Basic Electrical Parameters ( Basic Electrical Engineering)

This presentation contains information about some basic electrical parameters such as Voltage, Current, EMF, PD, Electric Power, Energy Ideal & Practical Sources, Types of Resistance, Heating Effect, Magnetic effect & Chemical effect of Electric Current etc.

1. Basic Electrical Parameters Mr. C D Patil Dept. of EE

2. Definition of Basic Terms Current – Flow of electrons is known as Electric Current Current has 2 types 1. Alternating Current 2. Direct Current Frequency – Number of cycles completed in one second. In India, supply frequency is 50 Hz .

3. Definition of Basic Terms Electromotive Force (EMF) :- The electrical force which causes the electrons to move or flow. Potential Difference (PD) :- The difference in Potential is known as Potential Difference.

4. Difference Between AC & DC

5. Type of Sources

6. Type of Sources 1. Ideal Voltage Source :- A voltage source is a two-terminal device whose voltage at any instant of time is constant Such a voltage source is called an Ideal Voltage Source   and have zero internal resistance. Vout = Vs Voltage Source

7. Type of Sources 2. Practical Voltage Sources :- Sources  having some amount of internal resistances are known as Practical Voltage Source. Due to this internal resistance; voltage drop takes place, and it causes the terminal voltage to reduce Vout = Vs- I*Rs Voltage Source

8. Type of Sources Voltage Source Ideal Voltage Source Practical Voltage Source

9. Type of Sources Current Source 1. Ideal Current Source: An ideal current source is a two terminal device which supplies constant current irrespective of load resistance. The value of current will be constant with respect to time and load resistance.  Here internal Resistance is infinity.

10. Type of Sources Current Source 2. Practical Current Source: A practical current source is a two terminal device having some resistance connected across its terminals. The value of current will be reducing nature with respect to time and load resistance.  Here internal Resistance is present

11. Electrical Work It is a workdone to transfer a charge from one point to other point. Workdone = Force x Distance W= F x D Unit of Workdone is Joule.

12. Electrical Power (P)

13. Electrical Energy (E) It is product of Electric Power & Time E = P x t Its unit is Watt-Hour

14. Resistance (R) Resistance  is a measure of the opposition to current flow in an electrical circuit Resistance  is measured in ohms(Ω).

15. Resistivity ( ρ ) The electrical resistivity is the electrical resistance per unit length and per unit of cross-sectional area at a specified temperature . Its symbol is ( ρ ) (rho) Its unit is ohm-m (Ω-m)

16. Conductivity ( σ ) It is the ability to conduct electricity through given material. the SI unit of conductivity is Siemens per meter (S/m) or mho and is usually represented by Greek letter sigma, σ, and its formula is given as;

17. Effect of Temperature on Resistance The electrical resistance changes with the change of temperature. The resistance does not only increase with the rise in temperature but it also decreases in some cases.

18. Effect of Temperature on Resistance The resistance of all pure metals increases linearly with increase in temperature over a limited temperature range. The resistance of all metals such as tungsten, copper, aluminum etc. increases linearly with increase in the temperature over a limited temperature range. For e.g. the resistance of copper is 100Ω at 0°c then it increases linearly up to 100°c. At a temperature of -234.5°c the resistance of copper is almost zero as shown in the figure. Hence Pure metal have positive temperature Coefficient of Resistance. 1. Effect of Temperature on Metal

19. Effect of Temperature on Resistance The resistance of semiconductor, Insulator, and decrease with increase in temperature. At zero temperature, the semiconductor behaves as a perfect insulator. As the temperature increases, some of the electrons acquire energy and become free for conduction. Hence, conductivity increase and resistance decrease with increase in temperature. Semiconductor has negative temperature coefficient of resistivity therefore since with the increase in the temperature the resistance decreases. 2. E ffect of Temperature on Semiconductor, Insulator

20. Types of Resistors

21. Types of Resistors Linear Resistor- The resistors whose value changes with the applied temperature and voltage, are called linear resistors . Non- Linear Resistor- Non-linear resistors are those types of resistors where the electric current flowing through it changes with the exchange in applied voltage or temperature Fixed Resistor - Fixed resistors are resistors with a specific value . Variable Resistor– The value of resistance can be changed according to requirement.

22. Types of Resistors Carbon resistors are mainly made of carbon clay composition covered with a plastic case. The lead of the resistor is made of tinned copper . The main advantages of these resistors are that they are readily available, low cost, and they are very durable . The main disadvantage of carbon composition resistors is that they are very temperature sensitive . These resistors are also available in a wide range of values, from as low as 1 Ω to as high as 22 Mega Ω .   It is used in power supplies and welding controls 1. Carbon Composition Resistor

23. Types of Resistors Wire wound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. The assembly is protected with a layer of paint, molded plastic, or an  enamel  coating baked at high temperature. These resistors are designed to withstand unusually high temperatures of up to 450 ° C. It is used in high power applications like transducers and televisions. It is also used as Temperature Sensors. 2. Wire Wound Resistor

24. Types of Resistors Metal film resistors have a thin metal layer as resistive element on a non-conducting body . The desired value of resistance of metal film resistor or carbon film resistor can easily be obtained by either trimming the layer of the thickness or by cutting helical grooves of suitable pitch along its length as shown in fig. Metallic contact cap is fitted at both ends of the resistor. The caps are in contact with the conductive film or helical grooves. The lead wire is welded to the end caps . It is used in active filters or bridge circuits. 3. Metal Film Resistor

25. Types of Resistors A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider . If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat . Potentiometers consist of a resistive element, a sliding contact (wiper) that moves along the element, making good electrical contact with one part of it, electrical terminals at each end of the element, a mechanism that moves the wiper from one end to the other, and a housing containing the element and wiper. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment.  4. Potentiometer

26. Types of Resistors Rheostat is a type of variable resistor, whose resistance can be changed so as to change the amount of current flowing through a circuit . It has two terminals, out of which one is fixed and the other one is a moving terminal. Some rheostats have three terminals just like potentiometer, although only two terminals are used (Only one of the two fixed terminals and the moving terminal are used ). It is used in Speed control circuits for motors, heaters and ovens. 5. Rheostat

27. Types of Resistors A trimmer potentiometer, also known as a trim pot, is a type of variable resistor or adjustable potentiometer that can adjust, tune, and calibrate circuits. These trimmer resistors are often used to initially calibrate equipment after manufacturing . It is used in radio  and television receivers, in the intermediate frequency (IF), oscillator and radio frequency (RF) circuits . 6. Trimmer

28. Types of Resistors The word thermistor means a thermal resistor. Its resistance value changes with the change in the temperature . A  thermistor  is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass. Most thermistors have a negative temperature coefficient which means its resistance will fall down when the temperature increases. These are normally made of semiconductor materials. Resistance up to a few mega ohms can be obtained from thermistors . Thermistors are used as temperature sensors.  7. Thermistors

29. Types of Resistors A Light Dependent Resistor (or LDR) will vary in resistance depending on the intensity of light falling on it. This is made of cadmium sulfide which contains a small number of electrons when it is not illuminated. When a light ray falls on it, electrons get ejected and hence the conductivity of it increases. Hence, it offers low resistance when light falls on it and offers high resistance in the dark . In the dark, a LDR can have a resistance as high as several  mega ohms  (MΩ), while in the light, a LDR can have a resistance as low as a few hundred ohms . It is used in alarm clocks, street lights, light intensity meters, camera light meters etc. 8. LDR (Light Dependant Resistor)

30. Heating Effect of Electric Current When current flows through a conductor, heat energy is generated in the conductor. The heating effect of an electric current depends on three factors : The resistance, R of the conductor. A higher resistance produces more heat. The time, t for which current flows. The longer the time the larger the amount of heat produced The amount of current, I . the higher the current the larger the amount of heat generated. Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I 2 Rt . This equation is called the Joule’s equation of electrical heating.

31. Heating Effect of Electric Current Applications of heating effect of electric current 1. In electrical heating Electric Cookers- electric cookers turn red hot and the heat energy produced is absorbed by the cooking pot through conduction. Electric Heaters- radiant heaters turn red at about 900 C and the radiation emitted is directed into the room by polished reflectors. Electric Kettles- the heating element is placed at the bottom of the kettle so that the liquid being heated covers it. The heat is then absorbed by water and distributed throughout the whole liquid by convection. Electric Irons- when current flows through the heating element, the heat energy developed is conducted to the heavy metal base raising its temperature. This energy is then used to press clothes. The temperature of the electric iron can be controlled using a thermostat.

32. Heating Effect of Electric Current Applications of heating effect of electric current 2. In lighting appliances Filament Lamps- it is made of a tungsten wire enclosed in a glass bulb from which air has been removed. This is because air would oxidize the filament. The filament is heated up to a high temperature and becomes white hot. Tungsten is used due its high melting point; 3400  The bulb is filled with an inactive gas e.g. argon or nitrogen at low pressure which reduces evaporation of the tungsten wire. However, one disadvantage of the inert gas is that it causes convection currents which cool the filament. This problem is minimized by coiling the wire so that it occupies a smaller area which reduces heat loss through convection. Fluorescent lamps- these lamps are more efficient compared to filament lamps and last much longer. They have mercury vapour in the glass tube which emits ultraviolet radiation when switched on. This radiation causes the powder in the tube to glow (fluoresce) i.e. emits visible light. Different powders produce different colors.

33. Heating Effect of Electric Current

34. Magnetic Effect of Electric Current When a current flows through the conductor, a magnetic field will produce across that conductor. Applications- Electric Crane, Electric Motor, Transformer, Electromagnet etc .

35. Chemical Effect of Electric Current

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