ELPT-1420-TY2-Fundamentals of Elec II HYBRID
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
Most transformer cores are assembled from many thin sheets of metal. This type of construction is called _____.
laminated
The output winding of a transformer is called the _____ winding.
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(n) _____ transformer.
step-up
What function is performed by dielectric oil?
All of the above
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 percent
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)
A delta connected set of windings has a phase voltage of 480 V. What is the line voltage?
480 V
A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?
480 V
What type of core is often found on high-voltage distribution transformers?
H-type
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.
H; X
If a three-phase load is a pure reactive load, then the power calculated has units of _____.
VARs
To correct the power factor to 100 percent an equal amount of capacitive VARs would be connected in _____ with the motor.
parallel
In a three-phase connection, what is the voltage measured across a single winding?
phase voltage
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.
primary; secondary
A tape-wound core is also called a(n) _____ core.
toroid
The three-phase connection in which one end of each of the windings are connected together is called a(n) _____ 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 alternator must supply the _____ for each of the loads.
line current
An RLC parallel circuit has an applied voltage of 208 volts. R = 68 Ω, XL = 87 Ω, and XC = 81 Ω. What are the VARsC?
534.12
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
An RLC series circuit has a 60-Hz, 120 V applied voltage. R = 50 Ω, XL = 137 Ω, and XC = 160 Ω. What is the inductance in the circuit?
0.363 H
A parallel circuit at resonance has ITANK = 1.00 A, ILINE = 0.05 A, Q = 20, and a voltage across the tank of 500 V. What is the impedance of the tank?
10,000 Ω
In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _____.
three
In a three-phase connection, what is the voltage measured between the lines?
line voltage
A three-phase connection in which three separate inductive loads have been connected together is a(n) _____ connection.
delta
The transformer that converts a high voltage from the power company down to 240/120 V for homes and businesses is called a(n) _____ transformer.
distribution
The amount of current that flows into a transformer primary when voltage is first applied is called _____ current.
inrush
In a three-phase circuit, the true power (watts) is found by _____.
multiplying apparent power by the power factor
For parallel resonant circuits, the correct formula relating ITANK, Q, and ILINE is _____.
Q = ITANK / ILINE
An RLC parallel circuit has an applied voltage of 240 volts. R = 48 Ω, XL = 100 Ω, and XC = 36 Ω. What is the total current?
6.57 A
A parallel tank circuit operating at its resonant frequency has an impedance of 10,000 Ω. At the points on either side of the resonant frequency that define the bandwidth, the impedance is approximately _____.
7,070 Ω
What is a magnetically operated device that can change values of voltage, current, and impedance without changing frequency?
a transformer
A transformer that has one winding, which is used for both the primary and secondary, is called a(n) _____.
autotransformer
In an open delta with single-phase loads, the high leg must be identified by _____.
both a and b
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 Ω of XL. The second load is delta-connected capacitors that have XC of 60 Ω. How much is the alternator phase current?
6.93 A
A transformer has a 2:1 turns ratio. 120 V is applied to the primary. What is the secondary voltage?
60 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 V
A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a(n) _____ transformer.
isolation
When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.
one
An RLC parallel circuit has an applied voltage of 208 V. R = 68 Ω, XL = 87 Ω, and XC = 81 Ω. What is the power factor?
0.337
A delta-connected set of windings has a phase current of 10 A. What is the line current?
17.32 A
An RLC series circuit has a 60-Hz, 120 V applied voltage. R = 75 Ω, XL = 100 Ω, and XC = 89 Ω. What is the circuit capacitance?
29.80 μF
An RLC parallel circuit has an applied voltage of 208 volts. R = 42 Ω, XL = 52 Ω, and XC = 18 Ω. What is the inductive current?
4 A
A transformer has a 240 V primary and a 120 V secondary. With a 30 ohm load connected, what is the primary volt-amps?
480
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
An RLC parallel circuit has an applied voltage of 240 volts. R = 60 Ω, XL = 20 Ω, and XC = 36 Ω. What is the capacitive current?
6.67 A
An RLC parallel circuit has an applied voltage of 277 volts. R = 82 Ω, XL = 50 Ω, and XC = 124 Ω. What is the true power?
935.72 W
In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____.
square root of three
In an RLC parallel circuit, the _____ is the same through all components and the _____ are out of phase.
voltage; currents
An open delta transformer is assembled from two 150 kVA transformers. The output power of the open delta is _____.
259.8 kVA
The power input winding of a transformer is called the _____ winding.
primary
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 line current?
1.6 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 primary phase current?
1.6 A
A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?
100 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
An RLC parallel circuit has an applied voltage of 240 V. R = 60 Ω, XL = 80 Ω, and XC = 40 Ω. What is the apparent power?
1200 VA
Three-phase voltages are _____ out of phase with each other.
120°
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 percent
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?
2.54 A
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 transformer has a 240 V primary and a 60 V secondary. With a 5 ohm load connected, what is the primary current?
3 A
An RLC parallel circuit has an applied voltage of 240 volts. R = 60 Ω, XL = 100 Ω, and XC = 32 Ω. What is the resistive current?
4 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 Ω each. What is the phase current in the alternator?
40 A
An RLC parallel circuit has an applied voltage of 240 V. R = 48 Ω, XL = 100 Ω, and XC = 36 Ω. What is angle theta?
40.48°
An RLC parallel circuit has an applied voltage of 240 volts. R = 64 Ω, XL = 120 Ω, and XC = 180 Ω. What are the VARsL?
480
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
An RLC parallel circuit has an applied voltage of 240 volts. R = 48 Ω, XL = 100 Ω, and XC = 36 Ω. What is the circuit impedance (Z)?
80 Ω
An open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____
86.6 kVA
In a parallel LC circuit, the difference in frequencies above and below resonance at which impedance is 0.707 of the maximum is called the _____ of the circuit.
bandwidth
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer.
control
Line voltage and phase voltage are the same in the _____ connection.
delta
In a transformer, even when there is no load connected, there will be some small current flow known as _____ current.
excitation
Any transformer flux that does not follow the core and escapes into the surrounding air is called _____.
flux leakage
If a RLC parallel circuit contains more inductive VARs than capacitive VARs, the circuit has a _____ power factor.
lagging
If a RLC parallel circuit contains more capacitive VARs than inductive VARs, the circuit has a _____ power factor.
leading
A transformer supplying a house with 240/120 V has a secondary which is center tapped. The conductor connected to the center is called the _____ conductor.
neutral
In three-phase power systems, the delivered power _____.
never falls to zero
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.
one-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
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
In a transformer, the turns of primary wire compared to the turns of secondary wire is called the _____ ratio.
turns
An open delta connection is made using _____ single-phase transformers.
two
If the power factor is corrected exactly so that the circuit is purely resistive, the power factor has a value of _____.
unity
A tape-wound core is assembled by _____.
winding a long continuous tape into a spiral
Line current and phase current are the same in the _____ configuration.
wye
