arc behaviour in small capacitive current interruption with high

advertisement
ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ARC BEHAVIOUR IN SMALL CAPACITIVE CURRENT
INTERRUPTION WITH HIGH-VOLTAGE AIR-BREAK
DISCONNECTOR
1
Y. Chai1*, P.A.A.F. Wouters 1, R.T.W.J. van Hoppe1, R.P.P. Smeets 1, 2
Electrical Power Systems Group, Eindhoven University of Technology, the Netherlands
2
KEMA T&D Testing Services, Arnhem, the Netherlands
*Email: <[email protected]>
Abstract: Small capacitive current interruption with air-break disconnectors in a high-voltage
network is an interactive event between circuit and arc with multiple re-ignitions during opening.
In order to investigate the transient phenomena, a set-up to measure arc characteristics is
developed and a series of interruption tests is performed. The system voltage is up to 150kV rms
and the interruption capacitive current is up to 0.35A rms. The voltages across load- and source
side capacitances and the current through the disconnector are recorded. Based on test data, arc
characteristics such as arc conductance, arc power and v-i characteristic are studied. A comparison
between the test and simulation shows good agreement.
2. EXPERIMENTAL SET-UP
1. INTRODUCTION
In a power substation, the disconnectors (in North
America, also called disconnect switches) are
commonly used mechanical devices. Besides having a
safety function, in practice they need to interrupt a
small capacitive current due to stray capacitances in the
power networks. Although not designed for
interrupting current, the disconnectors do have a
certain current interruption capability. According to the
IEC 62271-102 [1], this small capacitive current does
not exceed 0.5A for rated voltage 420kV and below.
However, nowadays with the fast development of
power networks in the world, user’s requirement for
small capacitive current interruption using air-break
disconnectors frequently exceeds the above stated
value.
Figure 1: Laboratory set-up for capacitive current
interruption with air-break disconnector.
The literature related to capacitive current interruption
with air-break disconnectors is quite sparse, for
instance [2]-[15]. The principal work in the past is that
of Andrews et al. in the 1940s. Some results from
literature such as [3], [8] were collected for IEC and
IEEE recommendations [11] as well. An overview is
provided in [12]. However, the literature provides only
a limited insight into the experiments on the capacitive
current interruption with an air-break disconnector. In
this contribution a more detailed approach to the
electrical phenomena based on experimental data from
tests in the laboratory is presented.
In order to investigate the interruption phenomena, a
set-up for laboratory experiments is developed. The
experimental circuit includes a power source, source
side capacitor (Cs), load side capacitor (Cl) and the
disconnector. Figure 1 shows the set-up top view. A
high voltage resonant system, capable to supply a 50Hz
high voltage up to 300kV and a current up to 4A, is
employed. It contains two reactors which can be
connected either in series or in parallel. The inductance
of each reactor can be tuned over a range of 40010,000H. The values of Cs, Cl are 2nF and 8nF
respectively. A center-break type disconnector with
rated voltage of 245kV is subjected to the test. The
corresponding equivalent circuit of the set-up is shown
in figure 2, wherein the disconnector is marked with D;
Rs represents the equivalent resistivity of the circuit
and Ls is the inductance of the resonant system. id is
current through the disconnector to be interrupted; us is
the voltage of the power supply; ucs, ucl are the voltages
across the source side capacitance and the load side
capacitance respectively. If ωLs=1/[ω (Cs + Cl)], the
circuit in resonance (Ls is tuned to about 1kH). In
order to measure voltages across the two contact blades
In this paper, firstly a set-up for measurement is
described in detail. Next, based on measured data, the
different arc characterises such as arc voltage, arc
current, arc conductance and arc power are
investigated. The re-ignition voltage versus time
against current is studied as well. Finally, simulations
related to this phenomenon are discussed, and
conclusions are drawn.
Pg. 1
Paper G-19
ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
Figure 2: Arc voltage and current measurement circuit.
10
|H|
of the disconnector, two capacitive voltage dividers are
designed, C1/C2 and C3/C4, (C1, C3 are the high voltage
arms, see fig.2). They are mounted parallel to the
insulators of the disconnector as shown in figure 3.
Each divider consists of 10 capacitors of 2nF, 40kV in
series, carefully selected to ensure equal division ratios
of both dividers. These capacitive voltage dividers
have a bandwidth up to about 10MHz and 10:1
division ratio (see figure 3). The dividers are connected
to PMK high voltage probes (1000:1 ratio, 14kV AC),
resulting in a total voltage division ratio of 10,000:1
approximately. For current measurement, two current
transformers (CT1, CT2) with a sensitivity of 0.1
volt/ampere and a bandwidth of up to 20MHz are
employed. Since the dynamic range of the current is
large, separate current probes are used for power
frequency and for high-frequency components in the
current. All test data are acquired and recorded by a 4channels (marked CHi in figure 2) Nicolet Genesis
digital system with a sampling rate of 25 MS/s (16 bit),
100 MS/s (14 bit).
5
0
∠H [°]
100k
1M
10M
90
0
100k
1M
10M
Frequency [Hz]
Figure 3: The voltage divider and its step wave
frequency response.
20
u (kV)
10
(a)
d
0
-10
-20
-100
0
100
200
300
400
500
600
time(ms)
1
(b)
d
i (A)
0.5
0
-0.5
-1
-100
The operating steps are as follows: firstly the system is
energized with the closed disconnector on a chosen
level of us. Next, the inductance Ls is tuned until Ls and
Cs in parallel with Cl become resonant. Once the
system is in resonance, the measurement is started. The
disconnector blades are opened and the voltages across
source and load side capacitor and the disconnector
current are acquired simultaneously.
0
100
200
300
400
500
600
time(ms)
50
1
0
Arc Duration
d
0
(C)
u (kV)
d
i (A)
id(A)
ud(kV)
3. TEST DATA ANALYSIS
A series of measurements is done with the voltages in
the range of 50kV to 150kV rms. The current through
the disconnector before interruption ranges from 0.12A
to 0.35A rms. In this section, recorded wave shapes for
voltage and current are shown and from the results the
arc behaviour is analyzed.
375
380
385
390
-50
395
time(ms)
0
During the measurement, the voltage ud across the
contacts of the disconnector is not measured directly,
but it is derived by subtracting the voltages across both
capacitances ud=ucs-ucl. Figures 4a-d show the voltage
and current of the disconnector and their enlargements.
The interruption starts at time=0 and stops at
time=473ms. The entire process consists of multiple
Arc Extinction
-1
d
0
d
Typical wave shapes for voltages and current
50
(d)
u (kV)
id(A)
ud(kV)
1
i (A)
3.1.
-1
-50
445
450
455
460
465
470
475
480
time(ms)
Figure 4: the disconnector’s voltage and current and
their expansions at period from 370ms to 400ms and
445ms to 485ms.
Pg. 2
Paper G-19
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
2
220
180
160
ir(kV)
ur(A)
1
i (A)
140
0
0
r
r
120
u (kV)
200
voltage(kV)
50
80kV
128kV
144kV
170kV
200kV
100
80
-1
60
40
-50
20
-200
-100
0
100
200
300
400
-2
0
500
time(ms)
100
200
300
400
500
600
time(ms)
Figure 5: Source side capacitance voltage ucs amplitude
decay versus time for different measurement.
ir(kV)
ur(A)
50
i (A)
Arc duration
0
r
0
r
1
u (kV)
periods with arc extinctions and re-ignitions. The TRV
(Transient Recovery Voltage) [16] period and arc
duration can be observed clearly from those figures.
There is one re-ignition in each half cycle at the
beginning, but there are several re-ignitions in each
half cycle just before the arc extincts completely
(figure 4d), since maintaining the arc is more difficult
with a larger air gap. Once a re-ignition occurs, the
voltage and the current contain high-frequency
components [17], which can be observed in figure 4c
and 4d as well.
Arc extinction
-1
-50
380
385
390
395
400
time(ms)
Figure 6: Arc voltage and current and its expansion
at period from 375ms to 400ms.
-3
x 10
Because the test voltage source is a resonant system,
the amplitude of voltage ucs (and also ucl) and current id
decay due to running out of resonance with power
frequency and due to arc losses. Figure 5 shows the
amplitude of ucs as a function of time for each
interruption. A group of test data with source voltage
level ranging from 100kV to 200kV peak is selected.
According to figure 5, the voltage decay becomes more
pronounced at the later stages of the interruption
process due to increasing energy dissipation with larger
air gap. Also the arc resistance becomes larger. That
the voltage ucs does not reach zero at the end point of
arc extinction is because of the long air gap’s dielectric
withstand capability when disconnector blades are
moving. Figure 4d also confirms the TRV is larger than
the last re-ignition voltage at the moment when the arc
extinct completely. This means the experimental
system works satisfactory even though there is decay in
source voltage, unlike the field situation.
conductance(siemens)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
50
100
150
200
250
300
350
400
450
time(ms)
-4
conductance(siemens)
x 10
2
1
0
280
290
300
310
320
330
time(ms)
In all cases the arc lasts less than 500ms with
interruption current level ranging from 0.18A to 0.5A
peak. With higher supply voltage the arc lasts longer as
observed from figure 5 as well.
Figure 7: Wave shape of arc conductance and its
expansion at time=275ms-330ms.
3.2.
voltage and current wave shapes are in phase which
indicates the resistive characteristic of the arc.
Arc behaviour
The arc voltage ur is obtained by selecting the periods
where the arc is present from the ud wave forms (e.g.
figure 4a). The arc current ir is equal to id during these
periods. An example of the wave shape of ur and ir is
shown in figure 6 with an interruption current of 0.35A
rms and resonant voltage of 145kV rms. The arc occurs
between time=0 and 473ms. In a half cycle, the voltage
firstly rises very quickly and then drops to a relatively
steady level which is in the order of a few kV. The
Based on the measured arc voltage and current
characteristics, the arc conductance ir(t)/ur(t), arc
power ur(t)×ir(t) and arc v-i characteristics are derived.
Typical results are plotted in figures 7, 8 and 9 for a
system voltage of 145kV and an interruption current of
0.35A. The arc conductance varies during each half
cycle. As the air gap between the disconnector blade
contacts becomes larger, the arc conductance decreases
Pg. 3
Paper G-19
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
3000
80
60
2000
40
1500
voltage(kV)
arc power(W)
2500
1000
500
0
0
50
100
150
200
250
300
350
400
450
500
20
0
-20
0.35A
0.30A
0.25A
0.22A
0.15A
-40
time(ms)
-60
1800
-80
0
1600
100
200
300
arc power(W)
400
500
time(ms)
1400
Figure 10: Re-ignition voltages versus
interruption current.
1200
1000
800
600
400
200
0
335
340
345
350
355
360
365
370
375
380
385
time(ms)
Figure 8: Wave shape of arc power and its
expansion at time=335ms-385ms.
4000
Figure 11: Simulation circuit for interruption
phenomena.
3000
2000
u (V)
1000
r
1
0
0.8
measured id
simulated id
-1000
0.6
-2000
0.4
-3000
0.2
d
-5000
i (A)
-4000
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0
-0.2
ir(A)
-0.4
Figure 9: Wave shape of arc voltage-current
characteristics.
(and the arc resistance increases) until the arc
extinguishes completely. For instance, it reaches a
value of about 1.5 mS corresponding to a resistance of
700Ω at time=150ms and decreases to about 0.1mS
corresponding to a resistance of 10kΩ just before
extinction. The arc power tends to increase with larger
air gap. Its value goes up to about 1.5kW. The
expanded plot in figure 8 shows that each half cycle the
arc power rises rapidly upon re-ignition. After that it
remains almost constant, and then starts to drop till
zero when the arc current goes to zero. The shape of
the voltage-current characteristics of the arc is a
hysteresis loop, owing to the arc nonlinear nature. The
arc is also non-stationary because of the dynamic
changes in arc length, as a consequence of electrodynamics forces and convection. The arc voltage
remains almost constant irrespective of the arc current.
-0.6
-0.8
-1
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
times(s)
Figure 12: Wave shapes for simulated and measured
current id.
measured id
simulated id
0.4
0
d
i (A)
0.2
-0.2
-0.4
-0.6
0.24
0.25
0.26
0.27
0.28
0.29
0.3
0.31
0.32
times(s)
3.3.
Figure 13: Expansion for figure 13 at 0.24s to 0.32 s.
Re-ignition voltage
Multiple re-ignitions occur during interruption. By
analyzing the wave shape envelope of the disconnector
voltage ud, the re-ignition voltage can be obtained: for
each arc re-ignition point in ud both re-ignition time
and voltage are taken. In order to present the re-
ignition voltage wave shapes, one group of test data is
selected with different current id as a parameter. The
results for the tests performed at currents ranging from
0.15A to 0.35A rms are given in figure 10. The curves
Pg. 4
Paper G-19
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
ISBN 978-0-620-44584-9
5. DISCUSSION AND CONCLUSION
3000
In this paper, a set-up is described to investigate
capacitive current interruption for relatively low
current phenomena with a high voltage air-break
disconnector. The current level ranges from 0.12A to
0.35A and voltage level is from 50kV to 150kV.
Although there is a drawback for resonant supply as
high voltage source in the test, the investigation shows
that set-up works satisfactory.
2000
arc voltage (v)
1000
0
-1000
measured ur
simulated ur
-2000
The small capacitive current interruption is a complex
phenomenon with multiple arc interruptions and reignitions that are confirmed by the test. Test data also
shows that, in order to maintain an arc at this small
current level, there is at least one re-ignition per half
cycle. The arc during interruption consists of single
power frequency loops that start with reignition and
interrupt at current zero, with the arc voltage having a
flat part of a few kV. The arc conductivity ranges from
0.1mS to 15mS with the interruption current level
0.12A-0.35A. The arc power is smaller than 1500W
and tends to increase with the blades moving with a
several certain drops in the entire interruption process.
Besides it shows the arc has a resistive nature, the
voltage-current characterises further show the arc
voltage does not increase with increasing of arc current.
-3000
-4000
0.255
0.26
0.265
0.27
0.275
0.28
0.285
0.29
time(s)
Figure 14: comparison between measured- and
simulated arc voltage.
clearly show that re-ignition voltage increases with air
gap when the blades open. The re-ignition voltage
reaches a value up to a few tens of kV. With the larger
interruption current, the re-ignition voltage drops
because there is a higher energy input to the arc upon
re-ignition. The arc path needs more time to recover its
dielectric strength.
4. COMPARISON WITH SIMULATION AND
MODELING
In this paper, although the capacitive current for
interruption in the test is relatively low, the arc
behaviour can be clearly observed. Most arc durations
are smaller than 500ms. The air gap re-ignition voltage
is about a few 10kV which is much lower than a few
100kV compared with test current level with 2A in
[17]. The reason is that the arc duration lasts shorter
and the air gap for re-ignition is smaller.
In order to compare with test, the experimental circuit
is modelled using Matlab for a specific condition with
a resonant voltage ucs of 145kV and a current of id
0.35A. The parameters in figure 11 are set as close as
possible to those parameters in the measurements:
us=1.31kVpeak, Rs=2040Ω, Ls=1013H, Cs=2nF,
Cl=8nF, LH=16µH, RH=50Ω. LH and RH are equivalent
inductance and resistance of the circuit. Their values
are obtained from the higher frequency components in
the test results [17]. The arc is modelled by the real
voltage wave shape, which is also obtained from the
test results. The simulated and measured current wave
shape id and its expansion are shown in figure 12 and
13. The contact separation is at 0.02s. The measured
and simulated currents have a good match.
The final project goal is to investigate how to improve
capacitive current interruption capability with high
voltage air-break disconnector. In the near future,
measurements will be performed at interruption current
level up to 4A, for different combination of
capacitances at source and load side.
6. REFERENCES
Even though the Cassie arc model is developed for
higher arc currents, as a first attempt in the simulation,
this classic arc model has been used. Based on a few
assumptions,
the
equation

1 dG 1  E 2
= 
− 1
G dt θ  E0 2 
[1] IEC Standard on “High-voltage switchgear and
control gear-Part 102: Alternating current
disconnectors and earthing switches”, IEC 62271102, 2001.
[2] P.A. Abetti, “Arc interruption with disconnecting
switches,” Master Thesis, Illinois, Institute of
Technology, January 1948.
[3] F.E. Andrews, L.R. Janes and M.A. Anderson,
“Interrupting ability of horn-gap switches”, AIEE
Transactions, Vol. 69, 1950.
[4] E.C. Rankin,” Experience with methods of
extending the capability of high-voltage air break
switches,” AIEE Transactions, Vol. 79, February
1960.
[5] A. Foti and J.M. Lakas, “EHV switch tests and
switching surges,” IEEE Transactions on Power
was
obtained [16], where E is arc voltage, E0 is constant, θ
is arc time constant, G is arc conductance. Through
calculation and parameters evaluation from test data,
E0=601V, θ=1ms, the compared result in a few cycles
is presented in figure 14. It appears that simulation and
test data do not match well. Especially the high arc
voltages just after re-ignition are not represented well.
The results suggest that this model is not suitable to
test. In our future work, more data will become
available also at higher interruption current, and more
emphasis will put on arc model investigation for an arc
current range up to several amperes.
Pg. 5
Paper G-19
ISBN 978-0-620-44584-9
Proceedings of the 16th International Symposium on High Voltage Engineering
c 2009 SAIEE, Innes House, Johannesburg
Copyright °
[12] D. F. Peelo, “Current interruption using high
voltage
air-break
disconnectors”.
Ph.D.
dissertation, Dept. Electrical Engineering,
Eindhoven Univ. of Technology, 2004, ISBN:
9038615337.
[13] D.F. Peelo, R.P.P. Smeets, L. van Der Sluis, S.
Kuivenhoven, J.G. Krone, J.H. Sawada and B.R.
Sunga, “Current interruption with high voltage airBreak disconnectors”, Cigre Conference, 2004,
Paris.
[14] D.F.Peelo, R.P.P Smeets, J. G. Krone, “Capacitive
current interruption in atmospheric air”, Cigre
A3/B3 Colloquium 2005, Tokyo
[15] S. Carsimamovic, Z.Bajramovic, M. Ljevak, M.
Veledar, N. Halilhodzic, "Current switching with
high voltage air disconnector", International
Conference on Power Systems Transients
(IPST’05), Montreal, Canada, June 19-23, 2005.
[16] L. van der Sluis, "Transients in power systems",
John Wiley & Sons Ltd, England, 2001.
[17] Y. Chai, P.A.A.F. Wouters, R.T.W.J. van Hoppe,
R.P.P. Smeets, D. F. Peelo, "Experiments on
capacitive current interruption with air-break high
voltage disconnectors", Asia-Pacific Power and
Energy Engineering Conference (APPEEC),
Wuhan, China, March 28-31, 2009.
Apparatus and Systems, Vol. 83, No. 3, March
1964.
[6] IEEE Committee Report, "Results of survey on
interrupting ability of Air Break, Switches", IEEE
Trans. on Power Apparatus and Systems, Vol.
PAS-85, No. 9, Sept. 1966.
[7] CEA Project 069 T 102 report, “The interrupting
capability of high voltage in disconnects
switches”, July 1982.
[8] D.F. Peelo, “Current interrupting capability of air
break disconnect switches”, IEEE Transactions on
Power Delivery, Vol. PWRD-1, No. 1, January
1986 and Correction, IEEE Transactions on Power
Delivery, Vol. PWRD-2, No. 4, Oct. 1987.
[9] S.G. Patel, W.F. Holcombe and D.E. Parr,
“Application of air-break switches for deenergizing transmission lines,” IEEE Transactions
on Power Apparatus and Systems, Vol. 4, No. 1,
January 1987.
[10] H. Knobloch, “Switching of capacitive currents by
outdoor disconnectors,” Fifth International
Symposium on High Voltage Engineering,
Braunschweig, August 1987.
[11] IEEE Std c37.36b, "IEEE Guide to Current
Interruption with Horn-Gap Air Switches", 1990
Pg. 6
Paper G-19
Download