US2872634A - Contact circuit for short circuiting device - Google Patents

Description

1959 HANS-JOACHIM KLEINVOGEL ETAL' 2,872,634

CONTACT CIRCUIT FOR SHORT CIRCUITING DEVICE Filed March 13, 1956 2 Sheets-Sheet 1 1&5

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| \K] I l \ILHA Feb. 3, 1959 HANS-JOACHIM KLEINVOGEL ETAL 2,872,634

CONTACT CIRCUIT FOR SHORT CI RCUITING DEVICE Filed March 13, 1956 2 Sheets-Sheet 2 Amy/V675 United States Fatent {35m CONTACT CIRCUIT FOR HORT CIRCUETING DEVICE Hans Joachim Kleinvogel, Berlin Siemensstadt,

Dietrich von Haehier, Berlin-Charlottenhurg, many, assignors to Siemens-Schucirertrverlre in. Berlin and Erlangen, many and (Ger- G., Germany, a corporation of Ger- My invention relates to a circuit for initiating the operation of a short circuiting device for short circuiting the contacts of contact converters of the type shown in copending application Serial No. 301,880, filed July 31, 1952, now Patent No. 2,759,128.

Contact converters of the type referred to above utilize a pair of cooperating contacts for synchronously connecting and disconnecting an A.-C. source and D.-C. load whereby an average voltage is impressed across the D.-C. load. Contact operation is carried out under as low a current as possible so that appreciable contact life may be attained. To this end, commutating reactors of the type described in U. S. Patent No. 2,693,569, to E. i. Diebold are connected in series with the cooperating contacts to ensure a step of current of relatively low magnitude in which the contact may be safely operated.

In the event of a fault or so-called are back, in order to prevent damage or destruction of the contacts, a short circuiting means therefore is usually provided, the operation of which is initiated by a means which senses this fault condition.

In the past, circuit means for sensing the fault condition and initiating the operation of the short circuiter are operative only after a contact is disengaged under fault conditions or disengaged at a time after the protective step of the commutating reactor has ended.

The principle of my invention is to provide circuit means which is operative to sense fault conditions even before the contact has disengaged, as well as after the contact has disengaged if the fault occurs at this time so that the short circuitiug protective means is energized as soon as possible.

More specifically, I provide within my novel circuit a first means to determine the point at which the commurating reactor step occurs and a second means to determine the point at which the contact is opened. I then compare these two times and if they do not coincide, then the short circuiter operation is initiated. Hence, if the contact is opened prior to the commutating reactor protective step, the short circuiter will be initiated at this very early time to thereby provide subsequent protection for the contact in the faulted phase as well as protection for contacts of any other phases present in the converter device. Similarly, if the contact opens after the protective step has ended, then as in the prior art protective means, my novel circuit will cause operation of the short circuiter for subsequent contact protection.

Accordingly, a primary object of my invention is to provide an energizing means for short circuiting devices.

Another object of my invention is to provide an energizing means for the short circuiter of a contact converter wherein a signal will be initiated if the cooperating contact is opened prior to a low current step.

A still further object of my invention is to provide an energizing circuit for short circuiters which initiates oper ation of the short circuiter when the contact is opened 2,872,634 Patented Feb. 3, 1959 either before the low current protective step or after the low current protective step.

Another object of my invention is to provide a circuit for operating a short circuiter device which measures the interval during which a commutating reactor is unsaturated and if the contact in series with the communicating reactor is not opened within this interval, will then deliver a signal to operate the short circuiter.

These and other objects of my invention will become apparent when taken in conjunction with the drawings in which:

Figure 1 shows the current time characteristic of the current through the contact of a mechanical converter wherein contact interruption occurs within the low current step.

Figure 2 is similar to Figure 1 and shows contact interruption occurring after the end of the low current step.

Figure 3 is similar to Figures 1 and 2 and shows the point of contact interruption occurring prior to the beginning of the low current step.

Figure 4 shows a first embodiment of my novel circuit when taken in conjunction with a three-phase mechanical rectifier.

Figure 5A shows the voltage time characteristic of the voltage appearing on the auxiliary winding of the commutating reactors of Figure 4.

Figure 5B shows the voltage time characteristic of the voltage induced in the circuit of Figure 4 for indicating the point of contact interruption.

Figure 5C shows the voltage time characteristic of the resultant signal due to the voltage of Figure 5B.

Figures 6A and 6B show how the signal due to' the commutating reactor step and the signal due to the point of contact interruption are combined under normal contact interrupting conditions.

Figures 7A and 7B are similar to Figures 6A and 6B but are for the condition of contact interruption at a point prior to the initiation of the low current step.

Figure 8 shows a second embodiment of my novel invention wherein the circuitry for measuring the contact interruption point has been varied from that shown in Figure 4.

Figure 9 shows a still further embodiment of my novel invention when adapted to a converter having first contacts for making operation and second contacts for breaking operation.

Referring first to Figures 1 through 3, there is shown a current characteristic of the current passing through the contact of a converter device, this current being identified by the letter I. At the time r it is assumed that a contact of a succeeding phase is closed and the current of this succeeding phase and the phase of Figures 1, 2 and 3 commutate from the time t to the time 1 That is to say that during the interval t to t the current of the succeeding phase will increase from substantially zero to its maximum value whereas the current J of the Figures 1, 2 and 3 will decrease from their maximum value to a minimum value which is given by the magnetizing current of the commutating reactor creating the low step current.

In the case of Figure l, the time t which is approximately midway between the beginning and end of the low current step indicates the desired point of contact interruption. This point is to be desired since it affords a certain amount of flexibility to the operating means which operates the contact into and out of engagement. That is to say, small inaccuracies in this operating means will not be sufficient to move the point 1 out of the step interval.

In the case of Figure 2, it is seen that the point 1 which is the point of contact interruption is beyond the end of the step created by the commutating reactor.

This condition could be caused by any number of things such as echanical breaka'ge, rapid changes in electrical conditions and so on. Figure 3 indicates just the opposite possibility wherein the point of contact interruption t occurs prior to the initiatien of the low current step.

In the event of the existence of a condition as seen in Figure 2 or 3, viz. contact interruption outside of the low current protective step, it is understood that arcing will occur which arcing could be followed by contact destruction as Well as subsequent contact destruction of other phases of the unit. In order to prevent this, it has been the practice to provide short circuiting devices which will short circuit the converter contacts and the unit is subsequently disconnected from .the main power source by other circuit interrupting equipment.

In the past, however, operation of the short circuiting devices was not initiated until after the end of the low current protective step and the occurrence of a relatively large amount of reve'rsec'urrent through the faultycontact. As will be shown hereinafter, my invention contemplates a circuit for initiating operation 'of' the short circuiting equipment at a time prior tothe occurrence of this relatively large magnitude of reverse current in the event that the contact is opened prior to the low current step as is shown in Figure 3. i

Figure 4 shows the schematic View of a three-phase rectifier which is provided with a short circuiting protective means, this short circuiting protective means being energized by my novel circuit. More specifically, Figure 4 shows a converter which is energized by windings R, S and T which'could be the secondary windings of a threephase transformer energized from an A.-C. line. In series with each of the'phases R, S and T is the main winding 1 of a commutating reactor 2, a pair of stationary contacts 3, and the D.-C. circuit including a stabilizing choke 5 and a D.-C. load 6. The stationary contacts 3 are synchronously engaged by the movable bridging contact 7 which moves into and out of engagement with the contacts 3 in accordance with the frequency of the A.-C. source by a motor schematically indicated as motor M. i

A short circuiter shown generally at 8 is then provided and comprises a movable winding 9 and a plurality of stationary contacts It). It is seen that each of the contacts it} is connected to each phase in such a manner as to bypass the contacts of each phase and the D.C. load when the armature 9 is moved into engagement with the contacts 10.

A 'coil 11 is then shown as being provided for the short circuiter 8, it being understood that coil 11 could be but one coil of a complicated magnetic system wherein energization of the coil 11 is efiective to move armature 9 into contact engagemen'twith the plurality of contacts 10, thus eflfecting short circuiting of these contacts. Hence by causing energization of the coil 11 at a time in which the'point of contact interruption does not fall within the low current protective step given by windings 1 of commutating reactors 2, it is seen that the desired protection is achieved. Y Y

My novel energization circuit is comprised of permament magnets 12 which are fastened to the movable magnets "7, windings 13 which are constructed to have the permanent magnets 12 movable therethrough upon movement of movable contacts 7, diodes 14-, the gas tube 16 having a grid 15, the cathode resistor 17, and condenser 18. A second gas tube 20 is then provided having a grid 19, the potential of which is determined by the potential of windings 21 of commutating reactor 2 and the direction in which the diodes 22 are connected for current conduction. a

It is to be noted thatthis tube 20 could be. replaced by any switching means having an output circuit which would include the energizing coil of a short circuiter and an input circuit for firing or triggering the switching means which would include the measuring output ofthe commutating reactor step and the point of contact interruption.

The potential of windings 21 appears on the grid resistor 23 which is connected to grid 19 and in series with cathode resistor 17 of gas tube 16. A first source of p itive plate potential schematically shown by terminal for gas tube 16 is shown as coming through the resistor 31, the plate of the gas tube 16, the cathode resistor 17 and back to a negative potential terminal 3112. ii i the positive plate potential for gas tube 2% is by the capacitor 24 which is charged in series schematically shown positive source terminal 32:! and resistor 32, this plate circuit including the plate of tube 2% and the winding 11 of the short circuiter 8. ordingly, it is now seen that when the gas tube 28 fires to appropriate grid potential on the grid 13 men the winding 3.1 will be energized and short circuiter operation will proceed.

The operation of the circuit of Figure 4 proceeds as follows: During movement of the movable contact '7, the permanent magnet is moved within the magnet 13 to thereby produce the output potential shown in Figure 5B for each of the three phases. It is seen that this output potential is unidirectional in view of the blocking action of the rectifiers 14 It is further noted that this potential is impressed in series with a capacitor 18 which converts the potential of Figure SE to the pulse like potential of Figure 5C. The potential of Figure 5C is then impressed across the plate circuit of thyratron i6 and an output of similar shape appears across the resistor 2.7. it is this potential across the resistor 17 as will be seen hereinafter which indicates the point at which contact interruption occurs for each of the phases and is compared to the step interval of the ccmmutating reactor.

A measure of the commutating reactor step interval is obtained from the windings 21 which have a voltage appearing thereacross during unsaturation of the commutating reactors 2. The potential appearing across the grid resistor 23 of tube 20 is seen in SA, this potential being a unidirectional one in view of the blocking diodes 22.

It is now to be noted that the potential due to the windings 21 of the commutating reactor is impressed on the grid 19 as negative potentials. The total potential on grid 19 may be seen to comprise the potential of Figure 5A across resistor 23 as well as the potential across resistor 17 which is in series with resistor 23 and is the pulse like potential of Figure. 50. Furthermore, the potential of Figure 5C whichfis impressed across the resistor i7 is in a direction opposite to the potential across the resistor 23.

Figures 6A and 6B show the operation of my. novel circuit whenthe potentials across resistors 17 and 23 are combined when the contact '7 is opened in the middle of the commutating reactor step. Figure 6A more specifically shows the contact current I and the point of contact interruption t occurring approximately in the middle of the low current step. Figure 6B which is plotted on the same time axis as Figure 6A then shows the superposition of the potential due to the step of the commutating reactor of Figure SA as well as the potential appearing across the grid resistor 17 of Figure 4 due to the opening of the contact 7. e

The line marked ignition voltage in Figure 6B to which the voltages of Figures 5A and 5C are referred to is the potential required on grid 19 of gas tube 20 to fire the tube. In the case of the normal operation of Figure 6A, it is seen that the superposition of the commutating reactor voltage and the contact voltage are insufficient to exceed this ignition voltage in a positive direction since the commutating reaction voltage which is negative exceeds the magnitude of the voltage of resistor 17 which is positive.

It is to be further noted that even if the contact open- ,ing interval had occurred at the. very beginning of the step where the commutating reactor step voltage is at its lowest value, the pulse voltage of Figure C when superimposed as in Figure 68 would still not have been sufiicient to exceed the ignition voltage of gas tube 20.

When, however, as in the case of Figures 7A and 7B, the point of contact interruption occurs prior to the commutating reactor step, then the superposition of the voltages appearing across resistor 23 and resistor 17 will indicate that at the point or" contact interruption, the only voltage present will be the voltage due to the opening of the contact 7 which voltage will exceed the ignition voltage of the gas tube 2a to thereby efiect firing thereof. That is to say, when voltage appears across resistor 17 in the absence of an opposing voltage in resistor 23, the gas tube 26 will be ignited. Upon ignition of the gas tube 2t it is now apparent that winding 11 ofthe short circuiter 3 will be energized, thus initiating the operation of the short circuiter for subsequent protection of the contacts 3.

A variation of Figure 4 may be seen in Figure 8 wherein the permanent magnet arrangement utilized for measuring the point of contact interruption is now replaced by means of D.-C. circuits for each contact which circuits include the stationary contact 25, D.-C. source 26, transformer primary windings 27, secondary windings 28 and the diode 29. In place of the cathode resistor 17 of Figure 4, I now utilize a resistor which serves the same function. In the case of Figure 8, it is seen that upon contact interruption that the voltage appearing between the stationary contact 25 and the movable contact 7 will appear across the primary winding 27. This voltage will then be induced into the secondary windings 28 which voltage is rectified by rectifier 29 and impressed across the resistor 3tl. Hence the beginning of this voltage for each phase serves to give a measure of the point at which contact interruption takes place and operation of the complete circuit will proceed in the same manner as described above in connection with Figure 4.

It is to be noted at this point that in the case of each of Figures 4 and 8, that short circuiter operation will be initiated whenever the point of contact opening is outside of the commutating reactor protective step, that is, if the contact is separated after the end of the low current protective step, then as in the case or" the prior art devices, short circuiter operation must subsequently follow. If, however, this point of contact opening takes place before the initiation of the low current protective step, then at this point, short circuiter operation will be initiated without having to wait for the appearance of reverse current throughout the arcing contact.

Figure 9 shows a further embodiment of my novel invention as specifically applied to a contact converter having one set of contacts for making operation only and a second set of contacts for only breaking operation. That is to say, contacts 3e operate after operation of contacts 3a to close the phase in which they are associated. Hence, they see making duty only. .Sirnilarly, contacts 3a are opened prior to opening of contacts 3e and hence are subjected to breaking duty only.

In the case of Figure 9, I provide a first short circuiter system which as in the case of the prior art is operative to cause short circuiter operation only after the end of the low current interval. I then, h wever, provide a second circuit which is efiective to cause short circuiter operation when the breaking contacts 3a are opened prior to the initiation of the low current step.

For the device which operates in the prior art manner, there is provided a current transformer 36 for each phase of the system and a rectifier 37 which rectifies the three phase output of the current transformer 35. This rectified output is impressed upon the winding 38 of transductor 39 while a second input to the transductor 39 is an input which is proportional to the D.-C. load current through the load 6 as is shown by the single wire 3942 through the center of the transdsctor.

During normal operation (in the absence of reverse current in any phase), the ampere turns due to winding 39 are suflicient to exceed the ampere turns of winding 38 to thereby maintain transductor 39 saturated in one direction. When, however, reverse current appears in any of the phases, the ampere turns of the winding 33 increases rapidly to overcome the ampere turns of winding 39a and thereby drive transductor 39 to unsaturation. Upon reaching this unsaturated condition, a voltage will be generated in winding 40 which voltage is effective to energize winding 41 of short circuiter 8 to thereby cause operation of the short circuiter.

I then provide a second circuit which is effective to cause operation of the short circuiter in the event that contact separation occurs prior to the initiation of the low current step. This circuit is seen connected across the breaking contact 3a, each phase being connected to a rectifier 43 which is connected to energize a winding 44 of the short circuiter 8. The current flowing through the winding 44 during normal contact opening conditions is as seen in the dotted portion of Figure 6A a relatively low current which is so adjusted as to be incapable of operation short circuiter 8. If, however, contact opening proceeds before initiation of the low current step, then as is seen in the dotted portion of Figure 7A, a current of relatively high magnitude will flow through rectifier 43 to winding 44 of the short .circuiter 8 to cause operation thereof. Clearly this same operation could be described in conjunction with a mechanical converter or an electromagnetically operated converter having a single contact for both opening and closing operation.

Although I have described preferred embodiments of my invention, it will now be obvious that many variations and modification may be made by those skilled in the art. I prefer therefore to be limited, not by the specific disclosure herein, but only by the appended claims.

We claim:

1. An energizing circuit for a short circuiter adapted to short circuit a pair of cooperating contacts; said pair of cooperating contacts having a commutating reactor connected in series therewith; said energizing circuit comprising a first and second measuring means; said first measuring means being constructed to measure the step interval of said commutating reactor; said second measuring means being constructed to measure the point of contact interruption of said pair of cooperable contacts and circuit connections for operating said short circuiter when said measured point of contact interruption is outside of said measured step interval of said commutating reactor.

2. An energizing circuit for a short circuiter adapted to short circuit a pair of cooperating contacts; said pair of cooperating contacts having a commutating reactor connected in series therewith; said energizing circuit comprising a first and second measuring means; and means tocombine the outputs of said first and second measuring means; said first measuring means being constructed to measure the step interval of said commutating reactor; said second measuring means being constructed to measure the point of contact interruption of said pair of cooperable contacts; said means to combine the outputs of said first and second measuring means being operative to operate said short circuiter when said measured point of contact interruption is outside of said measured step interval of said commutating reactor.

3. A short circuiter for short circuiting a first pair of electrical contacts; said short circuiter comprising a second pair of contacts and an energizing winding; said second pair of contacts being constructed to be moved to an engaged position responsive to energization of said energizing winding; a commutating reactor, said commutating reactor being connected in series with said first pair of contacts; an energizing circuit; said energizing circuit comprising a first and second measuring means; said first measuring means being constructed to measure the step interval of said commutating reactor; said second measuring means being constructed to measure the point of contact interruption of said first pair of cooperable contacts and circuit connections forenergizing saidshortci'r cuiter energizing winding when said' measured point" of contact interruption is outside of said measured'step interval of said conirnutating reactor;

4. A short cir'ciiiter for short circuiting a first pair of electrical contacts; said short circuiter comprising a sec ond pair of contacts andan energizing'winding'; said'second'pair of contacts being'constructed to be moved to an engaged position'respon'sive to energization of said energizing winding; a commutating reactor; said con1mutat ing reactor being connected'in's'eries with said first pair of contacts; an energizing circuit; a' switching means; said switching meanshaving" a'n output'circuit and input circuit; said output circuit being connected't'o sai i short circuiter energizingwinding;said input circuitincluriing a first means for measuring the step interval of said commutating reactor and a second means'for measuring the point of contact interruption of said second pair of contacts; said input circuit being operative to energize said switching means to'initiateenergization of said energizing winding through said output circuit when said measured point of contact interruption is outside of said measured step interval of said cornmutatingreactor;

5. A short circuiter for short circuiting a first pair of electrical contacts; said short circuiter comprising second pair of contacts and an energizing winding; said second pair of contacts being constructed to be moved to an engaged position responsive to energization of said energizing winding; 21 eominutating reactor, said commutator reactor being connected in series with said first pair or" contacts; an energizing circuit; a switching means; said switching means having an output circuit and an input circuit; said output circuit being connected to said short circuiter energizing winding; said input circuit including a first means for measuring the step interval of said commutating reactor and a second means for measuring the point of contact interruption of said second pair of contacts; said input circuit being operative to energize said switching means to initiate energization of said energizing winding through said output circuit when said measured point of contact interruption is outside of said meas ured step interval of said commutating reactor; said switching means comprising a grid controlled gas tube; said input circuit being connected to the grid cathode circuit of said gas tube.

6. A short circuiter for short circuiting' a first pair of electrical contacts; said short circuiter comprising a second pair of contacts and an energizing winding; said second pair of contacts being constructed to be moved to an engaged position responsive to energization of said energizing winding; a commutating reactor, said commutating 'reactorbeing connected in series with said first pair of contacts; an energizing circuit; a grid controlled gas tube; said grid controlled gas tube having an outputsufiicient to fire said gas tube, the net magnitude of bothof said potentials being of too low a magnitude to fire said tube.

7. In a contact, converter for exchanging energy be tween an A.-C. system and a DC. system; a cornmutat ing reactor and a pair of cooperating contacts; said pair of cooperating contacts being operated to connect said A.-C. system, D.-C. system and commutating reactor in, series in synchronism with the frequency of said A.-C.

system; a short circuiter adapted to short circuit said pair of cooperating contacts and an energizing circuit therefor; said energizing circuit comprising a first and second measuring means; said first measuring means be= ing constructed to measure the step interval of said cominutating reactor; said second measuring means being constructed to measure the point of contact'interruption' of said pair of cooperable contacts and circuit connections for operating said short circuiter 'when said measured point of contact interruption is outside of said measured step interval of said commutating reactor.

8, in a contact converter for exchanging energy between an A.-C. system and a D.-C. system; a commutating reactor and a pair of cooperating contacts; said pair of cooperating contacts being operated to connect said A.-C. system, D.-C. system and commutating reactor in series in synchronism with the frequency of said A.- C.

system; a short circuiter adapted to short circuit said pair of cooperating contacts and an energizing Winding therefor; circuit connections for passing contact current through said energizing winding immediately after contact disconnection; said energizing winding being constructed to operate said short circuiter when the current therethrough is of a magnitude due to contact disconnection prior to the initiation of step current by said commutating reactor; the magnitude of step current being insufiicient to energize said energizing winding for operation of said short circuiten Busemann July 20, 1954 Owen Oct. 16, 1956

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