Power flow study

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In power engineering, the power flow study (also known as load-flow study) is an important tool involving numerical analysis applied to a power system. Unlike traditional circuit analysis, a power flow study usually uses simplified notation such as a one-line diagram and per-unit system, and focuses on various forms of AC power (ie: reactive, real, and apparent) rather than voltage and current. There exist a number of software implementations of power flow studies.

In addition to a power flow study itself, sometimes called the base case, many software implementations perform other types of analysis, such as fault analysis and economic analysis. In particular, some programs use linear programming to find the optimal power flow, the conditions which give the lowest cost per kW generated.

The great importance of power flow or load-flow studies is in the planning the future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from the power flow study is the magnitude and phase angle of the voltage at each bus and the real and reactive power flowing in each line.

1 Data for Power Flow Studies
- 1.1 Ybus or Zbus
- 1.2 Load Data
2 Power Flow Methods

[edit] Data for Power Flow Studies

[edit] Ybus or Zbus

Either the bus self and mutual admittances which compose the bus admittance matrix, (Ybus matrix) or the driving-point and transfer impedances which compose Zbus may be used in solving the power flow problem. Other essential information includes transformer ratings and impedances, shunt capacitor ratings and transformer tap settings.

[edit] Load Data

Operating conditions must always be selected for each study. At each bus, except one, the net real power into the network must be specified. There are always three types of busses namely; load bus, generator bus, and swing or slack bus. At load bus(PQ bus), the real and reactive power are the controlled variables, thus it is always specified and held fix during power flow simulation. For generator bus (PV bus), the controlled variables are the bus voltage magnitude and the real power output of the generator. Swing or slack bus, on the other hand, is treated as a reference bus, thus the voltage magnitude and angle are specified.