US 3558977 A
Description (OCR text may contain errors)
FOR DETECTING THE LEADING EDGE OF THE ARC VOLTAGE AT THE CONTACTS THEREOF 5 Claims, 1 Drawing Fig.
0 United States Patent 1 13,55s,977
72] Inventor Remy A. Beaudoin  Reference Cited I N ;5':; UNITED STATES PATENTS :3 I Q 7 968 3,309,570 3/1967 Goldberg 317/1 1  Pmemed Jam 26, 971 3,408,538 l0/l968 Gurwicz 307/136X  Assignee La Telemecanique Electrique Primary Examiner-James D. Trammell Nanterre, France Assistant Examiner-Harvey F endelman  Priority Aug- 1967 Att0rneyRaym0nd A. Robic 133 France 31 1 117857  HYBRID CIRCUIT BREAKER HAVING MEANS ABSTRACT: A hybrid circuit breaker comprising a pair of contacts actuated by an electromagnet, a thyristor for shunt- US. Cl 317/ l 1, ing the contacts, an extinction condenser for the shunt 307/ l 36, 317/33, 3 l 7/3l thyristor, an extinction thyristor adapted to control the Int. Cl H02h 3/00, discharge of the condenser, and a circuit for controlling the H0lh 9/30 firing of the thyristors comprising a circuit for differentiating Field of Search ..33 5lllnquired Broom); the leading edge of the arc voltage across the contacts and a 3l7 l l 31,33, monostable multivibrator responsive to the leading edge of 307/136; 321-/(Inquired Bhoop); said arc voltage for generating an impulse for firing the shunt ZOO/(Inquired Macon) thyristor.
A "9 A f;(; 'f" r- 1- 1 1% PATENIH] JAN'26 I971 INVENTOR Remy A. BEAUDOIN ATTORNEY HYBRID CIRCUIT: BREAKER HAVING MEANS FOR DETECTING THE LEADING EDGE OF THE ARC VOLTAGE AT THE CONTACTS'THEREOF The present invention ,relates to circuit breakers called hybrid circuit breakers, inwhich a controlled rectifier, usuallya thyristor, shunts the contactsofthe circuit breaker when they are open usually by means of an electromagnet. This prevents the buildup of anarc across the contacts. but the latter, during the working cycle of the circuit breaker, generally carry alone the flow of current so that the thyristor is subjected to large thermalstrains only for short intervals of time. For this purpose, it is known to provide means for ensuring the extinction of the shunt thyristor, these means comprising, in certain hybrid, circuit breakers, a condenser and a thyristor which controls the sudden discharge of the condenser across the terminals of the shunt thyristor. A monitoring device responsive to the voltage, across the contacts ensures the ignition of theshunt thyristor and of the extinction thyristor. I
In accordance with the invention, the monitoring device, whose supply is provided by the source of the excitation current of the electromagnet which operates the contacts, is an electronic circuit comprising a network for differentiating the leading edge of the are voltage established at the contacts at the opening thereof, and means responsive to the pulse resulting from such differentiation for controlling the conduction of the shunt thyristor during a period of time which is short and well defines defined.
With the above arrangement, the shunt thyristor is subjected, at the opening of the contacts. only to an overload of very short duration and properly controlled, so that a thyristor having a relatively small power rating may be used and that consequently an important saving may be effected.
In accordance with a characteristic of the invention, the monitoring circuit is arranged so that the shunt thyristor is fired at each rebound of the/contacts for a period of time corresponding to that of the rebound-This permits to completely eliminate the risk of damaging the contacts.
The various characteristicsas-well as the advantages of the The attached single figure of drawing represents the electrical diagram of a hybrid circuit breaker in accordance'with the first embodiment.
The circuit comprises a thyristor TH, connected in parallel with contacts P operated. by an'electromagnet B. This combination controls the flow through aload L of a-current fed by a source of DC voltage connected between terminals V,, and ground.
Electromagnet B is excitedby a control current which may be fed orinterrupted by knownmeans illustrated in the drawing by means of an interrupter I, Thezcircuit illustrated in the drawing is particularly adapted.to}the case where the control current is a'fullyrectified single phase current,.but the invention is not limited to this case.
Likewise, the invention is not limited to the case where the source of voltage), is a DC source. However, it is in such a case that the problem of extinguishing the are which is initiatedat the opening of the contacts is more difficult to solve and, that,consequently, the interest of the invention is the largest.
The circuit further comprises a thyristor TH,, aresistor R,, a thyristor Th and a condenser'Q-connected as indicated in denser C, and'a resistor R and a circuitt'or selecting positive impulses comprisinga diode D,, resistors 27 and 28 and a Zener diode D2,.
Block A is a monostable multivibrator comprising two transistors T, and T resistors R, to R,,, and a condenser C BlockA, is a current amplifier comprising a transistor T,
I connected as an emitter follower by means of resistors R, and
Blocks A, to A, comprise a control chain for thyristor Th and for a thyristor Th The latter, together with resistors R and R formsa block A,, whose function will be explained later a I Block A includes a differcntiator circuit consisting of a condenser C connected to a junction point between resistors R9 and R of block A,,, of a resistor R,, and of a circuit for selecting negative impulses, comprising a diode D and a resistor R,,.
Block A,, is an inverter circuit comprising a transistor T,, a condenser'C, and resistor R and R,,.
Block A,, is a gate comprising diodes D and D, and a resistor R,,,.
Block A, is a ctlrrent'amplifier consisting of a transistor T and resistors R to R,,,.
Block'A wh ose function will be explained later, comprise s I a diode D, and a resistor R, connected in series to the excitation terminal of electromagnet B, and a condenser C, in parallel. I
Blocks A,,, to A,,, constitutes a control chain for thyristor Th Block A,,, is an'inverter circuit comprising a transistor T,,, diode D and resistors R, to R Block A,, includes a differentiator circuit consisting of a condenser C of a resistor R and of a circuit for selecting positive'impulses, comprising a diode D and a resistor R Block A,, is an amplifier comprising a transistor T,, which block A, comprises an impulse transformer T, and a resistor 24. The secondary winding of transfonner T, is connected, on the one hand to control electrode G and on the other hand to point M which'is common to resistor R, and thyristor Th The operation of the illustrated embodiment is as follows:
A few dozen milliseconds after electromagnet B has been energized, i.e. after, contacts P are closed. At the time of the energization of electromagnet B, thyristor Th, is not conducting so that, at theclosu'reof the contacts, the current fed by voltage source V,, flows through load L and through the contacts P only. In the absence of any bouncing of the contacts, it will beseenlater that the electronic circuit does not operate at the time of closure of the contacts. The device then works as a conventional circuit breaker, which is the result sought, because there is no formation of an arc and the operation of the shunt thyristor is not required.
At the time of closure of contacts P, the differentiator circuit including condenser C, and resistor R is subjected to a sudden variation of voltage, because the voltage across the contacts P drops'from +V,, to 0 volt. The negative impulse the drawing, and anelectronic circuit comprising the blocks A, to A which will now be disclosed. The invention is mainly concerned with the design of this electronic circuit. As a matter of fact, the use of athyristor to shunt the contacts P (such a s TH,),-of a thyristor (such as TH,,) to control the the extinction of the shunt thyristor,.and of a condenser-(such as C) whose discharge causes the above extinction is well known in the technique of hybrid circuit breakers. Moreover, thyristor Th, only performs, as it will be seen later, an auxiliary function.
which is thencreated across resistor R is obviously blocked by diode D,, so that the blocks A,, and A do not operate.
On the contrary,'when the contacts P bounce the voltage across them varies'suddenly from a null value to a value of the order tol2 volts, which corresponds to the beginning of the development of an arc.
The result of the above is a waveform which results in a positive'impulse at'the tcrminal'of resistor R This positive impulse flows through'D, and is applied through resistor R and R, to the base of transistor T,. Zener diode D has an inverse voltage characteristic which is higher than the amplitude of the impulse, so that it does not break down. Transistor T, becomes conductive and a negative impulse appears between its collector and emitter electrodes. Before the formation of this negative impulse, transistor T whose base is connected by means of resistor R,, to the positive supply voltage of the electronic circuit (this supply voltage is provided by condenser C charged through resistor R, by the excitation current of electromagnet B at the closure of interrupter l), was conductive and condenser C was charged.
The negative impulse causes the discharge of C through resistor R During the discharge of condenser C whose discharge time may be varied through adjustment of resistor R,,, transistor T is blocked. The result is that during this well defined period of discharge, there appears on the collector of transistor T a positive rectangular impulse. The impulseamplified by transistor T provides. through resistor R,,, the current required for the firing of thyristor Th,. The latter further has at its terminal the beginning of the development of the arc voltage and so becomes conductive during the whole period of the rebound.
At the end of the rebound, the contacts of the circuit breaker are closed, and the voltage across them and at the terminals of thyristor Th, becomes null so'that thyristor Th, is extinguished. Y
In order words, during each of the consecutive rebounds which may happen, the contacts of the circuit breaker are shunted by thyristor Th, which replaces the contacts. This is a very important advantage of the invention, because this prevents the dissipation of energy in the form of heat during the rebound, and eventually, the premature destruction of the contacts.
When a signal for opening the contacts is provided, the electronic circuit continues to be fed by a positive voltage during a time sufficiently long to permit its operation, through condenser C, whose discharge time constant through the circuit is chosen at a value sufficiently long to this effect. The result is that thyristor Th, is fired under the control of the chain A,, A A This chain works in the same way that when the contacts were open under the action of rebound, and so prevents the development of an are at the terminals of the contacts. lt will be seen later how thyristor Th, is extinguished at the end of a predetermined period. I
The firing impulse of thyristor Th, is moreover applied to block A,,' and differentiated by circuit C,, and R,,, which generates a positive impulse corresponding to the leading edge of the firing and a negative impulse corresponding to the trailing edgethereof. The negative only flows through diode D and is applied, by means of condenser C,, to the base of transistor T During the whole time a contact-closing signal is provided, that is, until the end of the rebounds, condenser C, has acquired and maintained a charge sufficient to feed the control electronic circuit. This renders transistor T conductive, its base being connected to one terminal of condenser C, through resistor R 13, and condenser C, is charged.
The negative impulse flowing through diode D causes the discharge of condenser C, and so blocks transistor T during a predetermined interval depending on the values of condenser C,, and resistor R,,. The result is the appearance during such period, of a positive impulse, which is applied through resistor R, to gate A,,.
As long as a contact-closing signal is provided, transistor T is conductive and its collector electrode is subjected to a small voltage. Indeed, condenser C,, is rapidly charged through resistor R,, as soon as interrupter l is closed. The base current of transistor T is then established before the appearance of the voltage at the terminals of capacitor C,, consequently before the collector voltage of transistor T exceeds the saturation value, namely 0.5 volt for example. This voltage of 0.5 volt is maintained as long as capacitor C,, stays charged, that is as long as the contacts of the circuit breaker are not opened. The positive impulse applied to resistor R,,, in case of rebound is then grounded through diode D and transistor T,,. 153 Blocks A, and A do not operate, which is desirable because the extinction of Th, must be produced at the end of each rebound and not controlled by Th On the contrary, when a contact opening signal is provided transistor T,, is blocked and gate A is opened. Capacitor C is then discharged through the control circuit in a few milliseconds, while capacitor C,, which is discharged in a much longer time through resistor R continues to feed the elec tronic circuit until the firing of thyristor Th Consequently, as soon as C,, is discharged, transistor T is blocked and its collector voltage takes the value of the voltage at the terminals of C,, that is for example 30 volts which is sufficient to block diode D The positive impulse applied to resistor R,,, is then amplified by transistor T The result is that the control electrode of thyristor Th is excited through resistor R,,, and that the control electrode of thyristor Th, is excited through resistor R,,,
The firing of thyristor Th so initiated causes, in a known manner, the discharge of the extinction condenser C and the appearance of an inverse voltage at the terminals of thyristor Th, which causes its extinction. Thyristor Th is extinguished as soon as the inverse discharge current of condenser C reaches the value of the sustaining current through thyristor Th which is produced for example in less that 500 microseconds. lt is important to note that when the contacts open, thyristor Th, remains conductive for a period of time which is rigorously determined by the duration of the impulses generated by monostable multivibrator A for example for l to 3 milliseconds depending on what is required to prevent the are, as a function of the speed of contact opening and of the value of the operating voltage. As a matter of fact, it is only at the end of these impulses that the firing impulse is initiated. The duration of the firing impulse which is determined by A is established at a value such as to cause the firing of the thyristor.
The firing of thyristor Th, caused by the positive impulse applied through resistor R, and resistor R, has the effect of discharging condenser C, through resistor R The electronic circuit ceases to be energized and the sequence of operation of the circuit breaker is terminated. Because of thyristor Th,,
7 the electronic circuit is no more energized after the extinction of thyristor Th, so that the overvoltage which occurs, across the contacts at the time of their effective opening, does not have any effect, which constitutes a useful safeguard.
If we consider now the control chain of thyristor Th,,, it is seen that, at the time of the closure of the contacts, block A, does not operate, which is the result sought as mentioned previously. As a matter of fact, at the time of closing the interrupter I, it has been mentioned above that the voltage between the collector and emitter electrodes of transistor T does not exceed the saturation value thereof, that is 0.5 volt for example. The variation of this voltage from O to 0.5 volt is insufficient to cause conduction of transistor T,.
On the contrary, upon the contact-opening signal being transmitted, it has been seen that the collector voltage of transistor T goes from 0.5 to 30 volts. The leading edge of the positive impulse corresponding to this variation is differentiated by circuit C,, and resistor R thereby initiating a positive impulse at the terminals of resistor R This impulse flows through resistor R to the base of transistor T and has the effect of rendering transistor T-, conductive, thereby causing the appearance of an impulse at the terminals of the secondary of transformer T, and, consequently, the firing of thyristor Th This thyristor, which only performs a secondary function, permits to obtain a more rapid charge on condenser C through resistor R (for example, a few milliseconds). The thyristor is extinguished as soon as the inverse charging current reaches the value of its sustaining current. The device has then come back to the initial rest position in which the thyristors are extinguished and condenser C charged.
If we now resume the operation which has been disclosed, we see that: v
(1) When a contact-closing signal is applied, the electronic circuit is fed as soon as the circuit of the electromagnet B is energized, but only operates in case of rebound-of the contacts, and only to render conductive the shunt thyristor exactly during the rebound period. The firing impulse of the shunt thyristor, generated at each rebound, has no action on the firing of the other thyristors because of the state of conduetion of transistor T which under these conditions blocks gate A which is provided to supply an enabling pulse to the extinction thyristor Th,.
(2) When a contact-opening signal is applied, the electronic circuit, operated by the leading edge of the voltage across the contacts (and not by the arc voltage) and by the breaking of the circuit of the electromagnet, causes successively the firing of the shunt thyristor and, at the end of a time interval determined by a monostable multivibrator, the extinction of the thyristor Th, by the firing of extinction thyristor Th and, at the same time, the firing of thyristor Th which cancels the supply of the electronic circuit (by discharging condenser C and finally the firing of thyristor Th which controls the charge of extinction condenser C. I
(3) The capacitor C, charged at the time of energizing the electromagnet, feeds the electronic circuit at the opening of the contacts and so permits the electronic circuits to perform the operations mentioned under (2) above.
(4) Condenser C being discharged at the time of the extinction of the shunt thyristor, the electronic circuit is then nonsensitive to the voltage impulse generated across the contacts at the time of the effective opening thereof.
(5) During the working cycle of the circuit breaker, the electronic circuit, being short-circuited by the closed contacts of the circuit breaker, is inoperative.
(6) A gate controlling the extinction being open only at the time of the opening of the contacts, the extinction condenser C cannot start to discharge too early.
It must be well understood that other modifications may be effected through the above-disclosed circuit, in particular, to adapt such circuit to other types of current, without departing from the scope of the invention.
l. A hybrid circuit breaker comprising: one pair of contacts; an electromagnet having an excitation coil serially connected with said contacts and an armature adapted for actuating said contacts; a controlled rectifier connected to across said contacts and having a control electrode; differentiator circuit means connected across said contacts and responsive to the leading edge of the voltage appearing across said contacts upon opening of said contacts; a monostable multivibrator connecting the said differentiator circuit means to the said control electrode, whereby the said controlled rectifier is fired upon each opening of said contacts; and further circuit means, connected across the said controlled rectifier for extinguishing the said controlled rectifier.
2. A hybrid circuit breaker comprising: one pair of contacts;
an electromagnet having an excitation coil serially connected with said contacts and an armature adapted for actuating said contacts; excitation means for applying contact-opening signals and contact-closing signals to said coil; a first thyristor connected across said contacts and having a control electrode; first differentiator circuit means connected across said contacts and responsive to the leading edge of the voltage appearing across said contacts upon opening of said contacts; a monostable multivibrator connecting the first differentiator circuit means to the control electrode of the first thyristor, said monostable multivibrator generating a pulse of predetermined amplitude and duration upon each opening of the said contacts whereby the said thyristor is fired upon each opening of said contacts; a first condenser and a second thyristor serially connected across the first thyristor, said second thyristor having a control electrode; supply means, connected to the first condenser for charging the said condenser; second differentiator circuit means; means connecting the second differentiator circuit means to the monostable multivibrator, the second differentiator circuit means being responsive to the trailing edge of the said pulse; gating means connecting the second differentiator circuit means to the control electrode of the second thyristor and means for opening said gating means when a contact-opening signal is applied to said coil, whereby the second thyristor is fired, the first condenser is discharged and the first thyristor is extinguished a predetermined delay after the said contact-opening signal is applied to the coil.
3. A hybrid circuit breaker as claimed in claim 2, further comprising a second condenser; means connecting the second condenser to the excitation means, for charging the said second condenser when a contact-closing signal is applied to the coil; means connecting the monostablc multivibrator and the gating means to the second condenser; and a third thyristor having a control electrode connected to the said gating means, said third thyristor being connected across the second condenser and providing a discharge path for the second condenser, whereby the third thyristor is fired and the second condenser is discharged after the said predetermined delay.
4. A hybrid circuit breaker as claimed in claim 3, wherein the means for opening said gating means comprise a transistor having a base, an emitter and a collector, the second condenser being connected across the said emitter and collector; and resistance-capacitance circuit means connecting the said base to the excitation means, said resistance-capacitance circuit means having a time constant which is substantially lower than the time constant of the charge of the second condenser.
5. A hybrid circuit breaker as claimed in claim 4, further comprising third differentiator circuit means connected across the said emitter and collector; a fourth thyristor connecting the said supply means to the first condenser, said fourth thyristor having a control electrode; and further gating means connecting the last-mentioned control electrode to the third differentiator circuit.