MP008 BASIC ELECTRICITY

8/7/2019 MP008 BASIC ELECTRICITY

1/25

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.


2/25

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.


3/25

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.


4/25


5/25


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


6/25


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.


7/25


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.


8/25


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.


9/25


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.


10/25


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.


11/25


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


12/25


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


13/25

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.


14/25


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.


15/25


16/25


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.


17/25


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.


18/25


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.


19/25

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


20/25


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.


21/25


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.


22/25


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.


23/25


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.


24/25


25/25

SERIES:

I = I1 = I2

V = I (R1 + R2)

V = VR1 + VR2.

VR1 = R1/(R1+R2). I

VR2 = R2/ (R1+R2)

Documents

MP008 BASIC ELECTRICITY