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

Drag link mechanism, why there is a different angular velocity in the two c...

why there is a different angular velocity in the two cranks of a drag link mechanism?

Determine hydraulic efficiency, A pelton wheel works at the foot of a dam b...

A pelton wheel works at the foot of a dam because of which the head available at the nozzle is 400m. The nozzle diameter is 160mm and the coefficient of velocity is 0.98. The diame

Buckingham''s pi-theorem, (a) Show by use of Buckingham's Pi-Theorem that t...

(a) Show by use of Buckingham's Pi-Theorem that the velocity through an orifice is given by V = √2gH  f D/H , M/ΡVH , σ/ΡV 2 H . Where H is the head causing flow, D is the diame

Array, sorting order of arra

sorting order of arra

Applied Elasticity, Can you prove an equation from Plane Stress and Plane s...

Can you prove an equation from Plane Stress and Plane strain?

How to observe water level, Q. How to observe water level? Site for ins...

Q. How to observe water level? Site for installing gauges should be properly selected. The reach should be reasonably straight and of uniform cross· section and slope. The leng

Tension testing, The first laboratory report, covering the two-part exercis...

The first laboratory report, covering the two-part exercise involving tension testing and stress concentrations is due in lab two weeks after the conclusion of fatigue testing.

Design the keys - shear keys, Design the keys - Shear Keys: A solid ci...

Design the keys - Shear Keys: A solid circular shaft is to transmit 200 kN at 200 rpm. If the maximum shear stress is not to exceed 80 n/mm 2 design the shaft. Design the key

Air-conditioning guidelines, The following guidelines are intended to assis...

The following guidelines are intended to assist the HVAC lead, designer or auditor in preparing an assessment of the quality of the HVAC engineering work for a specific project. T

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