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

Safety organization, Safety Organization Each industry must have a sa...

Safety Organization Each industry must have a safety organisation along with well defined objective and well identified functions. It has been experienced that safety policie

Change in gravitational force, prove that the weight of a body at an elevat...

prove that the weight of a body at an elevation of h from sea level is expressd by the equation

Explain the creation phase of radial drilling machine, Explain the Creation...

Explain the Creation Phase of radial drilling machine Objective:  "To generate alternative methods for providing the function, through creative thinking, brainstorming and

Define a crm and what are its uses, The process of learning more about clie...

The process of learning more about clients needs such as information about customers , sales, marketing effectiveness, responsiveness and market trends is called as Customer Relati

Arc strikes-metallurgical defects, Arc strikes Represent any localised ...

Arc strikes Represent any localised heat affected zone caused by an arc. Arc strike tends to produce hardening particularly in high carbon steels and alloy steels. Grinding of

Explain the gauge pressure, Explain Gauge Pressure (P gauge ) Gauge Pre...

Explain Gauge Pressure (P gauge ) Gauge Pressure is the pressure of a fluid contained in a closed vessel. It is all time more than atmospheric pressure. It is calculated by an

Magnitude of the normal force, A Mercedes-Benz 300SL (m = 1600 kg) is parke...

A Mercedes-Benz 300SL (m = 1600 kg) is parked on a road that rises 20° above the horizontal. (a) What is the static frictional force that the ground exerts on the tires? (b) Wh

Motion of connected bodies, Motion of connected bodies: Analyze motio...

Motion of connected bodies: Analyze motion of connected bodies that is connected by pulleys. Sol: The given figure shows a light and inextensible string passing over sm

Synthesize a mechanism to prepare a function, Synthesize a mechanism to pre...

Synthesize a mechanism to prepare a function y = log x for 1≤ x ≤ 2 where three precision points are needed, for these precision points Calculate φ 2 , φ 3 and ψ 2 , ψ 3 ; if Δφ

Bore - thermodynamics, Bore - Thermodynamics: The inner diameter of en...

Bore - Thermodynamics: The inner diameter of engine cylinder is called as bore. It can be measured by a vernier calliper or bore gauge. As engine cylinder wears out with the p

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