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GENERIC TRAINING
MP008 BASIC ELECTRICITY
OBJECTIVES:
The trainees should have a general understanding of basic electrical
theory and principles of operation of devices as such : Batteries,Generator, Motors, Transformers, Solenoids, relays, fuses and Circuit
Breaker.
They should be familiar with many of the terms that relate to the
production and use of electrical power and they should appreciate theimportance of producing and using electrical power safely and
effectively.
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Unit 1 - Fundamentals of Electricity
I - Electrons and Electricity
1. Atoms contain positively charged protons and negatively charged
electrons.
2. Opposite electrical charges of equal value cancel each other out.
3. Opposite electrical charges are attracted by each other.
4. Like electrical charges are repelled by each other.
5. Electric current is the movement, or flow, of electrons.
6. Current only flows when voltages is present and when there is a
complete circuit.
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Unit 1 - Fundamentals of Electricity-1
II - Producing Voltage, Part 1
1. Photoelectric cells use light to produce voltage - the more
intense the light, the greater the voltage produced.
2. Pressure can be applied to certain types of crystals to
produce voltage.
3. Thermocouples use heat to produce voltage. The voltage
produced is exposed to.
4. Voltage can be produced by friction between two materials.
The voltage produced by friction is usually more of a
nuisance than a useful type of voltage.
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Unit 1 - Fundamentals of Electricity-1
IV Therms & Symbols
1. Voltage is symbolized by capital V , E and is measured in volts.
2. Currents is symbolized by a capital I and is measured in amperes.
3. Resistance is symbolized by a capital R and is measured in ohms.
4. Ammeters, which measure current, are always connected in series in
a circuit.
5. Voltmeters, which measure voltage, are always connected in parallel,across a circuit.
6. Ohmmeters, which measure resistance, are only used on
components that have been disconnected from de - energized circuit
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Unit 1 - Fundamentals of Electricity-1
VI Using Ohms Law
1. Current is equal to voltage divided by resistance : I = E / R
2. Voltage is equal to current times resistance : E = IR
3. Resistance is equal to voltage divided by current : R = E / I
4. Current cannot flow through an open circuit
5. In a short circuit, there is minimum resistance andmaximum current flow.
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Unit 2 - Fundamentals of Electricity-2
I Series Circuits
1. A series circuit has single current path.
2. A parallel circuit has two or more parallel current paths.
3. The voltage drop across each resistor in a series circuitis directly proportional resistance of that resistor.
4. The sum of the voltage drops across the resistors in the
series circuit is equal to the source voltage.
5. The total resistance in a series circuit is equal to the sumof the individual resistances.
6. Current is the same through all components in series
circuit.
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Unit 2 - Fundamentals of Electricity-2
II Parallel Circuits
1. The voltage across each branch of parallel circuit is
equal the source voltage.
2. The total current in parallel circuit is equal the sum of
the currents in each branch.
3. The total resistance in a parallel circuit is less than theresistance in any of of the branches.
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Unit 2 - Fundamentals of Electricity-2
III Power
1. The electrical power is the rate at which work is done by
electrical energy.
2. Power is equal to voltage times current: P = E I.3. Power is measure in WATTs
4. In series circuit, power is calculated by multiplying the
source voltage times the total current or by adding the
power used by each device in the circuit.5. In parallel circuit, power is calculated by multiplying the
source voltage times the sum of branch currents or by
adding the power used device in the circuit.
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Unit 2 - Fundamentals of Electricity-2
IV Magnetism
1. Magnetism is really many lines of force.
2. Only certain metals can be magnetism.
3. Magnetic lines of force flow from one end of a magnet to
the other.
4. The poles of magnets have the ability to attract or repel
each other.
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Unit 2 - Fundamentals of Electricity-2
V Electromagnets
1. An electromagnet is a magnet that is produced when
current is passed through conductor .
2. The left hand rule for currents carrying conductors states
that if you could wrap the fingers of your left hand round
a conductor with your thumb pointing in the direction of
current flow, then yours fingers would points in the
direction of flow of the magnetic flux lines.
3. The strength of an electromagnetic field can be increased
by increasing the current flow, by forming the conductor
into a coil or by adding a metal core to the coil
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Unit 2 - Fundamentals of Electricity-2
VI Alternating Current
1. Alternating Current is current the flows in one direction,
stop and then flows in opposite direction.
2. AC current changes direction when the polarity of thepower source changes.
3. Sine waves are often used to represent AC voltage and
current.
4. The rate at which AC cycles are completed is known asfrequency, which is measured in Hertz (Hz).
5. Effective (RMS= Root Mean Square) values of AC current
and voltage are peak value times 0.707
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Unit 3 Battery, Generators and Motors
IBatteries-Part-1
1. Secondary cells must be charged before they
used.
2. When a lead acid cell is charged, the two
electrodes change to different material and the
electrolyte becomes chemically active.
3. A fully charged cell produces maximum voltage
but the cell discharge as its energy is used.
Eventually the voltage produced drops below a
useful level.
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Unit 3 Battery, Generators and Motors
IIBatteries-Part-2
1. A constant voltage charger keeps a battery fully charged
(but not overcharged) at all times. A hydrometer can be
used to test the state of charge of an individual cell.
2. To find out how long a fully charged battery will last,
divided the rate of discharge into the ampere-hour rating.
3. Work around batteries requires adequate ventilation,
proper protective gear and the correct tools.
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Unit 3 Battery, Generators and Motors
IVDC Generators
1. In DC generator, a commutator changes the produced AC
voltage to the required DC voltage.
2. Switching reduces the effect of`ripple in a DC generator
and thus increases the effective value of the output
voltage.
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Unit 3 Battery, Generators and Motors
VSingle Phase Motors
1. The interaction between two magnetic fields causes a
motor to turn
2. The construction of a DC motor is similar to that of a DC
generator but the operations is different.
3. The two basic types of AC motors are synchronous
motors and induction motors.
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Unit 3 Battery, Generators and Motors
VIThree Phase Motors
1. When a three phase generator and three phase motor are
connected, the motor keeps turning as long as the
generators keeps producing voltage.
2. In synchronous motor, the rotor travels at the same
speed as the stators magnetic field.
3. In induction motor, the rotor travels slower than the
stators magnetic field. This difference in speed (called :
slip) is necessary for the operation of an induction
motor.
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Unit 4 Transformers and Control Mechanisms
ITransformers, Part-1
1. A transformer is a device that increases or decreases AC
voltage.
2. A transformer uses current flowing through one
conductor (the primary) to induce voltage in another
conductor (the secondary).
3. Step transformers increase voltage; step down
transformers decrease voltage.4. There is a direct relationship between the number of
turns in each winding of a transformer and amount that
voltage is changed the primary to the secondary
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Unit 4 Transformers and Control Mechanisms
IITransformers, Part-2
1. The power that goes into a transformer and the power
that comes out of the transformer are equal.
2. In a transformer, primary voltage times primary current
equals secondary voltage times secondary current.
3. Transformers are typically cooled by air, mineral oil or a
solution of liquid chemicals.
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Unit 4 Transformers and Control Mechanisms
IIISolenoids and relays
1. The action of an electromagnetic pulling a core is called
solenoid action.
2. Three general types of relays are sensing relays, control
relays and power relays.
3. When a relay coil (with the core in the middle) becomes
an electromagnetic, it typically pulls a metals plate to it
or causes a metal plate to turn.
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Unit 4 Transformers and Control Mechanisms
IVFuses
1. Fuses interrupt current flow when a n excessive current
condition occurs.
2. The two types of fuses are plug fuses and cartridge
fuses.
3. Fuses have current ratings and voltage ratings.
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Unit 4 Transformers and Control Mechanisms
VCircuit Breaker (CB), Part-1
1. Arcs occur when switches are opened to interrupt
current flow. Current flow is not really interrupt until the
arc is extinguished.
2. The tree general ways to extinguish an arc: by increasing
the distance between the contact point, by cooling air
and by using dielectric.
3. Common techniques used by circuit breakers toextinguish arcs included: arc chutes, fiber arc splitters in
oil and blasts of compressed air.
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SERIES:
I = I1 = I2
V = I (R1 + R2)
V = VR1 + VR2.
VR1 = R1/(R1+R2). I
VR2 = R2/ (R1+R2)