power system representation

Power system representation, One line diagram another way Following methods are used to represent a power system:

  1. One line diagram
  2. Impedance diagram
  3. Reactance diagram


The symbolic representation of an electrical power system is known as one line diagram. A three phase power system is represented by a single phase power system. In a single phase system, there is a phase wire and a neutral wire. So to make an equivalent circuit, we show it through a symbolic representation as shown in the following figure:

one line diagram

one line diagram

In this diagram, three generators G1, G2 and G3 have been grounded separately through a reactor. The generators are connected to the bus bar through circuit breakers; furthermore the step up transformers are connected to the transmission line T1 through circuit breakers.


To represent electrical components in terms of impedances is known as an impedance diagram. The one line diagram can be converted into an impedance diagram as shown in the following figure:

impedence diagram of power system

impedence diagram of power system

 In the above diagram:

  1. Load impedances are represented by RL.
  2. The current limiting impedances between generators and their grounds have been omitted.
  3. The shunt impedances of transformers have been omitted.
  4. Transmission line is represented by a π circuit.


If all the components of a power system are represented through the reactances, then such a diagram is called reactance diagram of the power system. Resistance is also neglected in such a diagram. Therefore, there is not much difference between impedance and reactance diagram. The loads of rotating machines are usually neglected because of no significant effect on line currents during a fault. Synchronous motor loads are always considered during fault calculations but the generated emf is considered in short circuit currents. Induction motor is neglected while finding currents. The impedance diagram can be converted into reactance diagram as shown by the following figure:

reactance diagram of power system

reactance diagram of power system

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