US2756380A

US2756380A - Electromagnetic switch

Info

Publication number: US2756380A
Application number: US257398A
Authority: US
Inventors: Diebold Edward John
Original assignee: ITE Circuit Breaker Co
Current assignee: ITE Circuit Breaker Co
Priority date: 1951-11-20
Filing date: 1951-11-20
Publication date: 1956-07-24
Anticipated expiration: 1973-07-24

Description

y 4, 1956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC SWITCH Filed NOV. 20, 1951 9 Sheets-Sheet l $5 H 2.1 A. 34 2a 36 3 32 I l l IN VEN TOR.

[nu/44a Jams 26:01.0

J15- 5.. BY @M 'Jwh y 4, 1956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC SWITCH 115-4c I W 315. 4 a, tj iji INVENTOR.

July 24, 1956 E. J. DIEBOLD ELECTROMAGNETIC SWITCH Filed Nov. 20, 1951 9 Sheets-Sheet 3 ZEEO l/NE IN VEN TOR.

y 4, 1956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC SWITCH Filed NOV. 20, 1951 9 Sheets-Sheet 4 I I I A W22" I l 1 l I I 1 g 3 i 6 8 .155. 55.. INVENTOR.

y 956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC SWITCH Filed Nov. 20, 1951 9 Sheets-Sheet 6 t z. Q

I I E1154 JIE .[EC I Elie IN V EN TOR. [Du/lea Jam/v fi/euza y 1956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC SWITCH Filed Nov. 20, 1951 9 Sheets-Sheet '7 IN V EN TOR. O 6 [pa/moo Jew/v .P/eaaw BY dMM $40.1

July 24, 1956 E. J. DIEBOLD 2,756,380

ELECTROMAGNETIC swncu Filed Nov. 20, 1951 9 Sh0ets-Sheet 8 IN V EN TOR.

ddm

July 24, 1956 E. J. DIEB OLD ELECTROMAGNETIC SWITCH 9 Sheets-Sheet 9 Filed Nov. 20, 1951 IN V EN TOR. Eon/flea Jay/v 0056040 cfwm $5M,

United States Patent Ofiice ELECTROMAGNETIC SWITCH Edward John Diebold, Ardmore, Pa., assiguor to I-T-E Circuit Breaker Company, Philadelphia, Pa, a corporation of Pennsylvania Application November 20, 1951, Serial No. 257,398

8 Claims. (Cl. 321-48) My present invention relates to electromagnetic switches and more particularly to an electromagnetic switch having an auxiliary winding in combination with a commutating reactor.

Heretofore in the prior art various devices Were used to provide a uni-directional current from an alternating current. Each of these devices inherently have disadvantages which the present invention proposes to alleviate.

Dry cell rectifiers or selenium rectifiers have the disadvantage of ohmic losses in the forward direction and relatively low reverse resistance so that there are considerable losses as current flows in the reverse direction. Gas discharge tube rectifiers and mercury arc rectifiers present a substantial arc voltage drop. Moreover, the gas discharge tube and mercury arc rectifiers require an interval of time to heat up and are additionally sensitive to changes in temperature. A motor generator set used as a rectifier has the disadvantage of large initial cost, large bulk and has losses due to the transformation from electrical energy to mechanical energy and back again to electrical energy.

Mechanical rectifiers occupy a small volume and have high efliciency but they require a synchronous motor drive which makes them subject to backfire whenever the load, the voltage or the frequency exceed a relatively narrow limit.

The present invention overcomes the limitations of the prior art by providing an electromagnetic switch having a magnetization coil and a commutating reactor in series with the contacts. The commutating reactor essentially restrains the current through the switch to a relatively low value when the switch opens or closes.

It is then an important object of the present invention to provide an electromagnetic switch or valve which has a resistance when conducting in the order of rnilliohms or less.

Another important object of the present invention is the provision of a self-operating rectifier that is instantaneously ready for operation, independent of the ambient temperature and having a high efiiciency and small volume.

Another important object of the present invention is the provision of a novel electromagnetic valve where the inrush and break currents through the valve contacts are always maintained at a low value independent of the voltage load, number of phases or frequencies.

Another important object of the present invention is the provision of a novel rectifier having a control by means of a current which is much smaller than the output of the rectifier.

Another object of the present invention is the provision of a novel saturable transformer without an air gap having the characteristics of a transformer having an air gap.

Another important object of the present invention is the provision of a rectifier where the transition from one 2,756,380 Patented July 24, 1956 mode of commutation to another occurs without disturbance.

Further objects and advantages will become apparent on consideration of the following description in connection with the drawings in which:

Figure 1 is a schematic diagram of an embodiment of the novel electromagnetic switch of the present invention.

Figure 2 is an enlarged top view of a portion of the novel electromagnetic switch of the present invention.

Figure 3 is an enlarged front view of a portion of the novel electromagnetic switch of the present invention.

Figure 4 is a series of voltage and current v. time curves illustrating the operation of the novel electromagnetic switch.

Figure 5 is a fiuX current curve of the cornmutating reactor of the present invention.

Figure 6 is the flux current curve of the saturable transformer of the present invention.

Figure 7 is a schematic diagram of a modification of the novel electromagnetic switch of the present invention.

Figure 8 is a series of voltage and current versus time curves illustrating the operation of the circuit of Figure 7.

Figure 9 is a flux current curve of the saturable transformer 15b in Figure 7.

Figure 10 is a flux current curve of the commutating reactor in Figure 7.

Figure 11 is a series of circuit diagrams of a portion of the present invention.

Figure 12 is a series of voltage and current versus time curves of the circuits of Figure 11.

Figure 13 is a series of circuit diagrams of a portion of the present invention.

Figure 14 is a circuit diagram of a modification of the present invention.

Figure 15 is a series of voltage and current versus time curves for the circuit as shown in Figure 14.

Referring now to Figure 1 the novel electromagnetic valve circuitry of the present invention is connected between the

points

21 and 22. The source of alternating voltage 23 provides the power to the load 24 which is connected in series with the electromagnetic valve circuitry connected between 21 and 22 and the source 23. The load 24 may be inductive, capacitive or resistive, or any combination thereof.

The electromagnetic switch or valve 2:; has two

iron cores

26 and 27 which are connected electrically, as hereinafter described, to the two terminals of the switch 25. The

magnetic poles

26 and 27 are connected by a small bridge contact 23 which makes an electrical and a magnetic connection therebetween. In order to achieve a good electric and magnetic connection the movable bridge or armature 28 is made of a magnetically soft material, as iron, and coated with a layer of high conducting material, as silver or gold. The

stationary poles

26 and 27 as shown in Figures 2 and 3 are surrounded by

copper conductors

29 and 30 which serve the double purpose of carrying the current and conducting the heat generated in the small armature 28 away from its source. For high current carrying capacity the

conductors

29 and 30 may be equipped with cooling fins, not shown.

Referring again to Figure 1, the electromagnetic switch 25 has a main winding 31 connected in series with the

switch poles

26 and 27 and the armature 23. The winding 31 essentially magnetizes the

magnetic poles

26 and 27 when a current flows therethrough. The current flowing through the coil 31 causes the armature 28 to be attracted and held tightly against the

magnetic poles

26 and 27.

As shown in Figures 2 and 3, the current from the copper conductor 29 is carried to the armature 28 across a small silver plated steel plate 32 which lies across the pole face of the magnetic pole 26. An identical plate 33 carries the current to the conductor across the pole face of the magnet 27. The

plates

32 and 33 are each held in position by two screws 38. The armature 28 is suspended by spring 34 held between a clamped plate 35 and two insulators 3 6. The spring 34 resiliently restrains the armature 28 against the bumper 37 which is essentially a stack of thin laminations. The laminations absorb the shock of the armature 28 preventing rebound.

Referring again to Figure 1, the electromagnetic switch 25 carries a premagnetization winding, polarization winding, or auxiliary Winding 40 on the pole 26. The winding 40 carries a direct current supplied by a battery 41 which also provides through a coil 42 the preexcitation for the core 43 of the commutating reactor 44. The commutating reactor has its main coil 45 connected in series with the switch 25 and also with a winding 46 of the transformer 47. Connected then between the

points

21 and 22 in series is the winding 46, the winding 45, the pole 26, the armature 28, the pole 27 and the coil 31, all described above.

The transformer 47 consists of a core 50 having an air gap 51 upon which is wound the three coils 46, described above, 52 and 53. The coil 53 is connected through an impedance 58 across the alternating voltage source 23. The coil 52 is connected on one side to the junction between the

coils

46 and 45 and on the other side through a selenium rectifier 55.

The rise of current through the switch 25 is initiated through the selenium rectifier 55 and kept away from the armature 28 for the time interval necessary to close the switch plus an additional interval necessary to increase the current through the main winding 31 to a relatively high value sufficient to assure a good contact, as is hereinafter described in reference to the curves shown in Figure 4.

The curves drawn in Figure 4 have the same time aris and are hereinafter described before proceeding with the analysis of what occurs during the make or break intervals of the cycle during the times it) to t8.

Figure 4a shows the distribution of the voltage on the electromagnetic switch 25, indicated as 225, and on the load 24, indicated as e24. The curve of e24 shows that the voltage across the load is mainly positive and the curve of e25 shows that this voltage is mainly negative. Except for a short interval between the'times t1 and 12 at the beginning of the positive half cycle and between the times t5 and 8 at the beginning of the negative half cycle, the two voltages e24 and e25 in the positive and negative portion thereof are respectively equal to the generator voltage e23, which is shown as a solid line in Figure 4b.

Figure 4a shows the current i24 through the load 24, through the alternating voltage source 23 and through the coil 31. The current i24 is shown lagging the voltage e24 as the load 24 is considered for the present discussion to be resistive and inductive.

Figure 4b in addition to showing the voltage 223 also shows the voltage across the winding 46 of the saturable transformer 47.

Figure 4c shows the voltage e45 across the winding 45 of the commutating reactor 44-, and

Figure 4c shows the current 1'55 through the selenium rectifier 55.

Figure 4f shows the current 1'28 through the armature 28, and through the winding 45 as is hereinafter described.

Figure 4g shows the preexcitation current 1'53 flowing through the winding 53 of the saturable transformer 47.

The current 1'53 is limited by the reactor 58 and, therefore, lags the voltage 223 by 90 degrees. The winding 53 is wound in opposition to the winding 46 of the saturable. transformer 47 and, therefore, the current i53 appears to be reversed, i. e., leading the voltage e23 instead of lagging it. The sole purpose of the current i531, is to saturate the core 50 of the saturable transformer 47 at the beginning of the positive half cycle of the generator voltage e23 and to permit an early saturation of the core 50 at the end of the positive half cycle of the generator voltage e23 as is hereinafter described. The times t0 to t8 indicated in Figures 5 and 6 are the same instants of time as those of Figure 4. A preexcitation current 1'42 in Figure 5 is applied by the battery 41 in Figure l to displace the curve into the field of positive currents. 1'42 is a constant current which is very small compared to the main current 1'24 described above.

The curve shown in Figure 5 is the dynamic flux current curve of the commutating reactor 44. Figure 6 shows a similar dynamic flux current curve of the saturable transformer 47. Again the times 20 to t8 are the same times it) to 8 as in Figures 4 and 5. The preexcitation current 1'53 is an alternate current and varies between the limits of 1'53 and 1'53 In the following explanation of the operation of the electromagnetic valve it is assumed that 1'53 is equal to 1'53 during the time interval ti) to 3 and equal to 1'53 during the time interval t4 to t3. The zero line of 1'24 is therefore at two different places according to the time as shown in Figure 6. The appreciable slope of the magnetization curve of the saturable transformer 47 is due to the gap 41 in the core 50.

Consider the time It) at which the source voltage 023 becomes positive. The current 124 through the main line is 0 at this time and the armature 28 is pulled away from the stationary contacts by the spring 34. The core 545 of the saturable transformer 47 is saturated by the current 1'53 and a free passage for the current exists then only through the selenium rectifier 5 5 which commences to carry the current 1'55 in phase with the generator voltage e23 as shown in Figure 4e. The current 1'55 is equal to the current 124 during the time interval t0 to 12 since all of the current that flows through the load 24 flows through the series connection 55. When the current 124 flowing through the winding 31 reaches a value high enough to produce a magnetic flux sufficient to attract the armature 28 to the fixed

poles

26 and 2 7, the switch 25 closes. The armature 28 being very small and the attractive force being relatively high, the movement requires a time about th of a second which is negligible for the present considerations. The armature 28 closes at the instant l1 and a current i28 commences to flow through the switch 25. The current 1'28, however, is limited by the commutating reactor 44 which has the winding 45 in series with the contacts of the armature 28.

Figure 5 shows this action having the flux of the core 43 plotted against the current 1'25. After the time t1, the current 1'28 cannot rise to a value higher than iM unless the flux is fully reversed from practically its negative minimum to its positive maximum. The current limit iM can be made extremely small and hence protects the armature 28 from an excess of inrush current.

The reversal of the flux is due to the generator voltage e23 appearing substantially across the winding 45. The voltage 245 is shown as described above in Figure 4c. The time interval 131 to I2 is the time required to reverse the flux, after which the voltage e25 disappears and the current i28 is free to rise. Figure 4 shows how the current 1'28 is kept at the low value iM during the interval til to t2 and rises suddenly at the time 22.

The time interval t1 to $2 in Figure 4c is called the make-step. The make-step is a constant and is determined by the size and material of the core 43 and the voltage e45. In comparing Figures 411, 4b and 40, it is evident that the source voltage e23 is, during the make process, shifted from the switch to the commutating reactor and thence to the load.

The rise of current, then, through the electromagnetic valve connected between

points

21 and 22 is initiated by the selenium rectifier 55 and kept away from the armature 28 for a time interval t0 to :1 required to close a switch and for another time interval II to t2 required coil 131 and thence to the point 122. The electromagnetic switch 125 has two

poles

126 and 127 and an armature 128 mounted on a spring 134 and backed by laminations 137. The electromagnetic switch 125 also has a permanent magnet 163. The permanent magnet 163 is insulated from the remainder of the switch 125 by the insulator 164 and 165.

The contacts of the armature 128 are paralleled by a rectifier 166 in series with a parallel circuit containing a resistor 170 and a capacitor 171. The essential differences between the circuit of Figure 7 and that of Figure 1 resides in the absence of the pre-excitation winding 53 of Figure 1 and the stabilizing reactor 58 of Figure l. The flux current curve of the core 150 of the saturable transformer follows the curve shown in Figure 9 as compared to the Figure 6 which the core 50 of Figure 1 follows.

For obtaining the same change in flux during the opening period, the core 150 of the saturable transformer must have approximately twice the cross-sectional area of the core 50. The

coils

53 and 58 in Figure 1, however, can be omitted.

Figure 8 shows the various voltage and current time curves of the circuit as shown in Figure 7. Figure 8b shows the voltage e146 across the winding 146. As compared to Figure 4b, an additional voltage time area appears between the time t1 and t2. This additional area causes an additional delay in the load voltage e24 so that its average voltage is lowered by 8 to The by-pass or are suppressor circuit containing the

elements

170, 171 and 166 affords a passage for the residual current iB shown in Figure 8g which flows through the armature 128 of the electromagnetic switch 125 at the opening time t7.

This small current iB will charge the capacitor formed by the opening halves of the contact as this capacitor has an exceedingly small capacity. The voltage across this capacitor will rise to a very high value even with a very small current iB. The capacitor 171 connected across the fixed contacts 160 and 162 of the switch 125 has a much higher capacity and, therefore, a much lower recovery voltage for the same current iB. After the time t8, when the voltage e128 across the open contact rises suddenly to a high negative value, the selenium rectifier 166 prevents a reversal of current. When the voltage @128 rises again in the positive direction at the time to, the capacitor 171 is charged to this voltage. After the closing or make of the contact 128, at time t1, the capacitor 171 cannot discharge itself immediately as the selenium rectifier 166 is in opposition to the discharge current. In the time interval t1 to t7, the capacitor discharges itself through the resistor 170.

The. are suppressor circuit acts as a capacitor with high capacity connected in parallel to the opening armature 128 and thus absorbs the residual current. On the other hand, it does not discharge itself through the contacts when it is closed and thus prevents contact damage due to an inrush current. When the direct current voltage is reduced by delaying the make point, the arc suppressor circuit does not carry a forward current or damage the contact with a capacitor discharge.

The direct voltage regulation is provided by the circuitry associated with a saturable reactor 180 having a core 181 and two

windings

182 and 183.

The regulator coil 182 affords a delay for the make point of the contact 128 and thus a means to reduce the average direct current voltage output of the rectifier. The voltage e182 of Figure 8b appearing across the coil 182 is required to magnetize the core 181. During this magnetization period the current i155 through the coil 182 and the selenium rectifier is equal, to the magand close the electromagnetic switch 125. The voltage e182, shown in Figure 80, reduces the load voltage 124 shown in Figure 8e by delaying the beginning of the conduction period from the time t to the time 1.

The area under the voltage e182 of Figure 8c is equal to the flux change of the core 181 also shown as Ad 181 in Figure 10. The size of A I 181 determines the amount of voltage lost to the direct current load by the make delay. The flux change A I 181 does not reverse itself after the time t8 unless a current i183 in Figure 10 is appliedto the coil 183. When no current flows through the coil 183, the flux change A 1 181 is very small and the make point is not delayed resulting in the output voltage ofthe rectifier being high. If a current i183 flows during the interval t8 to t1 through the winding 183, in the direction given by the rectifier 184, connected from the coil 183 to a potentiometer 185, then the flux change he 181 is affected to an extent depending on the amount of current. If no 181 is reversed completely, the delay of the make point 1 from the highest point t1 is the longest possible and the rectifier works at the lowest possible direct current voltage. The flux reversal by means of coil 183 might be effected by several means and the example in Figure 7 shows a very simple one. A voltage proportional to the generator voltage 2128 is taken from the voltage divider 185 and pushes a current through the coil 183 according to the position of potentiometer 185.

The current flowing through the winding 182 of the voltage regulator is the small current i155 of Figure 8e and not the large current i124 of Figure 8g flowing through the load. The regulator nevertheless controls the voltage and current through the load. Moreover, the control current 183 of the regulator is again much smaller than the current i155; thus the ratio of control power to controlled power can be made to be one of a thousand or better. The response time of the regulation, as described above, is approximately one-half cycle.

Another possibility for regulation is to apply the output current of a small magnetic amplifier, not shown, to the control windings 183. This modification would be important for high power rectifiers with multi-anode circuits, as it is possible by this means to vary the output voltage of the rectifier, and therefore its power, within the full range from zero to rated value, by means of a control power which is exceedingly small and with an almost instantaneous response.

Instead of using a selenium rectifier 155 and a regulator coil 183, it is possible to use an electronic valve (not shown) where the voltage of the rectifier can be controlled by means of the grid control of the valve.

The regulator permits the output voltage of the rectifier to vary within a very wide range by means of a regulator coil 182 which acts like a magnetic amplifier with the added advantage of being exceedingly small and the speed of response attained is very high.

The premagnetization of the permanent magnet 163 in Figure 7 replaces the winding 40 of Figure 1. The permanent magnet 163 is insulated from the

pole pieces

126 and 127 by means of thin sheets of insulation 164 and 165. An air gap with very large area or low reluctance bypasses the permanent magnet 163. Thus a high shortcircuit current in winding 131 merely increases the flux through the air gap 190 and does not de-magnetize the permanent magnet 163.

The electromagnetic switch 125 can work without premagnetization, but then it requires a much higher current to operate.

In the foregoing description, a fundamental circuit was shown in Figure 1 and an equivalent circuit of slightly different design including voltage regulation Was shown in Figure 7. A great many other variations of the funda mental circuit and of the basic circuit elements are Poss bl The samrab e transf rmer 4 n F gu 1 and 147 i" Figure 7 consists of an easily saturable

magnetic core

50 or 150 with an

air gap

51 or 151. The properties of the magnetic cores 51 and $6.51 are shown in Figure 6 with pre-eXcitation and Figure 9 without pre-excitation. Figure 11 shows another design of a saturable transformer which offers the same properties when connected in a circuit as in Figure l or 7. Figure 1141 shows the saturable transformer core 250 with an air gap 251. Wound around the core 250 is a winding 252, which is connected in series with an AC. generator 223 and an air inductor 258. The Voltages on these three elements, i. e. the voltages e223, @258 and e252 measured across the

elements

223, 253 and 252, respectively, are shown in Figures 12a, 12b and 12c.

The generator voltage @223 in Figure 12a is a pure sine wave. The air inductor voltage 6258 in Figure 12b is equal to the generator voltage @223 as long the core 250 is saturated during the intervals t2t3, and t4zil. in the intervals ti-t2 and lf1-li i, the core is not saturated. Therefore, the coil 252 has a relatively high inductance as determined by the air gap 251. The generator voltage e223 therefore divides itself between the voltages c253 and proportional to the inductances of

coils

258 and 252. The inductance of coil 252 being higher than the inductance of coil 258, the voltage e252 is higher than the voltage 2258. The sharp cut off at the times t1, t2, t3, Z4 is due to the sudden saturation or unsaturation of the core 2%. Whenever the core 250 is saturated, the coil 252 has a negligible inductance and the voltage e223 equals the voitage The current is of Figure 12d flowing through this circuit reflects the sudden changes of inductance as during the intervals tl2 and t3t4 when the inductance is high the rate of change of the current is low, whereas during the times t2t3 and r4t1 when the inductance is low, the rate of change of the current is high.

Figure 11b shows a way of obtaining the same voltage and current curves with a saturable transformer core having no air Highly saturable magnetic cores are usually made Without air gap because the change in design required to make a core with air gap is highly detrimental to the magnetic properties, above all the ability to saturate fully at a low current. Figure 11b is almost identical to Figure lla except that the air gap core is replaced by the core 260 without an air gap but with a secondary winding 261 which is short-circuited by an inductor 263. For the time during Which the core 260 is saturated, the circuits 11a and 11b are identical and therefore also the voltages and currents. When the core 260 is unsaturated it exhibits the properties of a transformer with a very high mutual inductance and a very low leakage inductance. The inductance appearing on the primary is therefore the inductance 263 if the number of turns of coils 261 and 262 are equal to the primary coil. In such a case the circuits 11a and ill) are equivalent, the only difference will be a small internal current iA flowing through the

coils

261 and 263 which is shown in Figure 12e. Figure 11:: shows a simplified way of representing the equivalence of the two circuits shown in Figures 11a and 11b.

Figure 13a shows a part of Figure 1, comprising the saturable transformer 47 and the commutating reactor 44. Figure 13b shows schematically the same circuit except that the core 50 of the saturable transformer has no air gap and is replaced by a reactor 270 as described above.

From Figure 1 and Figure 7 it is evident that the

coils

46 and 45 have to carry the full load current and must therefore be made of heavy wire. It is possible to combine these two coils into one, as shown in Figure 130. The new coil 271 is wound around two cores 272 and 273 which are equivalent to the

cores

50 and 43 of Figure 1311. The secondary coils 274 and 275, similar to the

coils

52 and 53 described above, are wound only around the core 272 and the coil 276, similar to 42 above, only around the core 273. As a potential point between the coils 46 and 45' rangernent shown in Figure 130 is perfectly equivalent to Figure 13a except that it is much cheaper to manufacture.-

Single phase full wave rectifiers with true valves work.

either without overlap on capacitive or resistive load or with overlap on inductive load. The overlap is the time' during which both valves are carrying current in the same direction with the current in the first valve decreasing andthe second valve increasing. For resistive or capacitive loads the currents and voltages will be the same as for two single phase half wave rectifiers working in succession and for inductive loads the make of one valve occurs:

before the break of the preceding valve. Except for thefaster make and break and a shortening of the make and break steps, the operation for inductive load remains unchanged. Practically, the rectifier is designed for this latter case which is true commutation and will then be amply sufficient for the first case. The transition from one mode of commutation to another occurs Without disturbance of the electromagnetic valve thus exhibits the properties of a true valve.

A three phase rectifier circuit using three electromagnetic valves is shown in Figure 14. The operation of this rectifier is essentially the same as the single phase rectifiers described above in reference to Figures 1 and 7. The A. C. power supply (not shown) is connected to the A. C. terminals 1A, 1B, 1C. The terminals 1A, 1B and 1C are connected to a three phase transformer 3% which is connected in delta in the primary and in Wye in the secondary. The neutral 3011 of the transformer which is also the negative terminal of the rectifier is connected to the load 324. The secondary phases A, B and C of transformer 300 have voltages ea, eb, ec as their respective voltages against the neutral potential at 301.

In Figure 15a these voltages are plotted against time as dotted lines and are rectified by the recifier as is hereinafter described to yield a composite D. C. voltage shown as a heavy continuous line. As the three voltages ea, eb, ec are equal in magnitude and occur during equal time intervals, the rectification takes place in three equal cycles during one cycle of the sine wave of the A. C. line voltage. The D. C. voltage then has ripple of three times higher frequency than the A. C. frequency of the source.

For easier interpretation of the later figures, a simplified representation of the electromagnetic switch shown in Figure 14, is used. The whole switch is represented in the dotted boxes 325 wherein only the armature 328, the exciter coil 331 and the iron core 326 are maintained.

The phases A, B, C are connected through the commutating reactor windings 34-6 and electrons: tic switch 325 to the positive terminal 302.

The coils 346 are wound as described above on the saturable transformer cores 350 and cominutatii to; .or cores 343. The cores 356 also carry the seco 352 which are paralleled by the coils 376. 376 and 352 are connected to the main current 3, positive line 362 shown in heavy lines and to the control reactors 400. The control reactors 4th) have the

coil

382 and 383 wound on the cores 331. The coils connect the coils 352 to the electromagnetic switches 325 through the rectifiers 355. The cores 343 are prernagnetized by the windings 342 which are connected in series between main current carrying lines 391 and The cores 350 are prernagnetized by the windings 353 each connected through an inductor 3 58 to the negative main line 301 and to a phase preceding the phase the core 350 is in. Hence the pro-excitation voltage leads the preexcitation current by degrees which is the favorable phase relationship.

arenas? Whenev r the o tag of a phas exc ed e v lta on the direct current load by a certain positive amount, the electromagnetic switch of this phase will close. Whenever the current through an electromagnetic switch 325 decreases towards zero, the switch will open, operating exactly the same way as a half wave valve described above in reference to Figures 1 and 7.

The similarity of the operation is seen by comparing Figures 8 and 15; taking into consideration that Figure 8 concerns a half wave rectifier operating on a mostly resistive load whereas Figure 15 concerns a three phase rectifier operating on a load 4 24, 425 in which component 425 is a high inductance inserted into the direct current circuit and will maintain the direct current almost perfectly constant. The sum of the phase currents ia, ib, ic, then is constant where each of these currents consists of a series of pulses with a fiat top equal to the direct current. Due to the three phase rectification, the direct voltage is more continuous, as shown in Figure 15a as a solid line than the voltage @124 in Figure 8. During the change-over from one phase to another, the direct voltage assumes the average voltage of both phases as during the times t3t4 and 25-16 in Figure 15a which is a common property of all rectifiers.

In Figure 15c, the pre-excitation current i353a of the saturable transformer of phase A is shown as a dotted line. Comparing Figure 15c with Figure 15a shows that i353zz is leading in phase on the voltage ea of phase A. Figure 15c also shows the voltage e346a, which is the voltage across the common winding 346 of the phase A. In the time interval t1,-t4, the pre-excitation current i353a is positive and keeps the transformer core 350 saturated in the forward direction, therefore the transformer core 350 must be fully demagnetized and reversed before the line current can decrease to Zero. A longer break step is then caused during the interval t6t9, due to the

cores

350 and 343. These steps are represented by the voltage time areas enclosed by the voltage 346a in Figure 15c, which is the commutating reactor voltage of the phase A.

The commutating cores 343 are pre-magnetized with a direct current flowing through winding 342 and stabilized by the choke 426. The direct voltage is taken from the output of the rectifier itself.

When the voltage ea of phase A reaches .a positive value high enough to overcome the direct voltage between 301 and 302 at time to in Figure 150', a current 2355a starts flowing through the

windings

352, 370, 3.82,,the selenium rectifier 355 and the main winding 321 of the electromagnetic switch 325. Due to the easily saturable core 381, the current is limited to a very smallvalue approximately a few milliamperes. The entire voltage difference between the point A and the point302 appears on the winding 382 as the voltage e382a shown in Fig- 15D. This voltage also appears across the open contact 328 of the switch 325 shown as 2328:: in Figure 158. When the core 381 of the regulator. .coil 382 finally saturates, the voltage e382 disappears andthe current i355a rises freely as is shown in Figure 156 atthe time t1. The current i355a also flows through the windings 321 of the electromagnetic switch 325 and effects the closing of the switch 325 at the time t2 when it reaches the critical value to close the switch. A current 1328a, shown in Figure 15 starts flowing through the winding 3,46 and the armature 328 demagnetizing the commutating core 343. During the demagnetizing period of the core 343 or the make step which is the time r2-r3, the voltage difference between the points A and 302. appears on the Winding 346 shown as 23460: in Figure 15C. The current i328a is maintained at the value of the magnetizing current of the core 343 which is less than one ampere, as is shown in Figure 15F. During this time the current 1355a still rises because the voltage difference betweenA and 392 still exists. At the time t3,.the core- 343..is saturated and the current 1328a rises rapidlyto the value of the full direct current as shown in Figure 15F whereas 355? tieiir fas t a d ze s hein i e 1 6 The of Z3284 and i355a is the line current in shown in Figure 15E;

The rise of current in phase A is delayed by the time required to saturate the regulator core 381'by the voltage e 382. Depending on the amount of flux to be changed in the core 381, the commutation between the phases is moreor les s delayed giving a lower or higher average direct voltage output. This voltage regulation can be effected by means of the flux reversal of the core 38 1 which is obtained with an auxiliary current 2383 in the coil 383. The coils 383 are connected to selenium rectifiers 430 which prevent the current 2383 from reversing through limiting resistors 43].. The rectifiers 430 are connected to the secondaries 432 which control the amount of flux reversal to be effected. It is the phase voltage ca which is essentially used to perform the flux reversal.

A source 435 of a direct current 1436 of very low power approximately one watt) essentially determines the direct current output voltage of the rectifier. The Source 436 feeds through a resistor 435 which limits the control current i436 to the primary windings 434 of each phase. The windings 43.2 and 434 are wound on the cores 433 made ofanieasily saturable material. When the control current is ,z' erorthe auxiliary current i383 is limited in the forward direction only by the resistor 431. A high current i333 flows during the time that the phase voltage ea is negative', which reverses the flux of the core 3.81 and thus delays the current 355a, delaying in turn the closing of the switch 325 so that the rectifier delivers a verysmalldir ect voltage or none at all.

.When the control current i436 is high enough to magnetize the cores 433 which require only avery small current, the auxiliary current 1383 in turn is delayed by the flux reversalof the cores 433. The current 1383 .is unable to .rise to a sizeable ,value during .the time that the phase voltage ea is negative, and therefore the magnetic ilux in the core 331 remains unchanged. This in turn permits the currentYi355a to rise immediately when the phase voltage cr z exceeds the direct voltage, thus closing the switch land allowing the highest possible direct voltage output of .the rectifier.

It is obvious that an intermediate amount of the control curr ent i456 permits regulation of the output voltage ofthe rectifier to any desired value.

;The above described procedure is similar to the one described by .means of Figures 7 and 8, except thata new ciore433 was introduced. The control core 433 permits the v. r .egulation .of the rectifier by meansof adirect current:insteadof aipulsedcurrent and requires a control powerwhichcan be made aslow asone millionth of the power -outputof the rectifier. I

The aggregate of the control coil 433 and associated windings together with the selenium rectifier 430 forms a.se lf.saturatingmagnetic amplifier. Similarly,th e aggregate ofthe regulator coil 400 except that its output current i355aappears as double pulses acts as an amplifier. Thedirect current control isnot used immediately on theregul ator coilAQO, as it would greatly hamperthe correct interruption of the contact by introducing a flux reversal. gthetirnewhen the switch 325 is closed andi3 ais zlero. I

Comparing the output current of the rectifier tothe control current 1356 it appears thattit exhibits the properties .of an amplifier w h the advantages of ahigh efficiency, smallweight as the control elements are submitted to small cu'rrents only, fast respouse and an exceedingly high rate of amplification. i

To open the electromagnetic switch, the same procedure'is applied as in the examples described above in reference toFigures 1 and 7. The currentiia in the phase A is equal to the direct current of the output until'plia se B starts carrying current by the same pjr ocess as described above for phase A. When the current ib in phase B rises to the full value of the direct current during the time t to 26, the current in phase A decreases correspondingly, as shown in Figure E. At the time Z6, the current in has reached the point at which the saturable transformer core 350 unsaturates. The commutating voltage between the phases A and B appears on the winding 346 of phase A, shown as e346a in Figure 15C. The current in is limited by the inductance of the saturable transformer core 35!) and decreases in a less rapid slope as shown in Figure 15E. The voltage e346a is transformed into the winding 352 which has more turns than the winding 346 and is so proportionally higher. The transformer voltage is the cause of a new rise of the current 1355a as shown in Figure 156. Inasmuch as 1355a is rising, the current through the armature i328a decreases as shown in Figure 15F. At the time t7, the current 1323a reaches zero, and now the core 343 unsaturates as well, keeping 1328a at the zero value, as shown in Figure 15F. The current 1355a through the parallel path is now equal to the line current shown in Figures 15B and 156 and continues to decrease until it reaches zero at the time 19. At the time t8 the line current in which is reaches the limit of the holding current of armature 328 by means of the coil 321 and interrupts only the small magnetizing current allowed by the core 343 in coil 346.

The opening of the switch 325 always happens when there is no current flowing through it and at the natural cut off time of the electromagnetic valve.

The examples treated in the foregoing description are only a few of many possible connections as, for example, bridge connections, multiphase connection with interphase transformers, etc., may be used.

it is also possible to replace the selenium rectifier 355 in all these examples by a gas discharge tube, and control the output voltage of the rectifier by means of the grid control of this tube.

In the foregoing I have described my invention solely in connection with specific illustrative embodiments thereof. Since many variations and modifications of my invention will now be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein contained but only by the appended claims I claim:

1. A self-controlled rectifying circuit comprising an. electromagnetic switch, a saturable transformer, a commutating reactor and a dry cell rectifier; said commutating reactor having a main winding, said electromagnetic switch having an armature cooperating with a pair of stationary contacts and an operating winding; said armature being constructed to be moved into and out of engagement with said pair of stationary contacts responsive to energization of said operating winding, said saturable transformer having a primary and secondary winding, said commutating reactor main winding, saturable trans-- former primary winding, stationary contacts, and electromagnetic switch operating winding being connected in series, saiddry cell rectifier and said seocndary winding of said saturable transformer being connected in series with each other and in parallel with said series connec-- tion of said stationary contacts and said main winding; of said commutating reactor; said saturable transformer efiecting a decreasing current having a relatively largemaximum value to flow through said dry cell rectifier,v said cornmutating reactor maintaining the current at a relatively low value until said electromagnetic switch. opens.

2. A self-controlled rectifier comprising an electromagnetic switch, a saturahle transformer, a dry cell rec-- tifier and a cornmutating reactor; said commutating reac-- tor having a main winding, said electromagnetic switch having an armature cooperating with a pair of stationary contacts and an operating winding; said armature being; constructed to be moved into and out of engagement;

with said pair of stationary contacts responsive to energization of said operating winding, said saturable transformer having a primary and secondary winding, said commutating reactor main winding, saturable transformer primary winding, stationary contacts, and electromagnetic switch operating winding being connected in series, said dry cell rectifier and said secondary winding of said saturable transformer being connected in series with each other and in parallel with said series connection of said stationary contacts and said main winding of said comrnutating reactor; said saturable transformer and said commutating reactor restraining the current through said armature during its engagement with said stationary contacts, immediately after said engagement, immediately before its disengagement and during its disengagement, said dry cell rectifier being connected to block the line current when said electromagnetic switch is open.

3. A self-controlled rectifying circuit comprising an electromagnetic switch, a saturable transformer, a cornmutating reactor and a dry cell rectifier; said commutating reactor having a main winding, said electromagnetic switch having an armature cooperating with a pair of stationary contacts and an operating winding; said armature being constructed to be moved into and out of engagement with said pair of stationary contacts responsive to energization of said operating winding, said saturable transformer having a primary and secondary windding, said commutating reactor main winding, saturable transformer primary winding, stationary contacts, and electromagnetic switch operating winding being connected in series, said dry cell rectifier and said secondary winding of said saturable transformer being connected in series with each other and in parallel with said series connection of said stationary contacts and said main winding of said commutating reactor; said saturable transformer effecting a decreasing current having a relatively large maximum value to flow through said dry cell rectifier, said commutating reactor providing a low contact current interval until said contacts are disengaged, said commutating reactor and said electromagnetic switch having pre-magnetization means associated therewith.

4. A self-controlled rectifying circuit comprising an electromagnetic switch, a saturable transformer, a commutatlng reactor, a dry cell rectifier, and an arc suppressor circuit; said commutating reactor having a main winding and a pro-excitation winding; said electromagnetic switch having an armature cooperating with a pair of stationary contacts and an operating winding; said armature being movable between an engaged and ms engaged position with respect to said stationary contacts; said saturabie transformer having a primary and a secondary winding; said main winding of said cornmutating reactor and said primary winding of said saturable transformer being connected in series with said stationary contacts and said electromagnetic switch operating winding; said dry cell rectifier and said secondary winding of said saturable transformer being connected in series with each other and in parallel with said series connection of said stationary contacts; and said main winding of said commutating reactor; said saturable transformer effecting a decreasing current having a relatively large maximum value to flow through said dry cell rec tifier; said are suppressor circuit being connected in parallel with said stationary contacts; said commutating reactor maintaining the current at a relatively low value until said electromagnetic switch opens, said are sin pressor circuit comprising a dry cell rectifier and a capacitor and a resistor; said resistor and capacitor being connected in parallel with each other, said pr lei combination of said resistor and capacitor being connected in series with said dry cell rectifier; said are suppressor circuit acting as a capacitor with high capacity connects" in parallel with said opening electromagnetic switch absorbing the residual current.

5. In an electromagnetic rectifier for energizing a D.-C. load from an source; a by-pass" circuit including an electrical valve element, a pair of cooperable contacts, and an operating winding therefor, a commutating reactor and a saturable transformer; said commutating reactor comprising a magnetic core of saturable type material and a winding thereon, said saturable transformer comprising a magnetic core and afirst a'nd'secc ind winding thereon; said saturable transformer being constructed to'have a substantially linear flux current characteristic when said saturable transformer magnetic core is unsaturated; one of said pair of cooperable contacts being movable between a contact engaged and a contact disengaged position; said last mentioned contact being constructed tomove to said contact engaged positionresponsive to a predetermined value of current in said operating winding; said commutating'reactqr winding, pair of cooperable contacts, satur ab'le transformer first winding, operating winding, D.- C. lead and AEC. source being connected in series; said electrical valveelement'of said by-pass circuit and said saturable transformer second winding being connected in series with one another and in parallel with said series connected commutating reactor and pair of cooperable contacts; fiaiii saturable transformer second winding being connected to induce a current in said by-pass circuit in the direction of current flow of said valve element responsive'to a decrease in current through said saturable transformer first winding when said saturable transformer magnetic core is 'un saturated. W

6. A self-controlled rectifying circuit comprising an electromagnetic switch, a saturable transformer, a commutating reactor, a regulating circuit and a dry cell rectifier; said co'mmutatin'g reactor having a main winding; said electromagnetic switch having an armature cooperating with a pair of stationary contacts and an operating winding, said armature being constructed to be moved into engagement with said stationary contacts responsive to energization of said operating winding; said saturable transformer having a primary and a secondary winding; said, saturable transformer primary Winding, commutating reactor main winding, stationary contacts andelectromagnetic switch operating winding being connected in series; said dry cell rectifier and said saturable transformer secondary winding being connected in series with one another and in parallel with the series connection of said stationary contactsand said commutating reactor main winding; said saturable transformers effecting a decreasing current having a relatively large maximum value to flow through said first dry cell rectifier, said commutating reactor maintaining a low magnitude contact current interval during which said armature is disengaged from said stationary contacts; said regulating circuit including a saturable reactor comprised of a core of saturable type material having a first and second winding thereon and a source of control voltage, said first winding being connected in series with said dry cell rectifier whereby current can flow through said dry cell rectifier only after the fiux of said saturable reactor core is reversed, said source of control voltage being connected to said second winding to control the degree of flux reversal of said saturable reactor core 7. In an electromagnetic rectifier for energizing a D.-C. load from an A.-C. source; a by-pass circuit including an electrical valve element, a pair of cooperable contacts and an operating winding therefor, a 'commutating reactor, a regulating reactor, and a saturable transformer; said commutating reactor comprising a magnetic core of saturable type material and a winding thereon; said saturable transformer comprising a magnetic core and a first and second winding thereon; said regulating reactor comprising a magnetic core of saturable type material and a first and second winding thereon; said saturable transformer being constructed to have a substantially linear flux current characteristic when said saturable transformer magnetic core'is unsaturated; one of said pairof co'operabl'e" contacts being movable between'a contact engaged and a'contact disengaged position; said last mentioned contact being constructed to move to said contact engaged position responsive to a predeterminedvalue of current in said operating winding; said commutating reactor winding, pair of cooper'able contacts, saturable transformer first winding, operating Winding, D.-C. load and A.-C. source being connected in series; said electrical valve element of said by-pass circuit, said regulating reactor first winding and said saturable transformer second winding being connected in series with one another and in parallel with said series connected commutating reactor and' pair" of cooperable contacts; said saturable transformer'second winding being connected to induce a current in said by-pass circuit in the direction of current fiow of said valve element responsive to a decrease in current through said saturable transformer first winding when said saturable transformer magnetic core is unsaturated; a source of control voltage; said source of control voltage being connected to said regulating reactor second winding; said regulating reactor first winding preventing flow of current through said by-pass circuit and subsequent engagement of said cooperating contacts until the flux of said regulating reactor core is reversed, the voltage impressed onsaid regulating core reactor second winding by said source of control voltage adjusting the amount of flux to be reversed.

8. In an electromagnetic reetifierfor. energizing a D.-C. load from an 'A.- C. source; a by,-pass circuit including an electrical valve element, a pair of cooperable, contacts, and an operating winding therefor, a commutating reactor and a saturable transformer; said commutating reactor comprising a magnetic core of saturable type material and a winding thereon, said saturable transformer comprising a magnetic core and a first and second winding thereon; said saturable transformer being constructed to have a substantially linear flu current characteristic when said saturable transformer magnetic core is unsaturated; one of said pairj'of cooperable contacts being movable between acontact engaged and a contact disengaged position; said last mentioned contact being constructed to move to said contact engaged position responsive to a predetermined value of current in said operating winding; said commutatingreactor winding, pair of cooperable contacts, saturable transformer first winding, operating winding, D.-C. load and A.-C. source being connected in series; said electrical valve element of said by-pass circuit and said saturable transformer second Winding being connected in series with one another and in parallel with said series connected commutating reactor and pair of cooperable contacts; said saturable transformer second winding being connected to induce a current in said by-pass circuit in the direction of current flow of said valve element responsive to a decrease in current through said saturable transformer first winding when said saturable transformer magnetic core is unsaturated; an arc suppressor circuit connected across said pair of cooperable contactsjsaid arc suppressor circuit comprising a series connection of a dry cell rectifier and a capacitor having a discharge resistor connected in parallel therewith.

References Cited in the file of this patent UNITED STATES PATENTS er r fe es. ,1, l w va s) 17 Koppelmann et a1 Mar. 17, 1942 Koppelmann et a1. Feb. 9, 1943 Klemperer Mar. 5, 1946 Claesson May 31, 1949' Kesselring Mar. 7, 1950 Lamb June 6, 1950 Kesselring Oct. 2, 195 Belamin Feb. 5, 1952 18 Wettstein Sept. 9, 1952 Kesselring et a1. Nov. 11, 1952 Kesselring Nov. 25, 1952 Walker May 5, 1953 FOREIGN PATENTS Netherlands July 15, 1943 Sweden Mar. 13, 1945