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

Belt drive, how will u designate a v belt

how will u designate a v belt

Evaluate the actual over all efficiency of the turbine, (a) An engine uses ...

(a) An engine uses 6.5 Kg of oil per hr of a calorific value 30,000 kJ / kg. If the B. P. of the engine is 22KW and mechanical efficiency 85%. Calculate (i) Brake thermal eff

Difference between projectile motion and a rocket motion, Difference betwee...

Difference between projectile motion and a rocket motion? Ans) A projectile has no motor or rocket on it, so all of its momentum is given to it as it is opened. An example of a

Calculate net force on the piston, A vertical petrol engine 100mm diameter ...

A vertical petrol engine 100mm diameter and 120mm stroke has a connecting rod 250mm long. The mass of the  piston is 1.1kg. The speed is 2000 r.p.m. On the expansion stroke with a

What is the basic working principle of capacitive transducer, Answer any fi...

Answer any five questions. a) Describe calibration and state its types. b) Which are the kinds of test signals? c) What is the basic working principle of piezo-electric tr

Water jet machining, Water jet machining is an advanced method for cutting ...

Water jet machining is an advanced method for cutting plates using a high-velocity water jet mixed with abrasive powder. The jet comes out of a nozzle A of diameter d and follows t

Determine the force to pull box along a level surface, Determine the force ...

Determine the force to pull box along a level surface: A metal box having weight 10KN is pulled along a level surface at the uniform speed by applying horizontal force of 350

Illustrate the several kinds of chips, (a) Illustrate the several kinds of ...

(a) Illustrate the several kinds of chips formed during metal cutting with neat diagrams. (b) Why is Titanium Nitride a valuable tool coating? (c) Give the differences betwee

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