US2583263A

US2583263A - Mechanical current converter for circuit interruption

Info

Publication number: US2583263A
Authority: US
Inventors: Goldstein Alexander
Original assignee: Bbc Brown Boveri & Cie
Current assignee: BBC Brown Boveri AG Germany
Priority date: 1942-10-09
Filing date: 1947-12-29
Publication date: 1952-01-22
Anticipated expiration: 1969-01-22

Description

Jan. 22, 1952 GQLDSTEIN 2,583,263 MECHANICAL CURRENT CONVERTER FOR CIRCUIT INTERRUPTION Filed Dec. 29, 1947 2 SHEETS-SHEET 1 Jan. 22, 1952 A. GOLDSTEIN 2,583,26

MECHANICAL CURRENT CONVERTER FOR cmcurr INTERRUPTION Filed Dec. 29, 1947 2 Sl-IEETS-SHEET 2 Patented Jan. 22, 1952 MECHANICAL CURRENT CONVERTER FOB CIRCUIT INTERRUPTION Alexander Goldstein, Wettingen,

Switzerland,

assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland Application December 29, 1947, Serial No. 794,271 In Switzerland October 9, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires October 9, 1962 10 Claims.

The present application is a continuation-1m part of my prior application Serial No. 508,029 filed October 28, 1943, now abandoned.

The invention concerns a device for the sparkless interruption of a multi-phase circuit which is switched by periodically and mechanically operated contacts, for instance of a mechanical current converter, where a grid-controlled arc discharge vessel in series with an auxiliary voltage source is connected in parallel with the contacts and where reactors are located in the leads to the contacts. In the parallel circuit containing the discharge vessel and the auxiliary voltage there is also an impedance. If a common parallel circuit with a single anode discharge vessel is employed for several phases and connected in turn with the individual phases, certain difiiculties in connection with the switching occur which can cause complications in the operation of the plant. Special change-over devices can be avoided when in a circuit parallel to the contacts of several phases a common discharge vessel with a number of anodes corresponding to the number of contacts and having only one cathode is employed.

The direct connection of the parallel circuit containing the multi-phase discharge vessel with the contacts is only possible when the current is directed over the contacts of the mechanical converter in the individual phases to the common e direct-current positive pole (cathode). When the mechanical converter is, however, not connected in the manner which is usual with mercury arc converters, but for instance a multiphase connection enabling both half waves to be utilized is employed, where one part of the contacts have a common direct current pole and a current flowing in a direction opposite to that in the discharge vessel and which permits the direct voltage to be doubled with the same blocking of the contacts, then the direct connection referred to is no longer adequate. The present invention thus concerns device for the sparkless interruption of a multi-phase circuit which is switched by periodically mechanically operated 2 opened during the low-current interval and thus enable the contacts to be opened without sparklng.

constructional examples of the invention are illustrated diagrammatically in Figures 1 and 2 of the accompanying drawing where devices with a three-phase connection having three and six reactors respectively are shown.

In the figures U, V, W are the phase conductors of a three-phase alterating current network from which by means of a transformer not shown in the drawing and a mechanical converter with contacts K1 to'Ks actuated by cams C1 to C6 located on a common driving shaft not shown in the drawing and associated with the phase conductors the direct current consumer network G is supplied. The contacts are opened and closed synchronously with the frequency of the alternating current network. Commutating reactors D1 to D5 are located in the phase conductors. The contacts of the mechanical converter are bridged-over by a parallel circuit in which there is a discharge vessel E common to the contacts of all the phases and having a number of anodes with control grids corresponding to the number of contacts and only one cathode, this discharge vessel being connected in series with an auxiliary voltage source H and an impedance Z. The control grids of the discharge vessel E can be controlled in such a manner in dependence on the voltage changes in the reactors during the commutating process which occurs when the phases change that the contacts which open are always bridged-over by the parallel circuit. One suitable arrangement as indicated in Figs. '1 and 2 is to provide a winding G on each of the reactors D and inductively coupled thereto so that as the reactor impedance changes just before the contacts associated therewith are set to open, a voltage will be induced in the windings G and such voltage is applied over connections including a small biasing battery H between the corresponding grid and cathode of valve ,E to render the proper anode-cathode circuit of the latter conductive. To simplify illustration only the winding G associated with the grid circuit controlling the discharge path through anode A1 has been shown on the drawing, but it will be understood that a like arrangement is provided for each of the other anodes of the switching valve E.

The ignition of the discharge vessel before the contacts open, which makes a small opening current possible, can also be achieved by means of a grid control coupled with the contacts, auxiliary contacts being employed which cause the ignition to occur at a definite time before the contacts open.

Transformer T is a multi-phase transformer, which can have more than two windings per phase. In order to prevent the phases mutually influencing each other it may be expedient that the connection should be made by means of a single phase transformer for each contact. Connecting the discharge vessel by means of transformers has the advantage that the current in the valve circuit can be transmitted to the contacts with the opposite sign.

To avoid pre-magnetisation of the transformer and distortion of the reproduction of the valve current impulses on the contacts, it is advisable that the connection of the parallel circuit at the mechanical converter side should be made at points between which a pure alternating voltage prevails. The transformer connection on the alternating current side can be made directly in front of the contacts in delta, ring or star arrangement.

The impedance Z in the parallel circuit containing the discharge vessel and the auxiliary voltage source can be in the cathode conductor or in the anode leads, or in both places at the same time (see Z3. and Z11 in Figures 1 and 2). The impedances Za associated with the individual anodes are adjusted to the individual phases.

The leakage of transformer T must be adjusted to suit the impedance Z and should preferably be kept small on account of the necessary steep rise in the valve current impulses. The transformer can be built with closely coupled windings :z:

having a very low leakage.

The auxiliary voltage source can be in the form of a direct current voltage source (battery H, Fig. 1) common to all phases. It is, however, also possible to use auxiliary alternating voltages which are associated with the individual anodes as regards their phase position in such a manner that the anode voltage at the moment of ignition has the right positive value for the form of the current impulse. The auxiliary alternating voltages can for instance be taken from the alternating supply network by means of the multiphase transformer T1 (Fig. 2) which preferably has a low leakage.

The operation of the arrangement is now explained in more detail by means of Fig. 1 and the time diagrams shown in Figs. 311-3 The arrangement according to the present invention is fundamentally of the same kind as that shown in my co-p'ending application Serial Number 767,223, now U. S. Patent No. 2,465,682.

The curves of Fig. 311 show the alternating current voltages between the terminals U, V, W of the arrangement shown in Fig. l and the neutral point of the supply network. Fig. 3b shows the closing times of the contacts K1-Ke. Contacts K1, K3 and K5 are always closed when the associated phase voltages have their maximum positive value, whilst contacts K1, K4 and K1; are closed when the alternating current voltage has a maximum negative value. The currents 1K1, Z'Ka for the contacts K1, K3 respectively, are shown in Fig. 3c. At the moment I contact K3 closes and contact K1 opens at the moment 3; during the time from 1 to 3 contacts K1 and K3 are both closed. At the moment 2, the current iK; has attained the full direct current value, whilst iK1 has dropped to a very low value at which the iron core of reactor D1 is not saturated. The inductance of reactor D1 is thus very large and this prevents any great change in the current 1131 (Fig. 3e) passing through the reactor winding up to the moment 4. By way of the closed contacts K1 and K3 and the reactor D2 saturated by the current iKs, the reactor D1 is connected during this time to the line voltage between the conductors U and V and takes a voltage (VU) indicated by the shaded area in Fig. 311, which shows the curve of the reactor voltage am. The negative half wave of the reactor voltage occurs in the same may when contact K2 is replaced by contact K1.

As long as contact K3 is closed, the secondary transformer winding on the converter side connected to the anode A1 of the discharge vessel E is connected over this closed contact in parallel with contact K1. The voltage of reactor D1 is connected to the grid associated with anode A1. Anode A1 thus ignites at the moment 2 due to the positive reactor voltage impulse. From the auxiliary voltage source H a current W1 is now forced over the transformer T, impedance ZA1, discharge vessel E (anode A1) and the impedance Zr. The current W1 is transmitted by transformer T to the mechanical contact converter side and flows over contacts K1 and K3. Fig. 3c shows the current iD1 of the unsaturated reactor D1 flowing over the contact K1 and the current 1V1 coming from the discharge vessel. These currents oppose and partly neutralize each other. The resultant current iK1 is shown in Fig. 3 It has to be interrupted at the instant 3 by the opening contact K1.

The timely course of the current W1 is determined by the impedances ZA and ZK and can be adjusted to the reactor current iD1 by suitably choosing these impedances.

After contact K1 has opened, the reactor current iD1 continues to flow over transformer T and the ignited anode A1 in parallel connection. When the current 1'D1 flattens out, that is at the moment 4, $131 passes through zero and anode A1 extinguishes.

During the next commutation between two successive contacts, the same process occurs again with the anode of the discharge vessel associated with the contact which has been relieved. Only 'one anode of the discharge vessel E is current conductive at any one time and there are always only two coils on one column of transformer T simultaneously effective for transmission purposes. The arrangement shown in Fig. 2 operates in exactly the same way as regards the parallel circuit.

I claim:

1. The combination with multi-phase mechanical converter apparatus in which rectification from a multi-phase alternating current supply source is attained by sets of switch contacts operated in timed relation with the phase voltage waves of the source, and in which commutating reactors are connected in each of the several phases; of means for minimizing sparking across the several sets of switch contacts at their respective opening periods, said means comprising, an auxiliary source of voltage, a multi-anode singlecathode type of discharge valve including contr l grids individual to each anode for controlling the conductivity of each anode-cathode path, a multi-phase transformer connecting the said discharge valve in parallel relation to said switch contacts, the several phases of the secondary side of said transformer being connected respectively to the several phases of said mechanical converter, and the several phases of the primary side of said transformer being star arranged and connected respectively to the several anodes of said discharge valve, the common cathode of said discharge valve being connected to the star point of said transformer primary, and means deriving control grid voltage pulses for the several anodes of said discharge valve from the correspondingly phased reactors to render the various anodecathode paths of said discharge valve conductive at the beginning of the low current intervals established respectively by said reactors.

2. Apparatus for minimizing sparking in mechanical converters as defined in claim 1 wherein an impedance common to all phases of the transformer is connected in the cathode side of said discharge valve.

3. Apparatus for minimizing sparking in mechanical converters as defined in claim 1 wherein an impedance is connected in each anode lead of said discharge valve.

4. Apparatus for minimizing sparking in mechanical converters as defined in claim 3 and further including an impedance connected in the cathode lead of said discharge valve.

5. Apparatus for minimizing sparking in mechanical converters as defined in claim 1 wherein the primary and secondary windings of said transformer are closely coupled with a low leakage characteristic.

6. Apparatus for minimizing sparking in mechanical converters as defined in claim 1 wherein said auxiliary voltage source is constituted by a multi-phase alternating voltage.

'7. Apparatus for minimizing sparking in mechanical converters as defined in claim 6 wherein said auxiliary alternating voltage source is constituted by the secondary of a multi-phase transformer, the primary of which is fed by the alternating current supply source.

8. Apparatus for minimizing sparking in mechanical converters as defined in claim 7 wherein the transformer supplying said auxiliary voltage has a, low leakage characteristic.

9. The combination with a multi-phase mechanical converter apparatus of the voltage doubler type in which rectification from a multiphase alternating current supply source is attained by switch contacts operated periodically to open and closed positions in timed relation with the phase voltage waves of the source, and

each phase of said supply source includes a commutating reactor connected in series therewith and two sets of switch contacts extending in parallel therefrom to opposite terminals of the rectified output, one set of switch contacts of each phase being closed when the respective phase voltages have their maximum positive value and the other set of switch contacts of each phase being closed when the respective phase voltages have their maximum negative value, there being an overlap in the closure periods of corresponding sets of switch contacts of successive phases to be rectified; of means for minimizing sparking across the several sets of switch contacts at their respective opening instants, said means comprising an auxiliary source of voltage, a multi-anode single-cathode type of discharge valve including control grids individual to each anode for controlling the conductivity of each anode-cathode circuit, inductively coupled first and second windings individual to each anode-cathode path, each said first winding being connected in series with said auxiliary source of voltage and its corresponding anode-cathode circuit, and each said second winding being connected in parallel respectively with the several phases of said alternating current supply source, and means deriving control grid voltage pulses for the several anodes of said discharge valve from correspondingly phased reactors to render the various anode-cathode circuits of said valve conductive at the beginning of the low current intervals established respectively by said reactors, said intervals coinciding in time respectively with the overlap in the closure periods of said sets of switch contacts thereby to induce in the circuits through the latter a current of opposite direction to said rectified current.

10. The combination with multi-phase mechanical converter apparatus in which rectification from a multi-phase alternating current supply source is attained by sets of switch contacts operated in timed relation with the phase voltage waves of the source, and in which commutating reactors are connected in each of the several phases; of means for minimizing sparking across the several sets of switch contacts at their respective opening periods, said means comprising, inductively coupled first and second windings individual to each phase of said alternating current supply source, a multi-anode single cathode discharge valve including a gridcontrolled anode-cathode path individual to each of said first windings, an auxiliary source of voltage, circuit means arranging each of said first windings in series with its associated anodecathode path and said auxiliary voltage source, circuit means connecting each of said second windings in parallel respectively with its associated phase of said alternating current supply source, and means deriving control grid voltage pulses for the several anode-cathode paths from correspondingly phased reactors to render said paths conductive at the beginning of the low current intervals established respectively by said reactors, said intervals coinciding in time respectively with the closure periods of said sets of switch contacts to thereby induce in the circuits through the latter a current of opposite direction to said rectified current.

ALEXANDER GOLDSTEIN.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 1,934,227 Ehrensperger Nov. 7, 1933 2,279,729 Bedford Apr. 14, 1942 2,293,296 Jonas Aug. 18, 1942 2,301,752 Schulze Nov. 10, 1942 2,465,682 Goldstein Mar. 29, 1949