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OBJECTIVES

To familiarize with power world simulator, how to make a power flow analysis,

contingency analysis, fault analysis and contouring.

Theory

Load flow analysis is probably the most important of all network calculations since it

concerns the network performance in its normal operating conditions. It is performed

to investigate the voltage magnitude, phase angle of the voltage, real and reactive

power [1].

Load flow analysis has a great importance in future expansion planning, in stability

studies and in determining the best economical operation for existing systems. Also

load flow results are very valuable for setting the proper protection devices to insure

the security of the system. In order to perform a load flow study, full data must be

provided about the studied system, such as connection diagram, parameters of

transformers and lines, rated values of each equipment, and the assumed values of real

and reactive power for each load.

Bus Classification

Each bus in the system has four variables: voltage magnitude, voltage angle, real

power and reactive power. During the operation of the power system, each bus has

two known variables and two unknowns. Generally, the bus must be classified as one

of the following bus types [2]:

Slack(swing) bus:

This bus is considered as the reference bus, to supply the real and reactive power

losses in the system which will not be known till the end of the power flow solution.

At this bus, the generator voltage magnitude and its phase angle are specified so that

the unknown power losses are also assigned to this bus in addition to balance of

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generation if any. The voltage angle of the slack bus serves as reference for the angles

of all other bus voltages, the particular angle assigned to the slack bus voltage is not

important because voltage-angle differences determine the calculated values of Pi and

Qi. The usual practice is to set δ=0.

Voltage controlled bus(PV-Bus):

During the operation the voltage magnitude at this the bus is kept constant. Also, the

active power supplied is kept constant at the value that satisfies the economic

operation of the system. Most probably, this bus is connected to a generator where the

voltage is controlled using the excitation and the power is controlled using the prime

mover control (as you have studied in the last experiment). Sometimes, this bus is

connected to a VAR device1 where the voltage can be controlled by varying the value

of the injected VAR to the bus. Certain buses without generators may have voltage

control capability; such buses are also designated voltage-buses at which the real

power generation is simply zero.

Load Bus(PQ-Bus):

This bus is not connected to a generator so that, both real and reactive power drawn

from the system is known.

Many manual methods are used for power flow analysis (i.e. GAUSS-SEIDEL

METHOD); also we could use computer software’s to do this analysis. Large

electrical grid forces you to use these software’s.

In this experiment we used power world simulator, but not just for power flow

analysis, also we use it for contingency and fault analysis.

1 Static Var Compensator (SVC) is one of the advanced power electronics equipment which

provides fast and continuous capacitive and inductive power supply to the power system

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Contingency Analysis

Contingency analysis (CA), as a part of static security analysis, is critical in many

routine power system and power market analyses. Its purpose is to analyze the power

system in order to identify the overloads and problems that can occur due to a

"contingency". A contingency is the failure or loss of an element (e.g. generator,

transformer, transmission line, etc.), or a change of state of a device (e.g. the

unplanned opening of a circuit breaker in a transformer substation) in the power

system. Therefore contingency analysis is an application that uses a computer

simulation to evaluate the effects of removing individual elements from a power

system [3].

After a contingency event, power system problems can range from:

None - when the power system can be re-balanced after a contingency,

without overloads to any element.

Severe - when several elements such as lines and transformers become

overloaded and risk damage.

Critical - when the power system becomes unstable and will quickly collapse.

By analyzing the effects of contingency events in advance, problems and unstable

situations can be identified, critical configurations can be recognized, operating

constraints and limits can be applied, and corrective actions can be planned.

Fault Analysis

The fault analysis of a power system is required in order to provide information for

the selection of switchgear, setting of relays and stability of system operation[4].

Faults usually occur in a power system due to insulation failure, flashover, physical

damage or human error. These faults may either be three phases in nature involving

all three phases in a symmetrical manner, or may be asymmetrical where usually only

one or two phases may be involved.

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Fault types include:

- Single line to ground.

- Line to line.

- Double line to ground.

- Three phase balanced.

Analysis

Power flow analysis.

Figure 1 shows a single line diagram for a simple network, it consists from two buses,

one slack generator and a load.

The following data were inserted to the simulator:

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(Figure 2-A) First bus

(Figure 2-B) Second bus

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Figure (2-C) Transmission line

(Figure 2-D) Slack generator

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We improved this network to have the following single

line diagram:

(Figure 2-E) Load

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Figure 4 shows the new data that were inserted:

Figure (4-A) Third bus

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Exercise

Single line diagram

(Figure 4-C) Second load

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Bus types

Bus number Bus types

1 Slack Bus

2 Load Bus

3 Load Bus

4 PV Bus

Data Collection

Line Data:

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Bus Data

Data analysis

MW analysis:

There are two points of generation:

Generation point MW

At bus 1 187

At bus 4 318

Total 505

And there are four points of MW consumption:

Consumption point MW consumption

At bus 1 50

At bus 2 170

At bus 3 200

At bus 4 80

Total 500

The MW loss is 505 – 500 =5W which is 1% (∆𝑃) .It is mainly due to the resistance

of transmission lines.

Line, bus-bus MW losses

1-2 0.41

1-3 1.27

2-4 1.55

4-3 1.63

Total 4.86

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Building the oneline diagram

The number of busses in the area was:

We used Area/ Zone Filters and we set all areas to "No" except for area IP.

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Then we displayed filters set to ‘yes’, used Case Information/Power Flow List,

entered bus number 32353 and the data we got:

Contingency Analysis

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We choose single transmission line from auto insert/contingency dialog. There were

11 contingences.

Then we processed the contingencies by clicking on Start Run. There were 11 violations.

Fault Analysis

We applied this tool on B7FLAT.PWB case not on B7FaultExample.pwb.

A- Bus fault

Single line to ground fault at bus # 3.

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In line to ground fault, this simulator assumes phase A to ground. We notice that the voltage

on phase A (Bus three) is zero and the fault current is 3.99 p.u. (Angle=-76.46 deg.)

B- In-Line fault

Line-line fault at the mid (location=50%) of the transmission line between bus one and bus

two.

The simulator assumes the fault between phase B and phase C.

We see the magnitude of the fault current is 6.137 p.u.(Angle -130.65 deg.).

Contouring

We applied this tool on B7FLAT.PWB.

We changed the color values to maximum 1.05, and minimum to 0.95, the following

contrast appeared on the diagram:

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We changed the color values to maximum 5, and minimum to 1, but as you can see

there is no contrast in the diagram.

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That’s because in the single line diagram the maximum voltage per unit is 1.05 and

the minimum is 0.95, this range is a small portion for the range 5-1, so there is no

contrast in the diagram.

Conclusion

Load flow analysis is important of all network calculations since it concerns the network

performance in its normal operating conditions. From it you can know two important

parameters, the actual values for the voltage on the busses and ∆P (losses), so that you can

improve your system to have less loss.

Fault and contingency analysis are also important in determining the performance of the

network in its up normal conditions, so that you can know how secure the system is.

Doing these analyses manually is difficult and inaccurate, so we need software to do it. Power

World Simulator is one of these software’s.

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References

[1] http://en.wikipedia.org/wiki/Power_flow_study

[2] http://www.sayedsaad.com/montada/showthread.php?t=11269

[3] http://www.powerworld.com/WebTraining/I10ContingencyAnalysis.pdf

[4] http://www.elect.mrt.ac.lk/EE423_%20Fault_Analysis_Notes.pdf