Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Electrical Holy Shit > chapter 28, 29, 30 text book questions > Flashcards

chapter 28, 29, 30 text book questions Flashcards

1
Q
  1. What are some of the ways magnetism is utilized?
A

Magnetism is used to produce most of the electricity consumed, develop rotary motion in motors, and develop linear motion in solenoids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q
  1. Where is magnetic flux the strongest and why?
A

Flux is most dense at the ends of a magnet. For this reason, the magnetic force is strongest at the ends of the magnet.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q
  1. What is solenoid and how is it used?
A

A solenoid is a device that converts electrical energy into a linear, mechanical force. Solenoids produce a linear, mechanical force when electricity is applied to the coil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q
  1. Which electromagnetic principle provides the basis for transformer operation?
A

The electromagnetic principle of mutual induction states that when the magnetic flux lines from one expanding and contracting magnetic field cut the windings of a second coil, a voltage is introduced in the second coil. The amount of voltage introduced in the second coil depends on the relative position of the two coils and the number of turns in each coil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q
  1. Explain the difference between a step-up transformer and a step-down transformer.
A

A step-up transformer is a transformer in which the secondary coil has more turns of wire than the primary coil. A step-up transformer produces higher voltage on the secondary coil that the voltage applied to the primary. A step-down transformer is a transformer in which the secondary coil has fewer turns of wire than the primary coil. A step-down transformer produces a lower voltage on the secondary coil than the voltage applied in the primary.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q
  1. How are transformers rated?
A

Trabsformers are rated by their volt-amphere (VA) or kilovolt-amphere (kVA) output. Small transformers are rated in either VA or kVA. Large transformers are rated in kVA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q
  1. List the basic types of transformers.
A

The basic types of transformers include appliance/equipment, control, bell/chime, instrument (current), distribution, isolation, neon sign, and power transformers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

is caused by the resistance of the copper wire to the flow of the current.

A

Copper loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

is caused by the induced currents that are produced in mental parts that are being magnetized.

A

Eddy-Current loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

occurs every half-cycle of AC when the current reverses direction and some magnetism remains in the iron core.

A

Hysteresis loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q
  1. What is the limiting factor in transformer loading and why?
A

Temperature is the limiting factor in transformer loading.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q
  1. When does a transformer become overloaded?
A

A transformer is overloaded when it is required to deliver more power than its rating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

are transformers that dissipate heat through the air surrounding the transformer. Heat produced in the windings and core is dissipated into the surrounding air by convection. Convection heat transfer is increased by adding radiating fins to the transfer.

A

Self-air cooled transformers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

cooled transformers are transformers that use a fan to move air over the transformer. Using a fan to speed the convection process increases the power that the transformer can deliver by about 30 percent over the power that can be delivered without a fan. Multiple high velocity fans are used in some applications to increase the transformer power output by more than 30 percent. The fans maybe designed to remain ON at all times or may be automatically turned ON when the transformer reaches a set temperature.

A

Forced-air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

are transformers that use refined oil to help cool refined oil or synthetic oil to help cool the transformers windings. The transformer coils and core are enclosed in a metal tank which is immersed in the oil. The oil is used to conduct heat from the windings and core to the outer surface of the transformer. The oil helps slow the heating process by increasing the heat storage capacity of the transformer.

A

Liquid-immersed/self-air cooled transformers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q
  1. Explain how to size 3 transformer.
A

a. Determine the total voltage required by the loads if more than one load is connected. The secondary side of the transformer must have a rating equal to the voltage of the loads.
b. Determine the amperage rating or kVA capacity required by the load(s). Add all loads that are (or may be) ON concurrently.
c. Check the frequency of the load(s) or nameplate. The frequency of the supply voltage and the electrical supply voltage and the electrical load(s) must be the same.
d. Determine the type of 3 voltage available. This includes three-wire no ground or three-wire no ground or three-wire with ground (four wire).
e. Check the supply voltage to the primary side of the transformer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q
  1. How is transformer current draw calculated?
A

I = kVA cap X 1000/E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q
  1. What is transformer normal ambient temperature?
A

Transformer normal ambient temperature is 40 degrees C.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q
  1. How is a transformer derated when the maximum temperature exceeds the average temperature by more than 10 degrees C?
A

A transformer is derated by 1 ½ percent for each 1 degree C above 40 degree C when the maximum ambient temperature exceeds 10 degrees C above the average temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q
  1. Describe delta transformer connection.
A

A delta configuration is a transformer connection that has each transformer coil connected end to end to form a closed loop.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q
  1. What is the advantage of a delta-to-delta transformer connection?
A

The advantage of a delta-to-delta connection is that if one transformer is disabled, the other two may be used in an open-delta connection for emergency power.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q
  1. What does it mean to balance the loads of a transformer?
A

The loads connected to a transformer should be connected so that each coil of the transformer carries the same amount of current for the various loads, such as for several motors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q
  1. Describe the purpose of transformer taps.
A

Transformer taps are connecting points that are provided along the transformer coil. Taps are available on some transformers to correct for excessively high or low voltage conditions. The taps are located on the primary side of the transformer. Standard taps are provided for 2% and 5% of rated primary voltage.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q
  1. What conditions must be met before a single-phase transformer can be connected parallel?
    .
A

a. Primary and secondary voltage ratings are identical.
b. Frequencies are the same
c. Tap settings are identical.
d. Impedance of either transformer is within plus or minus 7% (93% to 107%) of the other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q
  1. Define load and provide a few examples of loads.
A

A load is any device that converts electrical energy to motion, heat, light, or sound. Common loads include heating coils (electrical energy to heat), lamps (electrical energy to light), speakers (electrical energy to sound), and motors (electrical energy to motion).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q
  1. Why is Ohm’s law not always directly applicable to complex Dc and AC circuits?
A

Ohm’s law and the power formula cannot always be directly applied to more complex DC circuits and most AC circuits. For example, the digital clock circuit includes inductance (step-down transformer) and capacitance (capacitors) in addition to resistance (R).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q
  1. How is conductor resistance kept to a minimum?
A

Conductor resistance is kept to a minimum by limiting the temperature in the circuit and by using the correct size, length, and material.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q
  1. Explain how resistivity indicates the quality of material as a conductor.
A

Materials with high resistivity are poor conductors (good insulators) and materials with low resistivity are good conductors (poor insulators).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q
  1. What is inductance?
A

Inductance (L) is the property of a circuit that causes it to oppose a change in current due to energy stored in a magnetic field.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q
  1. List the factors that determine the inductance of a coil.
A

Number of turns in a coil, Length and spacing of the coil, Core material and relative permeability of the core material, Size of the wire used to make the coil.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q
  1. What is the difference between an inductor and a transformer?
A

The difference between an inductor and a transformer is the number of coils used. Inductors use one coil and transformers use two or more coils.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

consist of a coil (copper wire) wrapped around a form (plastic, ceramic, or Bakelite) with no material in the middle.

A

Air-core inductors

33
Q

of a coil (copper wire) wound around a laminated steel ore.

A

Iron-core inductors

34
Q

consist of a core made up of ceramic material (ferrite).

A

Ferrite-core inductors

35
Q
  1. What determines the amount of inductive reactance in a circuit?
A
  1. The amount of inductance (in henrys) of the coil (inductor). Inductance is normally a fixed amount.
  2. The frequency of the current. Frequency may be a fixed or variable amount.
36
Q
  1. Describe inductive reactance in DC circuits.
A

At zero frequency (DC circuits), there is no opposition due to inductance. In DC circuits, a coil has low resistance. In DC circuits, a coil has low resistance and no inductive reactance. Current flow through a coil connected to DC is limited only by the resistance of the wire. The inductor has no resistance except the small resistance of the wire. Thus, for a steady direct current without any change in current, inductive reactance is normally considered to be zerp. The amount of resistance is less with a large wire or less turns. The amount of resistance is greater with a small wire or more turns.

37
Q
  1. What is capacitance?
A

Capacitance is the ability of a component or circuit to store energy n the form of an electrical charge.

38
Q
  1. Define capacitator.
A

A capacitator is an electric device specifically designed to store a charge of energy.

39
Q
  1. Describe the composition of a capacitator.
A

A capacitator consists of two conductors (plates) separated by an insulator (dielectric), which allows an electrostatic charge to be developed.

40
Q
  1. Name several types of material used as dielectric.
A

The dielectric may be air, paper, oil, ceramic, mica, or any other nonconducting material.

41
Q
  1. Explain how capacitors are charged.
A

A capacitator is charged when its leads are connected to a DC voltage source. The positive terminal of the voltage source attracts electrons from the plate connected to it and the negative terminal of the voltage source repels an equal number of electrons into the negative plate. Charging (current flow) continues until the voltage across the charged plates is equal to the applied voltage. At this time the capacitator is fully charged.

42
Q
  1. What factors determine the amount of capacitance a capacitator has?
A
  1. The area of the plates. The greater the plate area, the higher the capacitance value.
  2. The spacing between plates. The closer the plates, the higher the capacitance.
  3. The dielectric used. The better the dielectric material, the higher the capacitance value.
  4. Connection arrangement. Capacitors are connected in parallel to increase total circuit capacitance.
43
Q
  1. Explain the difference between a fixed capacitator and a variable capacitator.
A

A fixed capacitator is a capacitator that has one value of capacitance. A variable capacitator is a capacitator that varies in capacitance value.

44
Q
  1. Identify the polarity of dielectric materials.
A

Mica, paper, and ceramic capacitators are not polarized.

45
Q
  1. Which dielectric provides the most capacitance for its size?
A

Electrolytic capacitators provide more capacitance for their size than any other type of capacitor.

46
Q
  1. Describe the operation of variable capacitators.
A

Variable capacitators normally use air or mylar as the dielectric and include movable and stationary metal plates. The capacitance is maximum when the moveable plates are fully meshed (but not touching) with stationary plates. Moving the plates apart lowers the capacitance.

47
Q
  1. What three factors affect current flow in an AC circuit?
A

In an AC circuits, resistance, inductive reactance, and capacitive reactance all limit current flow.

48
Q
  1. Define impedance.

.

A

Impedance is the total opposition to the flow of alternating current, consisting of any combination of resistance, and capacitive reactance

49
Q
  1. What is the purpose of a substation?
A

A substitution is an assemblage of equipment installed for switching, changing, or regulating the voltage of electricity. Substations contain transformers and secondary switches that distribute the low-voltage levels (208 V to 480 V) feeder panels, other secondary transformers, and branch circuit panels.

50
Q
  1. Why is it not practical to limit all circuits to a 120 V level?
A

It is not practical to limit all circuits to a 120 V level. This is because the lower the voltage, the higher the current for any given power (wattage) rating. Increasing the voltage level allows for a more practical installation because conductor size, conduit size, and switching equipment size is determined by the amount of current.

51
Q
  1. What kind of transformer (single-phase or three phase) do power companies normally use to distribute power to customers?
A

Power companies primarily use single transformers connected in different combinations to deliver the correct power to customers.

52
Q
  1. List the Common commercial distribution wire services.
A

Common commercial distribution systems include 120/240 V, single phase transformers, 3-wire; 120/208 V, 3 phase, 4-wire; 120/240 V, 3 phase, 4-wire; and 277/480 V, 3 phase, 4-wire services.

53
Q
  1. Explain the effects on a motor when the applied voltage is lower than the rated voltage.
A

All motors are designed to operate at a given (nameplate rated) voltage. A motor operates if the voltage varies below or above the rated voltage, but there is a change in the motor’s performance. Normally the applied voltage should be within plus or minus 10% of the motor’s rated voltage. A motor delivers less torque and operates at a higher temperature when connected to a voltage source lower than the motor’s voltage. However, this does not adversely affect the motor unless the motor is operating in an application that requires it to deliver full-rated power. In such applications, the motor size and/or the delivered voltage must be increased.

54
Q
  1. How high can the voltage on an incandescent lamp become?
A

The voltage on incandescent lamps can vary from 0 V to 10% higher than the lamp’s rated voltage.

55
Q
  1. What is the standard color for a grounding conductor?
A

The color green always indicates the grounding wire.

56
Q
  1. What kind of conductor uses a white-colored wire?
A

The color white or natural gray is used for the neutral (grounded circuit) conductor.

57
Q
  1. What color are ungrounded (hot) conductors?
A

Ungrounded conductors can be any color other than white, natural gray, green, or green with a yellow stripe. Black is the most common color used for ungrounded conductors.

58
Q
  1. Define wire marker.
A

A wire marker is a preprinted peel-off marker designed to adhere when wrapped arounf a conductor. Wire markers resist moisture, dirt, oil. etc. and can be used to identify conductors of the same color that have different meanings.

59
Q
  1. Differentiate between illumination, brightness, and contrast.
A

Illumination is the effect that occurs when light falls on a surface. The unit of measurement of illumination is the foot candle. Brightness is the perceived amount of light reflecting from an object. Brightness depends on the amount of light falling on an object and the reflecting ability of the object. Contrast is the ratio of brightness between different objects. For example, the black-on-white letters on a printed page have a high contrast.

60
Q
  1. What is a foot candle?
A

A foot candle is the amount of light produced by a lamp (lumens) divided by the area that is illuminated.

61
Q
  1. What type of lamp is most widely used?
A

Incandescent lamps are the lamps that are most widely used.

62
Q
  1. What is a filament?
A

A filament is a conductor with a resistance high enough to cause the conductor to heat.

63
Q
  1. What are the basic incandescent lamp base configurations?
A

A bayonet base is a bulb base that has two pins located on opposite sides. The pins slide into slots located in the bulb’s socket. Screw bases are used in low-vibration applications.

64
Q
  1. Describe how power is calculated.
A

P = E X I; Watts = volts x current

65
Q
  1. List common applications of tungsten-halogen lamps.
A

Tungsten-halogen lamps are used for display lighting, outdoor light, and photocopy machines because they produce a large amount of lighting instantly.

66
Q
  1. Summarize the operation of fluorescent lamps.
A

Is a low-pressure discharge lamp in which ionization of mercury vapor transforms ultraviolet energy generated by the discharge into light. The bulb contains a mixture of inert gas (normally argon and mercury vapor), which is bombarded by electrons from the cathode. This provides ultraviolet light.

67
Q
  1. Define Cathode.
A

A fluorescent lamp consists of a cylindrical glass tube (bulb) sealed at both ends. Each end (base includes a cathode that supplies the current to start and maintain the arc. A Cathode is a tungsten coil coded with electron-emissive material that releases electrons when heated.

68
Q
  1. How is a compact fluorescent lamp different from a conventional fluorescent lamp?
A

A compact fluorescent lamp is a fluorescent lamp that has a smaller diameter than a conventional fluorescent lamp and a folded bulb configuration.

69
Q
  1. Explain the effect of temperature on fluorescent lamps.
A

Fluorescent bulbs do not start well in cold climate conditions because the electrons released by the heated cathode are thermally released. The colder the bulb, the longer the time required to heat the cathode and release electrons into the mercury vapor.

70
Q
  1. Define luminaire temperature on fluorescent lamps.
A

Luminaire temperature is the temperature at which a amp delivers its peak light output. Moderate changes in ambient temperature (50 degrees F to 100 degrees F) have little effect (less than 10%) on light output. Temperatures lower than 50 degrees F or higher than 105 degrees F have a greater effect on light output.

71
Q
  1. Describe preheat, instant-start, and rapid-start circuits.
A

A pre-heat circuit is a fluorescent lamp-starting circuit that heats the cathode before an arc is created. Pre-heat circuits are used in some low-wattage lamps (4 W to 20 W) and are common in desk lamps. An instant-start circuit is a fluorescent lamp-starting circuit that provides sufficient voltage to strike an arc instantly. The instant-start circuit was developed to eliminate the starting switch and overcome the starting delay of preheat circuits. A rapid-start circuit is a fluorescent lamp-starting circuit that has separate windings to provide continuous heating voltage on the lamp cathodes. The lamp starting time is reduced because the cathodes are continuously heated.

72
Q
  1. What are two common applications for high-intensity discharge (HID) lamps?
A

HID lamps are common in streets and parking lots.

73
Q
  1. What is color rendering?
A

Color rendering is the appearance of a color when illuminated by a light source. For example, a red color may be rendered light, dark, pinkish, or yellowish depending on the light source under which it is viewed.

74
Q
  1. How is a low-pressure sodium lamp started?
A

On start up, an arc is discharged through the neon, argon, and sodium-metal. As the sodium-metal heats and vaporizes, the amber color sodium is produced.

75
Q
  1. List the different types of mercury-vapor ballasts.
A

Mercury-vapor ballasts include reactor, high-reactance autotransformer, constant-wattage autotransformer, and two-winding, constant-wattage ballasts.

76
Q
  1. What is a reactor ballast?
A

A reactor ballast is a ballast that connects a coil in series with the power line leading to the lamp. Reactor ballasts are used when the incoming supply voltage meets the starting voltage requirements of the lamp.

77
Q
  1. How does a metal-halide lamp produce light?
A

A metal-halide ballast uses the same basic circuit as the constant-wattage autotransformer mercury-vapor ballast. The ballast is modified to provide high tarting voltage required by metal-halide lamps.

78
Q
  1. What is the main difference between a high-pressure sodium ballast and a mercury-vapor reactor ballast?
A

A high pressure sodium ballast is similar to a mercury-vapor reactor ballast. The main difference is the added starter. The reactor ballast is used where the input voltage meets the lamp’s requirement.

Electrical Holy Shit (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions