What is a Load Flow Study???
      It is a steady-state analysis whose target is to determine 
    the 
    Voltages
    Currents
    Real and Reactive power flows in a system under a 
    given load conditions
       A load flow study also known as power-flow study
    
     A load flow study is done on a power 
      A load flow study is done on a power 
      system to ensure that
      system to ensure that
      
      Generation supplies the demand (load) plus losses.
        Generation supplies the demand (load) plus losses.
      
      Bus voltage magnitudes remain close to rated values
        Bus voltage magnitudes remain close to rated values
      
      Generation  operates  within  specified  real  and  reactive 
        Generation  operates  within  specified  real  and  reactive 
        power limits
        power limits
      
      Transmission lines and transformers are not overloaded.
        Transmission lines and transformers are not overloaded.
     A Load Flow Study Specifically 
       Investigates the Following
      
       Bus bar voltages
        Bus bar voltages
      
       Effect of rearranging circuits and incorporating new 
        Effect of rearranging circuits and incorporating new 
        circuits on system loading.
        circuits on system loading.
      
       Effect of injecting in-phase and quadrature boost 
        Effect of injecting in-phase and quadrature boost 
        voltages on system loading.
        voltages on system loading.
      
       Optimum system running conditions and load 
        Optimum system running conditions and load 
        distribution.
        distribution.
      
       Optimum system losses.
        Optimum system losses.
      
       Optimum rating and tap range of transformers.
        Optimum rating and tap range of transformers.
   Power-flow Analysis Equations
  The basic equation for power-flow analysis is derived from the 
  nodal analysis equations for the power system.
   For example, for a 4-bus system 
   where Yij  are the elements of the bus admittance matrix,
              Vi are the bus voltages
              Ii are the currents injected at each node.
    
   •
   The node equation at bus i can be written as 
    Power-flow Analysis Equations
    Relationship between per-unit real and reactive power supplied 
    to the system at bus i and the per-unit current injected into the 
    system at that bus: 
    
      where Vi is the per-unit voltage at the bus; 
              Ii* - complex conjugate of the per-unit current injected at the bus; 
              Pi and Qi are per-unit real and reactive powers. 
     Therefore,