Detection of Power Quality Problem (Voltage Sag and Swell)

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Detection of Power Quality Problem (Voltage Sag and Swell)

1Pratyasha Singh, ²Alok Sahu, ³Mahendra Kumar Pradhan

1,2,3Department of Electronics and Telecommunication, Mats University, Aarang, Raipur

Abstract : In this time power quality problem is very big issue for everyone. This problem was affected to system which is used in industry for transfer power from one place to another place. The variation in terminal voltage, transients, and distortions of waveforms are the effects of poor power quality on electric grid. There are different kind of load was connected to the system and when the value of load was changed then this problem was occur.

The use of the non-linear loads in large scale as adjustable speed drives, traction drives, etc and power converters have contributed for the deterioration of the power quality and this has resulted in to a great economic loss. There are two main part of poor power quality i.e. Voltage sag and Voltage Swell. Now firstly we detect the problem of poor power quality (Voltage Sag and Voltage Swell) and it is also necessary to develop the equipment that can mitigate the problem of poor power quality. The most effective flexible ac transmission devices based on the VSI principle are Distribution Static Compensator (DSTATCOM) and the Dynamic Voltage Restorer (DVR). In my work, I have developed a model (matlab simulink model) for detection of power quality problems such as voltage sag and voltage swell and its mitigation using DVR.

Keywords ; Power Quality, DVR, Voltage Sag, Voltage Swell, Electrical power quality, Transient disturbances

I. INTRODUCTION

In this time poor power quality is very big problem for us and this problem occurs by changing the value of load means the load value was not balanced. In Electrical Power distribution networks, it is essential to balance the supply and demand of active and reactive power in an electric power system. If the balance is lost, the system frequency and voltage excursion may occur resulting, in the worst case, in the collapse of the power system. The distribution system losses and various power quality problems are increasing due to reactive power.

Currently electrical power transmission and distribution system face increasing demand for more power, better quality with higher reliability at a lower cost as well as low environmental impact. Present developing countries applying versatile voltage regulation and system stabilization measure, in order to utilize more effectively the latent capacity in existing transmission networks in preference to committing larger resources to new overhead lines and substations.

Power Quality is becoming an important issue as the increase in electricity use continues. The majority of the world today enjoys electricity as a basic commodity for everyday life. As the usage of electricity has increased so has the expectation that the electric power received will meet a standard, which will enable appliances to operate satisfactorily. Electrical appliance manufacturers have designed their products on the basis that a standard of power quality will be available such that their appliances will perform appropriately during consumption of electricity.

The expansion of, electrically sensitive, microprocessor based products into industry, a business and consumer product has forced the production of higher quality electrical power. Another important influence on the need for better power quality has been the deregulation of the electric power industry. The deregulation of the power industry means power delivery services have a greater obligation to provide a high-grade service. “In the new deregulated environment customers will demand higher levels of power quality to ensure proper and continued operation of sensitive equipment and processes”. Thus there is a definite need for enhanced power quality and electricity suppliers have to resolve this problem.

The analysis of power quality in electrical power systems includes the study of transient disturbances as frequency variations, sags, swells, flicker or interruptions. In this project, a measurement system of some transient disturbances i.e. Voltage Sag and Voltage Swell will be detected and further it will mitigated by using FACTS devices. The power quality of a power signal is generally regarded as the relative deviations from an acceptable signal in terms of voltage, current and frequency.

The acceptable power level deviations are based on the successful operation of sensitive devices using the power signal. The problem of achieving an acceptable level of power quality has been a difficult one and many resources (time and hardware) have been damaged due to the poor power quality. Thus, there is a definite power quality problem, which needs to be solved to reduce the losses to industry and consumers. The main features this study will consider are those concerning voltage and current deviations, such as: sags and swell and under and over voltages etc.

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II. VOLTAGE SAGS AND SWELLS

Voltage Sags and Swells are generally short duration falls and rises respectively of the power signal. Voltage sags are a decrease in the nominal voltage from 0.9 p.u.

to 0.1 p.u.. Voltage sags arise from faults on the power system, but also occur by energy of heavy loads, such as large motors starting. Faults on the power system such as single-line-to-ground faults may cause large fault currents and a drop in bus voltages. Sub-station breakers are used to clear these faults, which can occur for a number of cycles.

The starting of heavy industrial machinery often draws large currents and these in turn result in a reduction of the nominal voltage for a short period. A voltage “swell”

is an increase in nominal voltage in the range from 1.1 pu up to 1.8 pu and can last from a fraction of a cycle to 1 minute. Voltage swells can occur during system faults in a similar way to voltage sags. They are also caused by switching off large industrial loads.

III. EFFECTS OF VOLTAGE SAGS AND SWELLS

The effect of voltage sags has been increased in recent times due to the abundant use of computers and other electronic components that rely on consistent voltage levels to transform ac signals to the appropriate on and off states. If voltage sags occur digital based devices can lose memory or produce erroneous results. Voltage swells have similar effects to users as sags, but they can also exceed equipment limits and thus cause damage.

Thus voltage sags have become an important power quality issue in the present age of a heavily computerized industrial sector.

IV. DYNAMIC VOLTAGE RESTORER, (DVR)

Now I have developed a model for detecting the problem of poor power quality (Voltage sag and Voltage swell). Then we know that this all problem occur by this uncontrolled load. Now to mitigate this load problem we connect a FACTS device to this model and the best FACTS device is DVR (Dynamic Voltage Restorer) for mitigate the problem of poor power quality.

The series voltage controller is connected in series with the protected load in fig.1 usually the connection is made via a transformer, but configurations with direct connection via power electronics also exist. The VSC converter generates the reactive power needed while the active power is taken from energy storage. Fig.2 shows the schematic diagram of a DVR, which is a circuit represents the Thevenin’s equivalent circuit of DVR system.

Fig.4.1. Standard Configuration of DVR

Fig.4.2. Schematic diagram of a DVR

DVR is a powerful controller. The DVR is used for detection of voltage sag and swell. This is used for improving voltage quality and power quality of power signal. The DVR employs the same blocks as the D- STATCOM, but in this application the coupling transformer is connecting in series with the AC system in the basic configuration of DVR. There are a VSC (voltage source converter) is connected this circuit which is generate three phase AC output voltage. The output voltage is controllable in phase and magnitude.

Now these voltages are injected into the AC distribution system in order to maintain the load voltage at the desired reference.

V. METHODOLOGY

5.1. Basic Description:

This is a model which is prepared by me for detection of voltage sag and swell. The poor power quality is a very big issue for industry purpose. This is consisting three phase voltage source, a RLC circuit, a step-up transformer and different type of load. Now there are different circuit breaker are used. When we give different value to the circuit breaker than this circuit show the voltage sag and voltage swell. This circuit is basically prepared for detection of voltage sag and swell.

And this model simulate in the MATLAB.

5.2. Power Quality Fundamentals:

The power quality of a power signal is generally

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signal in terms of voltage, current and frequency. The acceptable power level deviations are based on the successful operation of sensitive devices using the power signal.

The problem of achieving an acceptable level of power quality has been a difficult one and many resources (time and hardware) have been damaged due to the poor power quality. Thus, there is a definite power quality problem, which needs to be solved to reduce the losses to industry and consumers. The major types of power system disturbances are:

 Impulsive transients

 Under voltages

 Short Interruptions

 Voltage Swells (surges)

 DC offset (distortion)

 Power Frequency Variations

 Overvoltage

 Voltage sags (dips)

 Harmonics (distortion)

 Notching (distortion)

 Noise (distortion)

 Power frequency variations

The main features this project will consider are those concerning voltage and current deviations, such as: sags, under and over voltages etc. The goal of the artificial intelligence monitoring techniques used will be to recognize a particular power quality deficiency, such as a voltage surge and flag and communicate the problem to appropriate power electronic device capable of rectifying the problem.

5.3. Catalogue of Power Quality Problems:

The two core power quality issues analyzed are:

 Voltage sags and swells

 Frequency deviations

VI. MODELLING AND SIMULATION

Continuous powergui

+v - Voltage Measurement targetV

To Workspace3

inputt To Workspace2 TARGETI

To Workspace1 Vline

To Workspace

AB C ab c

Step

Magabc Phase Sequence

Analyzer

Scope3 Scope2

Scope1

Scope A

B C A B C

RLC

Clock

Tm A m BC 30 MW ,

33 KV A

B C

a2 b2 c2 a3 b3 c3 25 MVA , 11/33 KV

A B C 25 KW

33 KV , 1

A B C

25 KW 33 KV , A

B C 11 KV,

50 Hz ^{A B C}

a b c S3 ^A ^B ^C

a b c

S2 AB C

ab c S1

A B C

RLC Load VabcIabc A

B C ab c

Fig.6.1. Simulation model for detecting Voltage Sag and Voltage Swell

We are prepared a model for detection of voltage sag and swell. Voltage sag and swell is a very big problem of the poor power quality. Now this model is used for detection this problem. And we mitigate this problem by using DVR or DSTATCOM. This model is simulating by using MATLAB. We are using a three phase voltage source and a RLC circuit, and a step down transformer.

This is change the value of 11KV to 33KV. We connect different type of load to this circuit.

There are different type of switch breaker circuit are connected. This was present for give the value for this model. When we are change the value of this breaker circuit then the output give different plot for the voltage sag and voltage swell.

VII. RESULT

7.1. Voltage Sag

Fig.7.1. Result of Voltage Sag

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Fig.7.2. Current Plot of Voltage Sag

Fig.7.3. Line Voltage Plot of Voltage Sag 7.2. Voltage Swell

Fig.7.4. Result of Voltage Swell

Fig.7.5. Current Plot of Voltage Swell

Fig.7.6. Line Voltage Plot of Voltage Swell

VIII. ADVANTAGES

There are many advantages of power quality improvement:

i. The problem of unexpected power supply failures like breakers tripping, a fuse blowing was not occurring.

ii. Because the poor quality of power many types of equipment are fail and equipment overheating is big issue. Then these two problems are avoided by this project.

iii. Increase the life of equipments and decrease the system losses.

iv. When the system received poor quality of power then there was a interference occur in the communication. Now the information was corrupted.

IX. CONCLUSION

A procedure to measure the problem of voltage sag and voltage swell by using the ANN (Artificial Neural Network) has been present. For this type of working we need to design a feedback neural network. This is help to train the back propagation method, using input/output data supply with computer simulation. The method of neural network was satisfied for detection of voltage problem.

Now in my work we studied the simulation and modeling of DVR system and the DVR system is used foe mitigate the problem of voltage sag and voltage swell and poor power quality. In this method we are using PSCAD/EMTDC for simulating and modeling of DVR system. The simulation carried out showed that the DVR provide excellent voltage regulation capability.

Now first we detect the problem of voltage sag and voltage swell then mitigate by DVR system.

X. ACKNOWLEDGEMENT

I sincerely acknowledge for the valuable guidance received from staff of Electronics and telecommunication department of Mats School of Engineering & I.T. I would like to deeply thank our HOD Mr. Mahendra Kumar Pradhan and my Guide Mr.

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giving me the opportunity to share my knowledge in this field. I would also like to thanks all the faculties of our department for giving idea for this presentation.

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