One of the negative sequence current phase failure protection circuits

It is a phase failure protection circuit designed by taking advantage of the phenomenon that the negative sequence current increases sharply when one phase of the motor power supply is disconnected . Negative sequence current can be detected through a negative sequence current filter. This type of circuit requires that the magnetic flux in the transformer core is not saturated
, that is, the core cross-section is required to be large enough.
    The circuit is shown in Figure 4-30. It consists of current
  transformers TAi, TA2, resistors, R2 and capacitor
  Cl.
    When a phase of the power supply is missing, a negative sequence current
  is generated . The negative sequence current filter has a voltage signal output,
  the thyristor V is triggered to conduct, the contactor KM
  coil is short-circuited, KM loses power and is released, and the motor
  stops. .