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