Ch 4 Transformers

A transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 80 volts. If the windings were connected subtractive, what voltage would appear across the entire connection?

160 V

A transformer has a turns ratio of 1:6. The primary current is 18 amperes. What is the secondary current?

3 A

A transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 80 volts. If the windings were connected additive, what voltage would appear across the entire connection?

320 V

A transformer has a primary voltage of 480 volts and a secondary voltage of 20 volts. If the secondary of the transformer supplies a current of 9.6 amperes to a load, what is the primary current? (Disregard excitation current.)

400 mA

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

I = VA / E

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

True

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.

True

All values of a transformer are proportional to its:

Turns ratio

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.

false

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.

potential

What do the dots shown beside the terminal leads of a transformer represent on a schematic?

the polarity of the windings

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.

true

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 ____.

winding voltage

What is a transformer?

A machine which can change values of voltage, current, and impedance without changing frequency.

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

False

The primary leads of a transformer are labeled 1 and 2. The secondary leads are labeled 3 and 4. If polarity dots are placed beside leads 1 and 4, which secondary lead would be connected to terminal2 to make the connection additive?

Terminal 4