transformer final
In a three-phase connection, the voltage measured across a single winding is the _____ voltage
phase
A transformer in which secondary voltage is less than the primary voltage is called a ________ _______ transformer.
step down
The magnetically operated device that can change values of voltages, current, and impedance without changing frequency is the ____________.
transformer
A three-phase load has a phase voltage of 240 V and a phase current of 18 A. What is the apparent power of this load?
12,960 VA
How many degrees out of phase with each other are the voltages of three-phase system?
120
Three-phase voltages are _____ out of phase with each other.
120
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the secondary phase current?
3.2 a
A wye-connected alternator that has phase voltages of 277 V is feeding two loads. The first load is wye-connected inductors that have 40 W of XL. The second load is delta-connected capacitors that have XC of 60 W. How much is the alternator phase current?
6.93
A Transformer has a 240v primary and a 120v secondary. With a 30ohm load connected, what is the primary volt-amps.
480
A delta connected set of windings has a phase voltage of 480 V. What is the value of the line voltage?
480 v
An open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____.
86.6 kVA
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?
8.66:1
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
In a three-phase connection, the voltage measured between the lines is the _____ voltage.
line
In three-phase power systems, the delivered power _____.
never falls to zero
another name for the three phase wye connection is the_____ connection
star
A Tape wound core is assembled by
tightly winding 1 long continuous silicon steel tape into a spiral.
A tape wound core is also called a ________ core.
toroid
If the load in Question 7 is connected in wye, what would be the line voltage and line current supplying the load?
EL = 415.68 V
In a three-phase circuit, the true power (watts) is found by _____.
multiplying apparent power by the power factor
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
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.
one line
Often in calculations of values in three-phase systems, the square root of three occurs. The approximate value of this constant is _____.
1.732
If a three-phase load is a pure reactive load, then the power calculated has units of _____.
VARs
Any transformer flux that does not follow the core and escapes into the surrounding air is called ________
flux leakage
what type of core is often found on high voltage distribution transformers?
h-type
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary phase current?
1.6 amps
A delta-connected set of windings has a phase current of 10 A. The line current is _____
17.32 a
In an open delta with a center-tapped transformer, label the two ends of the center-tapped transformer as L2 and L3 and label the high leg as L1. The current flow in the neutral (center tap) is equal to _____.
AN = A1 + (A2 - A3)
When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced.
false
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.
h,x
A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a ________ transformer.
isolation
The alternator must supply the _____ for each of the loads.
line current
dielectric oil performs which of the following
all of the above
A transformer that has one winding, which is used for both the primary and secondary, is called a _______ __________.
autotransformer
In an open delta with single-phase loads, the high leg must be identified by _____.
both a and b
When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.
1
A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
20:1
a wye-connected load has voltage of 480 V applied to it. What the voltage dropped across each phase?
277.136
In calculating power in a three-phase circuit, the phase values of voltage and current are multiplied by _____.
3
A transformer has a 240v primary and a 60v secondary. With a 5 ohm load connected, what is the primary current
3 A
A wye-delta transformer has a secondary phase voltage of 480 V. A delta-connected resistive load has a resistance of 12 Ω in each leg. What is the current in each load leg?
40 A
A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 W each. What is the phase current in the alternator?
40 a
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the current flow is in each load resistor?
5.54
A delta connection has 30 A of current flowing through each phase winding. How much current is flowing through each of the lines supplying power to the load?
51.96 A
A delta connection has a voltage of 560 V connected to it. How much voltage dropped across each phase?
560 v
A delta-wye transformer has a turns ratio of 9:1. The primary line voltage is 3600 V. What is the secondary line voltage?
692.8
In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating.
75%
What is the apparent power of the circuit in Question 9?
VA = 166,272
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a _________ transformer.
control
Line voltage and phase voltage are the same in the _____ connection.
delta
A transformer supplying a house with 240/120 V has a secondary winding which is center tapped. The conductor connected to the center is called the ______ conductor.
neutral
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
A wye-connected load has phase current of 25 A. How much current is flowing through the lines supplying the load?
25 A
An open delta transformer is assembled from two 150 kVA transformers. The output power of the open delta is _____.
259.8 kVA
A transformer has a 2:1 turns ration. 120v is applied to the primary. What is the secondary voltage?
60 v
What are the two main types of three-phase connections
wye and delta
A delta connected set of windings has a phase voltage of 100 V. The line voltage is _____.
100 v
An alternator with a line voltage of 2400 V supplies delta-connected load. The line current supplied to the load is 40 A. Assuming the load is a balanced three- phase load, what is the impedance of each phase?
103.919 w
The three-phase connection in which three separate inductive loads have been connected together is the _____ connection.
delta
A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?
480 v
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
11.55:1
The transformer that converts high voltage from the power company down to 240/120 V for homes and businesses is called a _________ transformer.
distribution
In a transformer, even when there is no load connected, there will be some small current flow known as _______ current.
excitation
Line current and phase current are the same in the _____ configuration.
wye
The three-phase connection in which one end of each of the windings are connected together is called the _____ connection.
wye
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
The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size.
150%
The amount of current that flows into a transformer primary when voltage is first applied is called ________ current.
inrush
Most transformers cares 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 core
The transformer winding, which is the power input winding, is called the ________ winding.
primary
A delta-wye transformer has its _____ connected as a delta and its _____ connected as a wye.
primary; secondary
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.
primary; secondary
The transformer winding, which is the output winding, is called the __________ winding.
secondary
A transformer in which the secondary voltage is more than the primary voltage is called a ______ _______ transformer.
step up
An Isolation transformer has the same input and output voltages. (T or F)
true
In a transformer, the turns of primary wire compounded to the turns of secondary wire is called the __________ ratio.
turns
An open delta connection is made using _____ single-phase transformers.
two
