U.S. patent number 3,736,437 [Application Number 05/105,933] was granted by the patent office on 1973-05-29 for vacuum switch apparatus.
Invention is credited to Akira Nabae, Mikio Okawa.
United States Patent |
3,736,437 |
Nabae , et al. |
May 29, 1973 |
VACUUM SWITCH APPARATUS
Abstract
A vacuum switch apparatus comprising a vacuum switch having a
pair of electrodes, and a series circuit consisting of a resistor
and capacitor disposed between one of said electrodes and ground to
suppress the oscillation of abnormal voltage generated at the
opening of said switch. The resistor preferably has a value of 100
ohms and the capacitor preferably has a value of 0.1.mu.F.
Inventors: |
Nabae; Akira (Setagaya-ku,
Tokyo, JA), Okawa; Mikio (Machida-shi, Tokyo,
JA) |
Family
ID: |
26336027 |
Appl.
No.: |
05/105,933 |
Filed: |
January 12, 1971 |
Current U.S.
Class: |
307/327; 307/104;
361/13 |
Current CPC
Class: |
H01H
33/59 (20130101); H01H 33/66 (20130101) |
Current International
Class: |
H01H
33/66 (20060101); H01H 33/59 (20060101); H01f
027/42 () |
Field of
Search: |
;317/DIG.6,11C,11R
;307/104,92,93 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Rovnyak, R. M.; Arc, Surge, and Noise Suppression; Electronic's
World; May, 1967..
|
Primary Examiner: Hohauser; Herman J.
Claims
What we claim is:
1. A vacuum switch apparatus comprising at least one vacuum switch
having a pair of electrodes and an RC surge suppressor circuit
coupled between one of said electrodes and ground, said surge
suppressor circuit being comprised of a series connection of a
resistor R and a capacitor C, the values of said resistor R and
capacitor C satisfying the following:
n .gtoreq. 8(m+1)/m-8
m > 8
R.sub.1 .ltoreq.R.ltoreq.R.sub.2
where
n=C/Ce, m=Ce/Cs, q=1+n+m and ##SPC2##
Ce: load side stray capacity
Cs: source side stray capacity
Lo: line stray inductance.
2. A vacuum switch apparatus according to claim 1 comprising three
RC surge suppressor circuits, and wherein said vacuum switch is of
the three phase type having three pairs of electrodes, one
electrode of each pair being connected to ground through a
respective RC surge suppressor circuit.
3. A vacuum switch apparatus according to claim 1 comprising test
means connected to said surge suppressor circuit for a short
circuit test thereof.
4. A vacuum switch apparatus according to claim 1 wherein said
resistor is chosen to have a resistance of 100 ohms and said
capacitor to have a capacity of 0.1.mu.F.
5. A vacuum switch apparatus comprising at least one vacuum switch
having a pair of electrodes and an RC surge suppressor circuit
coupled between said electrodes, said surge suppressor circuit
being comprised of a series connection of a resistor R and a
capacitor C, the values of said resistor R and capacitor C
satisfying the following:
n.gtoreq. 8(m+1)/m-8
m > 8
R.sub.1 .ltoreq. R .ltoreq. R.sub.2
where
n=C/Ce, m=Ce/Cs, q=1+n+m and ##SPC3##
Ce: load side stray capacity
Cs: source side stray capacity
Lo: line stray inductance.
6. A vacuum switch apparatus according to claim 5 comprising three
RC surge suppressor circuits, and wherein said vacuum switch is of
the three phase type having three pairs of electrodes, each surge
suppressor circuit being connected between respective pairs of said
switch electrodes.
7. A vacuum switch apparatus according to claim 5 wherein said
resistor is chosen to have a resistance of 100 ohms and said
capacitor to have a capacity of 0.1.mu.F.
Description
The present invention relates to a vacuum switch apparatus. Vacuum
switches and vacuum breakers have broad applications due to their
excellent dielectric recovery and extinction characteristics and
easy maintenance. However, switches of such type cause an abnormal
voltage to be generated by current chopping or reignition at the
opening of the switch, with the result that a load is subject to
damage due to the abnormal voltage.
Appearance of abnormal voltages due to current chopping may be
eliminated using electrode materials in which there takes place a
low degree of current chopping. With respect to generation of
abnormal voltage due to reignition, however, the cause is not
clearly defined and there have not yet been proposed fully
satisfactory countermeasures, with the result that the load is
still subject to damage due to generation of abnormal voltage at
the opening of the switch, particularly that resulting from
reignition.
There have been conducted in connection with the present invention
a large number of experiments and analyses of phenomena to search
for the cause of the aforementioned reignition. As a result, it has
been found that the reignition originates with oscillations in an
L-C circuit consisting of line inductance and stray capacity on the
source and load sides. There will now be described this fact by
reference to the equivalent circuit of FIG. 1 representing the case
where there was used a conventional vacuum switch in the circuit of
an induction motor. Referring to FIG. 1, numeral 11 denotes a power
source, 12 a vacuum switch, 13 an induction motor, 14 source
inductance, 15 source stray capacity, 16 line stray inductance and
17 load side stray capacity. When the switch 12 is opened in said
circuit, current is cut off at the following zero point, and there
appears a recovery voltage across the terminals of said switch 12.
The wave form 18 of a load side voltage impressed in this case is
illustrated in FIG. 2 and the wave form of an interelectrode
voltage of the switch 12 in FIG. 3. Normally when current is cut
off by the switch 12 at point 20 in FIGS. 2 and 3, the load side
voltage is progressively reduced to zero potential as indicated by
a dotted line 21, while oscillating with a certain frequency
expressed by the following formula:
f = 1/2.pi..sqroot.LeCe
Where:
Le = reactance of load 13
Ce = stray capacity of the same
However, when the opening of the switch 12 happens to cause current
to be cut off not exactly at the zero point but in its
neighborhood, the switch contact has just been disconnected, only
leaving a very slight gap and full insulation is not yet regained.
Accordingly, even if insulation is realized at the zero point,
there will immediately occur reignition at point 22 in FIG. 2 with
the resulting conducted state, causing the voltage to be brought
back to the level prevailing on the source side. Since this
conduction appears in the L-C circuit, the load side voltage
overshoots up to point 23 in FIG. 2 from the source voltage.
Assuming that there is no circuit loss, said overshooting portion
of the voltage is substantially equal to the interelectrode voltage
at the time of reignition. Current passing through the contact of
the switch 12 upon reignition travels through a circuit including
line inductance 16 and stray capacities 15 and 17 with a frequency
f expressed by the following formula:
f = 1/2.pi. (.sqroot.Cs + Ce/LoCeCs
where:
Cs = stray capacity 15 on source side
Ce = stray capacity 17 on load side
Lo = line inductance 16
With a vacuum switch, however, insulation is restored very quickly
with respect to vacuum arcs, so that high frequency current is cut
off at the zero point, the so-called high frequency extinction.
Immediately upon current cut off, there appears recovery voltage or
reignition across the electrodes for which there is not yet
restored full insulation. This phenomenon of reignition continues
until the switch contact is fully opened, permitting the resulting
insulation to overcome the occurrence of any recovered voltage.
The present invention has been accomplished by taking
countermeasures for the fact that said phenomenon of reignition
originates, as described above, with the L-C circuit included in
the switch circuit. It is accordingly the object of the invention
to provide a vacuum switch wherein there is provided a high
frequency oscillation control circuit on the switch so as to
prevent the generation of abnormal voltage at its opening.
According to Summary of the Invention an aspect of the present
invention, there is provided a vacuum switch apparatus including a
series connection of a capacitor and resistor which is connected
between one of the electrodes of vacuum switch and ground or
between the electrodes, to suppress the oscillation of abnormal
voltages generated at the opening of the switch.
The present invention can be more fully understood from the
following detailed description when taken in connection with the
accompanying drawings, in which:
FIG. 1 is an equivalent circuit diagram representing the case where
there is used a prior art vacuum switch;
FIG. 2 shows the wave form of load side voltage appearing at the
time of reignition in the circuit of FIG. 1;
FIG. 3 indicates the wave form of voltage occurring across the
switch electrodes at the time of reignition in the circuit of FIG.
1;
FIG. 4 illustrates a vacuum switch circuit according to an
embodiment of the present invention;
FIGS. 5 and 6 are equivalent circuit diagrams of FIG. 4;
FIG. 7 is a co-ordinate representation showing the values of the
capacitor and resistor constituting high frequency oscillation
control means used in the vacuum switch of the present
invention;
FIG. 8 presents the wave form of load side voltage in the circuit
of FIG. 4 when it is opened;
FIG. 9 shows the wave form of voltage across the switch electrodes
in the circuit of FIG. 4 when it is opened; and
FIGS. 10 and 11 are circuit diagrams using vacuum switches
according to other embodiments of the invention.
Referring to FIG. 4, numeral 30 represents a vacuum switch which is
connected to a power source 33 and load 34 through cables 31 and 32
respectively. The load side electrode of the vacuum switch 30 is
grounded through a series circuit consisting of a resistor 35 and
capacitor 36. This series circuit constitutes high frequency
oscillation control means 37 which effectively controls the
oscillation of abnormal voltage which would progressively increase
with repetition of reignition occurring at the opening of the
vacuum switch 30.
Referring to FIG. 5 which illustrates an equivalent circuit of FIG.
4, numeral 38 denotes load side stray capacity, 39 source side
stray capacity, 40 line stray induction and 41 source induction.
FIG. 6 taken out of FIG. 5 shows a circuit through which a high
frequency current flows when the reignition occurs. The
non-oscillatory conditions are expressed by the following
formulas
R.sub.1 .ltoreq.R .ltoreq.R.sub.2 (1)
m > 8 (2)
n.gtoreq.8(m+1)/m-8 (3)
where
n=C/Ce, m=Cs/Ce, q=1+m+ n, and ##SPC1##
C: capacity of capacitor 36
Ce: load side stray capacity 38
Cs: source side stray capacity 39
Lo: line stray inductance 40
FIG. 7 illustrates the results of determining the conditions for
preventing oscillation in the case of, for example, m=40. The
values of the resistor 35 and capacitor 36 were so chosen as to
fall within the hatched region of FIG. 7, and to satisfy the said
three non-oscillatory conditions (1), (2) and (3).
There were made further tests on a vacuum switch 30 used in the
circuit of an induction motor, transformer and reactor. The results
show that when the capacitor 36 was chosen to have a capacity of
0.1.mu.F and the resistor 35 to have a resistance of 100.OMEGA.,
then there was completely eliminated, as seen in FIGS. 8 and 9, the
abnormal voltage which has frequently occurred in a prior art
vacuum switch due to recurring reignition, fully preventing the
danger of dielectric breakdown on the load side. FIG. 8 represents
the case where there appeared reignition only once and FIG. 9 the
case where there was not observed any reignition.
In another embodiment of FIG. 10, there are connected a series
connection of a capacitor 36 and resistor 35 between the paired
electrodes of the vacuum switch 30 to constitute high frequency
oscillation control circuits 37. FIG. 11 shows a circuit for a
short circuit test of the vacuum switch apparatus according to this
invention. One electrode of the paired electrodes of each vacuum
switch 30 is grounded through a high frequency control circuit 37
and connected through a cable 31 and reactor 43 to respective ones
of output terminals of a short circuit generator 42, and the other
electrode of each vacuum switch 30 is grounded. In any of the
aforementioned embodiments, the vacuum switch including the control
circuit of the present invention effectively prevents the
generation of abnormal voltage. The high frequency oscillation
control circuit 37 consisting of resistors 35 and capacitors 36 may
be integrally placed in a cubicle together with the vacuum switch
to render it compact.
As mentioned above, connection according to the present invention
of a series circuit including a capacitor and a resistor between
one of the electrodes of a vacuum switch and ground, or between the
electrodes of the switch itself effectively suppresses the
oscillation of transient recovery voltage and in consequence the
occurrence of abnormal voltage, thereby ensuring the safety of the
load side.
* * * * *