Chap 1

• An electric power system is a network of electrical components deployed to supply, transfer, and use electric power
• An example of an electric power system is the grid that provides power to an extended area
• An electrical grid power system can be broadly divided into generators, transmission system, and distribution system
• Smaller power systems are also found in industry, hospitals, commercial buildings, and homes
• The majority of these systems rely upon three-phase AC power
• Specialized power systems that do not always rely upon three-phase AC power are found in aircraft, electric rail systems, ocean liners, and automobiles
• Functions of Power Systems Analysis:

  • To monitor the voltage at various buses, real and reactive power flow between buses (Load flow Analysis)
  • To design the circuit breakers (Protection)
  • To plan future expansion of the existing system (Forecasting)
  • To analyze the system under different fault conditions (Fault Analysis)
  • To study the ability of the system for small and large disturbances (Stability studies)
• Components of a Power System:

  • Alternator
  • Power transformer
  • Transmission lines
  • Substation transformer
  • Distribution transformer
  • Loads
• A single-line diagram is a diagrammatic representation of a power system where components are represented by symbols and their interconnections are shown by straight lines
• The Per-Unit System provides values for voltage, current, power, impedance, and admittance in the same unit, making calculations easier
• Advantages of Per-unit system:

  1. Manufacturers provide equipment data with nameplate rating as a base

  2. Gives a clear idea of relative magnitudes of various quantities

  3. Impedance values fall in a narrow range regardless of equipment rating

  4. Simplifies impedance calculations for transformers

  5. Ideal for computerized analysis and simulation of complex power system problems

  6. Simplifies circuit laws and power equations
• Steps in Determining Per Unit Impedance Diagram:

  1. Obtain the one-line diagram based on the given data

  2. Choose a common base MVA for the system

  3. Choose a base KV in any one section

  4. Find the base KV of all sections present

  5. Find per unit values of all parameters: R, X, Z, E, etc.

  6. Draw the per unit impedance/reactance diagram
• The impedance diagram of the system with all reactances in PU is determined based on the given data