CEM Electrical Systems and Motors 5

Question 1

When performing a motor system energy audit, which field measurement tool is used to measure three-phase power, power factor, and harmonic content simultaneously?

Accepted Answer

Power quality analyzer

Answer

A power quality analyzer simultaneously measures voltage, current, real power, reactive power, power factor, and harmonic spectrum on all three phases.

Question 2

A motor rewind that reduces efficiency by 1-2% is most commonly caused by which practice?

Accepted Answer

Burnout oven temperatures exceeding 700°F degrading the lamination insulation

Answer

Excessive burnout oven temperatures damage the interlaminar insulation in the stator core, increasing iron losses and reducing efficiency by 1-2% or more per rewind.

Question 3

According to NEMA MG-1, what is the allowable voltage unbalance limit for motor operation without derating?

Accepted Answer

3%

Answer

NEMA MG-1 recommends that motors not be operated with a voltage unbalance exceeding 1% without derating; above 1%, derating is required and above 5%, motor operation is not recommended.

Question 4

What does a 'motor management' or 'motor rewind vs. replace' analysis typically use as the financial decision threshold?

Accepted Answer

The 40% rule: replace when rewind cost exceeds 40% of new motor cost

Answer

The commonly cited '40% rule' suggests replacement when rewind cost exceeds 40% of the cost of a new premium efficiency motor, accounting for efficiency improvement value.

Question 5

In a lighting system energy audit, what is the efficacy of a light source measured in?

Accepted Answer

Lumens per watt (lm/W)

Answer

Luminous efficacy is expressed in lumens per watt (lm/W), representing how efficiently a light source converts electrical power into visible light.

(CEM) Certified Emergency Manager Practice Test

(CEM) Certified Emergency Manager Practice Test

CEM Electrical Systems and Motors 5