• INTRODUCTION
• BASIC TECHNIQUES
• TYPE OF BUSES
• POWER SYSTEM COMPONENTS
• INPUTS REQUIRED
• OUTPUTS WE GET
• CORRECTIVE METHODS
• Power (Load) flow study is the analysis of a power system
in normal steady-state operation.
• This study will determine the following at each location:
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Voltages
Currents
Real power
Reactive power
In a power system under a
given set of load conditions
Purpose:
• Useful to make the feasibility study if a new plant is added.
• To ensure that Generation supplies the demand (load) plus losses.
• To estimate the power demand and losses.
• To expect the future load or Load forecasting.
• To monitor the real time status of the different network
configurations in terms of voltage magnitude and circuit flows at all
buses.
• To check and maintain the voltage profile of the system.
• To ensure bus voltage magnitudes remain close to rated values.
• Generation operated within specified real and reactive power limits.
• Transmission lines and transformers are not overloaded.
Power system components
• Generator
• Transmission Lines
• Load
• In a load flow study, assumptions are made about:
• Voltage at a bus or
• Power being supplied to the bus
For each bus in
the system
Types of Buses
• There are four possible variables that characterize the buses electrical
condition.
• The four variables are
• real and reactive power injection, Pi and Qi,
• voltage magnitude and angle, |Vi| and i , respectively
• Generation Bus
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Also called the P-V bus or voltage-controlled buses
Voltage magnitude |Vi| and real power Pi are specified
Able to specify (and therefore to know) the voltage magnitude of this bus.
Most generator buses fall into this category, independent of whether it also has load
• Load Bus
• Also called the P-Q bus
• Real power Pi and Qi are specified
• All load buses fall into this category, including buses that have not either load or
generation.
• Slack or Swing Bus
• Known as reference bus
• Voltage magnitude |Vi| and phase angle i are specified
• There is only one swing bus, and it can be designated by the engineer to be
any generator bus in the system.
• This generator “swings” to compensate for the network losses, or, one may
say that it “takes up the slack.”
INPUTS REQUIRED:
• Single line connection diagram SLD.
• Base parameters to be considered such as MVA, frequency etc.
• Grid/ Slack bus to be identified.
• Grid code, which defined the minimum and maximum reactive power
flow and minimum and maximum voltage limit criterion.
• Cable parameters such as length, type, size and impedance.
• Transformer details such as type, rating, impedance, vector
configuration and tap range (OLTC/OFTC).
• Generator parameters such as rating and reactive capability curve.
• Type of loads connected etc.
• Library to be created for each element inside database at back end.
Output
• Voltage with angle at each bus.
• Current with angle at each bus.
• Active and reactive power flows at each bus. (Power factor at each
location).
• Cable Under/Over loading.
• Transformer overloading.
• Total generation, demand load and losses in the system.
Corrective methods:
• Transformer taps to be operated in order to bring the voltage of
elements to within the limits which are connected at secondary.
• Shunt capacitors to inject reactive power and to maintain power
factor close to the limit.
Summary
• This will be input for the transient stability and reactive power
capability study.