Sept. 10, 1946. z_ Q_ 51' PALLEY 2,407,521 ELECTRIC PROTECTIVE SYSTEM Filed Oct. 1, 1945 Z2 - I Z‘I 50 29 33 ‘ 3| 36 , ’/ 32 Z7 37 FLU ID 1mm- MOTOR Morals?“ . ELECTRIC / /" MOTOR , v / / / / SPEEDOHETER _ 25 ’ 40 / mun: - l,—/\ 6 4| 210 I/ // WHEEL. 24 39 / DIFFERENTIAL Z8 TRACTION Z3 58 RELAY a4 / mum WHEEL ivsmuz rum. I’; - I ' Inventor‘: Zolt an O. StPalley; by His Attorney. _ Patented Sept. 10, 1946 2,407,521 UNITED STATES PATENT OFF-ICE 2,407,521 ‘ELECTRIC PROTECTIVE SYSTEM Zoltan 0. St..Palley, Pitts?elkL'Mass” ass'ignor to General ' Electric ‘New York Company, a corporation of Application Octoberv 1, 1943, Serial No. 5045575 3 Claims. 1 ((31. ‘105—51) 2 My invention relates to electric protective sys~ terms for alternating current motors, and, more particularly, to systems for protecting a plurality of alternating current electric traction motors against wheel slippage. The invention has for its principal object the provision of a new-and im proved protective system of-this type which re quires only a minimum of apparatus, but func ?gure of which is a diagrammatic representation of my invention as applied to an electrically operated vehicle, such as an electric locomotive. Referring vnow to the drawing, I have shown an alternating current supply transformer hav ing a primary winding l0 with one terminal grounded at I l and the-other terminal connected through a ,pantograph l2 ‘to a supply conductor tions with optimum e?iciency and reliability. In the operation of a plurality of electric motors 10 [3. The supply transformer is provided also with a secondary winding 14 'having one terminal separately connected to the driving axles of a grounded at E5 and having at its other end two vehicle, one pair of wheels connected to an axle electrically spaced voltage taps i6 and H. To sometimes slips on the track, especially when facilitate motor starting the grounded end of the rapid acceleration is attempted under heavy load conditions. ‘When this slipping occurs, the motor transformer winding .lll may, if desired, 'be pro vided with a plurality of taps £8 to which the connected to the slipping axle accelerates to a higher speed than the other motors and may reach a speed causing damage to the accelerated motor on account of the resulting high mechan motor circuit is sequentially connected by means of a suitable manually operable accelerating con troller diagrammatically illustrated as a slider i9. ical stresses. Furthermore, when the traction 'To the secondary winding M of the supply motors are connected for energization in parallel transformer there are‘ connected three conductors circuit relation, the slipping of one pair of wheels 2U, Z'Land 22 "for connecting a plurality of elec relieves the connected motor of any substantial tric ‘traction motors in parallel circuit relation. portion of the load so that the remaining motors, While conductors 21 and 22 are electrically connected to non-slipping wheels, may stall or 25 spaced the apart in potential by reason of the spac may be damaged'by high overload currents. ing or the taps l6 and i‘l,'the potential difference between the conductors 2| and 22 is small in ‘In carrying out my invention, I provide an alternating current supply transformer having at‘leas‘t'two‘variable'voltage taps and arranged relation to that between either one of these to supply'current to a' plurality of traction motors 30 conductors and the ‘conductor ‘28. Accordingly, I wish to have ‘it understood that for the pur or‘trac’tion groups connected inparallel circuit poses of this speci?cation, the term “parallel relation. Separate selector switching means are circuit relation” shall be understood to mean provided in connection'with‘each‘motor or motor connections'between the conductor 20 and. either group‘under the control of a wheel slippage de tecting device, such‘as'a diiferential speedometer, for controlling each selector switch independent 35 one of the conductors 2| or 22, A pair of series type electric traction motors having armatures 23 and 24 and series ?eld wind ings 25 and 26, respectively, are connected in tap on'the transformer in ‘accordance with slip parallel circuit relation across the transformer page conditions of that motor. Preferably, and to preclude vopen-circuiting of any‘motor, the selec 40 secondary winding Hi. It will be understood that the 'motor armatures 23 and 215 are sep tor switch associated with 'each‘moto-r or motor arately connected to independent driving axles group is so arranged that'at the instant ~of trans ofan electric vehicle (not shown). One terminal fer the terminals of the variable ‘voltage "taps of :each of the traction motors is connected t0 the are‘bridged. In order to‘ prevent short-circuiting of @the transformer between taps at the ‘instant 45 conductor 20. The otherterminals of the motors ‘ are ‘connected to separate tap changing. or selector of transfer a current limiting impedance is inter switches 21 and 28. ‘The selector switch 21 is posed between the transformer'and'the'?rst con associated with the ‘traction motor '23, 25 and nected switching'means-in such a position‘that comprises a pair of fixed contacts '29 and 30 it ‘serves to prevent short-circuiting of the var connected, respectively, to the conductors 2| and iable voltage tapsiby any of'the connected'switch 50 22 and moving ‘contact 3!. ‘Similarly, the tap ing means. changing switch 28 comprises a pair of ?xed For a more ‘complete understanding of my contact members 32 and 33 connected, respec invention, reference ‘should now 'be had to the tively,‘to the conductors '2! and 22 and a moving following ‘detailed'speci?cation taken'in conjunc contact '34. To ‘prevent short-circuiting of the tion with the accompanying-drawing, the single ly to connect each motorto a high or low voltage transformer "taps “l?‘and I1 ‘I provide in one'of 2,407,521 3 1i the fluid motor 36 so that the selector switch 21 is moved ‘back to the position shown in the the wires if or 22 between the supply transformer and the first connected selector switch a current limiting impedance, such as a reactor 35 in the conductor 2 l. The selector switches 21 and 2B are each actu drawing. In view of the foregoing description, it will now be evident that I have provided a wheel slippage protective system for an electric vehicle driven ated by a separate differential speed responsive mechanism which compares the speed of the as sociated traction motor or driving axle with a standard speed, such as that of an idler wheel upon the vehicle. It will be understood that the 10 particular form of such differential speed respon by parallel connected alternating current motors which is not only new and novel, but is particu larly attractive because of its simplicity and se lectability. My system not only provides com plete and independent protection for each trac sive mechanism is not an essential feature of my invention. For the purpose of illustration I tion motor or motor group, but it does so with a minimum amount of switching equipment. It have shown the tap changing switches 21 and 28 connected for actuation by suitable valve-con; trolled air or fluid motors 36, 31, respectively, the fluid motor valve being controlled by suitable er and the traction motors, and that only a single will be particularly noted that only three electric conductors extend between the supply transform current limiting impedance is needed to provide short-circuit protection for all or any one of the electromagnetic relays 38, 39, respectively, which motor tap changing switches. are in turn controlled, respectively, by contact making differential speedometers 40 and 41. The differential speedometer 40 is connected be tween the wheel or axle driven by the motor 23, 20 . While I have illustrated only a single preferred embodiment of my invention by way of illustra tion, many further modi?cations will occur to those skilled in the art and I therefore wish to have it understood that I intend in the appended 25 and suitable idler wheel 42 to detect slipping of the associated driving wheel, while the differ ential speedometer 41 is connected between the 25 claims to cover all such modi?cations as fall with in the true spirit and scope of my invention. wheel or axle driven by the motor 24, 26 and an What I claim as new and desire to secure by idler wheel 43 for a like purpose. It will of course Letters Patent of the United States is: be understood that, if desired, both differential 1. A protective system for independently pre speedometers may be connected to the same idler venting excessive overspeeding of each of a plu wheel. rality of driving axles of an electrically driven I wish to have it understood also that, while I ‘vehicle with respect to an idler wheel of said have shown single motors 23, 25 and 24, 26 con vehicle comprising a plurality of alternating cur nected in parallel circuit relation across the sec rent traction motors separately connected to said ondary winding it of the supply transformer, it driving axles, a supply transformer having a plu is within the scope of my invention tosubstitute rality of voltage taps, separate switching means for each of these motors a group of motors con for connecting one terminal of each of said mo nected in series or parallel circuit relation with tors independently to selected taps of said trans respect to each other. former, differential speed responsive means con In view of the foregoing explanation of the construction and arrangement of the various 410 nected between an idler wheel and each of said driving wheels for independently controlling each parts of my invention, it is believed that its mode of said switching means to select said taps, and of operation will be clear from the following means connecting the other terminals of said brief description. Let it be assumed that the motors together and to selectable taps upon said motors have been energized by proper actuation _ of the accelerating controller I9 and that the 45) transformer to accelerate said motors. 2. A protective system for independently pre wheels connected to the armature 23 begin to venting excessive overspeeding of each of a plu slip. With such slippage and loss of traction, the rality of driving axles of an electrically driven armature 23 speeds up very rapidly and causes vehicle with respect to an idler wheel of said actuation of the relay 38 through the differential speedometer £16. When the relay 38 is operated, 50 vehicle comprising a plurality of alternating cur rent traction motors separately connected to said’ the air or fluid motor 36 actuates the moving driving axles, a supply transformer having a sec contact 3| of the selector switch 2'! from the high ondary winding provided with a plurality of var voltage tap 33 to the low voltage tap 29 thereby iable voltage taps at each end thereof, means for to reduce the voltage applied to the traction mo connecting one terminal of each of said motors tor 23, 25 without affecting the voltage applied together and to selective taps at one end of said to the traction motor 2%, 26. It will be noted secondary winding to accelerate said motors, sep that the contact 3| is so constructed that at the arate selector switching means for independently instant of transfer of connections from the con connecting the other terminals of each of said tact to the contact 29 the two stationary con tacts 29 and 353 are bridged by the moving contact 60 motors to a selected one of said voltage taps at the opposite end. of said secondary winding, and 3|. At this instant, the variable voltage taps i6 differential speed responsive means connected be and il on the transformer winding M would be tween an idler wheel and each of said driving ‘ 1 short-circuited were it not for the current limit ing impedance 35. It will also be noted that, by , axles for controlling each of said selector switches reason of the interposition of the impedance 35 65 independently to reduce the voltage applied to any slipping motor. between the transformer tap H and the first con 3. A protective system for independently pre nected tap changing motor switch, the impedance venting excessive overspeeding of each of a plu 35 serves to prevent short-circuiting of the trans rality of driving axles of an electrically driven former tap by any of the connected motor tap vehicle with respect to an idler wheel of said changing switches. vehicle comprising a plurality of alternating cur The reduced voltage thus applied to the motor rent traction motors separately connected to said 23, 25 reduces the torque of this motor and pre driving axles, a single supply transformer having vents further slipping of the wheels. As soon as a first terminal and at least two voltage taps dif the wheel slip is stopped, the differential speed ferently spaced therefrom in potential, means for ometer "it and control relay 38 effect reversal of 5 2,407,521 connecting one terminal of each of said motors to said ?rst terminal of said transformer, sepa rate selector switching means for independently connecting the other terminals of each of said motors to a selected one of said voltage taps of said single transformer, di?erential speed re sponsive means connected between an idler wheel and each of said driving axles for controlling each of said selector switches independently to control the voltage applied to said motors, and a cur rent limiting impedance interposed between at least one of said voltage taps and said switching means to prevent short-circuiting of said trans former between said taps upon actuation of said switching means. ZOLTAN 0. ST. PALLEY.