Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
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.
(a) The following forces (all pull) act at a point : (6) (i) 20 N North-East (ii) 25 N due North (iii) 20 N 30o East of South (iv) 15 N due East (v) 30 N 60o South o
Change in entropy for reversible
need help with reports on thin thick and combined cylinder theory
1.Calculate the heat-removal factor for a collector having an overall heat-losscoefficient of 6 W/m2K and constructed of aluminum fins and tubes. Tube-to-tube centered distance is
a) Why cutting fluids are used for machining of metals? List different types of cutting fluids and additives for cutting fluids. b) What factors are responsible for surface fin
What is Time-Study ? How the standard time is determined in Time-Study ? What are the Merit-Rating ? Illustrate various methods of Merit-Rating. Describe the Break-Even-Analy
what is internal combustion engine
why 4R kinematic chain do not form different mechanisms?
Find out the moment of inertia of an annular area: Find out the M. I. of an annular area among two circles where difference of radius is quite small, around any centroidal axi
Determine the magnitude and nature of the stresses: A thin spherical hollow steel shell of 400 mm diameter & 5 mm thickness is immersed into a liquid container pressurized to
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd