1. PRACTICAL ELECTRICAL ENGINEERING BASICS
Fundamentals

2. Alternating Current System
Most common power generators in power stations generate AC voltages
Follow sinusoidal waveforms alternating between positive and negative peaks around zero axis
This waveform of voltage/ current is normally referred to as AC voltage and AC current in Electrical distribution

3. Typical AC Sinusoidal Wave Form
0 to 360 degree in the picture corresponds to one cycle of wave form, which is represented by one full circular motion

4. Why AC?
Almost entire power generation and transmission is by AC (alternating current)
AC lends itself to voltage changes easily
Voltage can be chosen for optimum efficiency and optimum capital cost
Thus better economy of power system operations

5. Alternating current system
Power generators generate AC voltages, which follow sinusoidal waveforms
Mathematically expressed as
V = Vp Sin(2 × f × t)
This voltage/current waveform normally referred to as AC voltage and AC current
V – Instantaneous magnitude of voltage
Vp – Peak value of voltage
F – Frequency
T – Time
Typical AC sinusoidal wave form

6. AC Waveform
Voltage or current in AC circuits varies cyclically number of times per second
This number is called frequency (f)
Time for one cycle is 1/f
Variation follows sine relationship and waveform is called sine wave
Electrical system can be of single or 3 phase type

7. Single Phase AC waveform7

8. Single and three phase generators

9. Three phase AC
Universally adopted because of lower equipment cost per unit power handled
Helpful while interconnecting several generating sources (sources tend remain in phase or stay synchromised)
Three phase AC motors (which account for most of the energy used) have simple design and are self starting

10. Benefits of 3-phase ac power system
Higher power output for a given size of motor
Better conductor economy per unit power
Self starting induction motors
Better synchronising torque makes parallel operation of alternators possible

11. Electrical Power and Energy
In DC circuits
Power = Voltage x Current (Watts)
Energy = Power x Time (Watt Hours)
In AC circuits instantaneous voltage and current keep changing as they follow a sine curve
Power is computed using Root Mean Square (RMS) voltage and RMS current

12. AC Power Fundamental Definition of Power:
In an AC circuit both are sinusoidal against time
Sinusoidal Voltage and Current are defined in RMS magnitudes where: 12 12 12

13. Power Triangle S Q f P 13

14. Typical Standard Inductive Circuit
Majority of electrical circuits are inductive in nature
A standard inductive circuit is normally represented with parameters called resistance R and inductance L, which are basically the measure of resistance offered by the circuit preventing/ limiting the flow of current

15. Formulae for Power Apparent power S = V*I Active Power P = V*I*Cos f
Reactive Power Q = V*I* Sin f
Cos f is known as the Power Factor and f is power factor angle
The angle depends on ratio of resistance to the reactance in a circuit

16. V & I for an Inductive Circuit
AC voltages/currents are normally represented in vector forms
Instantaneous positions of voltage and current in relation to each other are vectorially indicated as below with both V and I go on rotating full 360 degrees for each completed cycle

17. Three line diagram

18. Single line diagram

19. Advantages of a single line diagram
It requires much lesser space and hence leaves room for designer for providing other useful information in the drawing
It is very versatile and comprehensive because it can depict very simple DC circuits, or very complicated three-phase system
Simple, hence requires much lesser time for reader to understand the basic system design

20. Differences between single line and the 3-line diagram
One-line diagram
3-line diagram
Provide a basic roadmap to the interconnections of the electrical system, and serve as a building block from which all types of system analyses are based.
Prepared as a result of further working on the basis of single line diagrams as they provide details for electrical wiring connections.
Part of initial plant electrical design. Is usually a part of the initial tender document.
Part of detailed design document. Is prepared usually after the tendering stage i.e. before manufacture.
Mainly used for working out panel schedules, load schedules, fault analysis, protection system deign
Used for control designing circuit diagrams, control circuits, phase sequencing, differential relay settings, metering transformer connections etc.
Simplified notation for representing a three-phase power system. Since the loads on the three phases are identical , any one phase can be used for representing either of the phases
Here all three conductors of the three phase system are shown
individually.
Details of the power and the control circuits are also shown as per actual field connections.

21. Power network Generation Transmission/sub-transmission Distribution
Utilisation

22. Three phase power network
All AC generation, Transmission and Distribution is through 3 phase systems
Exception: Single phase/SWER distribution systems
Utilisation can be 3 phase (motors and rectifiers for drives, furnaces) or single phase (commercial and lighting)
Ability to transmit larger amount of power for a given voltage/conductor volume
Availability of rugged 3 phase cage motors with self starting capability

23. Power system
Power generation plants are located based on fuel availability
Other considerations like water, pollution issues etc.
Often they are in remote locations
Loads are situated in population centers
Transporting generated power to population centers for use requires a power system

24. A 400 kV Transmission line and Structure

25. Substations A facility incorporating Indoor or Outdoor type
Transformers
Switching/isolation equipment
Control/protection/measuring
Auxiliary power equipment
Indoor or Outdoor type
Air-insulated or gas-insulated
Different configurations

26. Outdoor 330 kV switchyard (Transmission)
Typical indoor distribution substation

27. Voltage classification BS and IEC
Circuits supplied at nominal voltage up to and including 1000 V a.c. or V d.c. are said to be in the low voltage range, and equipment rated for voltages above these values are classified as high voltage (HV) equipment.

28. Voltage classification as per IEEE 141:1993
Low voltage (LV)
Systems of nominal voltage up to 1000V
Common usage: 380V, 415V, 480V
Medium voltage (MV)
Systems of nominal voltage 1000V and above but less than V
Common usage: 4160V, 6900V, 12000V, 13800V, 34500V, 69000V
High voltage (HV)
Systems of nominal voltage V and above and up to V
Common usage: 115kV, 138kV, 230 kV

29. Basis of voltage selection
System segment
Generation: MV
Transmission: HV and Extra High Voltage (230kV+)
Sub-transmission: HV/MV
Distribution: MV/LV
Utilization: MV/LV

30. Distribution and utilisation voltages
Domestic, commercial and small industry loads at LV
Utilities distribute power at MV and also at LV
Large industries have a mix of MV drives, Transformers and LV loads
Distribution and utilisation can involve more than one voltage

31. Distribution voltage options for industries
Receiving and distribution at the same voltage
Avoids need for transformer
Difficult to regulate voltage
Independent earthing of plant system is not possible
Receiving at a higher voltage
Involves a transformer
Internal voltage independently variable through OLTC
Can choose system earthing independent of the utility
Transformer acts as a buffer (harmonics, voltage dips)

32. A typical utility system
Supply from a higher voltage
Normally open point
Supply from a higher voltage

33. Power distribution Distribution is done at lower voltage levels
Distances are much shorter than transmission
Voltage levels are typically 33 kV and less
Bulk of consumers draw power at lower voltages
This requires distribution at two different levels
Distribution substations convert power from transmission to distribution voltages

34. Governing principles of Power Distribution
Safety of operating personnel and plant assets
Reliable power supply (continuity of power)
Adequate quality of power
Prevention of load generated problems

35. Electrical safety and power security
Electricity-a good servant but a bad master
Safety is a predominant issue
Legislative requirements
Standards for ensuring quality and reliability
Good O&M practices to ensure power security

36. Industrial distribution components
An incoming section
In-plant emergency/standby generation and associated distribution system
A primary distribution system, usually medium/high voltage
A step down transformer section
A secondary low voltage distribution system
Controlgear for individual loads
Supervisory control system

37. Main equipment types Circuit isolation devices
Circuit switching devices (circuit breakers)
Transformers
HV and LV distribution equipment
Motor control panels
DC supply system
Power system protection
Cable (or overhead line based) distribution systems
Earthing system
Power quality improvement equipment

38. Types of distribution Radial Radial with redundancy
Selective
Looped or Ring type
Ring type with spur lines
Mesh connections 38

39. Radial distribution A single incoming feeder
Failure causes total disruption
Restoration only after the problem is rectified
Not desirable where critical production processes are involved
If at all used, internal standby source to be planned also 39

40. Redundancy Ensuring alternative supply such that
Any one of the sources/incoming feeders may take up full load (100% redundancy)
Only partial load can be taken up (partial redundancy)
Reduces period of interruption
Two types of redundancy (selective and looped) 40

41. Loop (Ring) type redundancy
Selective Redundancy:
Two feeders to each load
One feeder used at a time and can be selected
Automatic restoration schemes to switch feeders
Reduces time of interruption
Results in under-utilisation (because of 100% redundancy)
Loop (Ring) type redundancy 41

42. Loop (Ring) type redundancy

43. Ring type distribution
Favoured by power distribution utilities
Fault in a ring section of a closed loop cleared from both ends
Selective closing of isolators to detect fault
Easy to extend the ring for inclusion of additional loads
Supply can be restored to all consumers without waiting for repair of faulty section
Automation possibilities for restoration 43

44. Mesh type system Similar to ring type
Additional connections between some of the nodes
Usual in transmission systems
Distribution systems provide such connections for additional security
Complexity of protection 44

45. Industrial example of Incoming supply level redundancy

46. Industrial example of Main Transformer level redundancy

47. Industrial distribution-Typical47

48. Distribution Systems in Oil and Gas Facilities
Large facilities have power demands ranging from 30 MW and upwards to several hundred MW.
Voltage levels for high, medium and low voltage distribution boards are in the range of kV, 2-8 kV and V respectively.
Generated power is exchanged with mains or other facilities on the HV distribution board and relays are used to provide protection.

49. Distribution Systems in Oil and Gas Facilities

50. Distribution Systems in Oil and Gas Facilities
Electrical power needed for gathering station induction engines, injection steam generators & wells with units of mechanical & centrifuge pumping is supplied by kVA substations and 13.8/0.48 kV transformers.
Building facilities, external lighting, communication and automation are powered by 575/480/ V, 5 kVA to 15 kVA transformers.
13.8 kV, kVA capacitor banks are connected to the electrical distribution feeders to regulate voltage & correct power factor.

51. Distribution equipment
Switching and isolation equipment
Circuit breakers
Disconnectors
Control gear
Conductors for carrying power
Overhead bare
Overhead insulated
UG cables

52. Any questions ?