Introduction. A closed loop of wire is not an electrical circuit, a circuit requires

Size: px

Start display at page:

Download "Introduction. A closed loop of wire is not an electrical circuit, a circuit requires"

Roberta Newton
5 years ago
Views:

2 The Law of Charges Opposite charges attract like charges repel Lines of force can never cross each other The values are equal but the effect is opposite Strength of the attraction is exponential to its distance The electron is attracted to the nucleus

3 Electron Flow When one electron knocks another electron from its orbit electron flow is produced When the atom has only one valence electron, it moves easier when struck The electron being struck will strike another and start a chain reaction

4 Introduction A closed loop of wire is not an electrical circuit, a circuit requires A power source A control method (switch) A load device (light bulb) A conductor A return path

5 Introduction Power source L1 Return path S w i t c h Conductor Load L2

stands for amp The letter I stands for intensity We will use

6 Ampere Andre Ampere (a French scientist) determined One amp equals one Coulomb passing a point every second The letter A stands for amp The letter I stands for intensity We will use the letter I while using the amperage formulas to represent current

7 Electrical Circuits A complete path must exist for current to flow through a conductor

8 Electrical Circuits The load device provides the resistance and limits the amount of current flow

9 Electrical Circuits Open Circuits occur when a completed current path is opened by a switch or overload device (OCPD)

10 Electrical Circuits Any circuit that has no resistance creates excessive current is a Short Circuit

11 Electrical Circuits Any circuit that takes a different current path to complete the circuit is a Grounded Circuit

12 Grounding An appliance may short to ground making the cabinet or housing electrically energized With a green wire it has a current pathway to return to source The green wire is for your safety and must stay in the circuit

The Volt Voltage is Electromotive force (EMF) EMF is the pressure that pushes the current through the conductor If voltage were water it would be the pump The pipe

13 The Volt Voltage is Electromotive force (EMF) EMF is the pressure that pushes the current through the conductor If voltage were water it would be the pump The pipe would be the conductor and the resistance source The water would be considered the current flow We will be using the letter E to represent voltage during this class

14 Circuits 1. CAN BE DEFINED AS THE MEANS BY WHICH A DEVICE IS ACTUATED BY THE OPERATION OF SOME OTHER DEVICE TO WHICH IT IS ASSOCIATED: CIRCUIT INTERLOCKING

15 In 1981, the 32-watt T8 lamp was introduced in the United States, providing further improvements in 4-foot fluorescent lamps. Today, the T8 lamp is the standard for new construction and is a popular replacement for 34-watt T12 lamps. All major lamp manufacturers market T8 lamps of various wattages, and they are readily available in a variety of linear and U-shaped configurations. T-8 = 8 x 1/8 so 1 inch and t-12 = 1 ½ inch

16 Circuits PROVIDES A LOW VOLTAGE RELEASE AND LOW VOLTAGE PROTECTION: THREE-WIRE CIRCUITS

17 Circuits MOST CIRCUIT BREAKERS HAVE A CURRENT INTERRUPT CAPACITY OF 200,000 AMPS:

18 Circuits A SET OF NORMALLY OPEN RELAY CONTACTS ARE WHEN THE RELAY IS : OPEN, DE- ENERGIZED

19 Circuits CONTACTS SHOULD BE REPLACED:

20 Circuits. THE ARMATURES OF BOTH AC AND DC CONTACTORS MUST MOVE FREELY OR:

21 Circuits AN ELECTROMAGENT THAT HAS A MOVING ARMATURE INSIDE ITS OPERATING COIL IS DESIGNATED AS A: Solenoid

22 Circuits WHEN SEVERAL PUSHBUTTON STATIONS ARE TO PROVIDE THREEWIRE CONTROL OF A MOTOR THROUGH A MAGNETIC STARTER, CONNECT THEM SO THAT THE: The stop buttons are in series and the start buttons are in parallel

23 Circuits A RELAY IS A DEVICE WHICH CAN TRANSFER AN ACTION FROM ONE CIRCUIT TO ANOTHER WITHOUT AN ACTUAL ELECTRICAL CONNECTION BETWEEN THE TWO CIRCUITS: True

24 Circuits A WAY TO HELP CONFINE, DIVIDE, AND EXTINGUISH THE ARC FOR EACH SET OF CONTACTS IS TO USE: Arc Chutes

25 The Ohm The Ohm is a unit of resistance One Ohm is the amount of resistance that is required to allow one ampere of current to flow when one volt of power is applied to it Resistance is used to control current flow The higher the resistance the less the current flow Any time current flows through a resistor heat is generated We will be using the letter R to represent resistance

26 The Ohm Resistance is used to control current flow The higher the resistance the less the current flow

27 The Ohm Any time current flows through a resistor heat is generated We will be using the letter R to represent resistance

28 The wat Watts equal the amount of power being consumed To have Watts energy must be converted to either work or heat We will identify Watts with the letter P (power) for the duration of the class

29 Ohm s Law A mathematical formula that shows that current is directly proportional to voltage and inversely proportional resistance. E=I X R P=E X I R=E / I E=P / I I=E / R I=P / E

31 CIRCUITS TIME DELAY DEVICES ARE USED IN THE OVERLOAD RELAYS OF MOTOR STARTERS TO ALLOW FOR THE HIGH INRUSH MOTOR CURRENTS: DURING THE STARTING PERIOD

32 CIRCUITS THE CURRENT RATING OF A CONTACTOR OR STARTER IS RATING FOR:

33 Circuits. WHEN IS IT SAID THAT CONTINUITY EXISTS IN A LADDER RUNG? WHEN THERE IS CURRENT FLOW FROM LEFT TO RIGHT

34 A SHORT-CIRCUIT GROUND-FAULT DEVICE MAY CONSIST OF: A fuse or circuit breaker

35 Circuits TO INDICATE A GOOD DIODE, AN OHMMETER SHOULD SHOW: LOW RESISTANCE IN ONE DIRECTION AND HIGH RESISTANCE IN THE OTHER

36 Circuits A MOTOR CONTROL CIRCUIT THAT ALLOWS THE MOTOR TO AUTOMATICALLY RESTART AFTER POWER IS RESTORED: Two wire

37 Circuits STARTERS AND CONTACTORS ARE BASICALLY THE SAME, BUT HAVE THERMAL OVERLOAD PROTECTION AND DON'T: Starters / contactors

38 Circuits THE VARIALBE- SPEED DRIVE CONTROLS THE SPEED OF A MOTOR BY PROVIDING A SUPPLY OF PHASE VOLTAGE FREQUENCY: AT A DIFFERENT

39 Circuits ALWAYS REMOVE THE COMPONENT TO BE TESTED OR DISCONNECT THE LINE VOLTAGE FROM THE CIRCUIT WHEN MAKING A: RESISTANCE MEARSUREMENT

40 Permanent Magnets Permanent magnets Will retain magnetic properties after the magnetizing force is removed Require no power to maintain their fields Are nickel, iron, or cobalt Spin on their axis opposite to the rotation of its nucleus (electron spin pattern)

called lodestones Magnetic north is not the same as true north Are the

41 Magnetism 2000 years ago the Greeks found magnetic stones (Magnetite) They found that the stone would always point north True magnets are called lodestones Magnetic north is not the same as true north Are the most important thing in electricity Relays, motors, instruments, valves use magnetism

42 Magnetic Line of Force Magnetic lines of force Lines of Flux Repel each other Never cross

43 Electromagnets A basic law of physics states that whenever an electric current flows through a conductor, A magnetic field is formed around the conductor

44 Electromagnets If a conductor is wound into a coil, the magnetic lines of flux add to produce a stronger magnetic field. An increase in current flow will cause an increase in the magnetic field Ampere turns Multiply the number of turns by current flow The two factors that determine the number of flux lines produced by an electromagnet are the number turns of a wire and the amount of current flowing through the wire

45 Core Material Iron or Soft steel cores: Increases the strength of the magnet Reluctance: The measurement of a materials resistance to magnetism Saturation: A magnet is as strong as it can get Residual Magnetism: How much magnetic force is left after the current is removed Coercive Force or Retentivity The measurement of a materials ability to retain magnetism

46 Magnetic Measurement There are three different types of systems used to measure magnetism The English System Measures flux density The CGS System Centimeter-gram-second Measures one Maxwell The MKS System Meter-kilogram-second The unit of measurement is the dyne

47 Magnetism IS MADE WHEN AN ELECTRIC CURRENT FLOWS THROUGH THE TURNS OF A COIL? A MAGNETIC FIELD

48 Magnetism A MAGNET THAT LOSES ALMOST ALL ITS MAGNETISM AFTER THE MAGNETIZING FORCE HAS BEEN REMOVED IS CALLED: A TEMPORARY MAGNET

49 Magnetism IMPROPER ALIGNMENT OF THE POLE FACES CAN CAUSE EXCESSIVE HUM IN AN AC ELECTROMAGNET OR SOLENOID: True

50 Batteries

51 History 1791 Galvani: theorized that muscles worked by electricity 1800 Volta: Concluded that the chemical reaction of the copper, iron, and saltwater created the electricity in the frogs leg; not the other way around

This new battery was called a voltaic pile because individual cells are assembled in series

52 Volta created the first battery The battery is constructed using zinc and silver discs separated by a piece of cardboard soaked in brine or saltwater. This new battery was called a voltaic pile because individual cells are assembled in series A battery is several cells connected together The schematic symbols for an individual cell (left) and for a battery (right)

more than an AA-cell This is called current capacity A rating used is the ma-hr Also

53 The amount of current a particular type of cell can deliver is determined by the surface area of its plates A D-cell can deliver more than a Ccell which can deliver more than an AA-cell This is called current capacity A rating used is the ma-hr Also the watt-hour W-h=mA*E A D cell= 1.5 volts with a 10,000 ma-hr 1.5*10,000=15,000mWhr Or 15 W-hr

54 Combinations can add voltage and current capacity Series: Adds voltage, current stays the same Parallel: Adds current, voltage stays the same

55 Magnetic Induction Whenever current flows a magnetic field is produced The direction of current flow determines the polarity of the magnet The amount of current determines the strength of the field

56 Magnetic Induction This same basic law in reverse is the principle of magnetic induction, which states that whenever a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor.

57 Magnetic Induction When a conductor is moved up through a magnet field the current in the conductor moves one direction When the same conductor is moved down again the current flows in the opposite direction

58 The zero center-meter changes with the reverse in polarity, so we can say that the polarity of the induced voltage is determined by the magnetic field in relation to direction of movement.

59 The polarity of an induced voltage can also be changed by reversing the polarity of the magnetic field.

Moving Magnetic Fields The most important factors that relate to magnetic induction are a conductor, a magnetic field, and movement Most AC generators or alternators operate on the principle

60 Moving Magnetic Fields The most important factors that relate to magnetic induction are a conductor, a magnetic field, and movement Most AC generators or alternators operate on the principle of a coil of wire held stationary while a magnet is moved through the coil as shown in the picture. When the lines of flux cut through the windings of the coil they induce a voltage into them

61 How to reverse a single phase motor The following is how you would reverse a 120-volt or 240 volt split-phase motor. Reverse the StartWinding leads or the Run-Winding leads, but not both. This will reverse the direction of rotation for a splitphase motor.

62 How to reverse a three phase motor To reverse the direction of a three-phase induction type motor, you can reverse the leads in the starter. T-1, T-2, T-3. For example: Reverse T1 and T-2, or Reverse T-1 and T-3, or Reverse T-2 and T-3.

63 Voltage increases if the speed of the rotation is increased or the conductor has more lines of flux A simple one-loop generator More lines of flux added to the loop more lines are cut per second

64 Inductance If the turn of a wire is far apart they will have less inductance than turns wound closer together

65 Bateries A LARGER BATTERY STORAGE CELL, AS COMPARED TO A SMALL ONE HAS A: LONGER LIFE

66 Bateries DISTILLED WATER SHOULD BE ADDED TO A BATTERY: WHEN LEVEL IS BELOW PLATES

67 Bateries A PHASE IMBALANCE CAN CAUSE THREEPHASE MOTORS TO RUN: AT HIGHER TEMEPRATURES

68 Bateries STORAGE BATTERIES ARE RATED FOR AMPERE-HOUR CAPACITY AND: VOLTAGE

69 Bateries THE ELECTRICAL ENERGY A BATTERY CAN DELIVER IS MEASURED IN: AMP-HOURS

71 Advantages of Alternating Current 1. AC current can be transformed 2. Transmission Voltages are very high

of flow at periodic intervals One wave form frequently encountered is the square wave.

72 Thomas Edison advocated DC because it was safer. Alternating current won because it could be transmitted over long distances AC differs from DC in that it reverses direction of flow at periodic intervals One wave form frequently encountered is the square wave. Note the darker line on the illustration on the left Each time a voltage reverses polarity, the current flowing through the circuit changes direction. A square wave could be produced by a single pole-double throw switch connected to two batteries

73 AC Wave Forms (Sine Wave) The most common form of alternating current is the sine wave. These waves are mostly created by rotating equipment

74 AC Wave Forms (Sine Wave) A complete sine wave contains 360 electrical degrees Reaches peak positive voltage at 900, 0 volts at 1800, maximum negative voltage at 2700,and returns to 0 volts at 3600 over a certain time interval, usually 60 cycles A cycle is the length of time it takes for a sine wave to complete one cycle We use 60 cycles in this country. 60Hz = 60 times per second

75 90 0 When the loop has rotated 900, it is perpendicular to the flux line and is cutting them at the maximum rate, which results in the maximum (peak)voltage being induced into the circuit

76 E(inst)=The voltage at any point on the wave form E(max)= The maximum or peak voltage SIN = The sine of the angle of rotation (page1015 & 1016 first column) E(inst)= E(max)* SIN E(max)= E(inst)/ SIN SIN = E(inst)/ E(max)

causing the electrons to be repelled to the outside of the conductor (skin

77 When current flows through a conductor connected to a DC source the electrons flow through the entire circuit AC induces eddy currents into the conductor causing the electrons to be repelled to the outside of the conductor (skin effect) Skin effect is proportional to frequency the higher the frequency the more resistance

80 Are 90 to 99% efficient Are manufactured as Isolation Transformers Autotransformers or Current transformers

84 Turn Ratio: The number of turns of the primary compared to the number of turns of the secondary

85 Step Up 1: Step Down

86 Distribution transformers 10-10= A phase B phase = Neutral Distribution Transformers have a true neutral, (Grounded current conductor) That only carries the current that is not neutralized by the other current carrying conductor

87 20-10= Distribution Transformers have a true neutral (Grounded current conductor) That only carries the current that is not neutralized by the other current carrying conductor

88 10-20= Distribution Transformers have a true neutral (Grounded current conductor) That only carries the current that is not neutralized by the other current carrying conductor

4-12=8 4 12 8 Distribution Transformers have a true neutral (Grounded current conductor)

89 4-12= Distribution Transformers have a true neutral (Grounded current conductor) That only carries the current that is not neutralized by the other current carrying conductor

91 A special form of transformer having one winding, a portion of which is common to both the primary and the secondary circuits. The current in the high-voltage circuit flows through the series and common windings (see illustration). Typical autotransformer circuit. The current in the low-voltage circuit flows through the common winding and adds vectorially to the current in the high-voltage circuit to give the common winding current. Thus, an electrical connection exists between high-voltage and low-voltage windings. Because of this sharing of parts of the winding, an autotransformer having the same kilovolt-ampere (kva) output rating is generally smaller in weight and dimensions than a two-winding transformer. One possible disadvantage of auto-transformers is that the windings are not insulated from each other and that the autotransformer provides no isolation of the primary and secondary circuits. Autotransformers of large sizes are used for interconnecting high-voltage power systems. They are used in small sizes for intermittent-duty starting of motors. For this use the motor is connected for a short time to the common winding voltage, and then connected to the full line voltage. Small, variable-ratio autotransformers are used in testing and as components of other apparatus.

92 No load Current lags voltage by 90 deg. Current in the primary is 180 deg. out of phase with the secondary Voltage in the primary is 180 deg. out of phase with the secondary

94 No continuity continuity No continuity

95 Input and Output watts will be the same (minus the power factor)

96 Three-Phase Motors The magnetic field is concentrated between poles A1 and A2.

97 Three-Phase Motors The magnetic field is concentrated between poles of phases A and B.

98 Three-Phase Motors The magnetic field is concentrated between poles C1 and C2.

99 Three-Phase Motors The magnetic field is concentrated between poles C1 and C2.

100 Three-Phase Motors The magnetic field is concentrated between phases A and C.

101 Three-Phase Motors The magnetic field is concentrated between phases B and C.

102 Three-Phase Motors The magnetic field is concentrated between poles A1 and A2. The field has rotated 180.

103 Three-Phase Motors Synchronous Motors The operating speed and the speed of the rotating magnetic field (synchronous speed) are the same. It operates at constant speed from no load to full load. This motor can be used for power factor correction.

104 Three-Phase Motors Synchronous Motors A set of squirrel-cage bars known as the amortisseur winding are used to start the synchronous motor. A synchronous motor must never be started with DC current connected to the rotor. A field-discharge resistor is used to safely control excessive current and voltage.

105 Three-Phase Motors The field-discharge resistor is connected in parallel with the rotor winding during starting.

106 Motors BEFORE RE-SETTING TRIPPED OVERLOADS AND TRYING THE MOTOR AGAIN, YOU SHOULD ALWAYS: INSPECT THE MOTOR AND LOAD FOR OBVIOUS PROBLEMS

107 Motors WHICH DEVICES PREVENT MOTORS FROM DRAWING TOO MUCH CURRENT OVERLOADS

108 Motors WHICH OF THE FOLLOWING DEVICES WOULD NOT USE A MOTOR SPEED CONTROL? BLENDER SEWING MACHINES ELECTRIC DRILLS CLOCKS/TIMERS CLOCKS AND TIMERS

109 MOTORS COMBINATION STARTERS ARE DESIGNED TO HAVE THE DISCONNECT AND THE MOTOR STARTER INCLUDED IN: A SINGLE ENCLOSURE

110 MOTORS IN A PROCESS CONTROL, THE TIME IT TAKES FOR A CHANGE IN THE PROCESS TO BE FELT AT THE MEASURING DEVICE IS CALLED: DELAY

111 MOTOR A DEVICE USED TO MEASURE THE ROTATING SPEED OF A MOTOR IS CALLED A: TACHOMETER

112 MOTORS REVERSING CIRCUITS RUN THE MOTOR IN REVERSE BY SWAPPING THE POWER LEADS: TRUE

113 MOTOR THE IS THE DIFFERENCE BETWEEN THE SYNCHRONOUS SPEED AND THE ACTUAL ROTOR OR THE ACTUAL MOTOR SPEED: SLIP

114 MOTOR IF YOU WERE TO INCREASED THE FREQUENCY APPLIED TO AN INDUCTION MOTOR STARTER, THE ROTOR SPEED WOULD? INCREASE

115 Motors THE ACTUAL FULL LOAD AMPS OF A MOTOR ARE FOUND: NAME OF PLATE OF THE MOTOR

116 Motor Starters and Relays

117

118

119

120

121

122

123

124

125

126

127

128 Three-Phase Alternators Construction Alternators use the same operating principle as direct-current generators. However, alternators have no commutator to change the armature AC into DC. Most alternators are three-phase.

129 Three-Phase Alternators Basic design of a three-phase armature.

130 Three-Phase Alternators Construction There are two basic types of alternators: Revolving-armature-type alternators Revolving-field-type alternators

131 Three-Phase Alternators Revolving armature design.

132 Three-Phase Alternators Revolving field design.

133 Three-Phase Alternators Rotor The rotor is the rotating part of an alternator. The rotor is an electromagnet that provides the magnetic field needed to induce a voltage into the stator windings. Excitation current (DC) in the rotor is required to establish the magnetic field.

134 Three-Phase Alternators The alternator produces three sine wave voltages 120 out of phase with each other.

135 Three-Phase Alternators Rotator pole pieces become electromagnets.

136

137 Thank you

Unit 3 Magnetism...21 Introduction The Natural Magnet Magnetic Polarities Magnetic Compass...21

Unit 3 Magnetism...21 Introduction The Natural Magnet Magnetic Polarities Magnetic Compass...21 Chapter 1 Electrical Fundamentals Unit 1 Matter...3 Introduction...3 1.1 Matter...3 1.2 Atomic Theory...3 1.3 Law of Electrical Charges...4 1.4 Law of Atomic Charges...4 Negative Atomic Charge...4 Positive