Brijesh D. 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]

3 Electrical Engineering Department, Pacific School of Engineering, Surat,
Gujarat,

India.  [email protected]

 

Abstract: In recent trend we are using
interconnected power system to provide power to load. In this system we fulfil
the power requirement by managing power, but when it comes to load side we do
not have any control. So, when the system gets overloaded it goes down and
chances of blackout is high. Now we are introducing load shedding techniques
which will handle the load according to priority. It is a smart system; as load
increases more than its pre-set value, the system will disconnect the least
prior load and so on. With this load shaded power management techniques power
system stability can be enhanced.

Keywords: Load shedding techniques, load
shedding in power system, load management, priority wise load management.

 

1. INTRODUCTION

Blackouts of power systems always have been a
historical problem in interconnected power systems. However, in recent years by
improving monitoring and protection techniques, it is not possible to
completely prevent the blackouts. Sudden and large changes in generation
capacity such as the outage of a generator can produce a sever imbalance
between generation and load demand. This may lead to a rapid decline in
frequency, because the system may not respond fast enough. If voltage and
frequency are get out from permissible range that means the system is in
unstable condition. In this condition the system controllers are operate and
attempt to restore the voltage and frequency in the permissible range. If the
disturbance is so large the controller’s cant restore the voltage and frequency
in the permissible range. In this condition the last solution to avoid the
power system breakdown has been load shedding strategy. Blackout of generation
units is one of critical disturbances that may occur in the interconnected
power systems. In this condition frequency and voltage of power system are
rapidly decline and other generation units will be over load. If the other
generation units can’t suffer this condition, they will be blackout once to
once. Blackouts have irreparable economic effects on interconnected power
systems. In this paper effect of load shedding strategy on restoring the power
system to stable condition and preventing of other blackout in power system
will be study. The system may even collapse in sever imbalances. Rapid and
selective shedding of loads from the system may be a good option to restore the
balance and maintain the system frequency. 1

LITERATURE REVIEWED

Ghazanfar Shahgholian 1, All blackout conditions
that may occur have been investigated. Under frequency load shedding strategy
implement for conditions that frequency decline under the permissible range. According
to simulation results, proper load shedding when a blackout occurs can prevent
of voltage and frequency collapse and blackouts of other generators.

 P. Ajay-D-Vimal
Raj, M. Sudhakaran 2, A simple new method is developed to determine the
optimum location and the optimum quantity of load to be shed in order to
prevent the system voltage from going to the unstable.

Srinu Naik Ramavathu, Venkata Teja Datla, and
Harshitha Pasagadi 3, Abnormal condition in a power system created through
fault or sudden load addition/withdrawn or forced capacity outages or all at a
time generates a huge loss to the utility as well as to the consumers. The loss
reaches to an extreme if the abnormal condition leads to a system blackout.
Hence in this paper different simulation programs were developed for both
traditional load shedding model and existing model.

M.S.Sujatha, Dr M. Vijay Kumar 4, Due to the
shortage of electricity, load shedding is extremely common in India. To
overcome drastically decreasing frequency of the system, usually, load shedding
is performed. Automatic load shedding is required to anticipate and relieve the
overloaded equipment before there is loss of generation, line tripping,
equipment damage, or a chaotic random shutdown of the system.

2. LOAD SHEDDING

To prevent the complete collapse of the system,
Current transformers are used to automatically drop load in accordance with a
predetermined schedule to balance the load to the available generation in the
affected area. Such action must be taken promptly and must be of sufficient
magnitude to conserve essential load and enable the remainder of the system to
recover from the overloading condition. Also, by preventing a major shutdown,
restoration of the entire system to normal operation is greatly facilitated and
expedited.

Where individual operating utility companies are
inter-connected, resulting in a power pool, it is essential that system
planning and operating procedures be coordinated to provide a uniform automatic
load shedding scheme. The numbers of steps, the current levels and the amount
of load to be shed at each step are established by agreement between the power
pool members.

 

3. WORKING

We are using only electromagnetic relays to balance
the 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 at
the time of overloading it can be disconnected partially. When the system is
healthy the system will work normally and nothing changed in that but at the
time of overloading condition current and frequency will differ from its actual
value. Now when the value of current changes more than its permissible limit
the system will detect the overloading area and disconnect the least priority
load from the busbar.

Load shedding will appear when,

Total Generation < Total demand + Total loss Working of load shedding techniques will come in action when all connected generators are at full load capacity and still the load increases. At the time of overloading, the current transformer will sense the higher current passing through it and it gives the signals to relay unit which will disconnect the amount of load which is necessary to balance the system. Instead of disconnecting the whole line or busbar the system will shed the load partially as per predefined priorities of the consumers. In our project we gave first priority to emergency services after that second priority is commercial and industrial sector and at the end least priority to the domestic consumers. There is a timer which will connect line after several hours of disconnection. This timer we have provided will also work priority wise in the manner of it will connect first the most prior load after that second prior load and so on. 4. BLOCKDIAGRAM As shown in basic block diagram that there are two units of generators connected to feeder and at other end there are loads which we separated its type wise. Priority of loads are from top to bottom in decreasing order. C.T. is placed between load and generator which will decide the situation and operation of relay unit. Timer we have provided will reconnect load after some hours or peak period. 5. MATLAB SIMULATION HEALTHY CONDITION Simulation of healthy condition has been done and we can see that there is sever difference in currents of domestic side and industrial load side. We need to make settings of relay which will discriminate this condition of load and it operates reliably because in industrial load the magnitude of current is less than the current in domestic side. Figure 1 Healthy system circuit WAVEFORMS Figure 4 Industrial load   OVERLOAD CONDITION   Figure 5 Overload circuit   RELAY LOGIC CIRCUIT Figure 6 Relay logic diagram Relay logic circuit have been developed for this particular situation but this can be developed as per requirement and as per loading situation which is easy and reliable for our power system. And this logic is developed using existing equipment so no new equipment required for logic circuit. WAVEFORM Figure 7 Overloading condition waveform In overloading condition, the system will disconnect the least prior load and it will balance the system as well as it will maintain constant load on generator which is economically beneficial and it is also provides protection from overloading of system. As shown in waveforms we can see that at 0.2 sec there were disturbance but the relay operated and the system again become stable. 6. CONCLUSION The work presented here will increase reliability of power system as well as it will reduce the chances of fault due to overloading conditions. This project will maintain the power supply priority wise which is one more beneficial for emergency services. This system will also helpful in prevention and prediction of faults. With load shedding satisfactory power distribution can be possible.   7. REFERENCES 1 Ghazanfar Shahgholian, Member, IACSIT, Mahdi Ebrahimi Salary" Effect of Load Shedding Strategy on Interconnected Power Systems Stability When a Blackout Occurs" International Journal of Computer and Electrical Engineering, Vol. 4, No. 2, April 2012 2 P. AJAY-D-VIMAL RAJ, M. SUDHAKARAN "Optimum Load Shedding in Power System Strategies with Voltage Stability Indicators" Engineering, 2010, 2, 12-21 doi:10.4236/eng.2010.21002 Published Online January 2010 (http://www.scirp.org/journal/eng/). 3 Srinu Naik Ramavathu, Venkata Teja Datla, and Harshitha Pasagadi "Islanding Scheme and Auto Load Shedding to Protect Power System" International Journal of Computer Science and Electronics Engineering (IJCSEE) Volume 1, Issue 4 (2013) ISSN 2320-401X; EISSN 2320-4028 4 M.S.Sujatha, Dr M. Vijay Kumar "UNDER FREQUENCY LOAD SHEDDING FOR ENERGY MANAGEMENT USING ANFIS/CASE STUDY" INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), pp. 93-104 5  M. Moazzami and A. khodabakhshian, "A New Optimal Adaptive under Frequency Load Shedding Using Artificial Neural Networks," Proceedings of ICEE 2010, May 11-13. 6  Pukar Mahat, Zhe Chen and Birgitte Bak-Jensen, "Under frequency Load Shedding for an Islanded Distribution System with Distributed Generators," IEEE transactions on power delivery, vol.25, no.2, April. 2010. 7  C.-T. Hsu, M.-S. Kang and C.-S. Chen "Design of adaptive load shedding artificial neural networks "IEE Proc.-Gener. Transm. Distrib., Vol. 152, No. 3, May. 2005 8  S. J. Huang and C. C. Huang, "An adaptive load shedding method with time-based design for isolated power systems," Int. J. Elect. Power Energy Syst., vol. 22, pp. 51–58, Jan. 2000.

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