A dc shunt motor has the following characteristics: Va=250 V, Ra=0.2 Ω, Rf=100 Ω, and ω=1800 rp

step 1 In this problem first time we'll draw the magnetization curve. So just look at it carefully. The

A dc shunt motor has the following characteristics: Va=250...

A dc shunt motor has the following characteristics: $V_a=250 \mathrm{~V}, R_a=0.2 \Omega, R_f=100 \Omega$, and $\omega=1800 \mathrm{rpm}$. Use the magnetization curve in Figure P15.24 to find the torque developed by the machine.
Figure P15.24 can't copy

Key Concepts

DC Shunt Motor

A DC shunt motor is a type of direct current machine in which the field windings are connected in parallel (shunt) with the armature winding. This configuration typically yields a motor with relatively constant speed under varying load conditions because its field excitation remains nearly constant. Understanding the arrangement and operation of the shunt motor is fundamental to analyzing its performance characteristics such as speed, torque, and response to changes in load.

Magnetization Curve

The magnetization curve represents the relationship between the field current and the resulting magnetic flux in the machine. This curve is crucial because it shows the saturation characteristics of the motor’s magnetic circuit and helps determine the actual flux for a given field current. In analyzing a DC motor, the flux directly influences back EMF and torque, making the magnetization curve an essential tool in performance calculations.

Armature Circuit and Back EMF

The armature circuit of a DC motor consists of the armature winding, which carries the current that interacts with the magnetic field to produce torque. As the motor rotates, it generates a back electromotive force (EMF) that opposes the applied voltage. This back EMF is proportional to both the magnetic flux (from the field circuit) and the rotational speed. Accurate analysis of the armature circuit involves accounting for the voltage drops across the armature resistance, which then allows the determination of the effective voltage that drives the armature current.

Torque Production in DC Motors

The torque developed in a DC motor is primarily the result of the interaction between the armature current and the magnetic flux produced by the field windings. Torque is typically proportional to the product of the armature current and the flux. Thus, any analysis of motor performance, including calculation of the developed torque, must integrate the effects of both the electrical (current and voltage drops) and magnetic (flux as determined by the magnetization curve) aspects of the motor’s operation.

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