Classification Of System Buses & Variables




Classification Of System Buses


The buses can be classified into three types according to known and unknown variables:

1-PQ bus 

At this type , the net power Pi and reactive power are known (PDi&QDi is known from forecasting and PGi&QGi are specified). The unknowns are (Vi & δi ).A pure load bus( no generation facility at the bus ,i.e. (PGi=QGi=0 ) is a PQ bus.

2-PV bus 


At this type , PDi & QDi are known a priori and I Vi I & Pi (hence PGi) are specified. The unknowns are Qi (hence QGi) & δi. Its called also voltage control bus

3-Slack bus


At this type, distinguished from the other two types of buses by the fact that real & reactive powers at this bus are not specified . instead voltage magnitude and phase angle (normally set equal to zero) are specified at this bus .Normally there is only one bus of this type in a given power system.


Classification Of System Variables


Before power flow equation representation , the system variables can be classified into the following:

1-Demand variables:


Which consist of all values of real and reactive load demand p=[Pdi, Qdi], i=1……..n

2-Input (or independent or control) variables:


Which consist of all quantities, that, in principle can be manipulated at will to satisfy load\ generation balance within system operating constraints and objectives. In most cases , it consists of:

§  Voltage magnitude at all generation buses.
§  Real power generation at all but one generation bus.

Note: The remaining generation bus (so-called slack bus) is determined after the problem is solved. This is because the amount of generation is dependent on system losses, which are functions of the problem solution.

§  Switch status of capacitor and inductor banks (open or closed)
§  Tap setting of regulation transformers.

3-State variables:


These are defined as those variables the knowledge of which will enable one to compute all other relevant quantities of interest . in this case , system state variables consists of all complex bus voltage. These can be  expressed in polar or rectangular coordinates. in this case , system state variables consists of all complex bus voltage. These can be  expressed in polar or rectangular coordinates.













4-Output variables:

These are functions of the state ,input, and demand variables. examples of  output variables include:
§  real and reactive line power flows.
§  slack bus real generation.
§  line current magnitudes.
§  reactive generation.
§  injected bus complex currents.
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Ahmad Mohammad

Hi. I’m Designer of Mawsoo3a Blog. I’m Electrical Engineer And Blogger Specializing In Electrical Engineering Topics. I’m Creative.I’m Working Now As Maintenance Head Section In An Industrial Company.

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