Basics of Electricals 1

7/29/2019 Basics of Electricals 1

http://slidepdf.com/reader/full/basics-of-electricals-1 1/40

Deshmukhnv / Basics of Elect.

WELCOME

TO

BASIC ELECTRICITY

TRAINING




OBJECTIVES

To be able to identify and implement. Theory of Ohms Law.

Define electrical terms.

To be able to describe the interrelationship between voltage,current and resistance in electrical circuits.

To be able to identify digital multimeter features and itscapabilities.

To be able to correctly use the digital multimeter and understand

your findings when taking electrical measurements,in normal andfault finding situations




Basics of electricity

Types of energy-

- Electrical energy

- Heat energy

- Atomic energy

- Mechanical energy

- One form of energy can be converted into another

OIL - Heat , Water - Steam , Turbine - Mechanical energy

Generator - Electrical energy




What is Electricity

Matter

Molecule

Atom

ALL FORMS OF MATTER AREMADE UP OF MOLECULES

IN TURN THESE

MOLECULES ARE MADE UP

OF ATOMS

ATOMS ARE MADE UP OF

PROTONS ,NEUTRONS

AND ELECTRONS.

ELECTRONS MAINTAIN A

NEGATIVE POLARITY- ve

PROTONS MAINTAIN A

POSITIVE POLARITY +ve

NEUTRONS DO NOT

HAVE ANY POLARITY

(are neutral)

The centre of the atom is called the Nucleus

and contains Neutrons and protons.

ELECTRONS IN ORBIT

PROTONS WITHIN NUCLEUS

NEUTRONS WITHIN NUCLEUS




ELECTRONS IN ORBIT

NUCLEUS

What is ElectricityThree factor determine whether or not the Atom is a good or bad

CONDUCTOR(1) The number of electrons in the outer orbit.

2) The distance of the outer orbit from the Nucleus of the Atom.

(3) The density of the atoms within the element.

Rules

If the Atom has only one orbit,maximum number of electrons on orbit is two.

If Atom has more than one orbit maximum number of electrons on outer orbit is eight.

Gold, Silver and Copper have only one electron on their outer orbit Mercury has two,

Aluminium has three and remember Carbon has four.




ELECTRONS IN ORBIT

PROTONS IN NUCLEUS

NUCLEUS

COPPER ATOM ( good Conductor)

29 protons 29 electrons.But only one loose electron On The outer orbit

CARBON ATOM. 4 ELECTRONS ON THE OUTER ORBIT

(semi conductor)

What is Electricity




LIKE CHARGES REPEL EACH OTHER

What is Electricity

An excess of electrons creates a negative charge.

The absence of electrons creates a positive charge

OPPOSITE CHARGES WILL ATTRACT EACH OTHER

Normally an enormous number of Electrons flow.The basic unit of electric charge is the coulomb.

ONE COLOUMB EQUALS 6.25 X 1018 ELECTRONS,or 6,250,000,000,000,000,0000

ELECTRONS IN ORBIT PROTONS IN NUCLEUS




Electron flow

Conventional flow

load

battery

switch

Anode\positive

battery post

What is Electricity

+ -

Cathode\negative




Electron flow

Conventional flow

load

battery

switch

Anode\positive

battery post

+ -

The loss of an electron by an atom makes it a positive ion, therefore it will attract an electron from a

neighbouring atom,to again become balanced.





Electricity-

- There are variety of methods for producing electricity

- Through chemical reaction in a battery.

- For large amount of electricity electromagnetic

generators are used.




Current -

- Flow of electron.

- Conventional current is in opposite direction.

- High voltage to low voltage.

- Unit of current is ampere.

- Current is measured by ammeter, Connected in

series.

- Polarity in DC

6

Basics of electricity-





Potential - Ability to do work

Voltage - Potential difference.(work done in moving a unit +ve charge

from a point of lower to higher potential).- Unit of voltage is volt (v).

- Measured by voltmeter,connected across source.

- Sources can be Battery,DC generator,alternator etc.

- Can be AC or DC.

- Polarity in DC

- Equivalent to two water tanks,connected by pipe water

flows.




VOLTAGE CURRENT

VOLTAGE = ELECTRICAL PRESSURE

FUNDAMENTALS OF ELECTRICITY

VOLTAGEVoltage provides the electrical pressure or force that enables the current or electrons to flow.

Voltage is the difference in electrical pressure between two points in a circuit .

Voltage is measured in units called volts . The symbol for Voltage is E and the symbol for volt is





Resistance -

- Opposes flow of current.

- Unit is ohms.

- Measured by ohm meter connected across it.

- Depends upon type of material, area & length.

- Produces heat when current flows through it.

- Fixed and variable resistor (potentiometer).

10




Amps

electrons

RESISTANCE (OHMS).

Resistance is a restriction to current flow.

Increasing resistance will reduce flow of current.

Electrical resistance is measured in units called ohms, they areabbreviated by the letter R, and the symbol isW ( omega).

RESISTANCE






Inductor -

- Coil of wire.

- Opposes change in current.

- Used to create magnetic field for rotation.

- Unit is henry.

- Open and short inductor .





Capacitor -

- Two metal plates separated by a DI-electric (Max volts/mm which a

medium can withstand without breakdown).

- Gets charged when voltage is applied.

- Unit of capacitance is farad.

- Capacitor in series 1/C=1/C1+1/C2 & in parallel C= C1+C2.

- C = Q / V

- Practical unitsMicro and Pico farad.





Insulators and Conductors -

Conductors -

- Materials that have a low resistance to current flow

are classified as conductors.

- Copper and aluminium wires are conductors.- Conductors are used in electrical circuits to connect

components to one another.

- Conductors are wrapped in insulators to isolate from

one another.

Insulators -

- Materials that have a high resistance to current flow

are classified as Insulators.

- Glass, rubber & dry air are insulators

13






E

I R

E

I R

E E

I R I R

OHMS LAW

Ohms Law Pie Chart Resistance = Voltage over Current

Current = Voltage over Resistance voltage = Current times Resistance






APPLICATION OF THE POWER FORMULA.To find the power consumed by the resistor , the total current

(I t) has to be found first.

It = Va\R1

It = 10 volts \ 10 ohms

It = 1 AMP.

The power used by the resistor can then be found by :

DC POWER

P

V I

+

-

Va=10V

WR1

P = It x Vt

P = 1 amp x 10 volts

P = 10 Watts




The unit of power in mechanical system is the

HORSE POWER (hp).

One horsepower is equal to 0.746 kilowatts (KW).

TO CONVERT HORSE-POWER TO KILOWATTS.multiply horsepower times 0.746 KW.

EXAMPLE.

P = Horsepower x 0.746 Kw

P = 50 Horsepower x 0.746 Kw

P = 37.3 Kw

Therefore a 50 Hp motor will consume 37.3 Kw of power

P

DC POWER





AC Power-

- Alternating quantity is one which periodically passes through

a definite cycle of changes.- In AC RMS values are used .

- AC power is consumed by different types of load such as

inductive , resistive & capacitive.

- AC power is given by P= V x I x CosO

- Symbol for AC source.

- AC power is measured by Wattmeter.

- Unit of power is Watts.

18




THE FOLLOWING TABLE SHOW SOME COMMON ELECTRICAL TERMS

THEIR ABRIVIATION, UNITS OF MEASURE, SYMBOL

AND MEASURING INSTRUMENTS.

Term Abbreviation Unit Symbol Measuring Tool

Current I Ampere A Ammeter

Voltage E Volt V Voltmeter

Resistance R Ohm Ohmmeter

Power P Watt W Wattmeter

ELECTRICAL TERM





Series circuit -

- One path for current flow.

- Can have more than one load (e.g. resistance).

- Total load is sum of individual loads.

- Some voltage loss takes place across each load

and is called as voltage drop.

- Sum of voltage drops across each load is equal

to applied voltage.

- Current through each load is same.

- Open and short.

- Example - Chain of small bulbs.

20




OPEN AND SHORT CIRCUIT

R2

SHORT CIRCUITS occur when current does not go through its

intended path.This usually happens in circuits that have

improper wiring or defective electrical components.

In the diagram we have a series circuit in which R2&R3 are“shorted

out” to the source voltage. R2 and R3look like a wire and the total resistance of the circuit

limited to R1.

More current will flow because the total resistance is less.

current flows through the short.

no current flows through R2 or R3

current takes path of least

resistance.




OPEN AND SHORT CIRCUITS

+R1

R2

R 3

If a short occurs in a parallel circuit , most of the source current

will flow through the short because the current takes the path of

least resistance

Most current will flows through short .

no current will flow through R2 or R3




CAN JUST FEEL IT

DEATH

IT TINGLES

OUCH !

DIFFICULT

BREATHING

SEVERE BURNSAMPERES

1.0 6 AMPS TO

SOLENOID

0.2

200 mA

0.01100 mA

0.001

1 mA





DIGITAL MULTIMETER DESCRIPTION.

Measures Electrical Characteristics.

Measures Multiple Types Of Electrical Characteristics with a

single device.

Functions as a Ohmmeter,Ammeter and Voltmeter.

Includes an AC, as well as DC Voltage range.

Provides a Display “ Screen “.

Includes option for an analog format. The accuracy of the fluke meter is specified as

of the reading + ( number of least significant digits.)

EG. Voltage dc




ROTARY SWITCH.

To turn the meter on , turn the rotary switch from the OFF position .

The meter performs a selftest , then starts taking readings.

DIGITAL MULTIMETER DESCRIPTION




VOLTAGE MEASUREMENT

Ranges

0 to1000 Volts dc

0 to 750 Volts ac


Measure in parallel across

item to be measured





RESISTANCE MEASUREMENT


item to be measured

Ranges

320.0 ohms

thro

32.00 Mohms.




CURRENT MEASUREMENT

Measure in series with

item to be measured

Ranges

AC. 320 mAmps &

10 Amps

DC. 320 mAmps &

10 Amps.




Range

2 Volts dc.

Continuity test.

Bleep while

resistance is below

150 ohms


DIODE TEST


item to be measured




An electrical circuit can be compared to a simple hydraulic circuit.

Battery

Pump

Ammeter Motor

Voltage drop (volts)

Flow meter

Pressure drop (bar)

Source of pressure Flow rate Resistance to flow

Pump

Amperes

Liters / Min

The Electrical Circuit





Types of loads - (Resistor,inductor& capacitor)

Resistive load -

- In DC circuit (fig) the voltage and current waveforms

are straight lines because voltage is constant.

- In AC circuit with pure resistance,voltage and current

are always in phase.

- Power consumed in DC circuit is constant as

voltage and current are constant.- An AC ckt. that has only resistance produces a

positive power curve.

35





Types of loads - (Resistor,inductor& capacitor)

Resistive load -

- In DC circuit (fig) the voltage and current waveforms

are straight lines because voltage is constant.

- In AC circuit with pure resistance,voltage and current

are always in phase.

- Power consumed in DC circuit is constant asvoltage and current are constant.

- An AC ckt. that has only resistance produces a

positive power curve.





Inductive load -

- An inductor is a coil of wire. A common inductive

load is an electric motor.

- Current lag behind voltage by 900 since voltageis max at 900 while current is zero.

- Produce both positive and negative power. These

powers are equal in amplitude so their sum will

equal to zero.

- The inductor does not use real power still generator

supply it with voltage and current .

- So efficiency is lowered.

37



D h kh / B i f El t


Capacitive load-

- A capacitor opposes change in voltage.

- Current lead voltage by 900

since voltage across itis zero and the current is maximum.

- Produce both positive and negative power. These

powers are equal in amplitude so their sum will

equal to zero.- The capacitor does not use real power still generator

supply it with voltage and current .

- So efficiency is lowered. 39

Documents

Basics of Electricals 1