Negative sequence voltage phase failure protection circuit

Negative sequence voltage phase failure protection utilizes the asymmetric voltage system formed when the motor power supply is missing one phase, and uses a negative sequence voltage filter
to decompose the negative sequence voltage from the system to achieve phase failure protection .
    Negative sequence voltage protection cannot protect phase failure during no-load operation
. It can only operate reliably when the motor load rate exceeds 30%-40%. This protection device also cannot reflect the disconnection between the negative sequence voltage filter and the motor, as well as
the internal disconnection fault of the motor winding with the stator winding delta connection.
    The circuit is shown in Figure 4-32. In the figure, capacitor Cl and resistor scale 1, R2, Ra form a negative sequence voltage filter.
    Negative sequence voltage filter components must satisfy the following relationship:
    Ri =Rz=Rs—5.5/Cl(kfl)
    where the unit of Cl is VF.