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 preferred 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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