US2597100A - Unbalanced tap-changing on rectifier locomotives - Google Patents

Description

May 20, 1952 J HUBBARD I 2,597,100

UNBALANCEID TAP-CHANGING ON RECTIFIER LOCOMOTIVES Filed Jan. 26, 1951 j ommunicofion Szstem 32 33 \30 uence of WITNESSES: INVENTOR zfiv/ Lloyd J.Hibbord.

v BY flw 4 WM ATTORN EY Patented May 20, 1952 UNBALANOED TAP-CHANGING ON RECTIFIER LOCOMOTIVES Lloyd J. Hibbard, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 26, 1951, Serial No. 208,062

3 Claims.

My invention relates to rectifier-powered trol- Icy-energized equipments, and it relates more particularly to a special unbalanced tap-changing system for rectifier-power traction-motor equipments, whereby the even harmonics are balanced out in the line-currents which flow in the trolley-wire which energizes the electricrailway vehicle or trolley-energized coach.

My present invention is an improvement over the broad subject matter which is described and claimed in my application Serial No. 120,331,

,filed October 8, 1949, for Inductive-Interference Preventive-Means, in which a direct-current load-circuit, containing the traction-motor, and having a large direct-current ripple, is energized, from a single-phase trolley which is subject to inductive interference considerations, through a rectifier-system under such conditions that there is enough series inductance, on the supply-circuit side of the rectifiers, to produce a substantial angle of overlap of the half-wave rectifier-currents, during each half-cycle of the supply-current. Where is is necessary, (as is usually the case), a harmonic-reducing filter is also provided, as described and claimed in my copending application just mentioned.

My present invention is more particularly related to a rectifier-powered equipment of the type in which a direct-current load-means is energized from the secondary winding of a power-supply transformer through two rectifiers, the returncircuit of the load-means being brought back to the midpoint of the secondary winding. Each anode-current half-wave of each of the two rectifiers contains both even and odd harmonics. If the two anode-currents (or half-wave rectifiercurrents) of the rectifier-assembly are kept equal, the even harmonics of the two half-waves cancel each other in the alternating-current input-circuit, while they add to each other in the directcurrent load-circuit. On the other hand, with equal anode-currents, the odd harmonics cancel each other in the direct-current load-circuit, while they are in phase, and add to each other, in the alternating-current supply-circuit.

In ordinary rectifier-powered direct-current load-circuits of this nature, the anode-currents are kept equal, with the result that only even harmonics appear in the direct-current load-circuit, and only odd harmonics appear in the alternating-current supply-circuit. These conditions have heretofore been observed in rectifier-powered trolley-energized vehicles, where the singlephase trolley is subject to inductive interference considerations, so that the interference-suppressing means had to deal only with odd harmonics in the trolley-circuit and even harmonics in the direct-current traction-motor circuits, as discussed in my previously mentioned application Serial No. 120,331.

It is an important feature of rectifier-powered trolley-energized traction-motors, that the speed of the direct-current traction-motors can be very conveniently controlled by voltage-variation, obtained by suitable tap-changing means associated with the step-down transformer which energizes the rectifying-equipment from the trolley. Heretofore, in order to avoid second-harmonic ripples in the trolley-circuit, thereby confounding the induction-interference problems, it has been necessary to keep the anode-currents of each rectifier-pair balanced, so that the second harmonics of the two half-wave anode-currents would neutralize each other in the trolley-current. This has necessitated changing the secondary-taps simultaneously, and in equal amounts, on opposite sides of the secondary midpoint, and enough secondary taps have had to be installed, in order to obtain the necessary refinement of traction-motor control, thus requiring more taps than would have been required, if it had been possible to alternately advance the voltages, first on one side of the midpoint connection, and then on the other, during the acceleration of the traction-motors.

According to my present invention, the traction-motors of any rectifier-powered locomotive or car, or any group of simultaneously controlled locomotive-cabs or electrically-propelled cars, are divided into two equal groups, and the controller is so arranged that the secondary tap-positions are advanced, first on one side of the secondarymidpoint, and then on the other, so that each traction-motor group is alternately operated with unbalanced and balanced taps, with the limitation, however, that during the unbalanced conditions, one of the pairs of rectifying devices is unbalanced with a larger voltage on one side of its midpoint connection, while the other pair of rectifying devices is similarly unbalanced with a larger voltage on the other side of its midpoint connection. In this manner, during unbalanced conditions, the even harmonics which are produced in the line-current by the rectifier-pair for one of the motor-groups are exactly neutralized and cancelled out by the even harmonics which are produced in the line-current by the rectifier-pair for the other motor-group.

With the foregoing and objects in View, my invention consists in the circuits, systems, combinations, apparatus, parts, and methods of design and operation, as hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure or" which is a much simplified circuit-diagram, indicating circuits and apparatus which illustrate the general principles of my present invention, in an exemplary form of embodiment which has been chosen, out of many possible forms of embodiment, as a basis for the explanations which are contained in the following description.

In the much simplified diagrammatic circuit of the drawing, I have shown, by way of example, a single-phase power-supply circuit, one side of which is connected to, and includes, a trolley wire 30, while the other side of the supply-circuit is grounded, as indicated at 31. The trolley wire 30 is paralleled by a communication circuit 32, such as a telephone circuit, which makes it essential to consider the inductive interference effects of the power-line harmonics in the telephone circuit. The power-supply frequency may be either a previously known railway-electrification frequency, such as 25 cycles, or it may be a usual commercial frequency, such as 60 cycles, such as is used for commercial power and light circuits.

In the drawing, I have diagrammatically indicated some of the essential electrical parts or a single locomotive or railway-car, which is energized from the trolley wire 30 through a pantograph 33 and a step-down power-supply transformer 34 for that particular locomotive or car. The power-transformer 34 is provided with a secondary winding 35 which is used to energize the rectifier-powered traction-motor circuits.

In the illustrated example, there are four traction-motors, represented by their armatures A1, A2, A3 and A4. Each motor is provided with a series interpole winding 3 and a series mainfield winding 37, connected in a motor-circuit which includes a serially connected reactance or choke coil 33, as described in my previously mentioned application Serial No. 120,331. It is obvious, of course, that each motor could be replaced by a group of motors, connected either in series or in parallel, and that any even number of similar motors or similar motor-groups could be used.

It is essential, in carrying out my present invention, that the motors should be divided into two equal parts, which are separately energized through rectifiers. In the illustrated system, motors A1 and A2 comprise one group, which is supplied from an alternating-current supply-line comprising the conductors LI and L2; while the motors A3 and A4 comprise the other group, which is supplied from an alternating-current supplyline comprising the conductors L3 and L4. By way of illustration, one terminal of each motor, for example, the positive terminal, is energized from the common cathode-circuit 40 of a pair of rectifiers 41 and 42, each of which may be an ignitron or other single-phase rectifying device of a type which becomes substantially nonconducting, after a conducting period, only in response to a current-decrease to substantially zero. In other words, once a current-conducting arc is formed in either one of the rectifierdevices 4| or 42, that are will sustain itself, and will not become extinguished, until substantially current-zero.

The two rectifiers 4i and 42 of each of the rectifier-assemblies which powers each of the respective direct-current motors A1, A2, A: and

A4, have anode-leads 4i and 42', respectively, which are connected to the respective conductors of the associated alternating-current supplycircuit Ll-L2, or L3L4, as the case may be, the motors A1 and A2 being powered from the first supply-circuit LIL2, while the motors A: and A4 are powered from the other supply circuit L3-L4, as previously explained. Preferably, as shown, each pair of anode-leads 4| and 42' include serially connected anode-reactor windings 4i" and 42", which are preferably mutually coupled, on a common air-gap magnetic circuit 43, as explained in my companion application Serial Number 210,390, filed February 10, 1951, for Rectifier-Powered Equipment.

The two reactor-windings 4| and 42" of each pair are preferably coupled as closely as is practicable, as by having their respective coils interleaved with each other; there are the same number of turns in each of these reactor-windings; and the polarity of the reactor-winding connections is such that the two reactor-windings 4|" and 42" of each pair are in seriescircuit relation to each other, producing a maximum reactance in the reactor-transformer of which they are a part, for the commutating currents which flow between the two associated rectifying devices 4| and 42 during their overlapping conducting periods, all as described and claimed in the companion application which has just been mentioned.

Connected somewhere across each of the pairs of anode-leads 4l-42, either on the power-input side or on the rectifier side of the anodereactors 4l"-42", I preferably use a parallelresonant filter consisting of a capacitor 46 and a damping resistance 41, as described in both of my two previously mentioned copending applications. The capacitor is tuned in parallel resonance with the input-reactance, as seen from the filter-terminals, at some frequency in the range between the third harmonic of the line-frequency and 900 cycles, for the purpose of reducing the inductive interference in the trolley-line 30.

Preferably, the supply-leads for one of the groups of traction-motors, for example the supply-leads L3 and L4, include serially connected reactors 48 and 49 for the purpose of dephasing the line-current harmonics which are drawn by the two groups of traction-motors, particularly the harmonics in the range which are the most obnoxious from the standpoint of inductive interference, as described and claimed in my copending application Serial No. 140,475, filed J anuary 25, 1950, now Patent 2,554,248, issued May 22, 1951, for Dephased Inductive-Interference Prevention. As set forth in this last-mentioned application, comparable harmonic-dephasing results could be accomplished, also, by using different sizes of anode-reactors 4I"-42 in series with different rectifier-assemblies 4l42, or by using different sizes of filter-capacitors 46, across the anode-leads 4l'42' of the difierent rectifier-assemblies.

The several supply-circuit conductors LI, L2, L3 and L4 are energized from the midtaps of individual preventive-coils Pl, P2, P3 and P4, respectively, which are in turn energized from a tap-changing means which is associated with a plurality of voltage-controlling taps TI to T. The odd-numbered voltage-controlling taps TI to TB are disposed on one side of the midpointtap X of the secondary winding 35 of the stepdown power-supplying transformer 34, while the even-numbered taps T2 to TH provide corresp'onding voltages on the other side of said midpoint tap X of said secondary winding 35. It will be understood, of course, that a separate secondary winding 35, or even a separate complete transformer 34, may be provided for each of the two equal groups of motor-loads. In the particular installation which has been selected for illustration, all of the traction-motors A1 to A4 are regarded as being on the same car or locomotive. so that neither a plurality of secondary windings 35, nor a plurality of transformers 34, is necessary.

The preventive-coil PI of the lead Ll of the first supply-circuit L|L2, for the first half of the total traction-motor load, is provided with two input-terminals PIA and PIB. The input terminal PIA is energized, by means of any one of a plurality of tap-switches A, C, E, G, I, K or M, from the various even-numbered voltagechanging taps T2 to T|4 on the top half of the secondary winding 35, the tap-switch A being connected to the lowest-voltage tap T2. The other input-terminal PIB of the preventive-coil PI is similarly energized, through one of a plurality of tap-switches a, c, e. y, i, k or m, from the same even-numbered taps T2 to T|4, respectively.

In a similar manner, the preventive-coil P2, which is to 11 30 c. ti. the scan s ppiydeac s I2 of said first half of the motor-load, is provided with two input-terminals PZA and PZB, which are energized from the odd-numbered taps Tl to Tl3, on the bottom half of the transformersecondary 35, through the respective tap-switches B, D, F, H, J, L or N, for the input-terminal BZA, and through the respective tap-switches b, d, f, h, 9', Z or n for the input-terminal PZB.

It will be noted that the supply-line conductor Ll, for the first group of motors A1 and A2, is energizable with selected voltages, from the evennumbered taps T2 to TIA of the upper half of the secondary winding 35, while the second supply-lead L2 of said first motor-group A1 and A2 is energizable with selected voltages, from the odd-numbered taps T| to T|3 on the bottom half of the transformer-secondary 35.

Without going through all of the connections, it will suffice to say that the two preventive-coils P3 and P4 which energize the supply-circuit leads L3 and L4 for the second motor-group A; and A4 are energized from corresponding tap-switches which are similar to the tap-switches which have already been described, except for the addition of distinguishing prime-marks with this difference, namely, that the tap-switches B, D, F, H, J, L and N, and the tap-switches b, f, h. :i', Z and n are associated with the respective even-numbered taps T2 to T| of the top half of the transformer-secondary 35, while the remaining primed tap-switches are associated with the odd-numbered taps TI to T|3 on the bottom half of the transformer-secondary 35.

The negative motor-terminals are connected to the midtap X of the transformer-secondary which supplies the associated supply-line L|L2, or L3-L4, as the case may be. In the illustrated form of embodiment of my invention, since there is only one secondary winding 35, all of the negative motor-terminals are brought back to the same midtap-connection X.

The starting and acceleration of the tractionmotors A1 to A4 are controlled by means of a controller-handle 50 which controls the position of a multi-position controller 5|, which is diagrammatically indicated by means of a sequence-chart, in which the successive controller-positions are indicated by notches numbered from 1 to 28, (the off-position being not shown), while the various tap-switches are indicated by their respective letters. A closed position of any tap-switch is indicated by a small circle in the appropriate square of the sequencechart 5|. It will be noted that each primed tapswitch is controlled simultaneously with the correspondingly lettered switch having no prime.

The first notch of the controller 5| energizes the tap-switches A and A. The tap-switch A furnishes half-wave energization for the rectifier-assemblies associated with the first motorgroup A1 and A2, through half of the preventivecoil Pl, from the lowest-voltage tap T2 in the top half of the transformer-secondary 35; while the tap-switch A furnishes half-wave energization for the rectifier-assemblies associated with the second motor-group A3 and A4, through half of the preventive-coil P4. from the lowest-voltage tap TI on the bottom half of the transformersecondary 35. 1 Each of the two motor-groups Al-A2 and Aa--A4 thus draws even harmonics from the alternating-current supply-line, but these even harmonics are out-of-phase with each other, because the two motor-groups are energized from different halves of the transformer-secondary 35. Since the traction-motors are all similar, and all rotating at the same speed, the even harmonics of the supply-circuits are equal in magnitude, and thus cancel each other out, so that no even harmonics appear in the trolley-conductor 33. or in the primary winding of the transformer 34 (neglecting leakage).

On notch No. 2 of the controller 5|, the tapswitches B and B are energized in addition to the tap-switches A and A, with the result that all of the motors receive full-wave energization, in series with one-half of each of the associated preventive-coils Pl to P4, from the two lowestvoltage taps TI and T2 on opposite sides of the midtap X of the transformer-secondary 35. Since these two taps TI and T2 supply equal voltages, 180 out of phase with each other, the two anode-currents of each rectifier-pair are equal, so that the even harmonics balance out in each rectifier-pair, so that these even harmonics do not appear in the trolley line 30.

The third controller-notch 3 closes the tapswitches a and a, in addition to the tap-switches A, A, B and B which were previously closed, thereby cutting out the preventive-coil impedance of the preventive-coils PI and P4, leaving only two half preventive-coils P2 and P3 in circuit with the respective supply-circuits L|L2 and LS-LA of the two motor-groups, the motors still being energized full-Wave, from the lowestvoltage taps TI and T2.

The fourth controller-notch 4 closes the tapswitches b and b, in addition to the tap-switches previously described as being closed. The result is to remove all of the preventive-coil impedance from the supply-circuits L|L2 and L3L4 which energize the two motor-groups, full wave, from the balanced lowest-voltage taps TI and T2.

Thereafter, subsequent controller-positions alternately advance the voltages, first on one side of the midpoint connection, and then on the other, as will be evident from the sequence-chart 5|, so that the rectifier-assemblies are alternately balanced and unbalanced, receiving successively higher voltages, in such manner that the unbalanced connections are such that the pairs of rectifying devices ll-42 for one motor-group A1 and A2 are unbalanced with a larger voltage on one side of their midpoint connection X, while the pairs of rectifying devices 4l-42 for the other motor-group A3 and A4 are unbalanced with a larger voltage on the other side of their midpoint connection X, thus balancing out the supply-circuit second harmonics, so that they do not appear in the trolley-wire 30.

Experience has shown that the direct-current traction-motors A1 to A4 are well able to withstand the additional harmonics which are produced in the various motor-circuits by the abovedescribed unbalancing, without discoverable additional heating, and while still maintaining black or perfect commutation. My use or alternate unbalanced tap-connections, followed by balanced tap-connections, materially reduces the number of taps T! to T14 which have to be brought out from the secondary winding 35, thereby reducing the cost and the complication of the equipment, and also making it possible to operate the rectifier-s 4i and 42 of the various rectifier-assemblies without resorting to the expedients of delayed firing, or of excessive voltage-regulation, for the purpose of reducing the necessary number of taps.

While I have described only a single extremely simplified and illustrative or exemplifying form of my invention, designed to be indicative rather of the general principles of my invention than showing precise details of the actual complicated connections such as would be used in practice, I wish it to be understood that my invention is not limited to the illustrated form or circuit. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. Rectifier-powered equipment, comprising, in combination, two similar direct-current loadmeans; a single-phase supply-circuit; transformer-means energized from said single-phase supply-circuit and having a plurality of secondary taps including a midpoint tap and a rality of similar voltage-controlling taps on opposite sides of said midpoint tap; a separate rectifier-assembly for each of the direct-current load-means, each rectifier-assembly comprising a pair of single-phase rectifying devices; means for connecting one terminal of each directcurrent load-means to a secondary midpoint tap; means for connecting the other terminal of each direct-current load-means to like-polarity terminals of the associated pair of rectifying devices; a tap-switching means associated with each of the voltage-controlling secondary taps; and controlling-means for energizing each of the other-polarity terminals of each pair of rectifying devices through selected tap-switching means on opposite sides of the midpoint connection of the associated load-means; characterized by said controlling means, at times, providing unbalanced voltages to said other-polarity termi nals of each .pair of rectifying devices, in such manner that one of said pairs of rectifying devices is unbalanced with a larger voltage on one side of its mid-point connection, while the other pair of rectifying devices is similarly unbalanced with a larger voltage on the other side of its midpoint connection.

2. The invention as defined in claim 1, characterized by said controlling-means, at other times, providing only a half-wave operatingvoltage for each of the rectifier-assemblies, with the half-wave secondary tap of one rectifierassembly on one side of its midpoint connection, and with the half-wave secondary tap of the other rectifier-assembly on the other side of its midpoint connection.

3. The invention as defined in claim 1, characterized by said controlling-means having a plurality of controller-positions and being operative to provide progressively higher directcurrent voltages for said load-means, in successive controller-positions; the first controllerposition providing only a half-wave operatingvoltage for each of the rectifier-assemblies, the half-Wave secondary tap of one rectifier-assembly being the lowest-voltage tap on one side of the midpoint connection of the associated loadmeans, and the half-wave secondary tap of the other rectifier-assembly being the lowest-voltage tap on the other side of the mid-point connection of the associated load-means; a subsequent controller-position providing balanced full-wave operation of both rectifier-assemblies, with each of the rectifying devices energized from the lowest-voltage tap on its appropriate side of the midpoint connection; and subsequent controllerpositions alternately advancing the voltages, first on one side of the midpoint connection and then on the other, so that the rectifier-assemblies are alternately unbalanced and balanced, the unbalanced connections being as described in claim 1.

LLOYD J. HIBBARD.

No references cited.

Images