Review units 27 & 28

What are the 3 voltage ratio's of a transformer?

- 1:1 - 2:1 - 10:1

In three phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter ____?

- H - X

In three-phase transformer connections, the primary leads are labeled with the letter ___ and the secondary leads are labeled with the Letter ___?

- H - X

Name the four types of cores?

- H - shell - tape-wound - laminated

A transformer supply a house with 240/120 V How is a secondary data center topped. The conductor connected to the center is called the ______ conductor

Neutral

A transformer supplying a house with 240/120 volts has a secondary that is center tapped. The conductor connected to the center is called the _____ conductor.

Neutral

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?

Zero volts

What connection is used primarily for grounding purposes?

Zig-Zag connections

A transformer in which the secondary voltage is more than the primary voltage is called a(n) _____ transformer.

step up

Is a delta connection a parallel or series connection?

Series

What type of connection involves the use of two transformers to supply three-phase power?

T connection

define inrush current

The amount of current that flows into a transformer primary when voltage is first applied.

In a transformer, even when there is no load connected, there will be some small current flow known as _____ current?

excitation

The main power distribution system of a large industrial plant is generally shown using a ____ diagram?

one line

What is the common practice to indicate polarity of the transformer windings?

Using dots

A tape-wound core is also called a(n) _____ core.

toroid

An open delta connection is made using ___ single-phase transformers?

two

Name the main two types of transformers?

Auto & isolation

The change in output voltage from no load conditions is called what?

Induced voltage

What should the ohmmeter indicate when testing checks for shorted windings between the primary and secondary?

Infinity

A delta-wye transformer has its ____ connected as a delta and it's ____ connected as a wye.

- Primary - Secondary

A wye-delta transformer has its ___ connected as a wye and its ___ connected as a delta

- Primary - Secondary

In an open delta with single-phase loads, the high leg must be identified by ____?

- Using orange wire - tagging

List the 3 main parts of a transformer?

- core - primary winding - secondary winding

What function is performed by dielectric oil?

- insulator - prevents moisture formation - provides cooling

What functions are preformed by dielectric oil?

-cooling -prevents moisture formation -insulator

In a 60-Hz AC circuit, how many times does the voltage change polarity in 1 minute?

60 times

A transformer has a 2:1 ratio. 120 volts is applied to the primary. What is the secondary voltage?

60 volts

What are the polarities of a transformer?

Additive & subtractive

What is common practice to indicate additive or subtractive polarity on a transformer schematic?

Arrows

A transformer that has one winding, that is used for both the primary and secondary is called a ______ transformer

Auto

The industrial use transformer that normally has 240 V or 480 V primary and a 120V secondary is called a ________ transformer?

Control

The industrial use transformer that normally has 240 V or 480V primary and a 120 V secondary is called a _____ transformer?

Control

The current of the secondary induces a ______ in the secondary windings that is in opposition to the counter voltage induced in the primary.

Countervoltage

The current of the secondary induces a _______ in the secondary windings that is in opposition to the counter voltage induced in the primary.

Countervoltage

Closing the ____ permits more power to be supplied for the operation of the three-phase loads?

Delta

The transformer that converts a high voltage from the power company down to 240/120 volts for homes and business is called a _____ transformer?

Distribution

Which connection must have transformers that use two secondary windings that provide equal voltages?

Double delta connection

The current required to magnetize the core is called what?

Excitation current

The diametrical connection is not preferred because it requires one low-voltage winding on each transformer. True or false?

False

The nameplate lists the current rating of the windings. True or false?

False

When a load is connected to the primary, current begins to flow. True or false?

False

Any transformer flux that does not follow the core and escaped into the surrounding air is called ______?

Flux leakage

What type of core is often found on high voltage distribution transformers?

H type

What type of core is often found on high-voltage distribution transformers?

H-type

What terminal is always on the left on the high voltage winding?

H1

When using an open delta with a center-tapped transformer, one wire is the high leg. The high leg is the one that ____?

Has the highest voltage

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called an _______ transformer?

Isolation

How is the core constructed in most transformer?

Laminated

Most transformer cores are assembled from many thin sheets of metal. This type of construction is called ______.

Laminated

Most transformer cores are assembled from many thin sheets of metal. This type of construction is called ______?

Laminated

Moving coils farther apart increases the amount of _______?

Magnetic flux leakage

When testing a transformer, what will reveal problems of insulation breakdown that an ohmmeter will not?

Megger

When single-phase load are tied to a three-phase transformer, will the phase currents of the transformer will be automatically balanced?

No, they will not automatically balance

For installations that will have both three phase and single phase words on a three face transformer, the utility company often provides a ______ three face transformer.

Open delta with one transformer center tapped

For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides an _____ three-phase transformer.

Open delta with one transformer center tapped

Is a wye connection a parallel or series connection?

Parallel

It is sometimes necessary to connect the secondary windings of transformers in ______ to increase the current capacity.

Parallel

It is sometimes necessary to connect the secondary windings of transformers in _______ to increase the current capacity?

Parallel

What do dots on a transformer schematic represent?

Polarity

When making the T connection, the main transformer is connected directly across the _____?

Power line

The power input winding of a transformer is called the _____ winding?

Primary

The power input winding of a transformer is called the ______ winding.

Primary

What induces a voltage in the secondary for a transformer?

Primary current

In which connection are the secondary windings of each transformer providing the phases of a two-phase system?

Scott connection

What type of connection is used to convert three-phase power into two-phase power using two single-phase transformers?

Scott connection

The output winding of a transformer is called the _____ winding?

Secondary

The output winding of a transformer is called the ______ winding.

Secondary

Which should be disconnected first if it is necessary to remove one of the transformers for service? Either primary or secondary?

Secondary

A transformer in which the secondary voltage is less than the primary voltage is called a(n) _______ transformer?

Step down

A transformer in which the secondary voltage is more than the primary voltage is called a _____ transformer?

Step-up

A transformer in which the secondary voltage is less than the primary voltage is called a ______ transformer?

Strep-down

Define turns ratio

The turn of primary wire compared to the turns of secondary wire

What is a three phase bank?

Three single-phase transformers connected together

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 ____?

Three-phase bank

What is a magnetically operated machine that can change values of voltage, current, and impedance without changing frequency?

Transformer

What is expressed as a percentage? (%Z)

Transformer impedance

A buck connection is defined as connecting transformer windings as an auto transformer and testing for additive or subtractive polarity? True or false?

True

An isolation transformer has the same input and output voltages. True or false?

True

If the transformer bank has been properly sized for the max connected load, no one phase will become overloaded. True or false?

True

If the transformer bank has been properly sized for the maximum connected load, no one phase will become overloaded. True or false?

True

In a double-delta connection, the two delta windings are connected in reverse so that they have an angular difference of 180° with respect to each other. True or false?

True

Power input must equal power output, which enables the current rating for a winding to be determined. True or false?

True

Ripple is a pulsation of voltage? True or False?

True

The double-wye connection must have two secondary windings that produce equal voltage. True or false?

True

The polarity of transformer windings can be determined by connecting them as an auto transformer and testing for additive or subtractive polarity? True or false?

True

Three-phase transformers are sometimes connected in such a manner as to provide more than three phases. True or false?

True

Transformer impedance is determined by the physical construction of the transformer? True or false?

True

When the secondary side of the transformer bank is a delta connection, either a wye or a delta primary could be used. True or false?

True

When the secondary side of the transformer bank is a delta connection, either a wye or delta could be used. True or false?

True

Ripple is pulsations of voltage. True or false?

True.

A tape-wound core is assembled by ____.

Winding a long continuous tape into a spiral

Which connection is mainly used to establish a neutral point for the grounding of fault currents?

Zig zag connection

Which connection is mainly used to establish a neutral point for grounding a fault currents?

Zigzag connection

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a ____ transformer?

isolation

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a _________ transformer

isolation