US2225644A - Method and apparatus for putting into operation a multiphase converting device - Google Patents

Description

Dec. 24, 1940. F. KOPPELMANN 2,225,544

METHOD AND APPARATUS FOR PUTTING INTO OPERATION A MULTIPHASE CONVERTING DEVICE Filed Au 16, 1958 Vim KMILIW lu u a2 Patented Dec. 24, 1940 METHOD AND APPARATUS FOR. PUTTING INTO OPERATION A MULTIPHASE CON- VERTIN G DEVICE Floris Koppelmann, Berlin Siemensstadt, Germany, assignor to Patentverwertungs-Gesellschaft mit beschrankter Haftung Hermes, Berlin, Germany, a corporation of Germany Application August 16, 1938, Serial No. 225,126

In Germany August 16, 1937 3 Claims.

The present invention relates to a method for putting into operation and under load a multiphase converting device having periodically operated contacts and means for reducing thearcing at thecontacts, and, more in particular, to converters oi the type described in my copending application, Serial No. 114,965, filed December 9, 1936. s

The converting devices according to-the oo- 10 pending application are provided with means for biasing the curves of the operating current and the operating voltage so as to prevent arcing at the periodically actuated contacts even in the case or high intensities or voltages of the current 15 to be interrupted. These means comprise one or more saturable reactors (switching reactors) which are connected in series with the respective contacts, and one or more current paths, preterably capacitive, which are connected in parallel 20 relation to the respective contact breaks and designed to partially maintain the current when separating the contacts so that the restriking voltage across the contact gap increases only gradually. The switching reactors are provided with a magnetcoreconsisting of a high-graded iron whose magnetization curve presents a sharp saturation bend. The winding and the core of the reactor are so dimensioned that at very low current intensities in the neighborhood of the 30 zero value the iron is unsaturated, butis highly saturated during the remaining portion of the transmission period. As a result the resistance of the reactor is relatively high and the current curve is flattened in the neighborhood of the zero 35 passage of the curve so that .the current intensities remain at a lowvalue during an extended weak current interval. On the other hand, the resistance of the reactor is practically nil at higher current intensities so that the current may 40 pass without any hindrance. The value at which the iron is saturated amounts to a fraction of the effective value, 01' the normal current. The value of saturation, even in the case of very high efiective current intensities is preferably of the 45 order. of 1 amp. The above-mentioned means make it possible to provide the switching device with lifting contacts which as periodically operated contacts are particularly advantageous both from the mechanical and the electrical point of 0 viewas compared with the sliding contacts heretofore usual in commutating converters for heavy currents. I

' If a multiphase converting 'device of the above-mentioned character is put into operation while under load, it may happen that, owing to a 5 sudden application of the voltage, irregularities in the phase sequence occur as a result or transient eil'ects. Such irregularities tend to disturb the process of commutation so that the contacts may be damaged by the formation of arcs.

An object of the present invention is to prevent disturbances and damage of the nature just mentioned.

To this end, according to the invention, the starting of a converter of the type here referred to is effected in the following manner. At first the synchronous drive of the converter is put into operation, the contacts running idle in electrical respect. Then the contacts are connected with the load or supply circuit through a small auxiliary load represented by a finely graded starter rheostat. Thereupon the auxiliary load is gradually short-circuited. The small auxiliary load is so chosen as to be sufficient to bring about the variations of inductance of the switching reactors which are caused by the above-explained desaturation phenomenon and which are necessary for effecting the proper commutation. Finally the main load is switched in the circuit after the starter rheostat has been bridged.

The resistors of the rheostat may consist of a combination of ohmic resistors, inductors or capacitors. This combination is to be chosen in such a manner that it afiects in each starting position the phase position of the currents in the suitable manner as regards the operation of the mechanical switching contact. The individual impedance values of each step of the above-mentioned rheostat combination may be determined by tests, care being taken to avoid an arcing in any starting position during the starting process.

In the accompanying drawing, Fig. 1 exemplifies the complete diagram of connections of a converter arrangement according to the invention, and Fig. 2 shows details of the starter rheostat employed in the arrangement of Fig. 1.

The arrangement illustrated in Fig. 1 serves to change three-phase alternating current supplied from a circuit N into direct current furnished to a circuit B. The converting apparatus proper con- 50 and a variable resistor 5|.

sists of a contact device K. This device comprises two stationary contacts II and I2, 2| and 22, 3| and 32, respectively, and a movable contact I3, 23 or 33, respectively, in each of the three phases to be interrupted. Reciprocatory tappets I4, 24 and 34, respectively, serve to operate the movable contacts I3, 23 and 33 and are acted upon by cams I5, 25 and mounted on a common cam shaft which is operated by means of a synchronous motor 4|. The motor is connected with the A. C. circuit N through a switch S1, a transformer T1, and a phase shifter 42 consisting of an adjustable induction voltage regulator. An impedance path, consisting of a resistance 5, 2B or 35 and a capacitance I1, 21 or 31, is connected in parallel to each break of the three interrupter-s. The stationary contacts I2, 22 and 32 are connected with one another and with one pole 53 of the direct current circuit. Each of the other stationary contacts I, 2| and 3| is connected with one respective secondary winding of a transformer T2 through switching reactors E and a rheostat A. The neutral point of the secondary windings is connected with the other pole 52 of the direct current circuit, a switch S3 being inter posed between the D. C. circuit B and the two leads coming from the contact device and the transformer T2. The primary windings of the transformer T2 are connected with the A. C. circuit N through a switch S2. An auxiliary load G bridges the two direct current poles 52 and 53. The useful D. C, loads (not shown) are connected with circuit B.

The reactors C consist of a main winding I8, 28 or 38 series-connected with the respective interrupter, and a magnet core I9, 29 or 39. The cores are further provided with auxiliary windings I0, 20 and 30 which are series-arranged in a biasing circuit V together with a smoothening inductance The circuit V is fed with direct current from a suitable current source, for instance, from the D. C. load circuit, as indicated by dotted lines. The function of the reactors C is to flatten the current curve in the vicinity of the zero passages, and the biasing circuit V allows adjusting the value of the slight current intensity prevailing during the weak current intervals produced by the reactors.

The starting device A has three contact arms 6|, 62 and 63 which may be actuated by means of a hand wheel 64 through a common shaft 55, the contact arms sliding over a semi-circular contact path 1|, I2 and 13 respectively. The contact path is subdivided as shown in Fig. 2 into a plurality of segments 2, 3, 4, 5 and 6 between which are arranged impedance steps, some of which consist, for instance, of a series connection of an inductance 82, 82' or 82" and an ohmic resistance 83, 83' or 83", a capacitor 8 8&1 or 3 1" being ar-- ranged in parallel relation to the series connection. Another impedance step consists, for instance, of an ohmic resistanceiiS only. One of the two outermost contact segments is insulated, whereas the other 6 is connected to the main current circuit. The main, current is supplied to the movable contact arm. 61 through a above-described is shows the vice proper is still idle inclectrical respect as it is separated from both the supply circuit N and the load circuit B. Now the switch S2 is closed and the starting device A is rotated from the position shown to the short circuit position, care being taken to attain the most favorable operating conditions in the different intermediate positions as well as in the end position of the starter, if necessary, by adjusting the phase shifter 42 and/or the resistor 5| by regulating the magnetic bias acting on reactors C. During this procedure, the converter carries only the auxiliary load G. If now the operation is found to b in order, the switch S3 is closed and thereby the main load in circuit B switched-in. The passage from the auxiliary load to the full load is thus effected without disturbance and without appreciable arcing at the contacts. Accordingly, a readjustment with the aid of the phase regulator 42 or the bias regulator 5|, if necessary, is reduced to narrow limits.

What is claimed is:

1. In a multiphase alternating-current converter for connecting a supply circuit with a load circuit, having periodically operated contact interrupters series-connected with saturating reactors for reducing the current intensities in the neighborhood of the zero value of the current to be interrupted, and parallel connected with impedances for biasing the operating voltage of said current, the combination of a starter rheostat having a variable resistance arranged in series connection with each of said contact interrupters and designed to permit a gradual decrease of its resistance value to zero, an auxiliary load connected with the output side of the converter, and means for separating said converter and said auxiliary load from said load circuit during the operation of said rheostat, said rheostat comprising resistances having a reactive component and being dimensioned with relation to said reactors so as to prevent visible arcing at the contacts in intermediate positions of said rheostat.

2. In a converting arrangement for supplying current from a multiphase alternating current circuit to a direct current circuit having a contact interrupter ineach phase of said alternating cur rent circuit, phase-adjustable drive means for operating said interrupters in synchronism with the alternating current to be interrupted, saturable and magnetically adjustable reactors seriesconnected in each of said phases for producing weak current intervals, and impedances connected in parallel relation to said interrupters for biasing the voltage of said current during the opening period of said contacts, the combination of switching means for separating said converter from said direct current circuit, an auxiliary load connected across the converter side of said switch, and a starter rheostat having a graduated impedance combination arranged in series connection with each of said intcrrupters and designed to gradually decrease its resistance from a maximum value to zero when starting the operation of said converter, said impedance combinations comprising a capacitance and being dimensioned relative to said reactors so as to prevent visible arcing at the contacts during the starting period.

3. The method of starting the operation of a commutating alternating current converter having in each alternating current phase a contact interrupter and a starter rheostat connected in series with a magnetically adjustable saturable reactor for producing weak current intervals, and an impedance connected across the interrupter contacts for reducing the periodical increase of the operating voltage, which comprises the steps resistance of the rheostats down to the zero value while adjusting the mechanical operation of the interrupters and. the reactors relative to each other so as to maintain a proper communication,

and finally connecting the converter with the 6 load to be operated. n

FLORIS KOPPELMANN.

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