Detection of Power Quality Problem and Mitigate this by DVR (Dynamic Voltage Restorer)
1Pratyasha Singh, 2Alok Sahu, 3Mahendra Kumar Pradhan
1,2,3
Department of Electronics and Telecommunication, Mats University, Aarang, Raipur
Abstract : In this paper firstly we described the problem of voltage sag and voltage swell. This is very big problem of poor power quality. Now in my work firstly I am detecting the problem of poor power quality which is voltage sag and voltage swell. This problem occurs by the severe impact on non linear load and sensitive load. Now I am prepare a MATLAB Simulink model for detecting the problem of voltage sag and voltage swell. Because in this time the poor power quality is very big issue for industry work and in home also. Voltage sag and voltage swell is detected by the MATLAB model. Then for mitigating this problem I have using a FACTS Device. There are the best FACTS Device which was used in my work is known as DVR (Dynamic Voltage Restorer). The DVR is very popular FACTS Device because it has low cost effective solution for protection of sensitive load. Sensitive load is the big issue of the poor power quality. Now by using DVR mitigate this problem very easily. The simulation result show the problem of voltage sag and swell is not occurring.
Keywords : Power Quality, DVR, Voltage Sag, Voltage Swell, Electrical power quality, Transient disturbances
I. INTRODUCTION
Power Quality problems include a wide range of turbulence such as voltage sags/swells, flicker, harmonics distortion, impulse transient, and interruptions. 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.
The distribution system losses and various power quality problems are increasing due to reactive power. Voltage sags can happen at any instant of time, with amplitudes ranging from 10 – 90% and a duration lasting for half a cycle to one minute. Voltage swell, on the other hand, is defined as a swell is defined as an increase in rms voltage or current at the power frequency for durations from 0.5 cycles to 1 min. Voltage swells are not as important as voltage sags because they are less common in distribution systems. Voltage sag and swell can cause sensitive equipment (such as found in semiconductor or chemical plants) to fail, or shutdown, as well as create a large current unbalance that could blow fuses or trip breakers.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. 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”.
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.
There are lots of different methods to moderate voltage sags and swells, but the use of a custom Power device is considered to be the most capable method. Switching off a large inductive load or Energizing a large capacitor bank is a characteristic system event that causes swells.
This paper introduced the problem of poor power quality (Voltage sag and Voltage swell). This is detected by a simulink model which is designed in MATLAB. When we detect this problem then it mitigate by the DVR (Dynamic Voltage Restorer). By using DVR we get a best power without any problem.
II. 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.
Dynamic Voltage Restorer is series connected voltage source converter based compensator which has been designed to protect sensitive equipments like Programmable Logic Controllers (PLCs), adjustable speed drives etc from voltage sag and swell. Its main function is to monitor the load voltage waveform constantly by injecting missing voltage in case of sag/swell. To obtain above function a reference voltage waveform has to be created which is similar in magnitude and phase angle to that of supply voltage.
During any abnormality of voltage waveform it can be detected by comparing the reference and the actual waveform of the voltage. As it is series connected device so it cannot mitigate voltage interruptions.
Fig.4.1. Standard Configuration of DVR
Fig.4.2. Schematic diagram of a DVR
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.4.2 shows the schematic diagram of a DVR, and Fig.4.3 represents equivalent circuit of DVR system.
Fig.4.3. Equivalent circuit of 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.
III. 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.
IV. 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
V. METHODOLOGY
5.1. Basic Description:
This first model 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.
Now the second model which is shown below is prepared for mitigate the problem of voltage sag and voltage swell. It means the second model is prepared for removing the problem of poor power quality. I am using a DVR (Dynamic Voltage Restorer) circuit for mitigating the problem of poor power quality. We connect a DVR circuit in series with the loads which are used in this model. The main reason of poor power quality is suddenly change the value of load or the non- linear value of load. Then DVR connect with the load this control the value of load if the case of change the value of load. Then the problem of voltage sag and voltage swell was not occurring.
5.2. Power Quality Fundamentals:
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 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
Fig.6.2. Simulation model for mitigate the problem of Poor Power Quality with DVR We are prepared a model for detection of voltage sag
and swell which is shown in Fig.6.1. 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.
Now Fig.6.2 shows the simulation model for mitigate the problem of poor power quality (Voltage Sag and Voltage Swell). When we check the output of the first model which is shown above figure then I get the output with voltage sag and voltage swell in means it gives the poor power quality.
Then I am preparing a model using DVR circuit which is mitigate the problem of poor power quality. Because this problem occurs by the non-linear value of load or suddenly change the value of load. When we connect a DVR circuit in series with the load then this DVR control the non-linear value of the load and I get the output voltage without any problem. That means when I am using a DVR circuit in series with load then there are no power quality problem was occurring.
Now the result shows below, Fig7.1 shows the result of first model which shows the voltage sag occur in output and Fig7.2 which shows the voltage swell occur in output, now Fig.7.3 shows the result of the second model which is prepared by using DVR. There is no voltage sag and swell will be occur, this give a constant output. It means this model remove the problem of voltage sag and voltage swell. This is mitigating the poor power quality. In Fig7.3 show the constant output and in point 0.2 and 0.4 shows the charging and discharging of capacitor
VII. RESULT
Fig.7.2. Result of Voltage Swell
Fig.7.3. Output Voltage plot with DVR
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. And after this I prepare a simulation model to remove the problem of voltage sag and voltage swell by using a DVR. This DVR is connect in series with the load and easily remove the voltage sag and swell from the output which is occur because of non-linear value of load. Then I prepare this model for mitigate the problem of poor power quality.
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.
Alok Sahu and M.Tech coordinator Mr. G S Rathore for 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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