Power system security

May 14 • Notes • 4518 Views • 6 Comments on Power system security

Power system security – Introduction

Practically, the power system needs to be secured.We need to protect it from the black out or any internal or external damage.The operation of the power system is set to be normal only when the flow of power and the bus voltages are within the limits even though there is a change in the load or at the generation side. From this we can say that the security of the power system is an important aspect with respect to the continuation of its operation.

A very important aspect of the power system security is its ability to withstand the effect of contingency which is actually an output of either a generator, bus bars, transmission line, transformer etc. The contingency analysis technique is being widely used to predict the affect of the failures in the equipment used in power system. It is quite necessary task so as to keep the power system safe and secured. Though maintaining the security in power system is a challenging work for the engineers but it is even equally important to maintain the state of operation.

Power system security can be divided into two major functions.

Security functionspower system securitypower system security

1. Security control

2. Security assessment

Security control :- It determines the exact and proper security constraint scheduling which is required to obtain the maximized security level.

Security assessment :- It gives the security level of the system in the operating state.

The levels of power system security are classified into 5 states:-

1. Normal

2. Alert

3. Emergency

4. Extreme emergency

5. Restorative

  1. Usually the operation power system in the normal state where the voltages and the frequency of the system are within the range and no overloaded condition occurs.

2.The system is transferred into the next state that is the emergency state if any sort of     disturbance occurs. The system variables are not within the specified limits.

3.The control action which takes place during the emergency state includes generation tripping, generation run backup etc.

4.The system goes back to the further state when the extreme emergency comes into action that is occurrence of extreme disturbance. In this case the power system is in up stable state and may lead to shutting down of the major parts of the power system. Control action should be powerful such that the shedding of the load of the unimportant load are needs to be done.

Contingency

For the power system to be secured there must have continuity in the supply without any loses. Whenever the operating variable are out from the specified limits the power system comes into the emergency system. These violation of the operating variable result into the contingency occurring into the system. Thus an important of the security analysis moves around the power system to with stand affect of  contingency.

 

contingency analysis

contingency analysis

The  contingency analysis is time consuming as it involves computation of load flow calculation followed by the outages from the transmission line, generator, transformer etc.

Contingency analysis

The  contingency analysis basically involves the simulation of ever contingency of the power system. But this analysis involves three major difficulties

1. Difficulty to develop the appropriate power system model.

2. Confusion to choose contingency case.

3. Difficulty in computing the power flow and the bus voltages which leaves to high time consumption.

The contingency analysis is divided into three different stages

1. Contingency definition – It comprise of set of contingency that occur in the power system.

2. Selection – It is the process of selecting the most severe contingencies from the contingency list. Thus this process removes the  unimportant contingencies and hence the contingency list is shortened.

3. Evaluation – In this process it involves the necessary security action or control to function in order to remove the affect of contingency.

contingency analysis using sensitivity factor

It is  one of the easiest calculation way to provide quick calculation of the possible overloads. These factors show the changes in generation on the network configuration and are derived from dc load flow.

The system security assessment is carried out by calculating system operating limits in the pre contingency and post contingency operating states.

Pre contingency – It is the state of the power system before the contingency has occurred.

Post contingency– It is the state of the power system after the contingency has occurred.It is assumed that this type of the contingency has the security violations such as the line or transformer are beyond its flow limit or the bus voltage is within its limit.

Economic dispatch using linear programming formulation

Economic load dispatch means that generator’s real and reactive power are allowed to vary within certain limits so as to meet particular load demand with minimum fuel cost. It is the process of finding out the maximum output from the generation facilities to meet the load demand while serving the power in reliable manner at lowest possible cost.

The economic dispatch problem is defined as the

Min Ft =∑ Fn where n ranges from 1 to n

Subject to Pd =∑Pn where n ranges from 1 to n

Where Ft is the total fuel input to the system

Fn is the fuel input to the nth unit

Pd  is the total load demand

Pn is the generation of the nth unit

 

flowchart of the economic load dispatch

flowchart of the economic load dispatch

By making the use of the Lagrangian multiplier the auxillary function is obtained as

F=Ft +  λ (Pd -∑Pn)

Where λ  is the Lagrangian multiplier

Differentiating the F with Pn and then equating it to zero we get,

δF/ δPn = (δFt/ δPn ) +  λ(0-1) =0

since,

Ft=F1+F2+F3—-+Fn

Λ= δF1/ δP1= δF2/ δP2 =——= δFn/ δPn

Hence dFn/dPn is the incremental production cost of plant n in Rs.per MWhr.

The incremental production cost of the given plant over the limited range is givan by

δF/ δPn = Fnn Pn +  fn

where the Fnn slope of the incremental production cost curve

fn is the intercept of the incremental production cost curve.

Corrective rescheduling

It is basically defined as the measures taken to avoid the the faults after it is occurred i.e.to isolate the defective fault from the non-faulty part of the power system and then further rectify the fault.After the rectification of the fault in the power system it is then restored in the power system from where it was isolated.

Related question and answers

1. What is meant by power system security?

Ans:  The power system needs to be secured, we need to protect it from the black out or any internal or external damage.The operation of the power system is set to be normal only when the flow of power and the bus voltages are within the limits even though there is a profitable change in the load or at the generation side. From this we can say that the security of the power system is an important aspect with respect to the continuation of its operation.

2. What are the two functions of security?

Ans: Security function are of two type as follows:

Security control :- It determines the exact and proper security constraint scheduling which is required to obtain the maximized security level.

Security assessment :- It gives the security level of the system in the operating state.

3. Name the various security level.

Ans:  The levels of power system security are classified into 5 states:-

1. Normal

2. Alert

3. Emergency

4. Extreme emergency

5. Restorative

4. What is contingency analysis?

Ans: The  contingency analysis basically involves the simulation of ever contingency of the power system. But this analysis involves three major difficulties

1. Difficulty to develop the appropriate power system model.

2. Confusion to choose contingency case.

3. Difficulty in computing the power flow and the bus voltages which leaves to high time consumption

5.What is meant by pre and post contingency??

The system security assessment is carried out by calculating system operating limits in the pre contingency and post contingency operating states.

Pre contingency – It is the state of the power system before the contingency has occurred.

Post contingency– It is the state of the power system after the contingency has occurred.It is assumed that this type of the contingency has the security violations such as the line or transformer are beyond its flow limit or the bus voltage is within its limit

6.what is meant by corrective rescheduling??

It is basically defined as the measures taken to avoid the the faults after it is occurred i.e.to isolate the defective fault from the non-faulty part of the power system and then further rectify the fault.After the rectification of the fault in the power system it is then restored in the power system from where it was isolated.

7.explain the term economic load dispatch.

Economic load dispatch means that generator’s real and reactive power are allowed to vary within certain limits so as to meet particular load demand with minimum fuel cost. It is the process of finding out the maximum output from the generation facilities to meet the load demand while serving the power in reliable manner at lowest possible cost.

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6 Responses to Power system security

  1. yeshitela shiferaw says:

    phD scholar

  2. yeshitela shiferaw says:

    phD scholar

  3. Rachita Mishra says:

    This article is about electric power system Which is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region’s homes and industry with power – for sizable regions, this power system is known as the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power to nearby homes and industries.

  4. Palakpuja Panda says:

    This article gives us a lot of information about the power system and its security which is an important factor of electrical science.

  5. Shilpa Ranjan says:

    This article explains about the Power system security. Going through the post can be useful.The concepts are explained with the help of related formula and diagrams..!!!

  6. Ritika Savita says:

    This article takes up a very important issue of safeguarding & providing security to it from various factors. It taks up all the possible causes & its remedies!

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