Electrical Engineering ⇒ Topic : Deflecting torque of M.I. Instruments in Terms of Self-Inductance

T_d of M.I. Instruments in Terms of Self-Inductance

In a moving-iron instrument, soft-iron vane moves in the magnetic field set up by the operating current in the instrument coil. Therefore, self-inductance (L) of the instrument coil changes with the position of the moving iron i.e. coil inductance changes with deflection θ. Suppose at any instant, the alternating current flowing through the coil is i.

Energy stored in the magnetic field at this instant is