Calculate the motor efficiency, Mechanical Engineering

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.

Posted Date: 2/18/2013 2:50:43 AM | Location : United States







Related Discussions:- Calculate the motor efficiency, Assignment Help, Ask Question on Calculate the motor efficiency, Get Answer, Expert's Help, Calculate the motor efficiency Discussions

Write discussion on Calculate the motor efficiency
Your posts are moderated
Related Questions
Q. Formed heads of vessels? Formed heads are generally of 2:1 semi ellipsoidal form, but other heads may be used, such as hemispherical, torispherical, conical and toriconical.

Two shafts A and B are co-axial. A gear C (50 teeth) is rigidly mounted on shaft A. A compound gear D-E gears with C and an internal gear G. D has 20 teeth and gears with C and E h

Eccentricity : This is distance between the axis of rotation and CG of mass. Unbalance : This is the product of mass and eccentricity. Balancing : This is

Find out the intensity of the external pressure: A thick cylinder of 0.5 m external diameter & 0.4 m internal diameter is subjected simultaneously to internal & external press

what is the different torque rating of a helical gear one direction verses the other


FLUX SHIELDED ARC WELDING This process is popularly known as Submerged Arc Welding (SAW).This is a fully mechanised welding process. The electrode is a continuous metallic sol

what is the maximum principle stress

Evaluate power transmitted by belt.  Sol: Let T 1  = Tension in tight side of the belt T 2 = Tension in slack side of the belt V = Velocity of belt in m/sec.  = Π

In selection of material handling equipment itself Hageman indicates that the final consideration are: 1. Methods of Installation: Operating controls should be accessibl