Parmar1,Rahul Rai2, Ritul Varmora3,1 Ass. Professor , Electrical Engineering Department, Pacific School of Engineering,Surat, Gujarat,India. [email protected] 2 Electrical Engineering Department,Pacific School of Engineering, Surat, Gujarat,India.
[email protected] Electrical Engineering Department, Pacific School of Engineering, Surat,Gujarat,India. [email protected] Abstract: In recent trend we are usinginterconnected power system to provide power to load. In this system we fulfilthe power requirement by managing power, but when it comes to load side we donot have any control. So, when the system gets overloaded it goes down andchances of blackout is high. Now we are introducing load shedding techniqueswhich will handle the load according to priority. It is a smart system; as loadincreases more than its pre-set value, the system will disconnect the leastprior load and so on.
With this load shaded power management techniques powersystem stability can be enhanced.Keywords: Load shedding techniques, loadshedding in power system, load management, priority wise load management. 1.
INTRODUCTIONBlackouts of power systems always have been ahistorical problem in interconnected power systems. However, in recent years byimproving monitoring and protection techniques, it is not possible tocompletely prevent the blackouts. Sudden and large changes in generationcapacity such as the outage of a generator can produce a sever imbalancebetween generation and load demand.
This may lead to a rapid decline infrequency, because the system may not respond fast enough. If voltage andfrequency are get out from permissible range that means the system is inunstable condition. In this condition the system controllers are operate andattempt to restore the voltage and frequency in the permissible range. If thedisturbance is so large the controller’s cant restore the voltage and frequencyin the permissible range. In this condition the last solution to avoid thepower system breakdown has been load shedding strategy. Blackout of generationunits is one of critical disturbances that may occur in the interconnectedpower systems.
In this condition frequency and voltage of power system arerapidly decline and other generation units will be over load. If the othergeneration units can’t suffer this condition, they will be blackout once toonce. Blackouts have irreparable economic effects on interconnected powersystems. In this paper effect of load shedding strategy on restoring the powersystem to stable condition and preventing of other blackout in power systemwill be study.
The system may even collapse in sever imbalances. Rapid andselective shedding of loads from the system may be a good option to restore thebalance and maintain the system frequency. 1LITERATURE REVIEWEDGhazanfar Shahgholian 1, All blackout conditionsthat may occur have been investigated. Under frequency load shedding strategyimplement for conditions that frequency decline under the permissible range. Accordingto simulation results, proper load shedding when a blackout occurs can preventof voltage and frequency collapse and blackouts of other generators. P. Ajay-D-VimalRaj, M. Sudhakaran 2, A simple new method is developed to determine theoptimum location and the optimum quantity of load to be shed in order toprevent the system voltage from going to the unstable.
Srinu Naik Ramavathu, Venkata Teja Datla, andHarshitha Pasagadi 3, Abnormal condition in a power system created throughfault or sudden load addition/withdrawn or forced capacity outages or all at atime generates a huge loss to the utility as well as to the consumers. The lossreaches to an extreme if the abnormal condition leads to a system blackout.Hence in this paper different simulation programs were developed for bothtraditional load shedding model and existing model.M.S.Sujatha, Dr M. Vijay Kumar 4, Due to theshortage of electricity, load shedding is extremely common in India. Toovercome drastically decreasing frequency of the system, usually, load sheddingis performed.
Automatic load shedding is required to anticipate and relieve theoverloaded equipment before there is loss of generation, line tripping,equipment damage, or a chaotic random shutdown of the system.2. LOAD SHEDDINGTo prevent the complete collapse of the system,Current transformers are used to automatically drop load in accordance with apredetermined schedule to balance the load to the available generation in theaffected area. Such action must be taken promptly and must be of sufficientmagnitude to conserve essential load and enable the remainder of the system torecover from the overloading condition.
Also, by preventing a major shutdown,restoration of the entire system to normal operation is greatly facilitated andexpedited.Where individual operating utility companies areinter-connected, resulting in a power pool, it is essential that systemplanning and operating procedures be coordinated to provide a uniform automaticload shedding scheme. The numbers of steps, the current levels and the amountof load to be shed at each step are established by agreement between the powerpool members. 3. WORKINGWe are using only electromagnetic relays to balancethe system, which is beneficial in the matter of cost and complexity of system.All equipment is electrical or electromagnetic base so no need of programming. We have connected load as its priority wise so that atthe time of overloading it can be disconnected partially. When the system ishealthy the system will work normally and nothing changed in that but at thetime of overloading condition current and frequency will differ from its actualvalue.
Now when the value of current changes more than its permissible limitthe system will detect the overloading area and disconnect the least priorityload from the busbar.Load shedding will appear when,Total Generation < Total demand + Total lossWorking of load shedding techniques will come inaction when all connected generators are at full load capacity and still theload increases. At the time of overloading, the current transformer will sensethe higher current passing through it and it gives the signals to relay unitwhich will disconnect the amount of load which is necessary to balance thesystem.Instead of disconnecting the whole line or busbar thesystem will shed the load partially as per predefined priorities of theconsumers. In our project we gave first priority to emergency services afterthat second priority is commercial and industrial sector and at the end leastpriority to the domestic consumers.
There is a timer which will connect line after severalhours of disconnection. This timer we have provided will also work prioritywise in the manner of it will connect first the most prior load after thatsecond prior load and so on. 4. BLOCKDIAGRAMAs shown in basic block diagram thatthere are two units of generators connected to feeder and at other end thereare loads which we separated its type wise. Priority of loads are from top tobottom in decreasing order. C.T.
is placed between load and generator which willdecide the situation and operation of relay unit. Timer we have provided willreconnect load after some hours or peak period.5. MATLAB SIMULATION HEALTHY CONDITIONSimulation of healthy condition has been done and wecan see that there is sever difference in currents of domestic side andindustrial load side. We need to make settings of relay which will discriminatethis condition of load and it operates reliably because in industrial load themagnitude of current is less than the current in domestic side. Figure 1 Healthy system circuitWAVEFORMS Figure 4 Industrial load OVERLOAD CONDITION Figure 5Overload circuit RELAY LOGIC CIRCUIT Figure 6 Relay logic diagramRelay logic circuit have beendeveloped for this particular situation but this can be developed as perrequirement and as per loading situation which is easy and reliable for ourpower system. And this logic is developed using existing equipment so no newequipment required for logic circuit.WAVEFORMFigure 7 Overloading condition waveformIn overloading condition, the system will disconnectthe least prior load and it will balance the system as well as it will maintainconstant load on generator which is economically beneficial and it is alsoprovides protection from overloading of system.
As shown in waveforms we cansee that at 0.2 sec there were disturbance but the relay operated and the systemagain become stable.6. CONCLUSION The work presented here will increase reliability ofpower system as well as it will reduce the chances of fault due to overloadingconditions. This project will maintain the power supply priority wise which isone more beneficial for emergency services.
This system will also helpful inprevention and prediction of faults. With load shedding satisfactory powerdistribution can be possible. 7. REFERENCES1 Ghazanfar Shahgholian, Member, IACSIT, MahdiEbrahimi Salary” Effect of Load Shedding Strategy on Interconnected PowerSystems Stability When a Blackout Occurs” International Journal of Computer andElectrical Engineering, Vol. 4, No. 2, April 20122 P. AJAY-D-VIMAL RAJ, M.
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scirp.org/journal/eng/).3 Srinu Naik Ramavathu, Venkata Teja Datla, andHarshitha Pasagadi “Islanding Scheme and Auto Load Shedding to Protect PowerSystem” International Journal of Computer Science and Electronics Engineering(IJCSEE) Volume 1, Issue 4 (2013) ISSN 2320-401X; EISSN 2320-40284 M.S.Sujatha, Dr M.
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