EETC Transformers 2

Question 1

A transformer has 500 primary turns and 100 secondary turns. If the primary voltage is 240V, what is the secondary voltage?

Accepted Answer

48V

Answer

Vs = Vp × (Ns/Np) = 240 × (100/500) = 48V.

Question 2

What happens to the magnetizing current in a transformer when the core becomes saturated?

Accepted Answer

It increases sharply and becomes non-sinusoidal

Answer

Core saturation causes a sharp, non-linear rise in magnetizing current and introduces harmonic distortion.

Question 3

Which type of transformer winding connection introduces a 30-degree phase shift between primary and secondary voltages?

Accepted Answer

Delta-wye (Δ-Y)

Answer

A delta-wye (or wye-delta) connection inherently produces a 30-degree phase displacement between primary and secondary voltages.

Question 4

The impedance of a transformer expressed as a percentage (% Z) is primarily used to determine:

Accepted Answer

Short-circuit current available at the secondary

Answer

Percent impedance directly determines the available fault current: I_fault = I_rated / (%Z/100).

Question 5

In a transformer, the eddy current losses are proportional to:

Accepted Answer

The square of the frequency and the square of the flux density

Answer

Eddy current losses follow Pe ∝ f² × Bm², making them sensitive to both frequency and flux density.

(EETC) Electrical Technician Certification Practice Test