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Power Flow Studies Essay, Research Paper


Power-flow studies are of great importance in planning and designing the future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from a power-flow study is the magnitude and phase angle of the voltage at each bus and the real and reactive power flowing in each line. The best way to find the values of the other parameters is the computer. In our case we use the POWER WORLDE SIMULASION PROGRAM (PWSP). By using this program we can know what happen to the system at any time and we can modify the system and see the change in the system. In this project we will use (PWSP) to simulate the data of the five bus system’s and also to find two solutions to the system.


The line data and the bus data of a five bus system are given below:

The data line table

FROM-TO Impedance(p.u) Total Line Charging(p.u.) Tap position(p.u.) MVA Rating

1 to 2 0.02+j0.072 j0.03 115

1 to 3 .08+j0.288 1.05 115

2 to 3 0.06+j0.216 j0.02 69

2 to 4 .06+j0.216 j0.02 57.5

2 to 5 0.04+j0.144 j0.015 57.5

3 to 4 0.01+j0.036 80.5

4 to 5 0.08+j0.288 j0.025 0.95 57.5

The bus data table

Bus Code Bus Voltage(p.u.) PG(MW) QG(MVAR) PL(MW) QL(MVAR) Qmin(MVAR) Qmax(MVAR)

1 1.06+j0.0 – - 0 0

2 1.02+j0.0 40 – 25 15 20 60

3 – 0 0 65 45

4 – 0 0 70 35

5 – 0 0 0 0

Selecting Options

1- The simulation time requires is two hours with speedup 60s.

2- The load variation is 100% to 200% during the two hours.

3- Showing the animated flows on the single line diagram.

4-Enforce the line overloads

The single line diagram:

By using the data that are in the table and the above options we draw the next single line diagram.

Single line diagram without modification

Problems Faced During Simulation Time:

There were many problems in the above five buses system. The first thing at starting time, the per-unit voltage at bus 3 was .87 p.u., bus 4 was .87 p.u., and at bus 5 was .93 p.u. ,which are not in the range. After 13 minutes line 2-4 near to bus two started to be overload. At 00:28 the same line but near to bus 4 burned. 4 minutes later, the per-unit voltage at bus 2 goes down to .94 p.u. .At 00:40, line 2-3 started to be overload near to bus 2. At 01:01 line 1-2 near to bus 1 overloaded, line 2-4 also overloaded , but near to bus 4, and ‘Line 2-4 overheats! Protective measures take effect’ massage appeared, In the same time the system stopped working ,the next massage appeared direct after the last massage was ‘system can not Longer supply load BLACKOUT!!! Simulation must Be restarted’, line 2-4 was disconnected, all lines that connected to bus 2 burned, also line 1-3 from the direction of bus 3 overloaded. At that time the per-unit voltages at the buses were, bus one 1.00 p.u., bus two .0.85p.u., bus three 0.55 p.u., bus four 0.53 p.u, and bus five 0.73 p.u. . The system changed from the above diagram to the next diagram during one hour and one minute.

Single-line diagram after simulation of 01:01 hour

Commons About The System:

We have in the system two generators that give the power to the system, transmissions lines and transformers to transmit the power, and the loads. These three things consist any power system. For normal operation, the total power supplied by the sources must equal to the total power used by the loads plus the losses that happen during the transmission process. But in our system when the load varies the power that has to transmit through the transmission line more than the maximum power that can be transmitted through the line 2-4. When the line 2-4 disconnected the power that has to be supply by the other lines which means more power will be transmitted through these lines. In this case the power will be more than the maximum, which caused overloaded in these lines. After that the system can not work more, then it stopped.

Solutions To The System:

We faced many problems in our system and the system stopped working before finished two-hour simulation. For that, we will introduce two solutions for the original system

A: First solution :

We fined that the first line overloaded was line 2-4.for that we have to let the power be transmitted through other line from bus 2 to bus 4, but we can not put it in parallel to the original line. There is another way to do that, by increasing the number of the circuit from 1 to 2.By doing this the power that transmitted through line 1-2 will be divided into two line. But the other lines stayed the same. After that I changed the number of the circuit in the other lines and the transformers. By this way the system works for two hours and this means the power transmitted through double line not in one line. But, the per-unit voltage at bus 3, and 4 were not in 1.05-0.95 ring. To increase the per-unit voltage I put capacitor bank at bus 3 and 4. Adding capacitor bank means we supply extra reactive power to these buses. The rating values for both capacitor bank is 80(MVAR).

By doing that the system works for two hours without any problem as in the next diagram.

B: Second Solution:

From the bus-data table we fined that bus 2 has a limiting rang of (MVAR) between 20-60 (MVAR) and from the original single-line diagram we fined that the line 2-4 was the first line overloaded for that we can remove this line as the second solution. But, in this case the power will be supplies by the other lines to bus 2 and 4, which will caused extra power through the other lines that will let the other lines be overloaded. We can solve this problem by changing the circuit number from one to two, this means we doubled the lines and the transformers and this will transmit the power through two parallel lines no in one. The system after these change works without any overload in any line. But, the per-unit voltage at bus 2 and 4 were not in the rang. For that we put capacitor banks at bus 2 and 4 with rating value 80 (MVAR) each. After all these changes the system was simulated without any problem during the two hours. The diagram of the second solution after two hours simulation is :

Second solution after two hours simulation

Comparison and Discussion

The main point that the engineers care about is the cost. My comparison will consider this point. We can say that solution one better than solution two because:

1- we removed complete transmission line that was in the original system(2-4).this means we loss the cost of that line.

2- By removing line 2-4 the power will be supplied to bus 2 and 4 by the other lines, which means more power will be transmitted by these lines, which my overloaded them.

3- In the second solution the capacitor banks have higher rating value (100 MVAR) then the first one (80 MVAR)

4- If we want to change the simulation time ,we will find the first solution till take more time to stop working than the second.


The power flow studies are very important for any power system that will be built. And the best way to get the right solution is the computer program such as (PWSP).This way we can save a lot of many and time.

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