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How is primary power related to secondary power?

They will be the same. The power into the transformer is about equal to the power out of the transformer because of the high efficiency of the transformer (95–99%).

If the voltage of the secondary coil is half as large as the voltage applied to the primary coil, how will the secondary coil current be related to the primary coil current?

To keep the power in equal to the power out, the secondary coil current must double:

To have a larger voltage on the secondary coil of a transformer, will there be more turns than the primary coil or fewer turns?

Therefore, if volts_sec is to be larger, there must be more secondary turns and fewer primary turns.

If the voltage applied to the primary coil of a transformer is 55 volts AC and the secondary coil has a voltage of 165 volts AC induced in it, what is the ratio of turns between the primary coil and the secondary coil?

Voltage is proportional to the turns of the coils. Therefore, the ratio is 1:3.

If a transformer secondary coil has a power of 350 VA, what is the power of the primary coil?

350 VA power in = 350 VA power out.

How is a transformer primary winding different from a transformer secondary winding?

The primary winding has the voltage applied to it, while the secondary winding has the voltage induced in it.

What happens to the transformer secondary voltage as the load increases?

The voltage will decrease slightly because of the voltage drop across secondary winding caused by the increased current flow through the winding.

What are the two main types of transformer losses?

Core and coil (Copper or I^2R) losses.

What is done to compensate for secondary voltage drop?

Extra turns are added to the secondary winding, adding induced voltage to compensate for the voltage drop across the secondary winding.

What are the primary and secondary voltages of a transformer related to the voltage ratio related to the primary-secondary current ratio?

For the power out to equal the power into the transformer, the two must be inversely proportional.

What is meant by the term percent voltage regulation?

It’s the difference between the no-load and full-load voltage expressed as a percentage of the rated voltage. It expresses how much the output voltage changes as the load changes.

What transformer turns ratio is required if the primary current is 7 amps and the secondary current is 21 amps?

The ratio of transformer turns is inversely proportional to the current. Therefore:

The ratio is 1:3.

What are the three transformer functions?

Step up, step down, and isolation.

Which winding is always the primary winding of a step-up transformer?

The primary is the winding with the voltage applied to it, and if the transformer is a step-up, then the primary is the lower voltage or the X winding.

What is the purpose of the voltage correction taps on a transformer?

Using different turns on the transformer primary winding, the same nominal secondary voltage can be induced with primary voltages that are higher or lower than the nominal primary voltage.

What are the four considerations to remember when choosing a transformer?

• Supply and load voltages must match the transformer voltage rating.
• The KVA rating must be sufficient for the load.
• The transformer enclosure must be correct for the environment.
• The transformer temperature rating must be high enough for the environment’s ambient temperature.

A three-phase transformer has secondary-phase windings that each has 240 volts induced in them. What will the secondary line voltage of the transformer be if the windings are connected in a wye? In a delta?

In Wye (Y or Star) connection, the voltage would be:

In Delta connection, the voltage would be:

How is primary power related to secondary power?

They will be the same. The power into the transformer is about equal to the power out of the transformer because of the high efficiency of the transformer (95–99%).

If the voltage of the secondary coil is half as large as the voltage applied to the primary coil, how will the secondary coil current be related to the primary coil current?

To keep the power in equal to the power out, the secondary coil current must double:

To have a larger voltage on the secondary coil of a transformer, will there be more turns than the primary coil or fewer turns?

Therefore, if volts_sec is to be larger, there must be more secondary turns and fewer primary turns.

If the voltage applied to the primary coil of a transformer is 55 volts AC and the secondary coil has a voltage of 165 volts AC induced in it, what is the ratio of turns between the primary coil and the secondary coil?

Voltage is proportional to the turns of the coils. Therefore, the ratio is 1:3.

If a transformer secondary coil has a power of 350 VA, what is the power of the primary coil?

350 VA power in = 350 VA power out.

How is a transformer primary winding different from a transformer secondary winding?

The primary winding has the voltage applied to it, while the secondary winding has the voltage induced in it.

What happens to the transformer secondary voltage as the load increases?

The voltage will decrease slightly because of the voltage drop across secondary winding caused by the increased current flow through the winding.

What are the two main types of transformer losses?

Core and coil (Copper or I^2R) losses.

What is done to compensate for secondary voltage drop?

Extra turns are added to the secondary winding, adding induced voltage to compensate for the voltage drop across the secondary winding.

What are the primary and secondary voltages of a transformer related to the voltage ratio related to the primary-secondary current ratio?

For the power out to equal the power into the transformer, the two must be inversely proportional.

What is meant by the term percent voltage regulation?

It’s the difference between the no-load and full-load voltage expressed as a percentage of the rated voltage. It expresses how much the output voltage changes as the load changes.

What transformer turns ratio is required if the primary current is 7 amps and the secondary current is 21 amps?

The ratio of transformer turns is inversely proportional to the current. Therefore:

The ratio is 1:3.

What are the three transformer functions?

Step up, step down, and isolation.

Which winding is always the primary winding of a step-up transformer?

The primary is the winding with the voltage applied to it, and if the transformer is a step-up, then the primary is the lower voltage or the X winding.

What is the purpose of the voltage correction taps on a transformer?

Using different turns on the transformer primary winding, the same nominal secondary voltage can be induced with primary voltages that are higher or lower than the nominal primary voltage.

What are the four considerations to remember when choosing a transformer?

• Supply and load voltages must match the transformer voltage rating.
• The KVA rating must be sufficient for the load.
• The transformer enclosure must be correct for the environment.
• The transformer temperature rating must be high enough for the environment’s ambient temperature.

A three-phase transformer has secondary-phase windings that each has 240 volts induced in them. What will the secondary line voltage of the transformer be if the windings are connected in a wye? In a delta?

In Wye (Y or Star) connection, the voltage would be:

In Delta connection, the voltage would be:

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