1 ELECTRIC CURRENT

2 POTENTIAL DIFFRENCE

3 ELECTRIC POWER

4 POWER FACTOR

PRESNETED BY:

PARVEEN CHAHAL

SUBJECT- BASIC OF ELECTRICAL ENGINEERING

ELECTRIC CURRENT

Electric current in a wire, where the charge carriers are electrons, is a measure of the quantity of charge passing any point of the wire per unit of time. In alternating current the motion of the electric charges is periodically reversed; in direct current it is not. In many contexts the direction of the current in electric circuits is taken as the direction of positive charge flow, the direction opposite to the actual electron drift. When so defined the current is called conventional current. It is denoted by I and its unit is AMPERE.

POTENTIAL DIFFERENCE

In an electrical circuit, electric potential between two points is defined as the amount of work done by an external agent in moving a unit charge from one point to another.

Mathematically, E=WQ

Where, E = electrical potential difference between two points

W = Work done in moving a change from one point to another

Q = the quantity of charge in coulombs

The potential difference is measured by an instrument called voltmeter. The two terminals of a voltmeter are always connected parallel across the points whose potential is to be measured.

Electric power, like mechanical power, is the rate of

doing work, measured in watts, and represented by the letter P.

The term wattage is used colloquially to mean "electric power in

watts." The electric power in watts produced by an electric

current I consisting of a charge of Q coulombs every t seconds

passing through an electric potential (voltage) difference of V is

P= WORK DONE PER UNIT TIME=VQ/T

where

Q is electric charge in coulombs

t is time in seconds

I is electric current in amperes

V is electric potential or voltage in volts

POWER FACTOR Power factor is the relationship (phase) of current and voltage in AC electrical distribution systems. Under ideal conditions current and voltage are in phase and the power factor is %. If inductive loads motors are present, power factor less than 100% (typically 80 to 90%) can occur. Low power factor, electrically speaking, causes heavier current to flow in power distribution lines in order to deliver a given number of kilowatts to an electrical load.

Advantages of Electrical Energy : * Electrical Energy can be easily converted to other form of energy. * It is much cheaper than other forms of energy. * It can be easily transmitted to various location very conveniently and efficiently. * This form of energy can be controlled and monitored easily * It is silent * It can be used produce magnetic fields, which can be used to propel motors * It is very fast, virtually the speed of light * It can be used to produce other forms of radiant energy, such as radio waves, microwaves, radiant heat and light

* You can store it for use later

Disadvantages * It can kill you * We become dependent on it

* We use other dirtier forms of energy (nuclear, fossil fuels) to produce it

* There is growing concern that the magnetic fields around transmission lines may be unhealthy

Advantages of Electrical Energy over other types of energy Its most common form of energy used in houses and industry. And some reasons for its popularity are listed below:- * Its called "Clean and Green energy" . Clean because it does't have any byproducts and green because it doesn't cause any kind of pollution neither any of the resources of mother earth are exhausted when we use this form of energy. •It can be easily converted to other form of energy. •It is much cheaper than other forms of energy. •It can be easily transmitted to various location very conveniently and efficiently. * This form of energy can be controlled and monitored easily.

1 SERIES CONNECTION

2 PARALLEL CONNECTION

3 SERIES-PARALLEL CONNECTION

PRESENTED BY:

PARVEEN CHAHAL

SERIES CONNECTION Resistors are said to be connected in Series , when they are daisy

chained together in a single line. Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on. Then, resistors in series have a Common Current flowing through them as the current that flows through one resistor must also flow through the others as it can only take one path.

Then the amount of current that flows through a set of resistors in series will be the same at all points in a series resistor network. For example:

In the following example the resistors R1, R2 and R3 are all

connected together in series between points A and B with a common current, I flowing through them.

As the resistors are connected together in series the same current passes through each resistor in the chain and the total resistance, RT of the circuit must be equal to the sum of all the individual resistors added together.

REQ = R1 + R2 + R3 = kΩ + kΩ + 6kΩ = 9kΩ

Rtotal = R1 + R2 + R3 + ….. Rn etc.

Note then that the total or equivalent resistance, RT has the same effect on the circuit as the original combination of resistors as it is the algebraic sum of the individual resistances.

This total resistance is generally known as the Equivalent Resistance and can be defined as; a single value of resistance that can replace any number of resistors in series without altering the values of the current or the voltage in the circuit . Then the equation given for calculating total resistance of the circuit when connecting together resistors in series is

PARALLEL CONNECTION Resistors are said to be connected together in Parallel when both of their

terminals are respectively connected to each terminal of the other resistor or resistors. Unlike the previous series resistor circuit, in a parallel resistor network the circuit current can take more than one path as there are multiple paths for the current. Then parallel circuits are classed as current dividers.

Since there are multiple paths for the supply current to flow through, the current may not be the same through all the branches in the parallel network. However, the voltage drop across all of the resistors in a parallel resistive network IS the same. Then, Resistors in Parallel have a Common Voltage across them and this is true for all parallel connected elements.

So we can define a parallel resistive circuit as one where the resistors are connected to the same two points (or nodes) and is identified by the fact that it has more than one current path connected to a common voltage source. Then in our parallel resistor example below the voltage across resistor R1 equals the voltage across resistor R2 which equals the voltage across R3 and which equals the supply voltage. Therefore, for a parallel resistor network this is given as:

In the previous series resistor network we saw that the total resistance, RT of the circuit was equal to the sum of all the individual resistors added together. For resistors in parallel the equivalent circuit resistance RT is calculated differently. Here, the reciprocal ( 1/R ) value of the individual resistances are all added together instead of the resistances themselves with the inverse of the algebraic sum giving the equivalent resistance as shown.

This much quicker product-over-sum method of calculating two resistor in parallel, either having equal or unequal values is given as:

ELECTRICAL QUANTITIES

1 ALTERNATING CURRENT

2 DIRECT CURRENT

3 ADVANTAGES OF A.C OVER D.C

4 APPLICATION OF A.C AND D.C

ALTERNATING CURRENT Alternating current (AC) is an electric current which periodically

reverses direction, in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.[1][2]

The usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.

DIRECT CURRENT Direct current (DC) is the unidirectional flow of electric charge. A battery is a

good example of a DC power supply. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.[1]

The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.[2][3]

Direct current may be obtained from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current with an inverter or a motor-generator set.

Direct current is used to charge batteries and as power supply for electronic systems. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids

APPLICATION OF DIRECT CURRENT All electronics projects and parts for sale on SparkFun run

on DC. Everything that runs off of a battery, plugs into the wall with an AC adapter, or uses a USB cable for power relies on DC. Examples of DC electronics include:

Cell phones

Flashlights\

The LilyPad-based D&D Dice Gauntlet

Flat-screen TVs (AC goes into the TV, which is converted to DC)

Hybrid and electric vehicles

ADVANTAGE OF A.C OVER D.C We all know that we got ac supply in our homes and we got this supply by

transmitting ac over long distances. AC can be transmitted using step up transformers but direct current or dc can not be transmitted by this method.

The ac is easy to generate than dc.

It is cheaper to generate ac than dc.

The ac generators have higher efficiency than dc.

The loss of energy during transmission is negligible for ac.

The ac can be easily converted into dc. The variation of ac can easily be done using transformers either step up or step

down.

The value or magnitude of ac can be decreased easily without loss of excess of energy. This can be done by using choke coil.

ADVANTAGE OF D.C OVER A.C The power loss due to the formation of corona is given by:

To reduce corona effect in an AC transmission system, we use bundled conductors.

In an AC transmission system, the receiving end voltage is higher than the sending end voltage during no load or light load conditions. This is called Ferranti effect.

In an AC transmission system, capacitance comes into play

. An AC transmission system needs lattice supporting structures which come at a high price.

Electromagnetic Induction

When a magnet and a wire move relative to each other, a voltage is induced

Amount of voltage produced depends on: Speed: High speeds produce high

voltages Magnetism: Strong magnets produce

high voltages Shape of Wire: Many coils in the wire

produce high voltages

Electromagnetic

Induction

Electromagnetic Induction

Note: It is more difficult to push the magnet into a coil with more loops because the high current generates a stronger magnetic field which acts

against the magnet.

Electromagnetic Induction

Electromagnetic Induction:

Inducing voltage by changing the magnetic field around a conductor

ANY change in magnetic field will induce a voltage

i.e.) Traffic control signals

Faraday’s Law

The induced voltage in a coil is proportional to the number of

loops multiplied by the magnetic field changes within those loops.

MAGNRETIC FLUX In physics, specifically electromagnetism, the magnetic flux (often denoted Φ or ΦB) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface. The SI unit of magnetic flux is the weber (Wb) (in derived units: volt-seconds), and the CGS unit is the maxwell

How magnetic flux is generated? Magnet and Coil. When a magnet is moved into a coil of wire, changing the magnetic field and magnetic flux through the coil, a voltage will be generated in the coil according to Faraday's Law. ... The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change that produces it

Magnetic reluctance, or magnetic resistance it is a concept used in the analysis of magnetic circuits. It is analogous to resistance in an electrical circuit, but rather than dissipating electric energy it stores magnetic energy. In likeness to the way an electric field causes an electric current to follow the path of least resistance, a magnetic field causes magnetic flux to follow the path of least magnetic reluctance. It is a scalarextensive quantity, akin to electrical resistance. The unit for magnetic reluctance is inverse henry, H−

Permeability, also called magnetic permeability, is a constant of proportionality that exists between magnetic induction and magnetic field intensity. This constant is equal to approximately 1.257 x 10-6 henry per meter (H/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized µo. Materials that cause the lines of flux to move farther apart, resulting in a decrease in magnetic flux density compared with a vacuum, are called diamagnetic. The permeability factors of some substances change with rising or falling temperature, or with the intensity of the applied magnetic field. In engineering applications, permeability is often expressed in relative, rather than in absolute, terms. If µo represents the permeability of free space (that is, 1.257 x 10-6 H/m) and µ represents the permeability of the substance in question (also specified in henrys per meter), then the relative permeability, µr, is given by:µr = µ / µo

Faraday’s Law

When a magnet moves past different materials, the voltage induced is the same for each case

The most current will be produced in the material where the electrons are bound most loosely

i.e.) The magnet will produce a larger current when moving past copper than rubber

Generators and AC

As a wire moves back and forth past a magnet, the resulting current changes direction (AC)

Recall: A motor converts electrical energy (from the battery) into mechanical energy (rotation of the armature)

A generator converts mechanical energy into electrical energy

Generators and AC

Generators and AC

Generators and AC

Turbine: When the armature of a generator is connected to a wheel which captures wind, water, or steam in order to turn and produce electrical

energy

Transformers

Consider two coils side by side:

Primary Coil: Connected to a voltage source

Secondary Coil: Connected to a galvanometer

Transformers When the voltage source is turned on:

Current briefly surges through the secondary coil

When the voltage source is turned off: Current briefly surges through the

secondary coil in the opposite direction

The magnetic field building around the primary extends to the secondary Changes in magnetic field intensity

induce voltage in the secondary

Transformers

Placing a core within the coils will intensify the magnetic field

The secondary will intercept more of the field change

Transformers

Instead of switching a DC voltage source off and on, the device is connected to an AC voltage source

The rate at which the magnetic field changes = frequency of the AC current

This device is known as a transformer

Induction of Electric and

Magnetic Fields

According to Faraday: Electric fields are created in any region of

space where a magnetic field is changing with time.

According to Maxwell: A magnetic field is created in any region

of space where an electric field is changing with time.

These laws are inverses of each other and lead to the concept of electromagnetic waves

DC CIRCUIT THEOREMS

INTRODUCTION • Thevenin’s Theorem is a very important and

useful theorem.

• It is a method for the reduction of a portion of a complex circuit into a simple one.

• It reduces the need for repeated solutions of the same sets of equations.

Thevenin Equivalent Circuit Any two-terminal linear network, composed of voltage

sources, current sources, and resistors, can be replaced by an equivalent two-terminal network consisting of an independent voltage source in series with a resistor.

V-I Characteristic of Thevenin

Equivalent

Norto ’s Theore

SUPERPOSITION THEOREM

MAXIMUM POWER TRANSFER

THEOREM

THANKS