Analysis of unsymmetrical faults single line to ground fault. Fault analysis of an unbalanced distribution system with. It causes the conductor to make contact with earth or ground. This is the first part in the series called fault analysis in power systems, and in this series we will be going over the analysis of various types of faults that occur in power systems and at the same time intuitively understanding the hand calculations involved, now when we are talking about hand calculations we are actually talking about symmetrical.
The most common type of fault on a three phase system by far is the lineto ground lg, followed by the lineto line faults ll, double linetoground l lg. In the analysis of unsymmetrical faults, the following assumptions will be made. Pdf on aug 29, 2009, anamika jain and others published double phase to ground. A line to line fault occurs when two conductors make contacts with each other mainly while swinging of lines due to winds. Chapter 2 deals with the graph theory that is relevant to various incidence matrices required. This factor is the ratio of the rms phase to earth voltage at the fault point during the fault to the rms phase to earth voltage without a fault. The magnitudes of double line to ground fault currents are usually greater than those of line to line faults, but are less than those of three phase faults. Suppose the phase a is connected to ground at the fault point f as shown in a figure below. Single line to ground fault under loaded conditions. Power system analysis is a prerequisite course for electrical power engineering students.
The transmission line fault analysis helps to select and develop a better for protection purpose. A line to line fault occurs when two conductors are short circuited. Double line to ground fault analysis is explained clearly with neat diagrams. In double line to ground faults, two lines come into the contact with each other as well as with ground. Sep 23, 2017 unsymmetrical fault calculations part 27 double linetoground fault problem two generators a and b are of rating 50 mva, 11kv, threephase and 50 hz are connected in parallel and. The use of the positivesequence bus impedance matrix for threephase fault calculations in section 7. K e1 and k e2 are termed the earth fault factors and have a magnitude that typically range from 1 to 1. International journal for research in applied science. Also, since only one phase of the linetoground fault can experience higher interrupting requirements, the threephase fault will still contain more energy.
In this case, fault current will flow from the line to the ground within the involved phases, say, phase b and. Solving double line to ground fault using the mva method sequence networks of a power system can be so interconnected that solving the resulting network yields the symmetrical components of current at the fault. Final notes before visualizing fault analysis currents in p. Single line to ground fault analysis electrical concepts. Load, line, generator, t ftransformer fault analysis. Iib using symmetrical components, solve for the maximum fault current for a bolted threephase fault at location 1. In the figure shown below shows a three phase system with a line to line fault phases b and c. Double line to ground fault llg fault single line to ground fault is the most frequently occurring fault 60 to 75% of occurrence. Quantity generating plant switchyard fault type double line to ground double line to ground fault location 161 kv bus 161 kv bus ground potential rise 387 volts 1639 volts fault current 20. Between 2 and 3 seconds, phase b and phase c currents are almost equal whereas phase a current has lesser magnitude than phase b and c currents because of double line to ground fault. Iic using symmetrical components, solve for the maximum fault current for a phase to ground fault at location 1.
Pdf unbalanced distribution network fault analysis with. The connection of the sequence networks to simulate unsymmetrical double phase to ground fault is shown below. Pdf double phase to ground fault classification and fault distance. The worst type of three phase faults and why it happens. Analysis of faults in overhead transmission lines by. For the protection of transmission line we place the circuit breakers and its rating is depends on triple line fault. The phases are so labelled that the fault occurs on phase a. Lighting strokes cause most faults on highvoltage transmission lines producing a very high transient that greatly exceeds the rated voltage of the line.
Single line to ground fault,line to line fault,double line to ground fault. Method of fault location for double linetoearth faults in distribution. Unbalanced and double line to ground fault detection of three. Double line to ground fault is a type of fault in power system, fault analysis in power system includes the study of double line to ground fault analysis too. In line to ground fault, a conductor makes contact with earth or ground. To illustrate the independence of symmetrical components in balanced networks, consider the transmission line illustrated back in figure 20 of installment 3 of these notes. Pdf fault analysis with hybrid compensation for unbalanced distribution systems is proposed. Iia on a radial distribution feeder, what type of fault do we expect to produce the largest fault current. Fault analysis in unbalanced and unsymmetrical distribution systems. The ll fault is placed between lines b and c so that the fault be symmetrical with respect to the reference phase a which is unfaulted. In this thesis, a short circuit analysis method based on phase domain is.
Lecture notes eee 360 michigan technological university. Fault analysis of an unbalanced distribution system with distributed generation a thesis presented to the graduate school of clemson university. The faulted segment for a 2lg fault is shown in fig. Single line to ground fault lg fault, line to line fault ll fault and double line to ground llg fault are unsymmetrical faults that may occur at any point in a power system. Double line fault occurs when two lines are short circuited. These are less severe faults and its occurrence range may be between 1520%. The expressions for voltage drop in the lines may be written as a single vector expression. Calculation of double line to ground fault currents requires the use of symmetrical components analysis. Types of faults and effects in electrical power systems. That is linetoground fault line to lineto ground, that is double linetoground fault and linetoline faults.
When two lines touch each other and also touch the ground, the fault is called a double linetoground fault. The fault may in general have an impedance z f as shown the current and voltage to ground conditions at the fault are expressed as. Line to ground fault lg is most common fault and 6570 percent of faults are of this type. Pdf fault analysis in unbalanced and unsymmetrical.
In this case, fault current will flow from the line to the ground within the involved phases, say, phase b and phase c. Apr 25, 2018 it is recommended to go through these topics before analyzing single line to ground fault. You must read, concept of symmetrical components and calculation of symmetrical components let us consider a three phase system with earthed neutral as shown below. Aug 05, 2017 the phase current are then found from 10. This fault will occur when any one line is in contact with the ground. The steady state operating mode of a power system is balanced 3phase a. I a, i b and i c are the current and v a, v b and v c are the voltage across the three phase line a, b and c respectively. Double line to ground fault when both phases on the three phase line are accidentally connected to the ground. To analyze a slg fault, denote fault currents in phases a, b, and c as i af, 0, and 0 observe we are not changing the impedance matrix but rather adding a current source. Definition of unsymmetrical faults and symmetrical components. Ground faults for a bolted fault zf is set equal to 0. Unbalanced distribution network fault analysis with. Line toline or double linetoground fault studies may also be required for protective device coordination requirements.
Calculate the line current, fault current, line to neutral voltages and line to line voltages during the occurrence of fault conditions. Calculations of fault condition parameters in the event of a double linetoearth fault on different outgoing power lines were performed under the following. Sep 21, 2017 if a double line to ground fault occurs on y and b phases. Sequence connections for a line to line fault sequences. At the fault point f, the currents out of the power system and the single line to ground fault are constrained as follows. Analysis of faults in overhead transmission lines presented. Learning outlinelearning outline symmetrical components theorysymmetrical components theory sequence impedance. Sample smart ground report lightning protection by.
We present single line to ground, line to line, and double line to ground faults in sections 9. Fault analysis in power systems part 1 power system protection. Nov 12, 2015 heavy winds are the major cause for this fault during which swinging of overhead conductors may touch together. We present single linetoground, linetoline, and double lineto ground faults in sections 9. The analysis results are also summarized in the table below.
460 389 1035 896 733 580 22 1122 1674 12 1124 1216 1522 343 1438 592 1189 1647 106 417 886 1236 1599 1493 1361 1249 759 748 1440 163 1420 863 490 737