Electricity: measuring and testing – Electromechanical switching device – Circuit breaker
Reexamination Certificate
2002-05-17
2004-03-09
Le, N. (Department: 2858)
Electricity: measuring and testing
Electromechanical switching device
Circuit breaker
C361S117000
Reexamination Certificate
active
06703839
ABSTRACT:
The present invention relates to synthetic making/breaking-capacity test circuits with the characteristics specified in the preamble of claim 1. A synthetic breaking-capacity test circuit of this kind is already known from German patent specification 962 731, dated Apr. 3, 1942 by inventor Fritz Weil.
BACKGROUND OF THE ART
In the circuit diagram (FIG.
1
), which corresponds functionally to the original
FIG. 3
of the '731 specification, the original reference symbols have been supplemented with internationally recognized symbols representing the depicted circuit elements.
A partial oscillation of the high current i
hc
(FIG.
2
), fed by a generator G, flows initially in the high-current circuit as a result of the series connection of the auxiliary circuit-breaker
9
/B
a
and the test circuit-breaker
3
/B
t
. The high-voltage circuit does not operate as long as the switching spark gap
8
/SG
hv
is open, and it is additionally isolated from the high-current circuit by the open spark gap
7
.
At the instant t
0
(FIG.
3
), the high-voltage oscillating circuit with the capacitor
21
/C
hv
, which is charged to electrical potential, is closed when the switching spark gap
8
/SG
hv
is fired.
An oscillating-current half-oscillation i
hv
then flows via an “interrupter
6
with a high voltage drop”. The instant t
0
is selected so that the zero crossing of the oscillating-current half-oscillation occurs at the instant t
3
just after the zero crossing of the high current (instant t
2
). At the instant t
1
, which marks the “greatest coincidence of the two currents”—in
FIGS. 2 and 3
when the oscillating current has a relative instantaneous value of i
hv
/Î
hv
equal to 0.87, equivalent to a phase angle of 120°—“means are provided for eliminating the main current from the test switching point and conducting the current from the high-voltage source via the test switching point” (FIGS.
3
and
4
). The recovery voltage u
hv
of the high-voltage source follows the current zero of the currents of the high-voltage source (FIG.
5
).
The current curves on the graphs in
FIGS. 2
,
3
and
4
were determined without taking account of the arc voltage of the circuit-breaker; the same also applies to all other graphs of current curves.
The actual redirection of the high-voltage oscillating current from the high-voltage oscillating circuit, which was originally made operational outside the high-current circuit, into the test circuit-breaker located in the high-current circuit as a sequence current of the high current that must be eliminated synchronously is likely to represent the main problem with this synthetic test circuit.
To F. Weil, the state of the art which led to the invention was: “ . . . the known test setup has the disadvantage that the main-current curve just before its zero crossing and the use of the high voltage as recovery voltage respectively conflicts with the situation of the natural test. This is due to the fact that the high-voltage source is already switched to the test switching point before the main-current zero, so that the two currents are superimposed at the switching point and therefore yield a value which is too high. “The circuit diagram of this “test setup” is elementarily obtained by resituating the Weil circuit (
FIGS. 1 and 3
respectively).
This circuit is a synthetic test circuit which was already known to “AEG-Transformatorenfabrik Oberschoeneweide (Berlin)” under the designation “artifical circuit” (J. Biermanns); famous names in high-voltage engineering and circuit-breaker physics, such as G. Stem, J. Biermanns and O. Mayer, were associated with this factory, which established the world's first high-power testing laboratory (1912) but no longer exists today, and it is there that F. Weil worked.
The above-cited excerpt from the state of the art as base of the Weil circuit is the object of German patent specification 975 303, “Supplement to (Weil) patent 962 731”, dated Apr. 2, 1950, by inventor Guenther Dobke.
As already aptly mentioned by F. Weil, the superimposition of the main current and the current from the high-voltage source produces a significantly distorted synthetic current in the switching gap of the test circuit-breaker, compared to a homogeneous, sinusoidal current (
FIGS. 2
b
,
2
a
). Even if the synthetic current curve for the test circuit-breaker is determined graphically on the basis of physically correct assumptions about the oscillating current flow, the current distortion is still clearly visible: “Investigation of the AEG test circuit for high-power circuit breakers”, E. Slamecka, dissertation script, Graz Technische Hochschule in 1955 and IEC publication 60427, Third Edition 2000-04, page 95, FIGS. BB. 1 and BB. 2. Refer also to FIG. 12, Graph with broken polyline.
A synthetic test circuit with sequence current exclusively in the test circuit-breaker, and with a high-voltage oscillating circuit which is transferred during the operating time from a circuit connected in parallel with the auxiliary circuit-breaker to a circuit connected in series with the high-current source and the test circuit-breaker, is known from: IEC publication 60427, Third Edition 2000-04, page 97, FIGS. BB. 3 and BB. 4.
A more detailed examination reveals the relative complexity of calculating and handling this synthetic breaking-capacity test circuit. This is compounded by a further problem: in the event of a voltage breakdown in the switching gap of the test circuit-breaker—not an uncommon occurrence during the development phase of a high-voltage circuit-breaker—the insulation of the high-current circuit is abruptly stressed by the voltage of the high-voltage oscillating circuit.
A generally known solution for limiting the cost of synthetic breaking-capacity test circuits with synthetic current is to allow the zero of this current to be followed by a synthetic transient voltage, and to incorporate a second high-voltage oscillating circuit for this purpose using a second auxiliary circuit-breaker.
In German patent specification 1938 872 the first high-voltage oscillating circuit is initially connected in parallel with the test circuit-breaker with superimposed current and sequence current in the switching gap of this circuit-breaker~ the second auxiliary circuit-breaker is located in a conductor section of the first high-voltage oscillating circuit.
In German patent specification 25 28 100 the first high-voltage oscillating circuit is initially connected in parallel with the first auxiliary circuit-breaker, before changing to a series connection with the test circuit-breaker and the high-source; the second auxiliary circuit-breaker is arranged in a conductor section of the high-current circuit.
In the two synthetic, two-circuit test circuits the above-mentioned specific problems relating to the synthetic basic circuits still exist.
A synthetic test circuit for testing the making capacity of a high-voltage alternating-current circuit-breaker is known from IEC Publication 60427, Third Edition 2000-04, page 59, FIG. 6. A high-current switching spark gap is used to connect the high-current source to the test circuit-breaker electronically after the voltage from the high-voltage source has pre-arced in the circuit-breaker switching gap, to enable the high-current to follow the pre-arcing CUITent. With only one function, this spark gap is too little effective utilized in a synthetic test circuit from a technical and economical point of view.
The invention problems are as follows: first, to generate a transient high voltage, which continuously follows the zero crossing of the short-circuit current, at the switching gap of the test circuit-breaker in a high-current circuit with an auxiliary circuit-breaker, by means of a high-voltage oscillating circuit that cooperates with the high-current circuit by oscillating current supply into the auxiliary circuit-breaker and by transferring this oscillating current from the auxiliary circuit-breaker into the test circuit-breaker at a defined phase angle with constant parameters as sequence current of the hig
Grant Stephen L.
Hahn Loeser + Parks LLP
Le N.
Nguyen Vincent Q.
LandOfFree
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