Motor Efficiency Calculation Made Easy

Plan for success by learning how to answer motor efficiency calculation and related questions on your exam. Can you answer these questions correctly?

Question:

What is the efficiency of a 5 hp-230 volt single-phase ac motor?

Solution:

Use the single-phase efficiency formula

= 746 watts x Hp Rating/E x I

= 746 watts x 5 hp/230 volts x 28 amps

= 3730/6440

= .5792 x 100

=57.92% final answer.

Question:

What is the true power of a 5 hp-230 volt single-phase ac motor?

Solution:

To answer this question you need to know what true power is. True power is the power actually used by the system to do useful work. You also need to know that 746 watts equals 1 Hp.

True Power

= 746 x Hp Rating

= 746 watts x 5 hp

= 3730 watts final answer.

Question:

What is the apparent power of a 5 Hp-230 volt single-phase ac motor?

To answer this question you need to know what apparent power is. Apparent power is the power supplied to the system. It only has the potential to do work.

Apparent Power

= E x I

= 230 volts x 28 amps

= 6440 volt-amps final answer.

Question:

What is the efficiency of a 10 hp-230 volt three-phase ac motor?

Solution:

Use the three-phase efficiency formula

= 746 watts x Hp Rating/E x I x 1.732

= 746 watts x 10 hp/230 volts x 28 amps x 1.732

= 7460/11,154

= .6688 x 100

=66.88% final answer.

Question:

What is the true  power of a 10 hp-230 volt three-phase ac motor?

Solution:

True Power

= 746 watts x Hp Rating

= 746 watts x  10 hp

= 7460 watts final answer.

Question:

What is the apparent power of a 10 Hp-230 volt three-phase ac motor?

Apparent Power

= E x I x 1.732

= 230 volts x 28 amps x 1.732

= 11,154 volt-amps final answer.

Knowing which formula to use and how to use it can make all the difference! Learn how to answer any formula related exam question with confidence. Call 888-919-3926 and start preparing to pass your electrical exam today!