Question 1

If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a ____ bank.
A) consolidated
B) temporary
C) three-phase
D) triple consolidated

Accepted Answer

Three single-phase transformers can be connected in a variety of ways to form a three-phase transformer bank. Therefore, if a three-phase transformer of the appropriate size and turns ratio is not available, three single-phase transformers can be used to create a three-phase transformer bank.

Question 2

The primary windings of three single-phase transformers have been connected to form a wye connection. In a wye connection, the phase voltage is less than the line voltage by a factor of ____.
A) 0.577
B) 1.732
C) 3
D) 5.196

Accepted Answer

In a wye (or star) connection, the phase voltage is less than the line voltage by a factor of the square root of 3, which is approximately 1.732.

Question 3

A ____ diagram, which illustrates a delta-wye connection, is generally used to show the main power distribution system of a large industrial plant.
A) one-line
B) three-line
C) one-phase
D) three-phase

Accepted Answer

A one-line diagram is typically used to show the power distribution system of a large industrial plant and includes information on the voltage, current, and power sources as well as transformers, generators, and breakers. A delta-wye connection is a common connection used for three-phase power transmission and distribution, where three single-phase transformers are connected together to form a three-phase transformer. Therefore, the most appropriate choice is A, the one-line diagram.

Question 4

In a delta connection, the phase voltage and line voltage are the same, so it would be appropriate to say that EP(Secondary) = EL(Secondary).

Accepted Answer

In a delta connection, the phase voltage and line voltage are the same. Therefore, EP(Secondary) = EL(Secondary).

Question 5

Delta connections should only be checked for proper polarity after making the final connection and applying power.

Accepted Answer

Delta connections do not have polarity in the same sense as direct current systems; the concern with delta connections is more about correct phasing and ensuring the connections are made according to the intended electrical configuration before applying power. Checking for proper configuration should be done before power is applied to prevent equipment damage or safety hazards.

Question 6

One of the most common three-phase to six-phase connections is the ____ connection.
A) diametrical
B) zig-zag
C) interconnected-wye
D) interconnected-delta

Accepted Answer

The answer of One of the most common three-phase to...

Question 7

Only phase values of ____ can be used when computing transformer values.
A) voltage
B) current
C) voltage and current
D) wattage

Accepted Answer

Transformer values are computed using the phase values of both voltage and current, as these parameters are essential in understanding the transformer's behavior and performance in alternating current (AC) systems.

Question 8

Three single-phase transformers are connected to form a wye-delta bank. Once the voltage across each of the load resistors is known, the current flow through the phase of the load can be computed using the formula ____.
A) IP(Load) = R / EP(Load)
B) IP(Load) = 1.732 / EL(Load)
C) EP(Load) = IP(Load) / R
D) IP(Load) = EP(Load) / R

Accepted Answer

The formula for computing the current flow through the phase of the load is IP(Load) = EP(Load) / R, where IP(Load) is the current flow through the phase of the load, EP(Load) is the voltage across the load resistor, and R is the resistance of the load. Therefore, choice D is the correct answer.

Question 9

A three-phase transformer is connected in a delta-delta configuration. The load is connected as a wye, and each phase has an impedance of 7 ohm. The primary is connected to a line voltage of 4160 volts, and the secondary line voltage is 440 volts. Therefore, the turns ratio is 9.45:1.

Accepted Answer

The turns ratio is calculated by dividing the primary line voltage by the secondary line voltage, which in this case is 4160 volts / 440 volts = 9.45:1.

Question 10

A three-phase transformer is constructed by winding three single-phase transformers on a single core.

Accepted Answer

A three-phase transformer is indeed constructed by winding three single-phase transformers on a single core.

Question 11

If power is applied to the transformer bank before the delta connection is closed, the voltmeter should indicate ____ volts.
A) zero
B) at least 10
C) fewer than 50
D) about 100

Accepted Answer

If the delta connection is not closed, there will be no complete circuit and no voltage will be present in the system. Therefore, the voltmeter should indicate zero volts.

Question 12

A voltmeter is a low-impedance device.

Accepted Answer

A voltmeter is a high-impedance device, as it is designed to measure the voltage across a circuit without significantly affecting the circuit itself. A low-impedance device would draw current from the circuit and affect the measured voltage.

Question 13

A wye-delta transformer has its primary winding connected in a delta and its secondary winding connected in a wye.

Accepted Answer

The answer of A wye-delta transformer has its primary winding...

Question 14

The open-delta transformer connection is often used when the amount of three-phase power needed is not excessive, such as in a small business.

Accepted Answer

The statement is true. The open-delta transformer connection is commonly used in situations where the power demands are not too high, such as small businesses or residential areas.

Question 15

When three single-phase transformers are used to make a three-phase transformer bank, their primary windings are always connected in a wye connection.

Accepted Answer

The primary windings of three single-phase transformers used in a three-phase transformer bank can be connected in either a wye (star) or delta configuration, depending on the specific application requirements.

Question 16

When three-phase transformers are connected as a wye or delta, the primary and secondary windings themselves become the phases of a three-phase connection. This is true whether a three-phase transformer is used or whether three single-phase transformers are employed to form a three-phase bank.

Accepted Answer

When three-phase transformers are connected in a wye or delta configuration, the primary and secondary windings become the phases of a three-phase connection. This applies to both three-phase transformers and three single-phase transformers arranged in a three-phase bank.

Question 17

In a three-phase transformer, the phase value of the primary voltage can be computed using the formula EP(Primary) = ____.
A) EL / 1.732
B) 1.732 / EL
C) EL x 1.732
D) 3(EL) / 1.732

Accepted Answer

The primary voltage in a three-phase transformer is related to the line-to-line voltage by a factor of 1.732 (square root of 3). Therefore, EP(Primary) = EL / 1.732.

Question 18

The Scott connection is used to convert three-phase power into one-phase power using three single-phase transformers.

Accepted Answer

The Scott connection is used to convert three-phase power into two-phase power using two single-phase transformers.

Question 19

A connection involving the use of two transformers to supply three-phase power is the T-connection. In this connection, one transformer is generally referred to as the main transformer and the other is called the ____ transformer.
A) alternate
B) teaser
C) secondary
D) extra

Accepted Answer

The T-connection in three-phase systems involves two transformers where one is the main transformer and the other is referred to as the teaser transformer. This setup is used to convert between three-phase and two-phase systems or to provide a three-phase supply from a two-phase source.

Question 20

A dielectric oil provides electrical insulation between the windings and the ____.
A) three-phase bank
B) leads
C) transformer
D) case

Accepted Answer

Dielectric oil in a transformer provides electrical insulation between the windings and the case, ensuring that electrical paths do not form outside of the intended windings, which could lead to short circuits or other failures.

Quiz 8: Three-Phase Transformers

If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a ____ bank.

The primary windings of three single-phase transformers have been connected to form a wye connection. In a wye connection, the phase voltage is less than the line voltage by a factor of ____.

A ____ diagram, which illustrates a delta-wye connection, is generally used to show the main power distribution system of a large industrial plant.

In a delta connection, the phase voltage and line voltage are the same, so it would be appropriate to say that EP(Secondary) = EL(Secondary).

Delta connections should only be checked for proper polarity after making the final connection and applying power.

One of the most common three-phase to six-phase connections is the ____ connection.

Only phase values of ____ can be used when computing transformer values.

Three single-phase transformers are connected to form a wye-delta bank. Once the voltage across each of the load resistors is known, the current flow through the phase of the load can be computed using the formula ____.

A three-phase transformer is connected in a delta-delta configuration. The load is connected as a wye, and each phase has an impedance of 7 ohm. The primary is connected to a line voltage of 4160 volts, and the secondary line voltage is 440 volts. Therefore, the turns ratio is 9.45:1.

A three-phase transformer is constructed by winding three single-phase transformers on a single core.

If power is applied to the transformer bank before the delta connection is closed, the voltmeter should indicate ____ volts.

A voltmeter is a low-impedance device.

A wye-delta transformer has its primary winding connected in a delta and its secondary winding connected in a wye.

The open-delta transformer connection is often used when the amount of three-phase power needed is not excessive, such as in a small business.

When three single-phase transformers are used to make a three-phase transformer bank, their primary windings are always connected in a wye connection.

When three-phase transformers are connected as a wye or delta, the primary and secondary windings themselves become the phases of a three-phase connection. This is true whether a three-phase transformer is used or whether three single-phase transformers are employed to form a three-phase bank.

In a three-phase transformer, the phase value of the primary voltage can be computed using the formula EP(Primary) = ____.

The Scott connection is used to convert three-phase power into one-phase power using three single-phase transformers.

A connection involving the use of two transformers to supply three-phase power is the T-connection. In this connection, one transformer is generally referred to as the main transformer and the other is called the ____ transformer.

A dielectric oil provides electrical insulation between the windings and the ____.