**Induction Relay Torque Equation:**

In Induction Relay Torque Equation, Two magnetic fluxes Φ_{1} and Φ_{2} differing in time phase penetrate through a disc. These alternating fluxes induce emfs e_{1} and e_{2} in the disc which lag their respective fluxes by 90°. These emfs lead to the flow of eddy currents i_{1} and i_{2}. By the interaction of Φ_{1} with i_{2} and Φ_{2} with i_{1} a driving torque is produced.

The currents i_{1} and i_{2} lag the voltages e_{1} and e_{2} by the impedance angle λ of the disc. Figure (3.6) shows the vector diagram.

Let

Therefore, the resultant torque is given by.

Thus the induction relay is a sine comparator in which the maximum torque is developed when α is 90° or 270° and zero torque when α is 0° or 180°.