Explains about Basic of engineering BoE Unit 1.pptx

Basics of engineering

1. UNIT – 1 FUNDAMENTALS OF ELECTRICITY Basic laws -Method of Solving a Circuit by Kirchhoff’s Laws – Wiring Layout for a Residential Building- Basic Principles of Earthling- Un Interrupted Power Supply and its Types-Evolution of electric grid –Need for smart grid- National and International initiatives in smart grid- Comparison between conventional grid and smart grid.

2. OHM’s LAW Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points at a constant temperature. I = V/R 2

3. LIMITATIONS OF OHM’S LAW It is not applicable to non linear devices such as diodes, zener diodes, voltage regulators etc. It does not hold good for non- metalic conductors such as silicon carbide. The law for such conductors is given by V = k I m 3

4. POWER , VOLTAGE, CURRENT RELATION 4

5. PROBLEMS A current of 0.5 A is flowing through the resistance of 10Ω.Find the potential difference between its ends . Ans : V = IR = 0.5 X 10 = 5 V 2. Calculate the current and resistance of a 100 W,  200V electric bulb . Ans : I= P/ V = 100 / 200 = 0.5 A R = V/I = 200/0.5 = 400 Ω 5

6. Kirchhoff's Current Law (Current law or Point law) The sum of the currents flowing towards any junction in an electric circuit equal to the sum of currents flowing away from the junction . 6

7. Kirchhoff's Voltage Law : (voltage law or Mesh law) In any closed circuit or closed loop, the algebraic sum of all the electromotive forces and the voltage drops is equal to zero . Potential Rise = Potential Drop V s = I R 1 + I R 2 7

8. 8 MESH ANALYSIS Let us consider a simple network having only two meshes. Although the directions of the mesh currents are arbitrary But all must be either clockwise or anticlockwise . We shall always choose clockwise mesh currents . This results in a certain error-minimizing symmetry. Note that by taking mesh currents, the KCL is automatically satisfied.

9. STEPS IN MESH ANALYSIS V in 9

10. STEP 1 Identify all of the meshes in the circuit V in 10

11. STEP 2 Label the currents flowing in each mesh No of Meshes equal to No of Box i 1 i 2 V in 11

12. STEP 3 Label the voltage across each component in the circuit i 1 i 2 + V 1 _ V in + V 3 _ + V 5 _ + V 6 _ + V 2 - + V 4 - 12

13. STEP 4 Use Kirchoff’s Voltage Law i 1 i 2 + V 1 _ V in + V 3 _ + V 5 _ + V 6 _ + V 2 - + V 4 - 13

14. STEP 5 Use Ohm’s Law to relate the voltage drops across each component to the sum of the currents flowing through them. Follow the sign convention on the resistor’s voltage. 14

15. STEP 5 i 1 i 2 + V 1 _ V in + V 3 _ + V 5 _ + V 6 _ + V 2 - + V 4 - 15

16. STEP 6 Solve for the mesh currents, i 1 and i 2 These currents are related to the currents found during the nodal analysis. 16

17. STEP 7 Once the mesh currents are known, calculate the voltage across all of the components. 17

18. 12V 18

19. From Previous Slides 19

20. Substituting in Numbers 20

21. Substituting the results from Ohm’s Law into the KVL equations 21

22. Chugging through the Math One or more of the mesh currents may have a negative sign. Mesh Currents ( m A ) i 1 740 i 2 264 22

23. In the circuit below, find the currents and their directions.

24. Given Data Resistors: R 1  = 0,5 Ω; R 2  = 0,5 Ω; R 3  = 1 Ω; R 4  = 0,5 Ω; R 5  = 0,5 Ω; R 6  = 3 Ω; R 7  = 1 Ω. Batteries: E 1  = 20 V; E 2  = 20 V; E 3  = 6 V;

25. First, for each branch of the circuit, we arbitrarily choose a direction of the current. In the  EFAB  branch, Current   i 1  in the clockwise direction, in the branch  BE  the current  i 2  from  B  to  E , in the branch  EDCB   Current   i 3  is in the counterclockwise direction. Second , for each loop of the circuit, we assign a direction, also arbitrarily, to traverse the mesh. The α-mesh ( ABEFA ) is clockwise and β-mesh ( BCDEB ) is also clockwise (Figure 1).

27. Electrical wiring  is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure.

28. ELECTRICAL SYMBOLS

29. Contd.,

30. Eg : There are three D-cells placed in a battery pack to power a circuit containing three light bulbs. The resistor symbol represents each light bulb. The connecting lines are used to connect the symbols. At the same time, don't forget to put the switch in the circuit to control the current flow. The final sketch is shown in the following picture

31. DESIGN AND DRAWING OF INTERNAL WIRING SYSTEM

32. Contd., Wiring Should be done on distribution system with main branch distribution at convenient centers. Energy meter used to measure unit consumed by loads. Fuse arrangement present inorder to break the circuit during fault or overloaded conditions.

33. Layout House wiring

34. SINGLE PHASE WIRING

35. What Is Earthing The process of connecting metallic bodies of all the electrical apparatus and equipment to huge mass of earth by a wire having negligible resistance is called Earthing .

36. Concept of Earthing Systems All the people living or working in residential, commercial and industrial installations, particularly the operators and personnel who are in close operation and contact with electrical systems and machineries. It should essentially be protected against possible electrification. To achieve this protection, earthing system of an installation is defined, designed and installed according to the standard requirements..

37. Purpose of Earthing To save human life from danger of electrical shock or death by blowing a fuse. To provide an alternative path for the fault current to flow so that it will not endanger the user and safe path to dissipate lightning and short circuit currents. To provide stable platform for operation of sensitive  electronic equipments. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage.

38. ADVANTAGES: Improved Service Reliability Greater safety Improved Lightning protection Better system and equipment over current protection

39. SOLID OR EFFECTIVE GROUNDING 33 kV with total power not exceeding 5000 KVA DISADVANTAGES Due to high fault current system becomes unstable, therefore greater interference to neighboring circuit. Due to high fault current CBs are difficult to handle, therefore heavy contacts are to be provided. 46

40. A power system is said to be solidly grounded when the neutral of a generator. Power transformer or grounding transformer are directly connected to the ground through a conductor of negligible resistance and reactance. A part of a system or system is said to be solidly grounded when the positive-sequence impedance of the system is greater or equal to the zero sequence resistance. If impedance of generator is too low: Direct earthling of generator without any external impedance may cause an earth fault current from generator to exceed the maximum 3 phase fault current. If reactance of generator or transformer is too great: It is necessary that the earth fault current be in the range of 100% of 3 phase fault current to present the development of high transient over voltage.

41. RESISTANCE GROUNDING 2.2 kV and 33 kV with power more than 5000 kVA 48

42. Neutral connected to earth through one or more resistors. The value of resistance to be inserted: Where V L =Line to Line voltage I = Full load current It reduces the effects of burning and melting in faulted electrical equipment Reduces mechanical stresses in circuits carrying fault currents, reduce electric shock hazards Value of resistance to be used in the neutral to be earthed is such as will limit the earth fault current . Earth fault current may be limited to 5% to 20% of that which occur with a 3 phase fault.

43. ADVANTAGES Discriminative type switchgears may be used. Arc grounding are minimized. Influence on neighbor circuit is minimized. DISADVANTGES: Neutral is shifted during earth fault therefore equipments are subjected for greater voltages. Energy loss in neutral resistor is more. Expensive. 50

44. REACTANCE EARTHING The reactance grounding is used for long transmission line or cable system. In order to minimize transient overvoltages: The current through the reactance during fault should be limited to 25% of 3 phase fault current

45. ARC SUPPRESION COIL (or) RESONANT GROUNDING (or)PETERSON COIL GROUNDING It is an iron cored reactor connected in neutral earthing circuit. Arcing is extinguished itself. When earth fault on one of the line persists, this coil reduces the short circuit current to a very low value. 52

46. VOLTAGE TRANSFORMER EARTHING Advantages: Due to high reactance to the earth path , switching and arcing grounds are reduced. This type of earthing has all advantages of underground neutral system. Arcing grounds are eliminated. Disadvantages: System insulation will be overstressed when the earth fault occurs on any phase This type of earthing has all advantages of underground neutral system. Arcing grounds are eliminated.

47. EARTHING TRANSFORMER If the transformer or generators are delta connected or if the neutral points are not accessible then “ Artificially the neutral earthing point can be created with use of star connected earthing transformer “ Its having two equal parts in primary side and has no secondary. Under the faulty condition, the transformer offers a low impedance path to the flow of zero phase sequence currents. The value of fault current is limited in some cases by the use of resistor in series with the neutral earthing connection.

48. COMPARISON 55

49. SELECTION OF EARTHING Solid earthing of neutral used for low voltage systems (600V) For medium voltage systems (2.4 to 11 KV) earthing of neutral through a resistance preferred. While High voltage systems usually have the transformer neutrals on the high voltage side solidly earthed. Choice is each case should be made by considering the points mentioned: Magnitude of earth-fault current as a percentage of 3 Phase fault current Dip is line voltage due to fault conditions details of the system data should be known to enable calculate resistance or reactance to insert.

50. UPS An  Uninterruptible Power Supply , also   Uninterruptible Power Source ,  UPS  or battery/flywheel backup . It is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails.

51. Block diagram of UPS

52. Standby UPS diagram

53. Types of UPS There are three types of UPS are available. They are Offline UPS Online UPS Line interactive UPS

54. Offline UPS The mains to battery changeover time or battery to mains changeover time in offline UPS is very low as compared to inverter. Typically, changeover time in inverters is 500 milliseconds & Offline UPS has changeover time of 3-8 milliseconds . 

55. Block diagram of Offline UPS

56. Offline UPS In a time, when mains ac is present, Inverter provides the output as is the input mains. While, Offline UPS has built in Automatic Voltage Regulator (AVR) to regulate the output voltage close to 220V ac .  Offline UPSs are normal weight UPSs and are widely used for domestic computers .

57. Offline UPS circuit

58. Online UPS In this type of UPS, the system always remains on battery, whether mains ac is present or not. When mains ac is present, it provides power to DC supply of inverter section as well as charges the battery simultaneously. When mains ac is not present, it will run the connected load till the battery has a recommended dischargeable level .

59. Block diagram of Online UPS AC mains

60. Line Interactive UPS In this design, the battery to AC power converter (inverter) is always connected to the o/p of the UPS. Battery charging is done during times when the I/P AC power is normal when the I/P AC fails, transfer switch opens and then the inverter starts functioning to provide power to load immediately. 

61. Block diagram of Line Interactive UPS

62. COMPARISON Feature Offline (Standby) UPS Line-Interactive UPS Online (Double Conversion) UPS Power Source Direct from mains Mains with AVR Continuous double conversion (DC-AC) Switching Time 4-10 milliseconds 2-4 milliseconds 0 milliseconds (No interruption) Voltage Regulation No Automatic Voltage Regulator (AVR) Fully Regulated Protection Level Low Medium High Protects Against Power outages Power outages, voltage fluctuations Power outages, voltage sags, surges, and fluctuations Best For Home PC, Routers Offices, Networking equipment Servers, Medical, Industrial use Cost Low Medium High