What is load flow study?
- Voltage magnitude | Vi |
- Active power Pi
- Voltage phase angle δi
- Reactive volt-amperes Qi
Generator Bus
The bus which is used to determine the phase angle and voltage in a specified value of voltage magnitude and active power is called Generator Bus.
Swing Bus
The bus which first respond to a changing load condition wherein the voltage magnitude and phase angle are specified is called Swing Bus.
Load Bus
Buses which are neither generator nor load known as load buses. In this case, active power and reactive volt amperes are specified. The load is considered as the negative generation when any bus in a power system has both load and generator.
As the losses in the system remain unknown until the load flow solution is complete, one of the generator buses is selected as the reference bus. Therefore, one of the generator buses is made for taking the additional real and reactive powers to supply the losses. Hence, this bus is known as Swing bus. The voltage throughout the system should be close to 1. Therefore, the voltage on the slack bus is assigned to 1 per unit. The bus connected to the largest generating station is selected as the slack bus. This bus is numbered as bus 1. In load flow study the single phase representation with positive sequence network is used since power system is usually balanced under normal condition of operation. The voltage of the slack bus is taken as the reference and thus its angle is equal to zero.
The load flow study has the following solution.
- Solving and updating the changes of the values of the voltage and magnitude.
- Considering some values of all the unknown values. It is good to set all the voltage angle to zero value and all the voltage magnitude to 1 per unit value.
- Solving the load flow equations using all the values of voltages, angle and magnitude.
- Stopping condition is checked, if fulfilled, then the process is stopped otherwise repeat the steps again.
Conducting a load flow study assists the engineer in designing electrical systems which work appropriately, have sufficient power supplied by the power grid, where equipment is correctly sized, reactive power compensation is correctly placed and transformer taps are optimized. Software assists in conducting a load flow study conveniently and smoothly. The input of a skilled electrical engineer still requires for obtaining the required design. Therefore, the selection of input data, level of detail to model, verification and interpretation of the output and utilizing this are required. In order to achieve the required system design, a knowledge of the underlying mechanics of what the software is doing will enable the engineer to employ software modelling in his daily activities. A formal Load Flow Study is carried out in larger power distribution systems typically using software, with the results presented in a report.
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