Motors and transformers Final
The phases of the three-phase power supplied by the power company are __________ degrees out of phase with each other.
120
The stator windings of a three-phase generator are __________ degrees apart.
120
Which of the following is the most common value for a bleeder resistor?
15 K ohms
The average range of slip for a squirrel-cage induction motor is __________.
2-6%
If the phase-to-neutral voltage of a wye configured system is 120 VAC, what would be the phase-to-phase voltage?
208 VAC
The frequency of the AC electricity in most European countries is __________.
50 Hz
About __________ of the AC motors used in industry are induction motors.
95%
Which of the following statements is not true of an electrical schematic?
An electrical schematic shows all components in a circuit and how they are connected.
transformer is the current drawn by the __________. Primary winding itself
Autotransformer
The device that is used on a split-phase motor to disconnect the start winding when a predetermined speed has been reached is a __________.
Centrifugal switch
Which of the categories of transformers uses only one coil for the primary and secondary?
Control Transformer
A __________ compound configuration is created by connecting the series and shunt windings so that their magnetic fields have the same magnetic polarity.
Cumulative
The amount two electrical waveforms are out of phase is measured in __________.
Degrees
Which of the following is a type of transformer power distribution bank?
Delta-to-wye Wye-to-wye Wye-to-delta
A common application of a center tap on the secondary of a transformer is a(n) __________.
Distribution Transformer
Which of the following is not a component of a transformer?
Electrical coupling
Fault indicators are not needed on equipment that is powered by a three-phase delta system.
False
To get a control voltage of 120 VAC from a control transformer if the line voltage is 240 VAC, the primaries must be connected in series.
False
When a control transformer is used, NEC requires that both sides of the secondary must be connected to earth ground.
False
Which of the following is an application of a split-phase motor?
Fan Centrifugal Pump Business Machine
Which of the following is an advantage of a three-phase induction motor?
High efficiency Excellent speed regulation High power factor
Which of the following is a disadvantage of a capacitor-start motor?
Increased cost due to the addition of a capacitor
Which of the following allows you to control when the current will flow in a circuit?
Input device
Which of the following is an advantage of a split-phase motor?
Is available at a low cost
Which of the following statements is not true of a DC compound motor?
It has a field connected in series with the armature.
Which of the following statements is false about a separately-excited shunt motor?
It requires only one power supply.
Which of the following is an application of a three-phase induction motor?
Large pumps Large conveyor systems Machine tools
Which of the following is a method to troubleshoot a transformer?
Measuring the continuity of the coils
Which of the following is not a basic type of power plant?
None of the above
When checking a transformer with an ohmmeter, which of the following can you check for?
Opens in coils Shorts between coils Coils shorted to the core
Which of the following is a type of single-phase AC motor?
Permanent-capacitor Split-phase Capacitor-start
mutual inductance is found in a device called a __________. Transformer
Plate
The power relationship on a transformer states that __________.
Power in= Power out + loss
The current load of a transformer is the current drawn by the __________.
Primary Winjding itself
Which of the following is an application of a DC compound motor?
Punch Press Conveyors Bending Machines
The effective value of AC voltage is also called the __________ voltage.
RMS (Root Mean Square)
Which of the following is not a method that can be used to reverse the rotation of a split-phase motor?
Reverse the power leads
Which of the following is a basic component of a generator?
Shaft, Stator, Rotor
Which of the following is an application of a capacitor-start motor?
Small machines Pumps Power tools
In which of the split-phase motor windings will the current start to flow first?
Start winding Run winding
The squirrel-cage motor gets its name from the design of its __________.
Stator
Which of the following is a category of AC motors?
Three-phase
A __________ is an electrical device that converts AC electricity from one voltage level to another.
Transformer
A common application of mutual inductance is found in a device called a __________.
Trrnasformer
A disadvantage of a three-phase wye system is that if a fault occurs on any of the three phases, the whole system will shut down.
True
The NEC requires that for an output voltage higher than 50 VAC one side of a control transformer secondary be connected to ground or both sides of the secondary must be fused.
True
The operation of a motor and a generator are direct opposites.
True
The output voltage of a transformer can be determined if you know the input voltage and the turns ratio.
True
To avoid running separate lines to a machine for power devices and control devices, the higher voltage required by the power devices can be produced by using a control transformer to step up the control voltage.
True
To get a control voltage of 120 VAC from a control transformer if the line voltage is 480 VAC, the primaries must be connected in series.
True
Transformers are rated in units called Volt-Amperes (VA).
True
In order to calculate the output voltage of a transformer, divide the input voltage by the __________.
Turns Rartio
Transformers are usually rated in units called __________.
Volt Amperes
Delta winding
What type of distribution system is represented by the figure shown?
WYE phase winding
What type of distribution system is represented by the figure shown?
Which of the following is an application for a DC shunt motor?
Woodworking Machinery Cooling Fan Centrifugal Pump
A power factor of 100% is called __________.
absolute power factor
The power that is supplied to a load by an AC power source is called __________.
apparent power
A resistor that is used to reduce the sparking across the contacts of the centrifugal switch on a capacitor-start motor is called a __________.
bleeder resistor
The rate at which the electrical voltage or current cycle repeats is called __________.
frequency
When two phases of electricity do not start and end at the same time, they are said to be __________.
in-phase
The primary advantage of a DC compound motor is __________.
it provides a middle ground between a series and a shunt motor
A transformer uses the principle of __________.
mutual inductance
On a 4-wire wye system, the __________ conductor provides a common return path to the source for each phase.
neutral
A capacitor start motor produces more starting torque than a split phase motor because the capacitor creates a larger __________ shift between the winding currents.
phase
AC electricity flowing in a particular wire is called a __________.
phase
The ratio of active power to the apparent power in an AC circuit is called the __________.
power factor
The main set of windings in a split-phase motor is called the __________.
run windings
If the shunt field is connected to the same power supply as the armature, the motor is connected in the __________ configuration.
self excited
When a shunt field is connected to a different power supply than the armature, it is called a(n) __________ shunt field.
separately-excited
The waveform that is produced by alternating current looks like a __________.
sine wave
The difference between the synchronous speed and the actual speed at which an AC motor will run is called __________.
slip
The primary advantage of a DC shunt motor is that it provides excellent __________.
speed control
The speed at which the rotor/shaft of an AC motor must rotate to exactly match the speed of the rotating magnetic field is called __________.
synchronous speed
The cost of electrical power is based on __________.
the number of kilowatts consumed per hour (kWh)
Active power is __________.
the power used by a load
The fourth color band on a resistor represents __________.
the tolerance of the resistance value
The relationship between the input voltage and output voltage of a transformer is based on the __________.
turns ratio
Power factor correction capacitors are rated in __________.
volt-amperes-reactive (VAR)
The most common configuration used at a substation is __________.
wye
