Download .Power`World - A Software Approach to Transmission Line Fault

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.Power'World - A Software Approach to
Transmission Line Fault Analysis
A paper by Prajakta Dhawane under guidance of Prof. S.D.Kulkarni,
Bharati Vidyapeeth University College of Engineering ,
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A6stNcfTIle fad
a.aIysis is doIIe for tile thee
pIIase~..cOicaI fad a..t tile .asya_dricII fads.
TIle 1IaSpI..cOicaI fa.tts iIIdINIe ~
IDle to p1NI••••
IDle•• Iiae ••••••• We be •• pwIDId falllt. TIle ..tIIocI
e.pIoyed is bws _peda8ce ..atriI ftidt lias c:erWa
ana.aca
8YCr •••• aia·s ~
..edIed.. TIle
ana.a,:e of a.is approadlover co.vntioaal ..etIIod is
to make tbe analysis of tbree typical un-symmetrical
faults, namely single-line-to-ground fault, line-to-line
fault and double-line-to-ground fault more unified. So it
is ...a:ssuy
to c..belso.ady
aNlIIed thee scqllellU
Ddworks wItat cakaIatiJIg tile faIIIt voltages at cad ba
r-1IIt ~
~.....
GIICbws •• its
aeigllbo~
hIlS. TIle RSIIHs IIave beeII obWMd asmg
tile POWDtWORLD sm.•••••••.• ftidt _
tile ..etIIod
of Bas "peda8ce MatriL
~
Index Terms- - Bus impedance matrix, faul; analysis,
powerworld; thevenin's equivalent.
I. INTRODUCTION
T
he steady state operating mode of a power
system is balanced 3-phase ac. However due to
sudden external or internal changes in the system,
this condition is disrupted. When the insulation of the
system fails at one or more points or a conducting
object comes in contact with a live point, a short
circuit or fault occurs. A fault involving all the three
phases is known as symmetrical (balanced) fault
while one involving only one or two phases is known
as unsymmetrical fault. Majority of the faults are
unsymmetrical. Fault calculations involve finding the
voltage and current distribution
throughout the
system during the fault. It is important to -determine
the values of system voltages and currents during
fault conditions so that the protective devices may be
set to detect the fault and isolate the faulty portion of
the system.
II.
FAULTS IN A THREE PHASE SYSTEM
Pune
I.
SymmeIrical tbree-phase fimlt
2.
single line-to-ground fimlt (SLG)
3.
Line-w-JU.: fuuIt (LL)
4.
Double1ine-to-ground fimlt (DLG)
The most common type of &ubs by far is the SLG
fiIuJt. fplJowed in frequency of ~
by the LL
fault, DLG fault, and three-phase fault.
Out of the above four faults, two are of the line-toground faults. Most of these occur as a result of
insulator flashover dming eledrical
storms. The
balanced tbree-phase fault is the rarest in occurrence
and the least compJex in 5() far as tlii!fiIuIt current
calculations
are concemed. The other three
uosymmetricaI f.wlts WJlJ require the knowledge and
US(:
of symmetrical
components.
Unsynunetrical
faults cause unbalanced currents to flow in the
system. The method of symmetrical components is a
very powerful tool which makes the calculations of
unsymmetrical
faults almost
as easy as the
calculations of a three-phase fault.
To analyze un-symmetrical faults, one needs to
develop positive-,
negative-,
and zero-sequence
networks of the power system under study, based on
which one further needs to work out the impedance
of three thevenin equivalent circuits as viewed from
faulty point. Then the positive-, negative- and zerosequence components
of phase-a faulty-point-toground current can be calculated. To calculate threephase currents
flowing from one bus to its
neighboring bus and three-phase voltages at each bus,
one needs to connect three sequence networks
uniquely for each type of fault. This may make
circuit drawing very cumbersome. Furthermore by
using the network with three sequence networks
connected,
it is impossible
to appreciate
the
impedance matrix approach to calculate the sequence
voltage at each bus when fault occurs.
To overcome these two drawbacks, paper [1]
introduces a new approach to unify the analysis of
three typical unsymmetrical faults, namely singleline-to-ground
fault, line-to-line fault and doubleline-to-ground fault. This new method allows the
analysis of three typical un-symmetrical
faults to
share all steps except ODe. The only di.ffermt step is
how to calculate the positive-, negative-, and zerosequence components
of pbase-a-to-grou
fdult
current at f.mIty point. It also makes impedance
matrix apptoa:b more unde:rstandabJe when used to
calculate the sequence voltages at each bus.
All the above four fimIts ( L, 2., 3.,4.) are being
solved usiOg the bus impedance matrix and the same
results are obtained from the powerworld simulator.
a
b
c
(0
a
~c=J~_1
(0Zf
Ita ~
b
Ifb ~
c
r
HI. BUS IMPEDANCE MATRIX METHOD
V
----------1jf----------TL..
1
J.R:: ,
We can work out a universal representation of all
three
typical
un-symmetrical
faults.
This
representation is valid with the imposition of
different fault conditions for eacb typical unsymmetrical fault, sucb as for the single-line-toground fault, such as for the single-line-to-ground
fault,
the fault
conditions
being
V ka=ZrIra,
Fig.l. Single line to ground fault
Ifb=Ifc=O.
In the following
a
b
c
formulation,
per-unit
system
is adopted. Zero-sequence oltage at each bus
contributed by equivalent current source is
determined b
--------~--+--------
Zf
Fig.2. Line to line fault
This gives
AV(I)
If
Z(I)
II
Z(I)
12
Z(I)
Z(I)
I.
V(2)
If
_Z(2lJ(2)
lk
fa
AV(I)
2f
Z(l)
21
Z(l)
22
Z(l)
Z(I)
2Il
V (2)
2f
_Z(2)1(2)
21: ra
Z(I)
Z(I)
12
Z(l)
Z(I)
V (2)
kit
b
Z(I)
a2
Z{l)
Z{I)
AV(I)
Irf
=
u
Z(I)
AV(l)
.r
.1
0
_Z{J)I{')
11: fa
0
-Z{I)I(I)
2k
fa
n
n:
••
Ilk
V
-Z (2)1(2)
1:1: fa
(2)
.f
'42?
Z(2)=
~
z!!)
Z!~)
Z!~) Z!~)
-Z (I)I{I)
k1: fa
-~
=
U
-- z!:} --
~
-
4~) ~
--
Z(2)
lk
--
~
o
)
If pre-fault current is ignored, then the pre-fault
voltage at each bus is the same and equal to that at
fault bus k before fault occurs, which is assumed to
be V f . So the positive sequence voltage at each bus
when fault occurs can be written as follows.
~[
If
~'>
1f
=
~J}
J
A~')
~I}
2
A~')
2f
V:<'>
V:<I)
kf
k
=
AV:<')
kf
using powerworld.
v. -z!~~
v. -~~
If
+
Following figure shows the single line diagram of a
four bus system. Let the bus number 4 be faulted. Let
us perform the fault analysis for faults (1.,2.,3.,4.).
v,
+
-Z~~
Fig. 4. SingJe line diagram Iium POWER WORLD
=
Vr£..,;,kit
_?C'I~I)
In a similar way, the negative-sequence
each bus can be computed by
voltage at
TABLE I
SINGLE LINE TO GROUND
FAULT VOLTAGES
DOUBLE LINE TO GROUND FAULT VOLTAGES
-
__
~
••••.
.-,
~
~
~
__
ISai3I
••••
,.-
••••
-
••
«1..1I
-t.iI-
.alii
.u-
••••-
~,
, __
I~----~--~--~
'L
!__
nni
-,
I __
~~
~
~~
, __
un
_
1_1_1
~
:- ..:
!IlIim
.••
_
~
.••
~
u
~
_
.i.-
TABLE V
TABLE
II
IN·LINE
LINE TO LINE FAU LT VOLTAGES
--,- .-- -
)
--
...•
aJIIII!I:S
-ot;JDI
n4
~...
o;c- ••
...••
.,
-as.
....,.
•
~.
••
.....•..
' •••••
TABLE IV
--
..••...
- ~--
--
••.•.•.•••
...
...".
~
u-_
.•,.
J!aI
..;m.s:;
.•....
~
"""
~
'"'"'
•......
~
FAULT VOLTAGES
~I,~~~---------~
••••
me
_~n"71'_jn
IV. CONCLUSION
----..
'----- ~------.•..•...
r_ .---- --
~-----""-.-
.•
••
TABLE III
THREE PHASE BALANCED
FAULT VOLTAGES
~~
~JiIImt
This paper presents a method to tackle typical unsymmetrical fauhs, It is found Ibat the bus impedance
matrix
method
involves
comparatively
less
. computations than the thevenin's equivalent method,
1be software approacb using poweaworld for
analyzing the f.mlts invovlves the use of the stated
method, This further makes the caIcuJations less
tedious. regardless of the complexity of the
powersystem, 1be proposed approach bas another
advantage over- traditional method that it is more
intuitive when matrix approach is adopted to taclde a
fault problem.
V. REFERENCES
,
.
[1] Darning Zhang,"An alternative approach to
analyze un-symmetrical faults in power
system".