Calculate the motor efficiency, Mechanical Engineering

Assignment Help:

A 4- pole DC motor is known to have an armature resistance of 0.5 Ω, and is operated as a separately excited motor.

(a)  When the motor is connected to a 250V DC supply with no external mechanical load and with rated field current, it runs at a speed of 1488 rpm with an armature current of 4A. Calculate the no load rotational losses under these conditions.

(b)  The motor is now mechanically loaded until the armature current reaches 40A, under which conditions the DC supply voltage sags to 245V. Calculate the motor speed if the field current is unchanged.

(c)  Assuming that the motor rotational losses vary proportionally with speed, calculate the motor efficiency under the load condition of (b).

(d)  The motor field current is now accidentally set to half rated value. Calculate the DC supply voltage that is required to return to the same no load operating conditions of part (a)

(HINT: remember that the rotational power losses must stay the same if the speed is unchanged).

(e)  Discuss the two possible ways of achieving variable speed operation for a DC machine. Show the torque speed characteristics of a DC motor operating under both these types of speed control strategies, and discuss how they relate to the concepts of the "constant torque" and "constant power" regions of variable speed operation. Discuss the advantages and disadvantages of each speed control strategy.


Related Discussions:- Calculate the motor efficiency

What is the importance of safety at workshop?, (a) What is the importance o...

(a) What is the importance of safety at workshop? (b) What problems may arise, if we do not take safety precautions in the workshop?

Calculate the power of the engine, A Torsion dynamometer is used in a prope...

A Torsion dynamometer is used in a propeller shaft of a marine Engine. It is found that the shaft twists 2 o in a length of 20 meters at 120 r.p.m. If the shaft is hollow with 300

Thermodynamics, About zeroth law of thermodynamics

About zeroth law of thermodynamics

Stress plots, Problem:   The following machine component is loaded as s...

Problem:   The following machine component is loaded as shown.  It is fabricated from Al 6061-T6.   Determine the analytical solution to this problem and compare result

Superheated steam - thermodynamics, Superheate d Steam: When the dry ...

Superheate d Steam: When the dry saturated steam is heated further at constant pressure, the temperature of it rises up above the saturation temperature. This rise in tempera

Concept of continuum - thermodynamics, Concept of continuum - thermodynamic...

Concept of continuum - thermodynamics: Sol: Even the simplification of matter into molecules, atoms, electrons, etc. is too complex a picture for many problems of thermodyna

Explain the single cast component auger, Explain the Single Cast Component ...

Explain the Single Cast Component Auger Material for Single Cast Component Auger: Either Ni-Cr or Cast iron Length of components: 1250 mm. Outer Diameter of Auger compone

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd