EE 456: Power System Analysis I
Multiple Bus System Analysis
(Using Siemen’s PSSE)
Matthew J. Stobb
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Multi-Bus System PSSE Analysis:
Using Siemens’ Power System Simulator for Engineers (PSSE)
System Base Case:
The first part of this project was designed to introduce the concept of the system base case to students as well as allow
them to utilize the PSSE interface to create it. To do this, each student was required to follow the set of instructions
listed for Bus data, Branch data, Machine data, 2-windng data, and Area data to establish all variable needs for this
system. It was important to establish all impedance values in the per unit form for this system to work.
(1)
Bus Data:
For this part of the project, students were required to enter data such as Bus Number, Bus Names, Bus KV,
Area number, Zone number, and owner Number that all corresponded to blanks on the new case used to
describe each of the bus connections. By entering each of these variables we were able to establish multiple
buses and connections that were utilized in other steps of this project.
(2)
Branch Data:
The branch data was useful in establishing transmission line parameters such as line-bus connections, line
resistance and admittance, Charging Base, and other parameters that affect the functionality that the lines
serve in this small multiple bus system. The “Branches” (or Transmission Lines) are modeled as taps in the
system off of each of the pre-determined system buses.
(3)
Load Data:
Establishing the basic load data is important to determine the amount of Pload and Qload that are acting on
each of the lines. This data was pre-determined and was pre-determined by the book design problem and
was entered in by hand.
(4)
Generator Data:
The Generator data was used to determine the amount of power being delivered to the system and to
establish a system minimum and maximum MVAR value. The PGen Value that was selected for this system
was 490MW. The QMax was 250MVAR and the QMin was -100MVAR.
(5)
Transformer Data:
The transformer data was altered in the base case to provide its specified reactive impedances at 0.133pu.
This value was used for both transformers in the system that is being utilized as step down XFMRs for the
lines CROW and SISKIN.
(6)
Bus Codes, Zone Data, Owner Data:
The codes that were implemented correspond to the bus types and which buses that they may be connected
with. The bus codes that were input into the system correspond to the bus types being:
1-PQ buses that connect to loads
2- PV buses that connect to generators
3- Swing bus connects to any one generator
The Zone data corresponds to two different options in this system case. Zone 1 corresponds to an “Urban”
area and is assigned to buses that have the lower voltage levels (69KV). Zone 2 corresponds to a “Rural” area
for the higher voltage lines (161KV).
The Owner Data generally will correspond to the Owner of the selected lines, generators, transformers, and
other equipment used in the system. In a real work environment this would correspond to a company name
such as ITC, CIPCO, or MidAmerican Energy.
Once all necessary data was input into the system base case model, it was then ready for the general system analysis
that can be done with the PSSE command solve. After running the Base Case System Solve function, each of the base
case values that were previously entered were subject to change, depending on how the system reacted based on their
values and properties. And through this we were able to generate a bus diagram for the base case system:
Figure: 1.1
(System Base Case Diagram)
The vital information to find when solving this system was the per unit values of the voltages and the angles for all the
lines within the system. The results that were obtained are as follows:
Figure: 1.2
(Per Unit: Voltage & Angle Values)
The Real and Reactive power flows were also subject to change with this analysis solution. The values that was also
important to find for MW, MVARS, and Currents for all lines, XFMRs, and sending end. They are as follows:
Figure: 1.3
(Generator and Line MW & MVAR Values)
Figure 1.02 denotes the identified bus PU values corresponding to voltages and angles in both normal and emergency
conditions. Normal conditions being the general conditions of operation without dire need for change. Emergency
conditions may be needed for situations such as a fault. The emergency conditions relate to the highest or lowest
ratings of these values in situations of system duress.
Figure 1.03 shows the values of power flows (MW and MVARS) for all lines, XFMRs at the sending end. Located in the
table denoted GENERATORS, contains the information about the generation real and reactive outputs (MW & MVARS).
Multi-Bus Contingency Analysis:
The next step of this project was to change the base case by creating a contingency analysis study. For this study, due to
line congestion, line 5-11 was to be removed to see how the rest of the system would react to such a drastic change in
the system.
To begin the contingency Analysis, we uncheck the “in service” box on the branches tab to disconnect the between
buses 5 and 11.
Figure 2.0
(System Line 5-11 Removed)
The system must then be re-solved using the power flow simulator like was done with the system base case. Once the
system has been solved again, The values have changed and adjusted with the systems needs based on one of the lines
being disconnected. The new per unit voltage and frequency values have changed to the following values:
Figure: 2.1
(Per Unit: Voltage & Angle Values)
The new generation PGen (MW) and QGen (MVAR) values are listed below in figure 2.3. The new adjusted values for
the Lines Pload (MW) and Qload) are listed below in figure 2.3.
Figure 2.3
(Generator and Line MW & MVAR Values)
According to the newly found data that is adjusted to the system change with the removal of the line, the system values
change to compensate for the strain added to the system. Most of the per unit bus voltages and angles increased a little
in with the line removal. The generate data reflects an increase in the QGen (MVAR) variable values and a decrease in
the PGen value of the swing bus. This means that the remove of the branch (line) 5-11 from service will increase the
reactance in the system.