Deck 4: Single-Phase Isolation Transformers

Question 1

The polarity of transformer windings can be determined by connecting one lead of the primary to one lead of the secondary and testing for an increase or decrease in voltage. This is often referred to as a ____ connection.

A) buck or linked
B) patched or boost
C) patched or tied
D) buck or boost

Answer 1

D

Question 2

The primary winding of a transformer is the side of the transformer that is connected to the driven load.

Answer 2

False

Question 3

A transformer nameplate does not list the current rating of the windings. The current rating for a winding can be determined by dividing the kVA rating by the ____.

A) primary voltage
B) winding voltage
C) secondary voltage
D) kilowatt rating

Answer 3

B

Question 4

One of the formulas for determining current in a single-phase circuit is ____.

A) VA = I / E
B) I = VA / (E x 3)
C) I = VA / E
D) E = I x VA

Question 5

A good rule for any type of transformer is that power in is always slightly greater than power out.

Question 6

The amount of core material needed for a particular transformer is determined by the ____ rating of the transformer.

A) saturation
B) efficiency
C) primary
D) power

Question 7

A basic law concerning transformers is that all values of a transformer are proportional to its turns ratio.

Question 8

The reason that the isolation transformer can greatly increase any voltage spikes before they reach the secondary is because of the rise time of current through an inductor.

Question 9

According to ANSI rules, the high-voltage leads of a transformer are to be marked H1 - H2, and so forth, and the low-voltage leads are marked ____, and so forth.

A) L1 - L2
B) S1 - S2
C) V1 - V2
D) X1 - X2

Question 10

Magnetic materials contain tiny magnetic structures in their molecular material known as magnetic ____.

A) domains
B) realms
C) points
D) plains

Question 11

Assume that an isolation transformer has 240 turns of wire on the primary and 60 turns of wire on the secondary. This is a ratio of 4:1 (240/60 = 4). Now assume that 120 V is connected to the primary winding. The voltage of the secondary winding is ____V.

A) 25
B) 30
C) 240
D) 480

Question 12

There will always be some amount of current flow in the primary of any voltage transformer even if there is no load connected to the secondary. This is called the relaxation current of the transformer.

Question 13

A very common type of isolation transformer is the distribution transformer, which is used to supply power to ____.

A) hospitals and nursing homes
B) warehouses and factories
C) most homes and many businesses
D) power plants

Question 14

Transformers can be divided into several classifications, which include ____.

A) isolation, auto, and current
B) isolation, auto, and manual
C) isolation, public, and current
D) commercial, auto, and current

Question 15

When the primary of a transformer is connected to power but there is no load connected to the secondary, current is limited by the inductive reactance of the primary.

Question 16

Almost all transformer nameplates will list the primary voltage, secondary voltage, and kVA rating.

Question 17

A common type of isolation transformer found throughout industry is the control transformer, which is used to increase the line voltage to the value needed to operate control circuits.

Question 18

The ____ transformer is basically an isolation transformer with a high-voltage rating on the primary winding, and that is intended for use in metering circuits.

A) control
B) potential
C) distribution
D) latent

Question 19

The amount of inrush current in the primary of a transformer is limited by amount of applied voltage, resistance of the wire in the primary winding, and flux change of the magnetic field in the core.

Question 20

Factors such as the amount and type of core material, wire size used to construct the windings, number of turns, and the degree of magnetic coupling between the windings greatly affect the transformer's impedance.