Power Systems:

Electricity is generated at central power stations and then transferred to loads (i.e, Domestic, Commercial and Industrial) through the transmission and distribution system. A combination of all these systems is collectively known as an Electric Power System.

A power System is a combination of central generating stations, electric power transmission system, Distribution and utilization system. Each one of these systems is explained in detail in the next sections.

Fig. Basic Structure of an Electric Power System (Energy Supply System)

Electric Energy Supply System:

The transmission of electric power from a power station to consumers’ premises is known as the electric supply system.

An electric supply system consists of three principal components viz., the power station, the transmission lines and the distribution system. Electric power is produced at the power stations which are located at favourable places, generally quite away from the consumers. It is then transmitted over large distances to load centres with the help of conductors known as transmission lines. Finally, it is distributed to a large number of small and big consumers through a distribution network, supply system can be broadly classified into (i) d.c. or a.c. system (ii) overhead or underground system.

Nowadays, 3-phase, 3-wire AC system is universally adopted for generation and transmission of electric power as an economical proposition. However, distribution of electric power is done by 3-phase, 4-wire a.c. system. The underground system is more expensive than the overhead system. Therefore, the overhead system is mostly adopted for transmission and distribution of electric power.

Various methods of Power system analysis are

  1. Power flow analysis/load flow analysis: this analysis helps in calculating the unknown parameters from the known parameters in the steady state condition such as Real power reactive power, current, voltage etc and usually impedences/admittances are known values.
  2. Fault analysis: This analysis is done at the fault condition. The aim of the analysis is to predetermine the fault current in case of occurance. This pre-determination helps in designing and rating the protection devices required. The fault by default means Short circuit fault.
  3. Contigency analysis: This analysis is done at the time of line outage. Outage is the term used for open circuit fault or intentional opening of circuit. The power flow at the outage line is stopped hence the other parallel lines get burdened and may result in failiure. If the burdening continues it may result in black out. This is the aim of contingency analysis wherein the diverted path does not get overloaded.
  4. Stability analysis: This analysis is used to study the stability of the power system. It anlyses whether the system is in steady state or in transient/subtransient state or unstable state.

Power system analysis is an essential part of an electrical power system design. Calculations and simulations are performed to verify that the electrical system, including the system components, are correctly specified to perform as intended, withstand expected stress and be protected against failures.

Power system analyses include:

  1. Load flow analysis
  2. Short circuit and fault analysis
  3. Protective device co-ordination and settings
  4. Harmonic analysis
  5. Dynamic and transient analysis
  6. Earthing studies
  7. Switching over voltages and insulation co-ordination
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