MOVING IRON INSTURMENT

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CENTURION UNIVERSITY OF TECHNICAL AND MANEGEMENT :

CENTURION UNIVERSITY OF TECHNICAL AND MANEGEMENT Presented by---- Rajeev Ranjan (Electrical and Electronic Engg.) JITM(PARALAKHMUNDI)

MOVING IRON INSTURMENT :

MOVING IRON INSTURMENT Moving Iron Instruments          M.I instruments are mainly used for the measurement of alternating currents and voltages, though it can also be used for d.c measurements.                  

THERE ARE TWO TYPES OF MOVING-IRON INSTRUMENTS:

THERE ARE TWO TYPES OF MOVING-IRON INSTRUMENTS 1)ATTRACTION TYPE 2)REPULSION TYPE

ATTRACTION TYPE:

ATTRACTION TYPE     In this type of instrument, a single soft iron vane (moving iron) is mounted on the spindle, and is attracted towards the coil when operating current flows through it.

Deflecting torque equation:

Deflecting torque equation The force F, pulling the soft -iron piece towards the coil is directly proportional to; a) Field strength H, produced by the coil. b)pole strength ‘m’ developed in the iron piece. F α mH Since, m α H, F α H 2 Instantaneous deflecting torque  α H 2 Also, the field strength H = μi If the permeability(μ) of the iron is assumed constant, Then,   H α i Where, i  instantaneous coil current, Ampere Instantaneous deflecting torque α i 2 Average deflecting torque, T d α mean of i 2 over a cycle. Since the instrument is spring controlled,                                              T c α θ In the steady position of deflection, T d = T c                                              θ α mean of i 2 over a cycle                                                 α I 2                                                   

REPULSION TYPE:

REPULSION TYPE In this two soft iron vanes are used; one fixed and attached the stationary coil, while the other is movable (moving iron), and mounted on the spindle of the instrument

Deflecting torque:-:

Deflecting torque:-    The deflecting torque results due to repulsion between the similarly charged soft- iron pieces or vanes. If the two pieces develop pole strength of m 1 and m 2 respectively, then;                        Instantaneous deflecting torque α m 1 m 2 α H 2 If the permeability of iron is assumed constant, then;  H α i ,  where, i  is the coil current                           Instantaneous deflecting torque α i 2  Average deflecting torque, T d α mean of i 2 over a cycle.   Since the instrument is spring controlled, T c α θ  In the steady position of deflection, T d = T c                                                           θ α mean of i 2 over a cycle.                                                              α  I 2

MOVING IRON AMMETER:

MOVING IRON AMMETER

MOVING IRON VOLTMETER:

MOVING IRON VOLTMETER

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