how to calculate the actual power consumed in motor selection?

Answer 1

The question is not very clear.

We select motor based on the load BHP with a 10-15% margin.

The motor rating is the output power. To calculate the power input to the motor divide the output power by motor efficiency and power factor.

You can measure the input power by connecting a wattmeter in the circuit.

Answer 2

Hope the following article will be of some use to you.

You can get an estimate by looking at the motor rating information. Motors generally have a different draw current at start up and also draw a different amount of current depending on the load conditons.
There are many different types of motors therefore a single answer would not suffice.

Get an Audel's book on electrical motors to get a simplified answer.
Here is a general formula:

Power input in watts (power consumed) = E I X Power Factor
= HP X 746 / motor efficiency
where
E = voltage input
I = current used in amperes
HP (horse power) = 2pi R
x N x W / 33000 = T (in-lb) x N/ 63 025
where
R = radius of motor pulley in feet
N = revolutions per minute
W = weight in pounds
T = torque or twisting moment in inch-pound
pi = 3.1416

http://www.all-cordless.com/elbo.html

http://en.wikipedia.org/wiki/Electric_motor

Answer 3

Newton has disclosed many theories. The power consumed by a coil is based on the number of turns of the coil, and it is the base of the output voltage also. Normally a perfectly wounded motor would consume the minimum current. When the windings become loose the consumption would increase. Till now the formulae were in my head to give the calculation criteria of power consumption, but not now.