Experimental Evaluation of the High-Current Drawn Arc ... - Tavrida

Experimental Evaluation of the High-Current
Drawn Arc Energy Balance
V. A. Dmitriev 1 , V. N. Poluyanov 1 , I. N. Poluyanova 1
1 Tavrida Electric, 22 Vakulenchuka, Sevastopol, 99053, Ukraine
Abstract The distribution of energy between anode and
cathode of high-current drawn vacuum arc has been
experimentally evaluated for different CuCr based
contact materials. The energy distribution was
determined by measurement of the temperature rise with
one thermocouple soldered into drilled hole in the
holder of the electrode, which was in turns cathode and
anode. The measurements were carried out in the
commercial vacuum interrupter, 36-55mm in diameter
AMF electrodes were made from SSS CuCr 70/30 and
LSS CuCr 50/50. The contacts were separated by
magnetic actuator with stable and invariable average
opening speed 1m/s, maximum contact distance was
7мм. The arc duration was 8.5-9.5ms in all the tests.
The study of material influence on the energy
distribution has been done for the typical range of
currents for commercial vacuum interrupter 5кА – 40кА
and for the extreme, knowingly overheating regime with
current 60кА.
I. INTRODUCTION
Dielectric strength of the vacuum gap after the arc
burning is lower then the dielectric strength of the cold
gap. Prevalent explanation is based on Paschen
mechanism of hot breakdown - the breakdown in metal
vapour that originates from the molten electrode zones
and found in the gap up to some ms after current zero
[1,2]. Such obvious connection between hot vacuum
gap breakdown characteristics and contact surface
temperature stimulated direct measurements [3,4] and
theoretical estimations of «the temperature of failure»
[5-8]. The correctness of any heat calculations in this
case is determined not only by knowledge of
thermophysical properties of the contact material, but
also by knowledge of arc energy distribution between
anode and cathode.
In case of the low current vacuum arcs (both
electrodes are far from the melting) and pure metal
electrodes there were determined that 1) the distribution
depends on the contact material, 2) energy input into the
cathode falls within the range of [25-35]% out of arc
energy [9-11]. Energy input into the cathode does not
depend on the contact gap in the range 0,5-10мм [10].
Calculated value of the anode surface potential for Cu,
based on the experimental estimation of cathode
effective potential for Cu [10] is in a well agreement
with theoretical estimation based on ecton mechanism
of vacuum arc [12].
Dates for pure metals can not be used to evaluate
proper characteristic of CuCr composition due to the
1-4244-0192-5/06/$20.00 ©2006 IEEE.
XXIInd Int. Symp. on Discharges and Electrical Insulation in Vacuum-Matsue-2006
special conditions of heating of the components with
sufficiently different thermal conductivities
( 67Wt /( m⋅K
) for Cu and 394Wt /( m ⋅ K ) for Cr), as Cr
grains might be melted and effectively vaporized when
Cupper is not melted at all. It is therefore of interest to
know the distribution of arc energy in a high current
vacuum arc burning on the CuCr AMF electrodes in the
range of current densities which includes currents
densities when both electrodes are certainly not melted,
when only anode is melted and when both, anode and
cathode are melted.
II. EXPERIMENTAL PROCEDURE
The energy distribution was determined by
measurement of temperature increase due to the 50Hz
drawing arc for 2 CuCr composition (TABLE I).
TABLE I
TEST OBJECT IDENTIFICATION
Material D, Maximum current density, kA/cm2
mm 1 2 3 4 5-6
SSS 70/30 55 V V V V
SSS 70/30 50 V V V V
SSS 70/30 36 V V V V V
LSS 50/50 36 V V V V
Electrodes differed by contact diameters and contact
system design, provided different AMF levels (TABLE
II).
TABLE II
AMF LEVELS FOR DIFFERENT CONTACT SYSTEM DESIGN
Diameters Type of Design B/I, a.u.
50, 55 1 1
36 2 1.4
The arc duration was 8.5-9ms, the contacts were
separated by magnetic actuator, maximum contact
distance did not exceed 7мм in dynamic, steady contact
gap was 6mm, contact opening speed was 1m/s. Typical
oscillograms of the arc current, arc voltage, contact
movement and contact velocity are shown on the Fig.1.
Temperature was measured in one point by
thermocouple soldered into the drilled hole of fixed
contact holder (Fig.2). The polarities of current
impulses were alternated from shot to shot; the electrode
was in turns cathode and anode, which courses the
different changes of temperature rise in the point of
measurement (Fig.3).

Time, s
Current, 10 kA/div
Ipeak = 30 kA
Arc voltage, 10 V/div
Upeak = 40 V
Contact distance, 5 mm/div
Contact velocity, 1 m/s/div
Fig.1 Typical oscillograms of the arc current, arc voltage,
contact movement and contact velocity
Temperature, gradC
55
50
45
40
position of thermocouple
peak
Tanode
0
Tanode
fixed contact
bellows
Fig.2 Position of thermocouple
peak
Tcathode
0
Tcathode
peak
Tanode
0
Tanode
movable contact
peak
Tcathode
0
Tcathode
35
0 100 200 300 400 500 600 700 800 900
Time, ms
Fig.3. Temperature rise at polarities alternation .
The measurements were done in the point where the
temperature rise deliberately could not exceed 80C so
the thermophysical parameters might be accepted as
constant and the temperature was proportional to energy
input. Relation of differences between peak and initial
values of temperature when electrode was anode and
when electrode was cathode was equal to the relation
between energy inputs into the anode and cathode (1).
peak 0
ΔTanode = Tanode
− Tanode
∼ Q anode
peak 0
ΔTcathode = Tcathode
− Tcathode
∼ Q cathode (1)
Δ T anode
Δ T
=
Q anode
Q
cathode
cathode
Relative energy input into the anode RQanode
and
cathode RQcathode
were determined with assumption
what arc energy divides between electrodes only (2)
Q = Qanode
+ Qcathode
+ Q
Q 0
arc
out≈
Qcathode
RQ cathode = =
Qarc
1
ΔTanode
ΔTcathode
+ 1
(2)
Qanode
1
RQ canode = =
Q ΔT
arc cathode + 1
ΔT
out
anode
To grade possible influence of preliminary
interruptions the value of interrupted current for each
shot was selected stochastically from the sequence that
provided the same current densities for the contact of
different diameters (TABLE I). The last measurements
were done at the deliberately damaging current densities
5-6kA. There were done 5 impulses for each current
density level for each polarity, relative energy inputs
were calculated by average T and ΔT
.
Δ anode
cathode
III. EXPERIMENTAL RESULTS
Fig.4 demonstrates relative energy inputs into the
anode and cathode for the SSS CuCr 70/30 and contact
design of types 1 and 2 (TABLE II).
Fig.5 shows the relative energy inputs for different
CuCr compositions and contact design of type 2.
Relative arc energy inputs significantly depend on the
current density and contact system type (Fig.6).
For SSS CuCr 70/30 the arc voltage and therefore the
arc energy for contact system 36mm are smaller than for
the contact system 50 and 55mm (Fig.7), nevertheless
the influence of the contact system type is confirmed by
the dependence between energy inputs and arc energy
density (Fig.8).
Equalization of the anode and cathode energy input
for CuCr 50/50 comes at the smaller current/arc energy
densities in comparison with the CuCr 70/30 (Fig.9-10).
III. CONCLUSION
For the high current vacuum arc on CuCr AMF
electrodes the distribution of arc energy between anode
and cathode strictly depends on the current/arc energy
density and content of Cr.

Relative energy input
Relative energy input
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 10 20 30 40 50 60 70
1,2
1,1
1,0
0,9
0,8
Current (magnitude), kA
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 5 10 15 20 25 30 35
Current (magnitude), kA
cathode, 55 mm
anode, 55 mm
cathode, 50 mm
anode, 50 mm
cathode, 36 mm
anode, 36 mm
Fig. 4. Relative energy input for SSS CuCr 70/30.
cathode, SSS CuCr 70/30
anode, SSS CuCr 70/30
cathode, LSS CuCr 50/50
anode, LSS CuCr 50/50
Fig. 5. Relative energy input for SSS CuCr 70/30 and LSS 50/50,
contact type 2
Relative energy input
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 1 2 3 4 5 6 7
Maximum current density, kA/cm2
cathode, 55 mm
anode, 55 mm
cathode, 50 mm
anode, 50 mm
cathode, 36 mm
anode, 36 mm
Fig. 6 Dependence between relative energy input and maximum
current density for SSS CuCr 70/30
Maximum arc voltage, V
80
60
40
20
0
0 1 2 3 4 5 6
Maximum current density, kA/cm2
55 mm
50 mm
36 mm
Fig. 7 SSS CuCr 70/30, maximum arc voltage for different
contact design
Relative energy input
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 200 400 600 800 1000 1200 1400 1600
Arc energy density, J/m2
cathode, 55 mm
anode, 55 mm
cathode, 50 mm
anode, 50 mm
cathode, 36 mm
anode, 36 mm
Fig. 8 Dependence between relative energy input and arc energy
density for SSS CuCr 70/30
Relative energy input
1,2
1,1
1,0
0,9
0,8
cathode, SSS CuCr 70/30
anode, SSS CuCr 70/30
cathode, LSS CuCr 50/50
anode, LSS CuCr 50/50
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 1 2 3 4 5 6
Maximum current density, kA/cm2
Fig. 9 Dependence between relative energy input and maximum
current density for contact design 2

Relative energy input
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0 200 400 600 800 1000 1200 1400 1600
Arc energy density, J/cm2
cathode, SSS CuCr 70/30
cathode, LSS CuCr 50/50
anode, LSS CuCr 50/50
anode, SSS CuCr 70/30
Fig. 10 Dependence between relative energy input and arc energy
density for contact design type 2
ACKNOWLEDGEMENTS
Authors wish to sincerely thank Dr Chaly and Dr
Shkol’nik for encouraging this work and for fruitful
discussions. We would also like to thank all engineers of
Tavrida Electric Test Laboratory provided valuable
assistance to this work
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