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

• System Control Problem

• 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, Î´
• 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

•  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.