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

Stress-strain curves (compression), Stress-Strai n Curves (Compression): ...

Stress-Strai n Curves (Compression): For the ductile materials stress strain curves in compression are similar to those in tension at least up to the yield point for all the

Objectives-ceramics-refractory and abrasive materials, Objectives Afte...

Objectives After studying this section, you should be capable to: known properties that are essential to be present in a material for high temperature applications,

Ease of operation-factors in clutch design , Ease of Operation : For highe...

Ease of Operation : For higher power transmissions, the operation of disengaging the clutch must not be tiresome to the driver.

What is the rol of forecasting, a) Illustrate the important of Ergonomics i...

a) Illustrate the important of Ergonomics in a manufacturing sector or in service sector in the context of productivity. b) What is the rol of "Forecasting" Plays in production

Optimal feeder geometry, PART A A new process plant for ore processing ...

PART A A new process plant for ore processing is currently being planned. The design is only in the first stage. However, three requirements have already been clearly stated:

Construct the load displacement diagram, A suspended walkway in an undergr...

A suspended walkway in an underground cavern consists of a deck supported by three tie rods placed symmetrically about the centre as shown below: The rods are each of

Illustrate torsionally equivalent shaft, (a) Illustrate Torsionally Equival...

(a) Illustrate Torsionally Equivalent shaft. (b) Determine the natural frequencies and mode shapes for the system shown in figure I 1 = 10 Kg -m 2 I 2 = 40 Kg -m 2

Make evaluation for the engine efficiency, (a) Differentiate between carnot...

(a) Differentiate between carnot Heat pump and carnot Heat engine. What is the basic cycle for a carnot Heat pump ? Explain it. (b) A reversible heat engine delivers 0.6 K at po

Necessity of lubrication , Necessity of Lubrication To lubricate t...

Necessity of Lubrication To lubricate the various parts of engine. The supplementary function of lubrication is to cool and clean the engine parts. To prevent en

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