US2375609A - Arrangement for protecting circuit breakers - Google Patents

Description

y 1945' M. ZUHLKE v 2,375,609

ARRANGEMENT FOR PROTECTING CIRCUIT BREAKERS Filed July 10, 1941 2 ShGtS-Sht l lNVENTOR 'M/IRCEL Z Jm. AE

ATTORNEY.

y 1945. M. Z-UHLKE 2,375,609

ARRANGEMENT FOR PROTECTING CIRCUIT BREAKERS INVENTOR Mqaca Z (jHL/(E ATTORNEY Patented May 8, 1945 UNITED STATES PATENT OFFICE AKERS Marcel Ziihlke, Berlin No. 55, Germany; vested in the Alien Property Custodian Application July 10, 1941, Serial No. 401,786

In Germany May 23, 1940 4 Claims. (Cl. 175-294) This invention relates to an arrangement and a method for protecting circuit breakers, particularly relay contacts.

Relay contacts and many other contacts for switch gears are liable to be damaged by the current, particularly when being inserted in the circuit. The passage from the open to the closed position, during which the resistance of the contact has become sufliciently small in order to withstand the current occurring at the contact is not effected suddenly, but gradually. Consequently, if the current increases very rapidly upon the closing of the circuit as, for instance, occurs when switching in direct current or alternating current at a moment lying in the neighborhood of a maximum value of the current curve, the first sharp contact points evaporate. A metallic vapor arc is formed, by means of which a floating oi the contact may under circumstances occur, thus causing a considerable wandering of the material and under circumstances a welding of the contact.

The circumstances are still worse, if the contactarrangement vibrates as occurs mostly always with relay contacts, i. e., if the contact is lifted once more or several times before attaining the closed position. During this time a consumption of the contacts is not only caused by the corresponding switching-in operation, but also by the switching-off operation if the current has become sufiiciently high during this time. In the case of perfect contact arrangements all disturbing effects described above are avoided after a period of one millisecond or less.

The invention is based on this fact. The object of the invention is to provide means for protecting contacts which are operated at undetermined moments, by which means the current is limited to such a low value during the period of a possible deterioration of the contact as not to be detrimental, these means being caused to be actu ated automatically in accordance with the switching operation which begins at a moment impossible to be predetermined. I

A possibility of carrying the invention into practice consists in inserting a reactor of known type having a closed iron core in series with the contact and in bringing it to a predetermined state of magnetization before the beginning of the switching operation.

Figure 1 shows the magnetization characteristics of a closed iron core reactor in a switching circuit.

Figure 2 shows an iron core reactor in a simple est-ditching circuit.

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Figures 3, 4, 6 and 11 show the reactor applied to direct current circuits.

Figure 5 shows the reactor applied to either direct or alternating current circuits.

Figures 7 and 9 show forms of the invention suitable for alternating current circuits.

Figure 8 shows the relation of applied voltage to auxiliary exciting current in the case of Figure 7 Figure 10 shows the relation of applied voltage to auxiliary exciting current in the case of Figure 9..

Figure 11 shows a simplification of the arrange-- ment shown in Figure 3.

Fig. 1 shows the magnetization curve of a reactor with a closed iron core. If, as shown in Fig. 2, the reactor D is arranged in series with the circuit breaker S in the circuit of any device, resistance Z or the like, the magnetization curve of the reactor D shown in dotted lines varies when switching in the circuit breaker S from 0 (Fig. 1) up to the state of saturation in the case of correspondingly high current values owing to the current i brought about by the applied voltage u. Owing to the steep slope of the magnetization curve, the impedance of the reactor is at first, i. e. before the state of saturation is reached, very high so that the value of the current i immediately after the switching-in remains very low for a corresponding period, fOr instance, about a millisecond and may only thereafter vary in such a manner as it would do without the reactor. By suitably dimensioning the reactor a flattening of the current curve may be brought about at the beginning of the flow of the current in such a manner that the circuit breaker S is sufiiciently protected against damages by the current switched in.

If the circuit breaker s is again opened and therefore the current 1 tends to reassume the value 0, the value of the current flowing through the reactor varies only slightly owing to the high remanance in the iron core of the reactor; the reactor remains in the state of magnetization A. This is, as a rule, undesirable, since when the circuit breaker S is again closed only a considerably flatter saturation curve (shown in dotted lines) is attained which begins at the point A, so that during the second and all following switching-in operations of the circuit breaker S the desired flattening of the current curve is no longer attained. This difiiculty may be removed by bringing about a suitable state of magnetization by special measures before the beginning of a new switching operation, from which state a sufficient steepness of the magnetization curve is ensured up to the state of saturation during the following switching operation.

This may, for instance, be brought about by changing over the connections of the reactor between every two switching-in operations. The reactor winding is therefore connected substantially as is schematically shown in Fig. 3 with the circuit to be interrupted through change-over switches at, y. These change-over switches may be coupled in a suitable manner with the circuit breaker S or may be controlled under circumstances electrically in accordance with the circult breaker. If the reactor is then changed over after or during the reopening of the circuit breaker, the magnetization curve as regards the effect of the reactor is rotated 180 while retaining the state of magnetization present at this moment or in other words the starting point for the saturation is not the point A when the circuit breaker is again closed, but the point A of the magnetization curve. A sufilciently steep saturation curve is therefore again easily attained in order to flatten the current in a sufficient manner when switching in the circuit breaker. However, this arrangement and this method can be employed for direct-current circuits only, but not for alternating-current circuits, since in the case of an incidental switching-in of the current within the.

range of a negative half cycle the same drawback is again presented which should be avoided by the changing over of the connections of the reactor.

Another method of attaining a suitable state of magnetization at the beginning of the switching operation for direct-current circuits is shown in Fig. 4. Here the reactor is negatively saturated by an auxiliary direct current iv supplied by a voltage source E which is connected through a particular impedance J to an auxiliary winding of the reactor D. This auxiliary direct current maintains the reactor with the circuit breaker S open in a. predetermined state of saturation B which may be chosen in the neighborhood of the negative state of saturation (Fig. 1). Upon the closing of the circuit breaker S, the saturation curve varies beginning from the point B as shown in dotted lines so that also the desired steepness of the magnetization curve is ensured.

In most cases it will also be sufficient to connect the auxiliary winding of the reactor only instantaneously and not permanently to the auxiliary voltage by means of an auxiliary circuit breaker s arranged in the auxiliary circuit. The starting point for the magnetization curve is then the point B after the reopening of the auxiliary circuit breaker s.

Fig. 5 shows a form of the invention for direct-current circuits also in which the reactor is negatively saturated after the reopening of the circuit breaker S by an aperiodical discharge surge of a capacitor C which is charged by any suitable separate current source (not shown) and which may be connected by closing an auxiliary circuit breaker s to the auxiliary winding of the reactor D, preferably also through a particular impedance or a resistance R.

Fig. 6 shows a connection in which the current consuming device Z is supplied with energy through the circuit breaker S and the reactor D from a condenser K which is charged, for instance, by a current course (not. shown). In this case the desaturation or the negative saturation of the reactor D is effected after the reopening of the circuit breaker S by means of a surge serving to charge the condenser K and which is supplied by a direct-current source. for instance, by a rectifier G. The latter is preferably inserted togcther with a suillciently large damping resistance R in the same circuit in order that the current consuming device Z is not prevented from being supplied with energy by the condenser K.

The voltage of the source U is such that when the circuit breaker S is opened current passes through the reactor coil from right to left, thus charging the condenser and imparting to the reactor the desired negative saturation. When the circuit breaker is closed the excess charge on the condenser is discharged through the consuming device Z.

A further form of the invention which may be employed not only for direct-current circuits, but also for alternating-current circuits consists in the fact that the reactor after the reopening of the circuit breaker to be protected becomes desaturated by the periodically fading discharge current of a condenser. For this purpose. the same connection may be employed as shown in Fig. 5, except that the total resistance of the auxiliary circuit must be so dimensioned and tuned with the condenser C that the discharge fades out periodically, thus causing the state of magnetization of the reactor to traverse the hysteresis loop several times during the discharge of the condenser C, the state of magnetization finally assuming the value 0 or a value lying in the neighborhood of O, insofar as the amplitude of the current decreases constantly. The reactor is then again ready to operate in both directions; i. e.. the desired steepness of the saturation curve is ensured irrespective of whether the current is positive or negative at the moment when the switching-in operation occurs. Consequently, such a connection may not only be employed for direct current, but also for alternating current.

However, in contradistinction thereto connections in which the reactor not only becomes desaturated before the beginning of the new switching operation, but becomes saturated according to the polarity opposite tothe momentary value of the current during the switching operation (negative in the case of a positive inomentary value of the current) have the advantage in that the reactor may be utilized in a particularly favorable manner.

A form of the invention suitable for alternating-current circuits is shown in Fig. 7. Here the reactor D has an auxiliary winding which is biased by an alternating current of frequency equal to the applied voltage of the circuit to be closed, but of opposite phase with respect to the applied voltage. Fig. 6 shows the variation of the applied voltage u and the auxiliary exciting current iv with time. If the circuit breaker S is closed at any moment, the reactor is preexcited according to the polarity opposite to the corresponding momentary value of the applied voltage. When the momentary value of the applied voltage and of the auxiliary exciting current is zero the reactor is, however, in an undetermined state as to the relation between the state of magnetization and the polarity of the applied voltage, whereas in the case of switching operations which commence, for instance, incidentally in this moment or in the neighborhood thereof, the stress of the circuit breaker brought about by the current is also very small, since the applied voltage is approximately zero.

According to another form of the invention it is possible to attain with an alternating current at any moment of phase a pro-excitation of the reactor in a negative direction with respect to the corresponding value of the applied voltage. This is shown in Figs. 9 and 10. As shown in the connection in Fig. 9 an auxiliary reactor H is arranged in the auxiliary circuit. The curve of the auxiliary current iv (Fig. 10) is distorted by the auxiliary reactor H in such manner that it is considerably flattened when the current passes each time the zero value. By correspondingly arranging additional impedances J (inductances, capacities) in the auxiliary circuit the mutual position of phase between the applied voltage u and the auxiliary current iv Fig. 10) may be so chosen that the reactor D whose hysteresis loop is shown at the left side of Fig. 10 is negatively pre-excited at each moment with respect to the momentary value of the applied voltage.

The possibilities of carrying out the invention are by no means limited to the forms of invention described above. The above forms of the invention may be employed to advantage separately and jointly or in any combination in any type of switch devices.

Thus, for instance, Fig. 11 shows a simplification of the arrangement shown in Fig. 3.

Here the reactor D is provided with two wind-- ings connected in opposition or with a single winding having a tapping in the center thereof. The two-pole change-over switch at, y of Fig. 3 is combined with the circuit breaker S to form a single circuit breaker. To close the circuit, the circuit breaker S is move in the upward or in the downward direction. By such a periodical switching-in, the reactor as will easily be apparent is biased in the proper direction so that upon each switching in of the circuit breaker the point A of the magnetization curve according to Fig. 1 is the starting point for the saturation.

What is claimed is:

1. A device for protecting circuit breakers such as relay contacts comprising a reactor with a closed core connected in series with the circuit breaker and means for reversing the connections a to said reactor between successive closings of the circuit breakers.

2. A device for protecting circuit breakers comprising a reactor with a closed core connected in series with the circuit breaker and means for reversing the connections to the reactor on the opening of the circuit breaker.

3. The combination with a circuit breaker having three contacts and movable to connect either of two contacts with the remaining contact. a source of current, a reactor having a unidirectional winding, a source of current connected to an intermediate point of said winding and to said remaining contact and connections between said two contacts and opposite ends respectively of said winding, whereby on alternately closing the circuit through one and the other of said two contacts the magnetism of the core is reversed.

4. A means for protecting a circuit breaker comprising a source of current, a consuming de- Vice; a reactor with a closed core connected in series between said source, device and breaker, a condenser bridging said source, a circuit bridging said condenser and reactor, said circuit including an auxiliary source of unidirectional current of higher voltage than said first mentioned source and a resistance in series with said auxiliary source.

MARCEL ziiHLKE.

CERTIFICATE OF CORRECTION.

Patent No. 2,575,609.

May 8, 1914.5

MARcEL zi'IHLKE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 72, for "course" read "source"; page 2, second column, line 59, for "Fig. 6" read ---Fig. 8"; page 5, first column, line 56, for "move" read -moved-; and that the said Letters Patent shouldvbe read with this correction therein that the some may conform to the recorder the case in the Patent Offic e Signed and sealed'this 31st day of July, A. D. 1911.5.

(Seal) Leslie Frazer Acting Commissioner of Patents.

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