CEM Electrical Power Systems & Motors 3

Question 1

What is the typical full-load efficiency range of a NEMA Premium 100 HP, 4-pole induction motor?

Accepted Answer

95–96%

Answer

NEMA Premium 100 HP motors typically achieve full-load efficiencies in the 95–96% range, significantly above standard or energy-efficient tiers.

Question 2

A facility has a 500 kVA transformer operating at 60% load. Approximately what percentage of transformer losses are core (no-load) losses versus copper (load) losses?

Accepted Answer

Core losses dominate because they are constant regardless of load

Answer

Core (no-load) losses are constant and exist whenever the transformer is energized, so at low loads they form a larger fraction of total losses.

Question 3

What is the primary energy benefit of using soft starters on large centrifugal pumps?

Accepted Answer

They reduce mechanical stress and inrush current during starting, extending equipment life

Answer

Soft starters ramp voltage gradually, reducing inrush current (often 6–8× FLA) and mechanical shock, lowering maintenance costs and improving reliability.

Question 4

Which IEEE standard is the accepted method for measuring 3-phase induction motor efficiency in the US?

Accepted Answer

IEEE 112 Method B

Answer

IEEE 112 Method B is the US standard for measuring motor efficiency using input/output power testing with specified loss segregation.

Question 5

When rewinding a failed motor instead of replacing it, what is the main energy efficiency concern?

Accepted Answer

Poor rewind practices can reduce motor efficiency by 1–2% or more

Answer

If rewind temperature and process controls are inadequate, core losses increase and efficiency drops by 1–2%, costing more in energy over the motor's life.

(CEM) Certified Emergency Manager Practice Test

(CEM) Certified Emergency Manager Practice Test

CEM Electrical Power Systems & Motors 3