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