopts JTX type general-purpose small relay , and the pickup voltage is AC 36V.