Power Flow Study And SimPower Systems: A Lab Assignment

Following tasks the students are required to be performed by the students:

1. Identify bus type of each of the buses from the data provide in Table 1.
2. Covert bus power data in SI units using system base.
3. Convert transmission line impedance data in SI units.
4. Calculate resistance and inductance of each of the transmission line in SI unit and tabulate them.
5. Construct a SimPowerSystem model of the system under consideration.
6. Perform load flow analysis.
7. Generate a load flow report of the system.
8. 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. Students are required to submit a report on this laboratory work. On campus students  required to individually show their developed SimPowerSystem model during the laboratory works. Cloud students are required to send their model via email to the  lecturer and discuss their results during the Blackboard session.

Building the SimPower Systems Model

Power flow study plays a significant role in planning and design of power systems for future development in addition to determining the best operation of existing systems. Degree and phase angle of voltages at the buses, real and reactive power flowing in a transmission line are the principle facts achieved from a power flow study. SimPower Systems lets you to construct and simulate electrical circuits comprising of linear and nonlinear elements (Karris & Karris 2009). SimPower Systems is skill of the Physical Modeling surroundings. According to LI (2010), Lines that link normal Simulink ports > are referred to as signal lines while those that link terminal ports are known as electrical connection lines. Connection lines are non-directional and can be diverged. But you cannot link them to standard Simulink indication lines.

The key purpose of this laboratory work #1 is to build a model of simple power system by SimPower Systems and execute load flow studies of the system. 

In this lab assignment, we are to simulate a 4 bus power system as shown in below.

• To identify bus type of each of the buses from the data provide in Table 1.  

2. To covert bus power data in SI units using system base.
3. To convert transmission line impedance data in SI units.
4. To calculate resistance and inductance of each of the transmission line in SI unit and tabulate them.
5. We constructed a SimPowerSystem model of the system under consideration.
6. Load flow analysis was then performed.  
7. A load flow report of the system was then generated. 

Types of buses.

The types of bus represented by each bus are as follows:

Bus 1-Swing

Bus 2-Generator

Bus 3-Generator

Bus 4-Generator

Bus power in SI units.

P_base=Q_base=S_base=100 MVA

 P_act= S_base* P_pu    Q_act= S_base* Q_pu   

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		1 00	0	?

Table 1: The actual power values in SI units:

Transmission line impedance in SI units.

S_base=100MVA

V_base=15kV

         Z_act=Z_base*Z_pu

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	0.1225
Line 34	0.3375

Table 2: Transmission Network Data in ohms  

Inductance of the transmission line in SI unit.

Since the lines are lossless therefore the resistances of lines is zero.

X=2*∏*f

Therefore:

Therefore the inductance will be:

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: Inductance  

The simpower system model of the system has been attached to this report. The model is

 an.m file. From the load flow analysis we obtained the following results:

The Load Flow converged in 2 iterations!                                                     

 Sub network No 1 Summary                                                                           

  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 0.00⁰; 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     

Load Flow Analysis Results

   --> 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 12.82⁰                 

        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 -1.78⁰                  

        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 -7.61⁰                  

        Generation:          P= 0.00 MW          Q= 112.24 Mvar     

        PQ_load:              P= 0.00 MW          Q= 0.00 Mvar     

        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 

From the load flow analysis both reactive and active was well balanced through the circuit. At bus 1 generator 1 was supplying both active and reactive power. In addition, the bus was supplying power to all the other buses except that it received real power from bus 2. At bus 2, generator 2 was supplying power to the system. Both real and reactive power was flowing to bus 1 and bus 3 from bus 1. Bus 3, received real power from bus 1 and 2 while it supplied real power to bus 4. However bus 3 supplied reactive power to all the buses. Generator 3, supplied reactive power to the system. Finally at bus 4, generator 4 supplied only reactive power while supplying zero real power to the system. The bus received real power from bus 1 and 3 while supplying reactive power to these buses. 

Conclusion

The magnitude of the voltages in all the buses remained constant at 1 pu therefore operated at a flat voltage profile. However, the phase angle voltages varied from one bus to another. The phase angle voltages at the 3^rd and 4^th bus were lagging while at the 2^nd bus voltage phase angle was leading. The phase angle of the voltage at bus 1 was zero since it was the reference bus.

Reference

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.