Speed and Gross Torque Calculation of DC Series Motor

What are the speed and gross torque developed by a 220 V, four-pole DC series motor drawing 40 A?

Options:

a. 0.3376 *10⁻³ rpm, 2489*10^-1 NM

b. 33.76 rpm, 24.89 NM

c. 337.6 rps, 2489 N.M

d. 337.6 rpm, 248.9 N.M

Answer:

The speed of the four-pole DC series motor is approximately 337.6 rpm and the gross torque developed is 248.9 N.M.

The correct answer to the given question is option d. 337.6 rpm, 248.9 N.M.

The speed of a DC series motor can be determined using the formula:

N = (A * V) / (60 * Φ * Z)

Where:

N is the speed in rpm

A is the number of parallel paths, which is 2 for a wave wound armature

V is the voltmeter reading across the motor

60 is a constant to convert sec to minutes

Φ is the flux in Weber (Wb)

Z is the total armature conductors

Substituting given values, the speed (N) = (2 * 220) / (60 * 25 * 10^(-3) * 782), which is approximately 337.6 rpm.

Next, the gross torque Tg can be computed using:

Tg = (K * Φ * Ia) / A

Assuming K = 0.159 for four-pole motor, current (Ia) of 40 A and 2 parallel paths (A), we get a gross torque (Tg) of 248.9 N.M.

The correct answer to the given question is option d. 337.6 rpm, 248.9 N.M.