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STATISTICAL METHODS FOR IDENTIFYING SMALL DIFFERENCES IN THE THERMAL
INTERRUPTION PERFORMANCE OF SF6 ALTERNATIVES
* August 2023
* Plasma Physics and Technology 10(1):36-39
DOI:10.14311/ppt.2023.1.36
* License
* CC BY 3.0
Authors:
Joseph Engelbrecht
Joseph Engelbrecht
* This person is not on ResearchGate, or hasn't claimed this research yet.
Pawel Pietrzak
* ETH Zurich
Dennis Christen
Dennis Christen
* This person is not on ResearchGate, or hasn't claimed this research yet.
Philipp Simka
* ABB
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References (10)
Figures (4)
ABSTRACT AND FIGURES
This contribution will present thermal current interruption measurements
performed in pure CO2 with a puffer circuit-breaker test device and establish a
statistical method to assess the reignition probability as a function of the
prospective current slope. Its efficacy will be demonstrated with measurements
of the interruption limit scaling with respect to the pressure buildup inside
the test device. A separate contribution will apply these methods to evaluate
the influence of fluorinated additives on the switching performance.
Interrupter region of puffer CB test device.
…
a) Scatter plot of 44 test outcomes in CO2 as a function of blow pressure and
prospective dI/dt (data points may overlap) b) Box-plot representation of
measurement results.
…
a) Histogram of thermal interruption test outcomes as a function of prospective
dI/dt. b) Plot of estimated probability distribution and interruption limit
determined from measurement results.
…
Pressure scaling of thermal interruption limit, and accompanying ∆p fits.
…
Figures - available via license: Creative Commons Attribution 3.0 Unported
Content may be subject to copyright.
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Content may be subject to copyright.
doi:10.14311/ppt.2023.1.36
Plasma Physics and Technology 10(1):36–39, 2023 ©Department of Physics, FEE CTU
in Prague, 2023
STATISTICAL METHODS FOR IDENTIFYING SMALL DIFFERENCES IN
THE THERMAL INTERRUPTION PERFORMANCE OF
SF6
ALTERNATIVES
J. Engelbrecht∗, P. Pietrzak, D. Christen, P. Simka, C. Franck
High Voltage Laboratory, Swiss Federal Institute of Technology Zurich (ETHZ),
8092 Zurich, Switzerland
∗jengelbre@ethz.ch
Abstract.
This contribution will present thermal current interruption measurements
performed in pure
CO2
with a puffer circuit-breaker test device and establish a statistical method to
assess the reignition
probability as a function of the prospective current slope. Its efficacy will be
demonstrated with
measurements of the interruption limit scaling with respect to the pressure
buildup inside the test
device. A separate contribution will apply these methods to evaluate the
influence of fluorinated
additives on the switching performance [1].
Keywords: switching arcs, gas circuit breakers, thermal interruption, CO2,
SF6alternatives.
1. Introduction
A paradigm shift is underway in high-voltage power
transmission, with long-standing
SF6
-insulated de-
signs being phased out in favor of alternatives with
lower global warming potential. A number of pro-
posed solutions for
SF6
-free gas circuit-breakers use
CO2
-based mixtures. In such mixtures the thermal
switching behavior is mainly set by the
CO2
base gas,
making the influence of additives challenging to detect
experimentally. To investigate the switching processes
in these mixtures, a test device based on the puffer
circuit-breaker principle has been developed, enabling
the study of pure gas properties under highly con-
trolled conditions [
2
]. This contribution will present
thermal interruption limit measurements performed
with this device, and establish a statistical method
to assess the reignition probability as a function of
the prospective current slope. The method will be
used to show that the interruption limit in
CO2
fol-
lows a blow pressure scaling of 3
.
1
A
µs√bar
. Using this
approach, the interruption limit may be determined
with an uncertainty much smaller than the scatter of
individual test results, thereby allowing small changes
in interrupting performance to be detected.
2. Methods
Experiments were performed using the setup shown
in Fig. 1, introduced in [
2
]. A hydraulic drive acts to
separate arcing contacts and compress a puffer volume.
This generates a pressure difference ∆
p
that blows cold
gas through the arcing region inside a PMMA nozzle,
cooling and extinguishing the arc at a current-zero
(CZ) crossing. Measurements were performed in
CO2
at a fill pressure of 5
bar
for four blow pressure (i.e.
∆
p
) settings. ∆
p
was varied by changing the opening
speed of the drive via its throttle setting, while the
timing of the drive trigger was adjusted such that
the arc length measured by a linear potentiometer
Figure 1. Interrupter region of puffer CB test device.
was always 43
±
1
mm
at the first CZ crossing. Using
this method the pressure buildup may be controlled
to within
±
100
mbar
, as measured by two transient
pressure sensors located inside the puffer cylinder.
A synthetic test circuit was used to generate the test
conditions: a high-current circuit (HCC) sustained
the arc through the contact opening, and a current-
injection circuit (CIC) controlled the
dI/dt
at CZ and
the transient recovery voltage (TRV) rise, at a fixed
450 Ω surge impedance. This setup allows conditions
at CZ to be controlled with high reproducibility, in-
dependently of the peak HCC current, as the CIC
settings determine the prospective
dI/dt
, while the
puffer-breaker controls the pressure buildup with min-
imal influence from backheating. It should be noted
that this setup produces a sustained TRV rise for
at least 10
µs
, a more prolonged voltage stress than
would be applied in L90-like short-line fault (SLF)
tests at the same
dI/dt
and
du/dt
, where the first
line peak would occur within the first several µs[3].
To determine the thermal interruption limit, the
applied
dI/dt
and TRV must be varied while other
conditions at the interruption instant are held con-
stant. In practice, this was done according to the
procedure introduced in [
4
]: the charging voltage of
the CIC was varied in 1
kV
increments between 15
kV
to
30
kV
, corresponding to changes in the prospective
dI/dt
at CZ of approximately 0
.
33 A
/µs
over a range
from 5 A
/µsto
10 A
/µs
. Sets of 3–7 measurements
36
vol. 10 no. 1/2023 Statistical Methods for Evaluating Interruption Performance
Figure 2. a) Scatter plot of 44 test outcomes in
CO2
as a function of blow pressure and prospective
dI/dt
(data points may overlap) b) Box-plot representation
of measurement results.
were performed at each setting, covering a range from
100% success rate to 100% failure rate, providing a
good measure of the scatter of interruption outcomes.
3. Results & Discussion
3.1. Interruption Limit Determination
A scatter plot showing the outcome of each test per-
formed for one pressure setting in CO2as a function
of the prospective
dI/dt
is presented in Fig. 2a, with
interruption successes and failures indicated by color
and plotted as a function of the measured blow pres-
sure at CZ. Substantial scatter is evident, with both
successes and failures occurring over a 2 A
/µs
range.
In order to determine a limit value from this data, we
define the limit as the
dI/dt
at which there is an equal
likelihood of a reignition or a successful interruption.
The rate of change of the interruption probability with
respect to
dI/dt
should be maximized near this value,
minimizing the uncertainty.
One method for determining the limit is with quan-
tiles chosen to span the overlap of the two distributions.
This can be visualized with the box-plot shown in Fig.
2b. Here the data from the scatter plot is grouped
into two separate distributions for the interruption
successes and failures. To examine only the influ-
ence of the prospective
dI/dt
, all tests are treated as
having the same blow pressure of 5
.
8
±
0
.
1
bar
. The
box-plot denotes the quartiles of both distributions:
the colored regions represent the central 50%, bounded
at the upper and lower quartiles, while the whiskers
extend to the extrema of measured values that lie
within 1.5 interquartile range of the central distribu-
tion, with outliers plotted individually. Taking the
difference between the upper quartile of successes and
the lower quartile of failures provides an estimated
limit of 7
.
6 A
/µs
that can be perceived visually as the
midpoint between the blue and orange boxes.
This approach provides a reliable measure of the in-
terruption limit and a good representation of the scat-
Figure 3. a) Histogram of thermal interruption test
outcomes as a function of prospective
dI/dt
. b) Plot
of estimated probability distribution and interruption
limit determined from measurement results.
ter of test results, however it has several drawbacks.
The method is somewhat sensitive to the sampling
approach; e.g. if more measurements are performed
under low
dI/dt
conditions with a high likelihood
of success than are performed at high
dI/dt
where
more failures are expected, the limit may be skewed
to a lower
dI/dt
value. This issue can be somewhat
mitigated by a careful sampling approach centered on
the interruption limit, but this requires foreknowledge
of the expected limit and reduces flexibility during
testing. The uncertainty of the limit is also difficult
to quantify with this method, despite box-plots pro-
viding a good indication of the range in which the
outcome of an individual test is uncertain.
To establish the uncertainty, it is useful to consider
the data using statistical methods aimed at estimat-
ing the underlying probability distribution. Fig. 3a
contains a histogram with the measurements from Fig.
2. Each bin contains one
dI/dt
setting, and represents
the outcome of
n
independent trials, each of which
had nominally the same probability
p
of a successful
interruption, resulting in
nS
successes and
nF
fail-
ures. The results in each bin are therefore described
by the binomial distribution
B
(
n, nS, p
), where
p
is a
function of the prospective dI/dt.
With this description, an estimate for
p
and its
uncertainty at each
dI/dt
setting can be obtained
using the so-called Wilson score interval [5],
p≈nS+1
2z2
n+z2±z
n+z2rnSnF
n+z2
4,(1)
where
z
is set based on the target confidence level, tak-
ing a value of 1 for an interval spanning 1
σ
uncertainty.
Several methods have been proposed for estimating
37
J. Engelbrecht, P. Pietrzak, D. Christen et al. Plasma Physics and Technology
p
, however the Wilson interval has ideal properties
for describing the present experiment, namely that
it may be reasonably applied to datasets with a low
number of trials and/or values of pnear 0 or 1 [6].
In Fig. 3b, estimated confidence intervals and values
of
p
are plotted beneath the corresponding bins from
the histogram, demonstrating lower uncertainty for
settings with a higher number of trials. These points
indicate the probability of interruption
p
(
dI/dt
)with
meaningful uncertainty, and form a distribution with
empirically known properties.
p
should decrease mono-
tonically with
dI/dt
, approaching 1 at low
dI/dt
and
0 at high
dI/dt
. These properties describe an inverse
cumulative distribution function (ICDF). To evaluate
the interruption limit based on our estimated proba-
bilities, we make the assumption that the underlying
data is normally distributed and therefore can be fit
with a Gaussian ICDF, with the points individually
weighted by their uncertainties. This fit is shown in
Fig. 3b, and corresponds to a normal distribution with
a mean value
µ
= 7
.
6 A
/µs
and width
σ
= 0
.
7 A
/µs
.
For comparison with this fit, an empirical ICDF that
does not rely on assumptions about the distribution is
also useful. Binary datasets do not translate directly
to such an empirical representation, however one may
be estimated using the method proposed by Turnbull,
also plotted in Fig. 3b [7].
By definition,
µ
occurs at the
p
= 0.5 crossing of
the ICDF and so corresponds to the thermal inter-
ruption limit. The uncertainty of the limit is then
equivalent to
σµ
=
σ
n
, the uncertainty in the mean of
the distribution, and
σ
provides an indication of the
scatter around this value, i.e. the region in which the
outcome of an individual trial cannot be predicted
to within 1
σ
confidence. Hence the method yields an
interruption limit of 7
.
6
±
0
.
1 A
/µs
for
CO2
at a blow
pressure of 5
.
8
bar
, but indicates that for at least 84%
certainty of a successful interruption,
dI/dt
should
not exceed 6.9 A/µs.
3.2. Pressure Scaling in CO2
To confirm the efficacy of this method, it was used to
study the scaling of the thermal interruption limit in
CO2
with respect to the blow pressure at CZ. Pres-
sure dependence has been studied thoroughly in
SF6
and shown to scale approximately with
√p
[
8
], while
theoretical models predict the same
√p
scaling inde-
pendent of blow gas [
9
]. Fig. 4shows the results:
the interruption limit determined using the binomial
probability estimation method is plotted with error
bars indicating the limit uncertainty
σµ
. Good agree-
ment is observed between this method and the afore-
mentioned box-plot quantile method, with all data
points lying within the indicated uncertainty. Simi-
lar agreement is observed for the plotted fits to the
function
ap∆p
, with both methods yielding values of
a
= 3
.
1
A
µs√bar
. The expected scatter is indicated by
the shaded blue region in this figure, determined by
fitting the same
ap∆p
function to
µ
+
σ
and
µ−σ
,
providing an uncertainty band that agrees with the
experimentally observed scatter, as evidenced by the
extrema indicated with orange error bars.
An interruption limit of 7
.
7 A
/µs
was determined for
the highest investigated blow pressure of ∆
p
= 6
.
2
bar
.
This finding is comparable to other values reported in
literature: Uchii et al. showed a thermal interruption
limit for
CO2
near 7
.
5 A
/µs
in the absence of signifi-
cant nozzle ablation, however the blow pressure was
not reported [
10
]. Stoller et al. determined a limit
of approximately 11
.
2 A
/µs
at a higher blow pressure
of ∆
p
=11
bar
[
11
]; extrapolation of our fit predicts
a slightly lower limit of 10
.
4 A
/µs
at this pressure.
It should also be noted that this study assumed an
interruption performance scaling with the square-root
of the absolute stagnation pressure
p0
, contrary to our
findings, which suggest that the performance scales
with
p∆p
. Fitting our data instead to
√p0
produces
a noticeable mismatch, with the fit suggesting that
the interruption performance should increase more
slowly with blow pressure than is observed in our mea-
surements. This disagreement lies well outside of our
estimated uncertainty interval, however we note that
several factors influencing the uncertainty have not
been fully accounted for with the present approach,
and will be discussed in the following section.
3.3. Discussion
Without further knowledge of the interruption prob-
ability distribution, the use of a normal distribution
may be questioned. This assumption cannot be con-
clusively tested based on the limited number of ex-
periments performed, however all results show good
symmetry about
p
= 0.5, and the fits agree well with
the estimated empirical ICDF. If the assumed distribu-
tion is incorrect, the calculated interruption limit may
be affected, depending on the asymmetry of the real
distribution about
µ
. Any influence resulting from
such deviation should manifest as a systematic shift
that similarly influences all results, such that relative
comparisons between gases and other experimental
parameters may still be made. Upcoming work will
test this assumption by performing a large number
of trials with the same experimental configuration,
thereby allowing for both the long-term consistency of
the results and the underlying probability distribution
to be better characterized, affording higher confidence
to the stated uncertainties.
Another influence which could not be completely
controlled for throughout the pressure scaling com-
parison is the erosion of the PMMA nozzle. Tests
were performed at reduced peak current, limiting ero-
sion such that the pressure buildup at one experiment
setting of
∼
40 shots remained within the reported
±
100
mbar
uncertainty interval. It was thus inferred
that erosion in the throat region of the nozzle was
minimal, as previous measurements showed a decay
in blow pressure at higher currents with more sig-
nificant erosion. The same nozzle was then used to
38
vol. 10 no. 1/2023 Statistical Methods for Evaluating Interruption Performance
Figure 4. Pressure scaling of thermal interruption
limit, and accompanying p∆pfits.
perform tests at the different pressure settings. Af-
ter the measurement series of
∼
120 shots concluded,
minor erosion of the throat and converging region
of the nozzle was noted, suggesting that the average
flow conditions experienced by the arc may have var-
ied slightly between experimental settings. Looking
ahead to measurements in other
SF6
alternative gas
mixtures, comparisons will always be performed with a
new, un-arced nozzle, and so should share comparable
flow conditions over each measurement series.
In addition to these factors, our results show un-
characteristically late reignition times of up to 10
µs
after CZ [
4
]. Analysis of voltage collapse waveforms,
presented in [
1
], suggests the possibility of a different
failure mechanism for the later reignitions, perhaps
resulting from "hot dielectric" processes, as opposed to
the classical understanding of thermal failures driven
by runaway post-arc current heating. This finding
raises the possibility that the present results under-
estimate the true thermal limit in
CO2
, particularly
for SLF switching duties where the first line peak
occurs only a few
µs
after CZ. The alternative failure
mechanism may also explain the observed differences
in pressure scaling behavior.
4. Conclusions
A method has been demonstrated for determining the
thermal interruption limit in a puffer circuit-breaker
experiment by estimating the underlying probability
distribution. The method was applied to interruption
measurements in
CO2
, and compared with a simpler
approach based on the overlapping quantiles of in-
terruption successes and failures. The two methods
were shown to produce similar results, demonstrat-
ing that the interruption limit scales according to
3
.
1
A
µs√bar
across the four blow pressures investigated.
The probabilistic method allows for better estimation
of the likelihood of a successful interruption at an ar-
bitrary
dI/dt
setting, and of the certainty with which
the interruption limit may be determined based on
the measurements. The suitability of this method is
limited to experimental configurations where all test
conditions are able to be reproduced to a high degree
of precision, however it has been shown that in such
conditions and with a sufficient number of trials, the
interruption limit may be determined with a degree of
certainty much higher than suggested by the width of
the scatter. Such precision may prove invaluable when
assessing the influence of minor changes to experimen-
tal parameters including gas mixture composition, arc
length, and nozzle design.
Acknowledgements
The authors would like to thank Enrico Graneris, Fabian
Mächler, Mahir Muratovic, and Martin Seeger for their
valuable contributions to this work, which was made possi-
ble by financial support from Hitachi Energy Switzerland.
References
[1] P. Pietrzak et al. Thermal arc interruption performance
of CO2and CO2/C4F7N mixture. To appear in 24th
Symposium on Physics of Switching Arc, 2023.
[2] C. Franck et al. Comparative Test Program
Framework for Non-SF6 Switching Gases. B&H
Electrical Engineering, 15:19–26, 2021.
doi:10.3929/ethz-b-000508915.
[3] D. Peelo. Current Interruption Transients Calculation,
chapter 5, pages 111–123. John Wiley & Sons, Ltd,
2020. ISBN 9781119547273.
doi:10.1002/9781119547273.ch5.
[4] J. Engelbrecht et al. Evaluating conductance decay and
post-arc current in axially blown
CO2
arcs. To appear in
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and statistical inference. Journal of the American
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[7] B. W. Turnbull. Nonparametric estimation of a
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[8] A. Plessl. The Influence of Pressure Profiles on Gas
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39
CITATIONS (0)
REFERENCES (10)
ResearchGate has not been able to resolve any citations for this publication.
Binomial Confidence Intervals and Contingency Tests: Mathematical Fundamentals
and the Evaluation of Alternative Methods
Article
Full-text available
* Jul 2013
* Sean Wallis
Many statistical methods rely on an underlying mathematical model of probability
based on a simple approximation, one that is simultaneously well-known and yet
frequently misunderstood. The Normal approximation to the Binomial distribution
underpins a range of statistical tests and methods, including the calculation of
accurate confidence intervals, performing goodness of fit and contingency tests,
line- and model-fitting, and computational methods based upon these. A common
mistake is in assuming that, since the probable distribution of error about the
“true value” in the population is approximately Normally distributed, the same
can be said for the error about an observation.This paper is divided into two
parts: fundamentals and evaluation. First, we examine the estimation of
confidence intervals using three initial approaches: the “Wald” (Normal)
interval, the Wilson score interval and the “exact” Clopper-Pearson Binomial
interval. Whereas the first two can be calculated directly from formulae, the
Binomial interval must be approximated towards by computational search, and is
computationally expensive. However this interval provides the most precise
significance test, and therefore will form the baseline for our later
evaluations. We also consider two further refinements: employing log-likelihood
in intervals (also requiring search) and the effect of adding a continuity
correction.Second, we evaluate each approach in three test paradigms. These are
the single proportion interval or 2 × 1 goodness of fit test, and two variations
on the common 2 × 2 contingency test. We evaluate the performance of each
approach by a “practitioner strategy”. Since standard advice is to fall back to
“exact” Binomial tests in conditions when approximations are expected to fail,
we report the proportion of instances where one test obtains a significant
result when the equivalent exact test does not, and vice versa, across an
exhaustive set of possible values.We demonstrate that optimal methods are based
on continuity-corrected versions of the Wilson interval or Yates’ test, and that
commonly-held beliefs about weaknesses of tests are misleading. Log-likelihood,
often proposed as an improvement on , performs disappointingly. Finally we note
that at this level of precision we may distinguish two types of 2 2 test
according to whether the independent variable partitions data into independent
populations, and we make practical recommendations for their use.
View
Show abstract
Nonparametric Estimation of a Survivorship Function with Doubly Censored Data
Article
* Mar 1974
* Bruce W. Turnbull
A simple iterative procedure is proposed for obtaining estimates of a response
time distribution when some of the data are censored on the left and some on the
right. The procedure is based on the product-limit method of Kaplan and Meier
[15], and it also uses the idea of self-consistency due to Efron [8]. Under
fairly general assumptions, the method is shown to yield unique consistent
maximum likelihood estimators. Asymptotic expressions for their variances and
covariances are derived and an extension to the case of arbitrary censoring is
suggested.
View
Show abstract
Probable Inference, the Law of Succession, and Statistical Inference
Article
* Jan 1927
* Edwin B. Wilson
View
CO_{2} as an Arc Interruption Medium in Gas Circuit Breakers
Article
* Aug 2013
* Patrick Stoller
* Martin Seeger
* Arthouros A Iordanidis
* G. V. Naidis
CO2 is a possible alternative to SF6-which has a high global warming
potential-as the interruption medium in gas circuit breakers. The performance of
CO2 is investigated in this paper by carrying out experiments in representative
test devices and by performing computational fluid dynamic (CFD) simulations;
some comparisons with SF6 and air are given. It is found that the thermal
interruption performance of CO2 is lower than that of SF6, but higher than that
of air. The measured dielectric recovery after arcing is compared for CO2 and
SF6; a streamer model is used to calculate the breakdown voltage in CO2; good
agreement with measurement is found. The speed of sound and the adiabatic
coefficient, important parameters that influence pressure buildup and gas flow,
are compared for SF6, CO2, and air. CFD simulations of the pressure buildup in
CO2 and SF6 both illustrate the qualitative differences between the two and show
good agreement with measurements.
View
Show abstract
Current interruption limit and resistance of the self-similar electric arc
Article
* Jun 2005
* Thomas Christen
* Martin Seeger
A model for the axially blown cylindrical arc is derived. In contrast to earlier
theories, the model is gauge invariant with respect to energy, which is crucial
for investigating current interruption. We determine from our model the
dependence of the maximum interruptible current rate, (dI/dt)<sub>L</sub> , on
the pressure, on the parallel capacitance, and on the line impedance for an SF
<sub>6</sub> arc. (dI/dt)<sub>L</sub> scales, approximately independent of the
gas type, with the square root of the pressure. The arc resistance, at current
zero with current rate equal to (dI/dt)<sub>L</sub> , is pressure independent.
As a consequence, the arc resistance at current zero can serve as a figure of
merit for the interruption performance of gas circuit breakers.
View
Show abstract
Thermal interruption capability of carbon dioxide in a puffer-type circuit
breaker utilizing polymer ablation
Conference Paper
* Nov 2002
* Toshiyuki Uchii
* Takeshi Shinkai
* K. Suzuki
When adopting an alternative arc quenching gas to SF<sub>6</sub> which has
recently been recognized as a greenhouse gas, it is easily anticipated that the
thermal interruption capability of the GCB will be lower than that in using
SF<sub>6</sub>. In this paper, adopting CO<sub>2</sub> as an alternative gas,
the means utilizing ablation phenomenon of polymer materials as one of the
breakthrough technologies compensating the drop in the interruption performance
will be proposed and tested by a full-scaled GCB model. As a result, a change in
the blasting pressure characteristics was observed, and also the peak pressure
for the ablation application model was about 1.3 times higher than that of the
conventional model without the ablation element. Furthermore, even if compared
at the same blasting pressure condition at current zero, the thermal
interruption capability of the CO<sub>2</sub> gas in the ablation application
model was presumed to be improved with comparison to the conventional model
without the ablation element. The thermal interruption capability of the
CO<sub>2</sub> gas in the ablation application model could be estimated to be
about 50 % of that of SF<sub>6</sub> gas in the conventional model in this
interrupting test.
View
Show abstract
Thermal arc interruption performance of CO2 and CO2/C4F7N mixture
* Jan 2023
* P Pietrzak
P. Pietrzak et al. Thermal arc interruption performance of CO2 and CO2/C4F7N
mixture. To appear in 24th Symposium on Physics of Switching Arc, 2023.
Comparative Test Program Framework for Non-SF6 Switching Gases
* Jan 2021
* 19-26
* C Franck
C. Franck et al. Comparative Test Program Framework for Non-SF6 Switching Gases.
B&H Electrical Engineering, 15:19-26, 2021. doi:10.3929/ethz-b-000508915.
Current Interruption Transients Calculation
* 111-123
* D Peelo
D. Peelo. Current Interruption Transients Calculation, chapter 5, pages 111-123.
John Wiley & Sons, Ltd, 2020. ISBN 9781119547273. doi:10.1002/9781119547273.ch5.
Evaluating conductance decay and post-arc current in axially blown CO2 arcs
* Jan 2023
* J Engelbrecht
J. Engelbrecht et al. Evaluating conductance decay and post-arc current in
axially blown CO2 arcs. To appear in Proc. of the XXIII Int. Conf. on Gas
Discharges, 2023.
Show more
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* [...]
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In recent years, significant achievements have been made with respect to the
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currently proposed by manufacturers for SF 6 replacement. The basic analysis
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p>A free-burning arc experiment was performed in a gas mixture composed of CO2
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expansion angle of the electrode jet is estimated from the concentration of
metal vapor in the arcing region at different axial positions, using a basic
conical expansion model. The dependence of the measured voltage on the arc
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June 2022
* Joseph Engelbrecht
* Pawel Pietrzak
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p>A free-burning arc experiment was performed in a gas mixture composed of CO2
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current is varied, and a transition threshold for increased ablation at
electrode current densities above 50A/mm<sup>2</sup> is determined. The
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metal vapor in the arcing region at different axial positions, using a basic
conical expansion model. The dependence of the measured voltage on the arc
composition is examined, and a positive correlation between Cu content and arc
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June 2022
* Pawel Pietrzak
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p> Abstract—Voltage-current characteristics of free burning arcs in SF6 and air
have been known for decades. As the demand for an SF6-free solution is
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the voltagecurrent characteristics of SF6 alternative gases, which have not yet
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burning arc measurements were performed in a number of gases under consideration
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also performed in air and SF6 for comparison. Arc voltage was measured in each
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and SF6 show good agreement with previously published results. A linear
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influence on the voltage-current characteristic. The minimum arc voltage in all
measured gases was slightly higher than in SF6, but the arc in SF6 was the least
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View full-text
Last Updated: 03 Sep 2023
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