The main aim of this laboratory work #1 is to develop model of a simple power system using SimPowerSystems toolbox and perform load flow studies of the system. The following 4 bus power system is considered as the test power system where base power and voltage is considered to be 100MVA and 15kV respectively. It is required to maintain 1pu voltage at every bus of the power system which is commonly known as flat voltage profile.
The transmission network of the power system is loss less. Data related to the transmission network is provided below.
Table 2: Transmission Network Data
Transmission Line |
Reactance (pu) |
Line 12 |
0.15 |
Line 13 |
0.2 |
Line 14 |
0.1 |
Line 23 |
0.1 |
Line 34 |
0.15 |
Following tasks the students are required to be performed by the students:
- Identify bus type of each of the buses from the data provide in Table 1.
- Covert bus power data in SI units using system base.
- Convert transmission line impedance data in SI units.
- Calculate resistance and inductance of each of the transmission line in SI unit and tabulate them.
- Construct a SimPowerSystem model of the system under consideration.
- Perform load flow analysis.
- Generate a load flow report of the system.
- Analyse the load flow result of the system which should include (i) discussion on the power balance of the system, (ii) discussion on the power flow throughout the network, and (iii) voltage magnitude and angle at the buses.
Objectives
Title: Modelling of Simple Power System in SimPower Systems
Power flow study refers to as the arithmetical analysis of the flow of electric power in a power system. The core facets of the power system under investigation include the ac power parameters such as voltage phase angle and voltage magnitudes, real and reactive power flow and effects of errors on those parameters elements (Karris & Karris 2009, p.25). This study plays a vital role in deducing the best operational point of the system and in development of the future expansion of a grid system. Per-unit system and one-line diagram codes help to simplify the study. Simpower systems is one of the toolboxes in mat-lab and comes in handy in power flow study. In this lab assignment, we are required to perform power flow analysis of a simple power system in simpower sytem.
- To determine the type of bus
- To develop a model of a simple power system using SimPower Systems toolbox and perform load flow studies of the system as shown in below.
Loa
Figure 1: Four Bus Power System
Table 1: Bus Power Data
In this lab work the following tasks were performed:
- Identification of bus type of each of the buses from the data provide in Table 1.
- Conversion of bus power data in SI units using system base.
- Conversion of transmission line impedance data in SI units.
- Calculation of resistance and inductance of each of the transmission line in SI unit and tabulation.
- Construction of a SimPower System model of the system under consideration.
- Load flow analysis.
- Generation of load flow report of the system
The types of buses in power system are as follows;
Bus 1-Swing bus
Bus 2-Generator bus
Bus 3-Generator bus
Bus 4-Generator bus
To convert the pu unit values of the system the following formulas are applied:
P_{base}=Q_{base}=S_{base}=100 MVA
P_{act}= S_{base}* P_{pu} Q_{act}= S_{base}* Q_{pu} .................................equation 1
The actual power values are as shown in table 1 below:
Bus # |
Real Power Demand in MW |
Reactive Power Demand in MVAR |
Real Power Generation MW |
Reactive Power Generation MVAR |
1 |
100 |
50 |
? |
? |
2 |
0 |
40 |
400 |
? |
3 |
200 |
100 |
0 |
? |
4 |
200 |
100 |
0 |
? |
TABLE1: Actual values of the bus power data.
Impedance conversion from pu to SI units.
The actual impedance of the transmission lines will be given by:
Transmission Line |
Reactance (ohms) |
Line 12 |
0.3375 |
Line 13 |
0.45 |
Line 14 |
0.225 |
Line 23 |
0.225 |
Line 34 |
0.3375 |
TABLE 2: reactance in ohms
Determination of the resistances and inductances of the transmission lines.
From the information given that the transmission lines are lossless therefore their resistances are zero. The inductances of the lines can determined from the reactance as follows:
X=2*∏*f*L
Therefore:
The inductances were tabulated as shown below:
Transmission Line |
Inductances (mH) |
Line 12 |
1.0743 |
Line 13 |
1.4324 |
Line 14 |
0.7162 |
Line 23 |
0.7162 |
Line 34 |
1.0743 |
Table 3: the inductances of the respective transmission lines.
The power system shown in figure 1 below was constructed in simpower system as shown in figure 2 below and load analysis was performed on the system and report generated below.
Figure 2: Construction of the power system in simpower system.
The construction of the power system model in simpower system is attached to this report as an .slx file and the report as a .rep file. The summary of the report is as follows:
The Load Flow converged in 3 iterations!
Summary for sub network No 1
Methodology
Total generation: P= 500.00 MW Q= 412.78 Mvar
Total PQ load: P= 0.00 MW Q= 0.00 Mvar
Total Zshunt load: P= 500.00 MW Q= 290.00 Mvar
Total ASM load: P= 0.00 MW Q= 0.00 Mvar
Total losses: P= 0.00 MW Q= 122.78 Mvar
1: BUS_1
V= 1.000 pu/15kV 0.00^{0}; Swing bus
Generation: P= 100.00 MW Q=75.66 Mvar
PQ_load: P= 0.00 MW Q= 0.00 Mvar
Z_shunt: P= 100.00 MW Q= 50.00 Mvar
--> BUS_2: P= -147.91 MW Q= 16.62 Mvar
--> BUS_3: P= 15.55 MW Q= 0.24 Mvar
--> BUS_4: P= 132.36 MW Q= 8.80 Mvar
2: BUS_2
V= 1.000 pu/15kV 12.82^{0}
Generation: P= 400.00 MW Q= 88.91 Mvar
PQ_load: P= 0.00 MW Q= 0.00 Mvar
Z_shunt: P= 0.00 MW Q= 40.00 Mvar
--> BUS_1: P= 147.91 MW Q= 16.62 Mvar
--> BUS_3: P= 252.09 MW Q= 32.30 Mvar
3: BUS_3
V= 1.000 pu/15kV -1.78^{0}
Generation: P= 0.00 MW Q= 135.98 Mvar
PQ_load: P= 0.00 MW Q= 0.00 Mvar
Z_shunt: P= 200.00 MW Q= 100.00 Mvar
--> BUS_1: P= -15.55 MW Q= 0.24 Mvar
--> BUS_2: P= -252.09 MW Q= 32.30 Mvar
--> BUS_4: P= 67.64 MW Q= 3.44 Mvar
4: BUS_4
V= 1.000 pu/15kV -7.61^{0}
Generation: P= 0.00 MW Q= 112.24 Mvar
PQ_load: P= 0.00 MW Q= 0.00 Mvar
Z_shunt: P= 200.00 MW Q= 100.00 Mvar
--> BUS_1: P= -132.36 MW Q= 8.80 Mvar
--> BUS_3: P= -67.64 MW Q= 3.44 Mvar
It was deduced that bus 1supplied reactive power to all the other three buses to meet their demands and the losses of the transmission lines. Bus 1 also supplied real power to bus 3 and 4 while receiving real power from bus 2. Bus 2 supplied both reactive and real power to bus 1 and bus 3. Bus 3 received real power from bus 1 and bus 2 while supplying reactive power to bus 4. In addition, bus 3 supplied reactive power to the other buses. Bus 4 received real power from bus 1 and bus 3 while supplying reactive power to the two buses. The actual amount of the power supplied and received from the buses are given the report generated from simpower system model.
Finally, the system maintained a flat voltage profile. The voltage magnitude was maintained at 1 pu/15 kv across all the buses. However the phase angles of the voltages varied in each bus. The phase angle of the voltages in bus 1, bus 2, bus 3 and bus 4 were 0^{0}, 12.82^{0},-1.78^{0} and -7.61^{0}. The angles variations depicted the direction of flow of both reactive and real power.
Conclusion
From the load analysis we can conclude that the power was balanced throughout the power system. The total generation of the power system was 648.4 MVA with a total losses of 122.78 MVAR due to inductances of the transmission line.
References
KARRIS, S. T., & KARRIS, S. T. (2009). Circuit analysis I: with MATLAB computing and Simulink/SimPowerSystems modeling. Fremont, Calif, Orchard Publications. https://www.books24x7.com/marc.asp?bookid=30671.
LI, S. (2010). Power flow in railway electrification power system.
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