Load Flow Studies Important Points

  1. Load Flow Studies need to maintain the smooth operation of network system by resolve the given problems:

    • Load Flow Problems

    • Optimal Load Scheduling Problem

    • System Control Problem

  2. In Load Flow Studies, we study about :

    • Comprise the magnitude & phase angle of Load bus voltage

    • Reactive powers at Generator buses

    • Real & Reactive power flow in Transmission lines.

  3. Three types of Bus used in Load Flow Studies

    • Swing Bus or Reference Bus or Slack Bus

    • Generator Bus or Voltage Controlled Bus or PV Bus

    • Load Bus or PQ Bus

  4. Slack Bus

    • A bus which supplies the additional Real and Reactive power to recover the transmission losses.

    • Generator bus must be selected as a Slack bus.

    • Slack Bus usually numbered as a BUS 1 and assigned to 1 p.u.

    • Specified variable -  V, δ

    • Without Slack bus, Load flow will not possible.

  5. Generator Bus

    • Maintain the Voltage level to achieve the desired Reactive power injection.

    • Almost 10% of all the buses are Generator Buses

    • Specified variable - V, P

  6. Load Bus

    •  Almost 80% of all the buses are Load Buses

    • Specified variable - P, Q

  7. If two buses ith Bus and kth Bus are connected then

    • Active power flow always from leading angle bus to lagging angle bus.

    • Reactive power always flow from high potential bus to low potential bus.

    • If there is no potential difference between them, no Reactive power will flow.

    • If there is zero phase difference between both buses, Active power will not flow.

  8. Network load will be specified as Load Bus Matrix or Bus Admittance Matrix or Y-BUS Matrix

  9. Y-Bus Matrix

    • Y-Bus always a square matrix (n x n).

    • Y-Bus is prefered for load flow studies because it is a sparsity matrix (more number of Zero elements are present )

    • Sparsity matrix are required less memory due to present of Zero element

    • If the sum of all elements in each row of Y-Bus matrix is zero than corresponding Y-Bus is not having shunt elements.

    • In a given (n x n) Y-Bus matrix:

      • Total number of nodes = (n+1)

      • Including ground or reference node.

    • Total Number of Transmission Lines = No. of Non-zero element present either in upper triangle or lower triangle.

    • If degree of sparsity is inversely to  No. of transmission lines, then it decreases and No. of transmission line will increases.

    • If shunt capacitance/inductance are added in network, its only effects on diagonal elements of Y-Bus, off-diagonal elements remain same.

  10. Z-Bus Matrix

    • As opposite of Y-Bus, Z-Bus is a Full matrix.

    • Z-Bus is use in short circuit analysis because it will give more information about non zero elements.

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