Electrical 9

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

primary, secondary

Any transformer flux that does not follow the core and escapes into the surrounding air is called

flux leakage

T/F When single-phase loads are tied to a three-phase transformer, the pahse currents of the transformer will be automatically balanced

FALSE

T/F In an isolation transformer, all windings will have the same number of volts per turn

TRUE

Three-phase watts can be computed by

multilying apparent power by the power factor

In three-phse power systems, the delivered power pulsates, but

never falls to zero

A simplified schematic diagram of three-phase transformer connections is called a ___ diagram

one-line

Dielectric oil performs what function(s)

prevents moisture formation, acts as an insulator, provides cooling (all of the above)

The transformer winding which is the power input winding is called the ___ winding

primary

Another name for the three-phase wye connection is the ___ connection

star

A transformer tape wound core is also called a ___ core

toroid

The magnetically operated device that can change values of voltage, current, and impedance without changing frequency is the

transformer

In a transformer, the turns of primary wire compared to the turns of secondary wire is called the

turns

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

two

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

using orange wire OR tagging (either A or B)

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

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

neutral

In a three-phase wye connection, when the voltage is measured directly across a single winding, it is known as ___ voltage

phase

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

primary, secondary

A transformer in which the secondary voltage is less than the primary voltage is called as ___

step-down

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

step-up

T/F In a three-phase wye connection, the line voltage and the phase voltage are the same

False (line current and phase current)

The amount of current that flow into a transformer primary when voltage is first applied is called

inrush

If a single three-phase transformer of the proper ratings is not available, three single-phase transormers can be connected to do the job. When this is done, the connection is called a(n)

three-phase bank

T/F In a three-phase delta connection, the line voltage and the phase voltage are the same

TRUE

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 measured to ground

The transformer winding which is the output winding is called the

secondary

In a wye-connected three-phase system, the phase current is higher than the line current by what factor?

1

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a(n) ___ transformer

isolation

A transformer metal toroid is assembled by

winding a long continuous tape of metal into a spiral

A transformer tape wound core is assembled by

winding a long continuous tape of metal into a spiral

In three-phase equipment, when one end of each of the windings is connected together, this is what type of connection?

wye

When calculating values in three-phase systems, the square root of 3 occurs. The approximate value of this constant is

1.732

Three-phase power is superior to single-phase power. One of the reasons is that, for a given frame size, the horsepower rating of a three-phase transformer vs. a single-phase transformer is what percent greater?

150%

A transformer that does not isolate th eout from the input is called a(n) ___ transformer

auto

Correcting the power factor of three-phase loads normally involves adding

capacitance in parallel

The three-phase system in which all three of the Phases are connected end-t-end to form a closed loop is called a ___ connection

delta

In a three-phase delta connection system, the line current is higher than the phase current by a factor of

1.732

In a wye-connected three-phase system, the line voltage is higher than the phase voltage by what factor?

1.732

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

H, X

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

distribution

In a three-phase wye connection, when the voltage is measured between two external connections, it is known as ___ voltage

line

For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides a(n) ___ three-phase transformer

open delta with one transformer center tapped

In a transformer, even when there is no load connected, there will be some small current required to magnetize the core. This current is called ___ current

excitation

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

laminated

Three-phase power is superior to single-phase power. In a balanced three-phase system, the conductors are smaller, and need only be what percent of those in a single-phase system?

75%

The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) ___ transformer

control