Electrical 2
Three-phase voltages are _________ out of phase with each other
120 degrees
A delta-connected set of winding has a phase current of 10 A. What is the line current?
17.32 A
In the consequent pole motor, if the number of poles is doubled, the motor speed will be __________
Cut in half
The direct current that is an input to the alternator's rotor is the _________ current
Excitation
The frequency of the current in a squirrel-cage rotor _________ as the rotor approaches synchronous speed.
Decreases
The main power distribution system of a large industrial plant is generally shown using a _________ diagram
One-line
A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?
100 V
A squirrel-cage rotor induction motor has a synchronous speed of 3600 RPM and an actual rotor speed of 3450 RPM. What is the percent slip?
4.17% synchronous speed minus actual speed Divided by synchronous speed x 100
A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?
480 V
What function is performed by dielectric oil?
Acts as an insulator Prevents moisture formation Provides cooling
In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _______
Three
An open delta connection is made using _____ single-phase transformers.
Two
If a three-phase load is a pure reactive load, then the power calculated has units of _________
VARs
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 a _________ connection
WYE
Line voltage and phase voltage are the same in the __________ connection
Delta
Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the lower of the two voltages, the phase windings are connected in
Parallel
If a piece of machinery needs a replacement motor and will be damaged if the new motor rotated the wrong way. The test equipment needed to test the rotation direction of the new motor is a ____________
Phase rotation meter
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
The rotating party of a revolving-armature-type of alternator is called the _____________
Rotor
Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the phase windings are connected in
Series
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 open delta transformer is assembled from two 150 kVA transformers. The output power of the open delta is _____.
259.8 kVA
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 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 open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____.
86.6 kVA
What machines operate on the same principle of electromagnetic induction as DC generators, but they have no commutator?
Alternators
To reverse the direction of rotation of a three-phase motor, reverse ____________
Any two leads
The squirrel-cage rotor is constructed of _________ and end __________ embedded in steel laminations
Bars ; rings
Power is carried to the outside circuit of a revolving armature type of alternator via brushes riding against the __________
Commutators
To minimize interference, telecommunication cables are run as close to phase conductors as possible and as far away from the neutral conductor as possible.
False
The higher power output alternator use a revolving __________
Field
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 wound-rotor induction motor is popular in industry because it has ________ starting torque and _________ starting current.
High ; low
The revolving armature type of alternator is capable of __________ power output and is, therefore, ____________ often used than the revolving field type.
Less ; less
In a three-phase connection, what is the voltage measured between the lines
Line voltage
In three phase power systems, the delivered power _____________.
Never falls to zero
What is one factor that controls the output frequency of an alternator?
Number of stator poles and rotor rotation speed
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
When a squirrel-cage motor is first started, the value of current draw is ____________
Several times the running current
Three lines supply power to a three-phase motor. If one of these lines should open, the motor will be connected to single-phase power. This condition is known as ___________
Single-phasing
In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____
Square root of 3- 1.73
The non-rotating part of a revolving-field-type alternator is called the ___________
Stator
In a three-phase motor, the speed of rotation of the magnetic field is called the _________ speed.
Synchronous