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

Discover the suitable diameter of the shaft, Discover the suitable diameter...

Discover the suitable diameter of the shaft: A shaft is required to fail while the torque on the shaft is 20 kN-m. Discover the suitable diameter of the shaft of the modulus o

Safe access and location of buildings in plant design, The following items ...

The following items should be considered regarding the safe access and location of buildings: • The fire fighting pump house is usually located in a non-hazardous OSBL location

Determine wheel diameters at the pitch circle of blades, A pelton wheel wor...

A pelton wheel works at the foot of a dam because of which the head available at the nozzle is 220m. the nozzle diameter is 20 c.m. and coefficient of speed 0.98. The wheel operate

Find out the maximum bending stress in beam, Q. A rectangular beam of 200 m...

Q. A rectangular beam of 200 mm in breadth and 400 mm in depth is simply supported over span of 4m  and carries distributed load of 10 KN/m. Find out the maximum bending stress in

Calculate force required for equilibrium, Calculate force required for equi...

Calculate force required for equilibrium: A member ABCD is subjected to the point loads P 1 , P 2 , P 3   an d P 4   as shown in the figure given below

Magnitude of the centripetal acceleration of the car, A car travels at a co...

A car travels at a constant speed around a circular track whose radius is 2.2 km. The car goes once around the track in 400 s. What is the magnitude of the centripetal acceleration

Solid modeling, Solid Modeling: 3-D solid modelling techniques provide...

Solid Modeling: 3-D solid modelling techniques provide the user along with complete information regarding the model. These may be quickly created without having to describe in

Dynamic magnifier-forced vibration-synchronous whirl, Dynamic Magnifier: ...

Dynamic Magnifier: This is function of frequency ratio. Forced Vibration: While the system is continuously excited by an external force or internally produced force, the v

Strength of material and engineering mechanics, Di fferentiate between str...

Di fferentiate between strength of material and engineering mechanics Sol.: Three primary areas of mechanics of solids are statics, dynamics and the strength of materials.

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