Transformers Test #2

A transformer has a 240 V primary and a 60 V secondary. With a 5 Ω load connected, what is the primary current? a. 12 A b. 3 A c. 0.75 A d. 48 A

a

A transformer in which the primary and secondary and physically separated and not connected by a conductor is called a __ transformer a. isolation b. step-up c. step-down d. turns

a

A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio? a. 8.66:1 b. 1:8.66 c. 1:15 d. 15:1

a

In a three-phase connection, the current that flows in a winding is the __ current a. line b. phase

a

Line voltage and phase voltage are the same in the a. delta b. wye

a

Most transformer cores are not made from a solid piece of metal. Instead, they are assembled from many thin sheets of metal. This type of construction is called a. laminated b. toroid c. H core d. tape wound

a

The three-phase connection in which all three of the coils are connected end-to-end to form a closed loop is the __ connection a. delta b. wye c. open delta d. open wye

a

The transformer winding which is the power input winding is called the __ winding a. primary b. secondary c. tertiary d. tapped

a

A delta-connected set of windings has a phase voltage of 480 V. What is the value of the line voltage? a. 277.14 V b. 480 V c. 831.36 V d. 1440 V

b

A delta-wye transformer has its __ connected as a delta and its __ connected as a wye a. secondary, primary b. primary, secondary

b

A transformer has a 2:1 turns ration. 120 V is applied to the primary. What is the secondary voltage? a. 24 V b. 60 V c. 120 V d. 600 V

b

A transformer in which the secondary voltage is more than the primary voltage is called a __ transformer a. step-down b. step-up c. isolation d. auto

b

A wye-delta transformer has its __ connected as a wye and its __ connected as a delta a. secondary, primary b. primary, secondary

b

In a three-phase connection, the voltage measured directly across one of the windings is the __ voltage a. line b. phase

b

In three-phase transformer connections, the primary leads are labeled with the letter __ and the secondary leads are labeled with the letter __ a. X, H b. H, X c. L, X d. X, L

b

Line current and phase current are the same in the __ configuration a. delta b. wye

b

The three-phase connection in which one end of the windings are connected together is called the __ connection a. delta b. wye c. open delta d. open wye

b

The transformer that converts a high (7200 V) voltage from the power company down to 120/240 V for homes and businesses is called a __ transformer a. auto b. distribution c. control d. household

b

The transformer winding which is the output winding is called the a. primary b. secondary c. tertiary d. tapped

b

A delta-connected set of windings has a phase current of 10 A. The line current is a. 5.77 A b. 10 A c. 17.32 A d. 30 A

c

A transformer has a 240 V primary and a 120 V secondary. With a 30 Ω load connected, what is the primary volt-amps? a. 4 A b. 8 A c. 480 A d. 960 A

c

A transformer in which the secondary voltage is less than the primary voltage is called a __ transformer a. step-up b. isolation c. step-down d. auto

c

A transformer supplying a house with 120/240 V has a secondary which is center tapped. The conductor connected to the center is called the __ conductor a. equipment ground b. hot c. neutral d. ungrounded

c

A transformer that does not isolate the out from the input is called a __ transformer a. distribution b. step-up c. auto d. control

c

A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage? a. 160 V b. 277.14 V c. 480 V d. 554.28 V

c

In three-phase power systems, the delivered power a. falls to zero three times per cycle b. falls to zero once per cycle c. never falls to zero d. none of the above

c

Often in calculations of values in three-phase systems, the square root of three occurs. The approximate value of this constant is? a. 0.707 b. 1.414 c. 1.732 d. 2.236

c

The magnetically operated device that can change values of voltage, current, and impedance without changing frequency is the a. converter b. inverter c. transformer d. transistor

c

When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. the correct voltage reading is a. the rated secondary voltage value b. twice the rated secondary voltage value c. zero volts d. the sum of the three transformer primaries

c

Dielectric oil performs what function? a. acts as an insulator b. prevents moisture formation c. provides cooling d. all of the above

d

In a transformer, the turns of primary wire compared to the turns of secondary wire is called a. isolation b. step-up c. step-down d. turns

d

The industrial use transformer that normally has 240 V or 480 V primary and a 120 secondary is called a __ transformer a. auto b. distribution c. isolation d. control

d