Faults in the power system

Jun 2 • Engineering Notes, Notes • 11 Views • 3 Comments

Faults in the power system

FAULTS IN THE POWER SYSTEM

FAULTS IN THE POWER SYSTEM

The flow of current to the undesired path and the abnormal stoppage of the currents are termed as faults in the power system

Causes of it in the power system

1.These are caused either by the insulation failure or by the conducting path failure.The failure of the insulation results in the short circuit which may be very harmful as they can damage the equipment of the power system.Most of the faults in the power system are caused by the over voltages due to lightening or switching surges,or by the external conducting objects falling on the overhead lines.over voltages due to lightening or switching surges cause flash over on the surface of the insulators causing short circuits.

2.Some other causes are – direct lightening strokes,aircraft ,ice and snow loading,abnormal loading,earthquake,storms,creepers etc.

3.In case of the cables,transformers,generators and other equipment the causes are-

4.The failure of the solid insulation due to various factors such as aging,heat ,moisture,flash over due to the over voltage etc.

5.Sometimes the circuit breakers may trip due to errors in the switching  operation,testing or maintenance work,wrong connections etc.

Types- as per classification are

1.Three phase fault

2Three phase to ground fault

3.single phase to earth fault

4.Phase to phase fault

5.Double phase to earth fault

6.Simultaneous fault

Basically the faults are of two types

a.symmetrical (balanced) faults

b.Asymmetrical(unbalanced) faults

SYMMETRICAL FAULTS

These are those faults which involves all the three phases.Triple(L-L-L) line and Triple line to ground(L-L-L-g) faults are asymmetrical faults.In this all the three phases are short circuited.

ASYMMETRICAL FAULTS

These faults involves only one or two phases.Single line to ground(L-g),double line(L-L),double line to the ground faults (L-L-g) are asymmetrical faults.

Effects

1.The most  dangerous effect of the fault is the short circuit  and can have the following effects        is uncleared.

2.Heavy short circuit current may cause damage to the equipment or any other element of the system due to overheating and high mechanical forces set up due to the heavy current.

3.The  reduction in the supply voltage of the feeders which are healthy results in the loss of the industrial loads.

4.There may be loss of the system stability.

5.Arcs associated with the short circuits may cause fire hazards.

Effect of the fault impedance

The fault impedance consists of the two components

1)impedance of the arc

2)impedance of the earth.

The second component is present only when it involves the earth fault.and the first rerm appear when the faults due to the short circuit hazzards occurs.An approximate value of the impedances is to be obtained by the empirical’s relations.

 

Per unit Reactance

In this method the values are expressed as the fraction of the reference value.

Per unit reactance= (actual reactance )/(base reactance)

Initially the base KVA or MVA are choosen in the system then,

Base current Ib =(base KVA)/(1.732* base KV)

Base reactance Xb =( KVb /1000)/ (1.732/Ib )

Multiplying the KV at top and bottom

= K Vb2 * 1000/KVAb

EQUIVALENT IMPEDANCE DIAGRAM

Equivalent impedance diagram is defined as the just equivalent diagram representation of the electrical network with the impedance elements by representing the same value of the impedance in between the two terminals as it is in the previous electrical network.

Two element two terminal kind of the network

When the single impedance is in the network then it has two terminals to connect it to the other circuits.Even if the circuit is so simple as one but it cant be predicted about the number of the loops which there by increases the complexity of the circuit along with the number of the elements.

Two element networks consists of the two network elements either in the series or parallel also trivial.The smallest number of the elements i.e. non trivial is three and two non trivial kind of the transformations are possible one being the reverse transformation.

 

equivalent impedance diagram

equivalent impedance diagram

 

RELATED QUESTION-ANSWERS

1.WHAT ARE THE MAIN EFFECTS OF THE FAULTS??

Basically there are various effects of the faults but the most dangerous one is the short circuit which cause various adverse effects if it is uncleared.

The other effects are-

  1. There is the reduction in the supply voltage of the feeders.
  2. The stability of the system can be lost.
  3. Due to the arcs which are generated due to the short circuit can cause fire hazards.

2 WHAT IS MEANT BY THE TERM FAULT IN THE POWER SYSTEM?

Faults in the power system is defined as the current flow to the undesired path and abnormal hindrance in the flow of current in the power system.

3.WHAT ARE SIMULTANEOUS FAULTS??

When one or more faults occur in the system at the same time it is known as the multiple or the simultaneous faults.

4.LIST OUT THE MAIN CAUSES OF IT.

The faults are caused by the

a)Failure in the conducting path or failure in the insulation

b)The lightening and switching surges produce over voltages

c)Fall of external conducting objects on the overhead lines etc.

5.WHAT IS THE EQUIVALENT IMPEDANCE DIAGRAM

It is defined as the equivalent representation of the electrical network along with the impedance elements representing the same value of the impedance in between the two terminals as in the original network.

6.EXPLAIN THE PER UNIT REACTANCE CONCEPT

In the per unit reactance method the values are expressed as the fraction of the reference value.

Per unit reactance= (actual reactance )/(base reactance)

Initially the base KVA or MVA are choosen in the system then,

Base current Ib =(base KVA)/(1.732* base KV)

Base reactance Xb =( KVb /1000)/ (1.732/Ib )

Multiplying the KV at top and bottom

= K Vb2 * 1000/KVAb

GATE syllabus-

1. Gate syllabus for Electrical Engineering 2014

IES Syllabus-

1. IES Syllabus for Electrical Engineering 

2. IES syllabus for General Ability

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  • patlakshi Jha

    Power system is very important in electric life. Any damage or harm can lead to various problems. So we must know about the basic faults in the power system so that it could help us to remove those faults and make it quiet efficient .

  • http://www.facebook.com/dinesh1728 Dinesh

    I am from Tamilnadu here frequent power cut’s become casual, we always used to scroll the electricity board, but after reading this article i came to know about how much pressure they are facing every day, and the questions which you have listed will be very useful in any interview all the best

  • http://www.facebook.com/mithi12 Mitali Panda

    The main source where the power get divided throughout…… the power system faults are the most important to be known as due to a single fault the whole power system can crh down. This above post has shortlisted the causes why this can happen and how to get rid of these kind of problems.

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