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.
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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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