2000A Metamodel for the Analysis and Design of Organisations
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Digital Testing
of
High4oltage
Circuit
Breakers
circuit hreaker
is a
switching device that the
American National Staiidarcls Institute (ANSI)
defines as:
A
mechanical switching device,
capa
ble
of making, carrying,
ancl
breaking currents under nor-
mal circuit conditions and also making, carrying for a
Pieter J j , Schauemaker,i Lou uan der Suis ;
Rent+
PP Smeets VikrorKert&sz2
ence but also an art. Because of the
complex
phenomelia
involved,
circuit breaker
prototypes
have to
be
verified
by
practical tests in the laboratory.
In
high-pnwer labora-
tories,
the ability of circuit breakers to interrupt shart-
circuit currents
is
verificd in
test
circuits, which
are
in
intended to
operate
que
1 al
t
h
oug
h
infre-
some
types
are
suitable
for fre-
quent operation.
High-voltage circuit breakers play an impartant rolc in
transmission and distribution systems. They must clear
faults
and
isolate
faulted
sections rapidly and
reliably. In
short, they must
possess
th e followiiig qualities:
In
closed position, they
are good
conductors
In
open
position, they are excellent insulators
w They
can
close a
shorted circuit quickly and
safely
without unacceptable contact erosion
They
can interrupt a
rated
short-circuit
current, or
lower
current,
quickly without generating an
abnor-
mal voltage.
The only
physical mechanisiii that
can change
in
a
short
period of time from
a
conducting to an insulating state at
a
certain voltage
i s the arc.
It
is
this principle on w h i ch
all circuit breakers are Iiased.
The first circuit breaker
was
developed
by J.N.
Kel-
man in 1901. It was
the
predecessor
of
the
oil
circuit
breaker and capable of interrupting a short-circuit cur-
rent
of
200 to
300 A in a 40 kV
system.
The
circuit
hreak-
er
was
macle u p
of t w o
wooden barrels containing
a
mixture of nil
and
water, in which the contacts
were
immersed. Since then, circuit breaker
design
has
uncier-
gone
a
reinarkable dcvelopment. Nowadays. one
pole
of
a circuit breaker is capable of interrupting ti3
kA
in a 550
1 V
nctwork, with SF,,gas as the arc quenching medium.
Still,
the design of a circuit Iweakcr is not only
a
sci-
Delft l ln ivcrsity
of
Techriolnfiy
KEMA Iii~h-I'(JwerLaboratory
fact lumped
clement representations
of
the
power sys-
tcm. These test circuits must produce the correct wave-
forms
for
t h c
(short-circuit) current as well
a s
for
t h e
voltage
that
strikes th c circuit breakcr immediately after
the breaker has interrupted the test current. The wave-
forms of current and voltage to which the test object
is
subjected are laid down
i n ANSI and
lnternatioiial Elec-
trotechnical Commission (KC) standards.
These
stan-
dardized waveforms represent 9OX
of the
possible fault
conditions in the real system.
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Circuit reaker Switching and Arc
Modeling
The switching action, the basic function oi thc circuit
breaker, refers
to t h e
change from conductor to insula-
tor at a certain voltage.
Be€ore
nterruption, the (short-
circuit) current flows through the arc channet
of
the
circuit breaker.
Bccause of
the nonzero resistance
of
the
arc channel, this short-circuit current caiises a voltage
across the colitacts
of
the circuit breaker: the arc volt-
age. The arc
behaves
as a nonlinear resistance. Thus,
both arc voltage and arc current cross the zero-value at
the same time instant.
f
the arc is coded sufficiently at
the time the current
goes
through zero, the circuit break-
er interrupts the current,
because
thc electrical power
input
is zero.
During current interruption, the arc resis-
tance increases
from
practically zero to alinnst infinite in
microseconds. Immediately aftcr current interruption,
t h e transient recovery voltage builds u p across the cir-
cuit breaker. As
the
gas
mixture
in
the interelectrodc
space does
not change to
a completely
insulating s tate
instantaneously, the arc resistance is finite
at
that time,
and
a sniall
current
can
flow:
thc post-arc current,
Black-box arc models are mathematical descriptions
of
the electrical properties o l the arc. This type
of
model
does
not simulate th e complicated
physical
processes
inside the circuit breaker liut describes
the
electrical
properties
of
the circuit breaker. Measured voltage
and
current traces are
used to
extract the parameters for the
differential equations describing the nonlinear resistance
of the electrical
arc
for that specific measurement.
Digital Testing
The functionality of high-voltage circuit breakers
is
tcst-
ed in high-power laboratories, Due to the
ncccssary
power
and
the physical size of the equipment, testing is
rather expensive and timc consuming. In order t o obtain
as
much information as possible about the degradation
and
operating limits of t h e circuit breaker from the cost-
intensive tests,
a
project started with the following part-
ners: KEMA High-Power Laboratory,
The
Netherlands;
Delft University of Technology, T h e Nethcrlancls;
Siemcris
RG,
Germany; RWE Encrgie,
Germany;
and
Laborelec
cv,
Helgium. This project
is
sponsored
b y
the
Directoratc GeIieral XII
of
the ELiropcan Commission
in
Standards, Measurements, and Testing Prograiii under
contract
number SMt'4-CT96-2121.
The project is aimcd
at developing digital testing
of
high-voltage circuit break-
ers, i.e.,
a
software product for testing of
I
model of such
a device, once
i t s
characteristic fingerprints are ohtaincd
from rcfinecl ineasurements during standard tests. Digi-
tal testing offers
a
wide range of new possibilities for
users, manufacturers, standardizing bodies,
and
test lab-
oratories for fine tuning circuit hreakcr abilities in rela-
tion with standards and
real
power
systems.
Some
developments
arc:
Evaluation of t he relevance of future standar ds
with respect to real power systems
I Evaluation of the relevance of future standards for
different circuit breaker technologies
and
cxtin-
giiishing media
stimation of the circuit breaker's interrupting limit
Reduction of full-scale testing in high-power labora-
tories
w Iclentificatioii of network topologies that can
pose
spccial difficulties lo a circuit brealrer
Acceleration
of
development of new circuit breaker
clcsigns
Monitoring the aging processes f l t circuit breakers
in
service
Expansion O services for high-powcr laboratories.
The steps followed
so far
to enable digital testing are
described in the following sections. At the end of the arti-
cle, examples
of
digital tcsting are presented.
Measurements and Data
Analysis
I-ligh-resolution ineasurcmcnts
of
current and voltage
in
the
critical period around short-circuit current zero
must
supply the necessary parameters, characterizing
the breakers' behavior.
A
tailor-macle high-frequency
measuring system was realized for this purpose. This
system consists
of
a
number
of battery-pciwcred, single-
chaniicl, 40 MHz, 12 bit AD converters, each storing
the
data temporarily
in
on-board local RAM (2Stik
samples
each). The concept
of
on-site data storage is
necessary
for reaching a maximum overall
sysLern
bandwidth,
Cables
to the current and voltage S ~ I I S O ~ San t h u s be
kept
very
short, and thc sys tem can
operate
011 floating
potential. The arc
voltage i s measured with standard
brnad-band RCR-type voltage dividers; current
is
mea-
surecl with
a
spccial Rogowski coil. After
the remote
RAM
is fillcd, data is transmitted serially through optical
fibers to the proccssirig unit i n the c om m a nd ccntcr. The
greatest challenge with respect t o developing the equip-
rneiit in this application design
lies
in the electromagnet-
ic compatibility, since th e microelectronics
has
to
function in an extremely hostile environment of intense
EM fieldsof various origin.
The system relies heavily
on
digital signal processing
methods for reconstructing the actual voltage
and
cur-
rent signals from the raw scnsor output. On
the
one
hand, t h i s h a s to dc) with the specific frequeiicy
response of the sensors and on the other hand, with cor-
rections needed
fnr
the (reproducible) induced voltages
and capacitive current that distort the measured
signals.
'rests
in various laboratorics have proven that
t h c
sys-
tern can measure post-arc current as small as S
mA,
microseconds after the interruption of many tens
of
kA.
Data analysis software has been produced to carry
out the signal reconstruction practically
o n
line during
the tests (Figure
l ,
and to evaluate
the
performance
O
the tcst object. Even the newest profcssionat multipur-
pose
mathematical or laboratory software
is
not
corn-
petitive to this custom-made software considering
April2000
93
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Short-circuit Current
\
L\
Fails
to Break
I
I 1 m s
. . . . . . . . . . . . . . .
I
.,,
.............
Figure
1.
Vdfage
and
c u r r e n t
mensurrment
data
Z gure
2.
Perameter extraction
software
flexibility and speed in visualizing and data processing
of
practically unlimited amount
of
measured data in
a
user-friendly
way.
After an
extensive
series
ol
the most critical fault
interruption duty
for
circuit breakers (the so-called
“short-line fault,”see the section on “Applications
of
Digi-
tal
Testing”),
a
test database
from
various
types
of
com-
0 50
....
0
10
20 30 40 50
O
70
Sequential
Number
of
Tesl
F u r ~
3.
Degradation oPthe circuit b r e d e r poles
mercially available circuit breakers was
set up.
With this
experimental material, an empirical arc model
Iiased
on
classical arc models
was
validated that
gave very good
coverage
of the
observed processes. From the total num-
ber
a
> E O )
interruption attempts, the result
of
the
atte mpt (failure/success) was predi cted correctly in
mo re
than
90 of
the cases
by
evaluating
the
character-
istics
of
the a rc behavior with the model.
The inodel has a set
of (three) parameters, which are
extracted autninatically during the cvaluation
of
each
test (Figure
2 .
Automated analysis
of
th c collection
of
all
the
parameter
sets (in nther words, the breakers’ “finger-
prints“) obtained from a whole series
of
tests makes it
possible to evaluate various physical quantities as a
function
of
test conditions.
The aim of using this method is t o quantify the hreak-
er performance (the margin M
of
interruption), indicat-
ing how successful
the
breaker passed
the
test (M > 0) or
how
far off it is
from passing
it (M
An
example is given in Figure 3, where the clegracla-
tion
of
the three breaker poles (A, B, and C) is presented
during
a
sequence
of
successive tests.
It
can
be
seen
clearly
that the margin of the breaker decrcascs with
every
test. The rate
of
margin
decay
(among others)
s a
Ineasure of the endurance of the breaker with respect
to
this type o t tests.
0).
Arc Circuit Interaction
Software
At
the final
stage of
the realization of digital testing, mea-
sured arc model parameters will be used as input for the
arc model. Of
course,
this arc model behaves a nonlin-
ear
element
in
the electrical circuit ancl must therefore
be analyzed with
a
dedicated
cnmputer
program. The
analysis
of
arc-circuit interaction iiivolving nonlinear clc-
ments
in
relation to
stiff
differential equations
makes
it
necessary
to perform t h e
calculations with
a
variable
step
size
and
adjustable accuracy
of t he
computed cur-
rents, voltages, and canductaiices.
Because
they
have
fixed step-size solvers, EMTP ancl comparable programs
are less suitable for this purpose
and
thercfore
a n e w
approach, the integration of differential algebraic cqua-
tions (DAE) by means of the backward differentiation for-
mulas @DO
method, has been chnsen
in cleveloping
a
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new softwarc package
lor
electrical transients computa-
tion. This
new
transient program, XTrans, has been
developed at the Delft University
of
Technology especial-
ly lor
arc-circuit interaction studies. The program runs
on
a
PC
with
the
MS-Windows operating system
and
works
fully graphical, as shown
in
Figure
4.
The program
is
in
use
at
several high-power and high-voltage laborato-
ries
in
the
world.
The program makes use
of
libraries that contain
infor-
mation about the behavior of element models. The pro-
gram structure is depicted in Figure 5 .
This
structure has
been realized with object-oriented programming. The
compiled code
of t h e
element
m o d e l s is
placed
i n
dynamic link libraries @Us). he models are, thereforc,
separate from
the
main program, which makes it easy to
create new models and use them in the main program.
A full
working demonstration version of
thc
XTrans
program can
h e downloaded rom the
homepage
of
the
electrical power systems group at the
Delft
University of
Technology,
http://eps.et.tuclelft.nl .
Applications of Digital Testing
Influence of
Parallel
Capacitance
Powerful possibilities with digital testing a re created
when the arc model, validated
as
described
in
the sec-
tion on Measurements and Data Analysis, is coupled
with a circuit analysis packagc. Then, the performanceof
a
circuit breaker, the fingerprints of which were obtained
from real tests, can be estimated in circuits other than
the test circuit.
For examptc, the influenceof various standard substa-
t ion
components on the breakers'
capaliilities
can be
estimated through digital testing.
Here the influence of
a
parallel capacitance
is
calculat-
ed
(for
example,
the
parasitic capacitance
at
a
current
transformer, CT,) in the substation.
In
Table 1, the perfor-
mance of
a short-line fault interruption i s compared in
the presence of two types
O
CTs:
CT 1, having
200
pF of
parasitic capacitancc,
and
C1 2, having 400 pP.
These
CTs can be located near the circuit breaker and remote
(the latter implying a n additional 50
pH
of busbar
between CT and breaker). s a reference, the case with-
out CT has a performance
o f
1 .O.
Table 1
shows
that the difference between the two
types
of
CTs
is
rather sinall when compared to the gain
obtained
by
the CT that
was
installed to the breaker as
closely as possible.
Critical
Line
Length
Determination
One of the most severe currents for a circuit breaker to
interrupt
is the
short-line fault (SLF).
In
the case
of a
short-line
fault,
the short-circuit point
is
on
a
high-volt-
age transmission line
a few
kilometers
away
from
the
breaker terminals. After current interruption, a
very
steep, triangular-shaped
waveform
(with a rate of rise
of
5-10
kV/microsecond) stresses
the
extinguishing
medi-
um between the contacts. The percentage SLF indicates
to what extent the short-circuit current is reduced by the
transmission line, e.g., a short-circuit current
of
40 kA is
reduced to 36 kA in case of a 90% SLF In the
IEC
stan-
dard,
75
and
90% SLF
tests are prescribed.
A s
an example
of
digital testing, the critical line
length,
the
short-line fault percentage that
stresses
the
circuit
breaker
most , will be determined
for a 145
kV,
Figure
4.
X Tr ans
transient program
Libraty
Library I
L
_IL __ I__
I
Figure
5.
Structure o f the
XTrnns
transientprogram
http://eps.et.tuclelft.nl/http://eps.et.tuclelft.nl/
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8/15/2019 Ieee Schavenmaker 2000a (1)
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Artificial
Lino
r - - - - - - - - - - 1
_.
- - -
r
I F 3 -
Model
I'
F-*
Figure 6.
A direct SLF
test
circuit i n the XTrans program
31.5
kA,
SF, circuit breaker.
A
direct SLF test circuit
is
shown in Figure 6, hrce different indicators, active at
different
time
intervals (before current zero, at current
zero, and
after current
zero)
are
used
to quantify
t h e
slress
on
the circuit breaker
model.
Before ciirrent
zero:
the t imc
before
current zero
where
the
arc
resistance
equals
thc surge imped-
ance
of
thc transmission line
t H
=
3
he closer
thc
value
is to current zero,
t he
more severe the
breaker
is
stressed by the test circuit.
At current zero: the
arc
resistance XO. The
lower
the arc resistance
value
at the current zero
cross-
ing,
the
stronger the breaker
is
stressed by the
test
circuit.
After current zero: thc post-arc ener.gy Epa. This
value is t h e integral nf the multiplication of the
small post-arc current
and
the recovery voltage. It
is clear that
only
for successful interruptions an
Epa value
can
be calculated. The higher t h e Epa
value is, the mo r e severe the breaker is stressed by
the
test
circuit.
The actual computation s based on 75 current zero
recordings
of the circuit breaker of whi c h t he
circuit
breaker model parameters
have
been determined. For
cwh sct of parameters, the
stress
at the various short-
h i e
fault percentages is computed. At last, the overall
stress is visualized
which
is shown in Figure
7.
All three indicators
show
that the circuit breaker
model
is
stressed most severely at a
93 SI
,F,whereas a
90 SLF is prescribed in the
IEC
standard. This
shows
that digital testing can
h e
applicd
to use
the information
o1)tainecl
from
laboratory tests
for
the development nf
fuuture
stantlards.
Acknowledgments
The authors are indebted to the Ih-ectornte Gencral X1I
of
the Eurc-
penn
Cominissiori
i n
Stiuidartls, Measurements, aiitl l 'esting Program
for sponsoring. The effort
nf
the other pa rtne rs involvcrl in the
project
is greatly appreciated .
Fo r Further Reuding
K.P.P.
Sinccts, V. Kertesz, Lvaluatinn
of
high-vollage circuit Imakcr
performance with a ncw arc
model," IEE
Pmreed iqs ort Gerierorion
1.5
1,4
5 1,2
g
1 3
1 , l
5 1
, 0,9
.-
5 0,8
a,7
W
0 5
8 86 07
00
09 0 91 92
93
94
95
%
SLF
I _
- RO (R=Z)
Epa
Figure Z riticai h e
ength
determination by m e u m f l fd ig td esthi
Tmrisrriission,orid Uislribuliori,
N.I).H.
Hij l
L van
tlcr
Sluis.
Ncw
approach to th e calculatinn of
electricnl transients
,
Ewopetm Trmmtuhms on E clcctrictd Pou; w h g i -
m e r i n g
(ETEO,
Volume 8 . Niiinlicr
3 .
pp. 1 7 5 -1 7 9 arid
181-IR6.
May/June 1998.
Biographies
Pictcr
H.
Scliavemaker
ohtaiiietl his
MSc
in electrical engineering
from
t lw Delft Univcrsity of
Technulqy
i n
1994.
Alter
gratluntion, he per-
Iorinccl r s nr h OIL puwer system s tate estimation with the Power Sys-
tems 1 .abora to ry . In
1995,
lic s t a r t e d as an app l ica t ion eng ineer
programming Stilistatlon Control S ystems with
ABU
in the Netherlands.
Since 1996, he
hns
bccn
with
thc Power
Systems
I.ahoratnry, where h e
is currently assistant prnfessor.
He
is working 011PhD rcscai-cli
011
cligi-
tal testing
of
high-voltage circuit tireakers within the framework of a
Luropenn project. His rnniii rcscarcli inte rests include power
system
transients antl power system calculations. H e is
a
member
1 KEE.
He
can be read ied by E-mail, P.H.Schavcinakc~i ts . tudelf t ,r~l .
Lou van der S l u i s
ob ta ined h is
MSc
i I i e lec t r ica l eng ineer ing
from th e Delft I lniversity of Technology in 1974. H c julrrcd thc
KEMA
High-Powcr
Labriratory in 1977
as a test
enginccr and
was
irivolvcd
in t h e d e v e lo p m e n t of ;t data acquisition system fur thc Higti-Puwer
Laboratory, cornputer calculations of
test
circuits. ancl the analysis
of
test
da ta by digita1 cornputer. In 1990, l i e became a part- l ime pro-
fessor, a n d , s incc 1992, tic
has beer i
employed a s
n
full-t ime profes -
sor a t t h e llelft
Unlvcrsity
1
T c c t i ~ i u l u g yn
the P n w e r S y s t e m s
Depar tment .
He
is a
senior
m e m b e r
of IKEE arid
cor ivc~ic rof WG
CC-03
of Cigrb
and Circd to s tudy t he t rans ien t recovery voltages
in metliutn and high
vo l tage
networks. IIe c a n h e reached by Bmail,
L.vanderSluisQits.tiidellt.nl.
R e d P.P, Smeetsohtninetl
his
MSc in physic s trorl1 tlie Eiridhrwen
University
of Technology
in
1981. Hc
ohtairwtl the PtiD
degree
in 1987
for research work on vaciiiiin
arcs
at tlic sninc university. From 1983 c
1995, tic was a staIf rriember of the Riiergy Systems Ulvision of thc
Fac-
ulty of Electrical Engineering, Einrlhoven Unlvcrsity. During tlie ycar
1991 hc spcrit
a
sddiatical leave
at
'I'oshilm Corporation's Heavy Appa-
ratus EIigiricerinR Laboratory
i n
Japan.
1111995, 11c
joined KEMA for
R8rD
1 thc High-Power Lilboi-atory.
I
IC is
n
memticr of Cigrd WG 13.04,
the Current Zero Club, Cigr6, and the IEEE
I
le
can
he reached hy 1
niail, r.~~.~~.smeetsQkemn.ril.
Viktor Kcrt6az
otitained his
MSc
in electrlcal engincerlng
irotn
Butlapcst University nf TechndoLy iii 19G6, Phi in 1976, and nSc in
1989. Hc jclirlccl the High-Puwer Laboratory
of t h e
Electrical Power
Research Institute,
Uutlapcst,
as
a rcscarcher arid t a t
erigirieer
i n 1966.
He
ihecainc
a
professor of mathematics at the Budapest Ilniversity o l
'I 'ctchiiology n I979 arid has hcld thc chair of full professor s ince 1989.
He has had
n
scicntiflc contact w i th
KEMR
in the iield
of
circuit breaker
measuring
prolilenis
antl the analysis of arc
pticnnmcna slncc 1978.
He
contributed
as
a m e m l w t n C i gr t W(; 13.01 (arc niotlclirig).
He can
tle
reached by
L m a i l ,
kertes7.vQelender.liu.