June 6, 1950 C. A. THOMAS 2,510,669 DYNAMOELECTRICMACHINE WITH RESIDUAL FIELD COMPENSATION Filed Sept. 15, 1949

InN/entor : Charles A.Thomas :

-2-YHis attorney. 213-4- - Patented June 6, 1950 2,510,669

UNITED STATES PATENT OFFICE 2,510,669 DYNAMoELECTRIC WITH RESD UAL FIELD coMPENSATION Charles A. Thomas, Fort Wayne, Ind., assignor - to General Electric Company, a corporation of New York Application September 15, 1949, Serial No. 115,907 2 Claims. (Cl. 322-79) 2 My invention relates to dynamoelectric ma volves added expense and requires additional chines incorporating means for eliminating field maintenance. which is due to residual magnetism It is, therefore, another object of my inven in the field and, more particularly, to dynamo tion to provide a dynamoelectric machine in electric having residual field Com Corporating a residual field compensator which pensating windings and associated non-linear does not require additional Switches or auxiliary impedance elements for rendering said windings contacts, but which is, nevertheless, effective inoperative when not required, without the use during periods of zero field excitation by the of switches. control field Windings and ineffective when the in certain types of dynamoelectric machines, O control windings supply excitation. the presence of the usual residual magnetization My invention, therefore, Consists essentially remaining in the field poles of the machine after of a dynamoelectric machine having a residual field excitation has been removed is undesired magnetization compensator which includes a and troublesone. This is especially true in ar- . compensator field winding connected in the air nature reaction excited dynamoelectric ma 5 nature circuit of the machine and associated chines having compensation for secondary ar non-linear impedance elements to render the nature reaction and commonly known as ampli winding ineffective when normal field excitation dynes. By the nature of these machines, the is Supplied. field excitation required is only of the same order For a better understanding of this invention, of magnitude as the residual field magnetiza 20 reference may be had to the following descrip tion. If control of the machine is, therefore, to tion taken in connection with the accompany be maintained by the regular field windings, ing drawing, and its scope will be pointed out the residual field magnetism must be Overcome in the appended claims. or compensated for in some manner. This is In the drawings, Fig. 1 is a schematic view particularly necessary in the usual applications of an incorporating my invention in of the amplidyne where it is used as a generator which the residual compensation winding is con whose output magnitude and polarity nected between the amplidyne are required to correspond to the input brushes which are conventionally short-cir to one or more excitation or control windings cuited, and Fig. 2 is a schematic view of another and where the amplidyne is continu 30 embodiment of my invention in which the resid ously rotating, the output voltage magnitude and ual compensation winding is connected across polarity being completely determined by the con the output terminals of a dynamoelectric ma trol windings. The elimination of, or compensa chine. tion for, the residual field in Such machines has Referring to Fig. 1, there is schematically heretofore been accomplished by such elaborate 35 shown an amplidyne having armature output expedients as applying a low alternating cur commutator brushes 2 and 3 connected to out rent voltage to a field winding of the machine. put terminals 4 and 5. Between 2 and This often necessitates the use of a separate terminal 4, as is characteristic of the amplidyne voltage generator. generator, a compensating field winding 6 is It is, therefore, an object of my invention to O connected to compensate for Secondary arena provide a dynamoelectric machine having resid ture reaction. One or more control or field ual field compensation which is simple, reliable, excitation windings, such as , may be provided. and economical. . Two additional commutator brushes 8 are pro It is an other object of my invention to provide vided which are normally short-circuited, but in a residual field compensator which does not re 45 this embodiment of my invention, a residual field quire a separate source of alternating. current compensating winding 9 is connected between voltage for its operation. these brushes. Connected in parallel with winds in some dynamoelectric machines, it has been ing 9 is a non-linear impedance such as re the previous practice to obtain residual field versely connected rectifiers 0. These rectifiers compensation under zero field excitation con 50 may be electric valves of either the vacuum or ditions by connecting a compensating field acroSS gas-filled type, or rectifiers of the dry type, such the armature terminals of the machine by means as copper oxide or copper sulfide rectifiers. I, of a separate switch or an auxiliary contact on however, prefer to use the copper sulfide recti the main switch for the machine. The provision fer, due to its ability to handle high current of a separate switch or auxiliary contacts in- densities and due to the low voltage at which 2,510,669 4. current conduction begins. The advantage of chine which is effective when it is needed, i. e., the latter feature will appear from the following when the regular field excitation is reduced to explanation of the operation of my invention. Zero, but without the use of switching means is Residual field compensation winding 9 is con rendered ineffective to interfere with the regul nected with such a polarity that any residual lar field excitation. field magnetization causes a current to flow be While the present invention has been de tween the armature brushes 8 through winding 9 Scribed by reference to particular embodiments to set up a which opposes the thereof, it will be understood that numerous residual magnetization. When control field modifications may be made by those skilled in winding 7 is energized, compensating winding 9 10 the art without actually departing from the in will then oppose the resulting control field wind vention. I, therefore, aim in the appended ing magnetization. However, when the voltage claims to cover all such equivalent variations as across brushes 8 increases to the voltage value at come within the true spirit and scope of the which rectifiers O become conductive, the Wolt foregoing disclosure. age across these terminals will thereafter never 15 What I claim as new and desire to secure by exceed the rectifier conduction voltage and the Letters Patent of the United States is: rectifiers thereby serve as an impedance with a 1. In an amplidyne generator having at least fixed voltage drop. The excitation of Com One control winding, a residual magnetization pensating winding 9 thereby never exceeds a compensation winding, direct phase current col value corresponding to the fixed voltage drop 20 lectors and quadrature phase current collectors, across brushes 8, as determined by the conduc said residual excitation compensation winding tion through rectifiers O. When the control being connected across said quadrature phase signal is removed from control field winding 7, current collectors, and a pair of reversely-con the compensating winding 9 is again effective to nected rectifiers connected in parallel with said oppose and eliminate the residual magnetization. 25 winding to limit the excitation voltage across In Fig. 2, there is shown a second embodiment said winding to a predetermined maximum of my invention in which the residual elimina value. tion winding 9 and rectifiers 0 are connected in 2. In a dynamoelectric machine having a sta series with a current limiting resistor across tionary magnetic field structure, a magnetic ar the output terminals 4 and 5 of the amplidyne 30 mature adapted to rotate within said and generator. Resistor prevents the current including a commutator, armature current col through rectifiers to from becoming excessive lectors associated with said commutator, a resid and thereby lowering the output voltage across ual magnetization compensation winding and a terminals 4 and 5 when full excitation is Sup resistor connected in series between two of said plied by control winding 7. Resistor is pref 35 current collectors and a pair of reversely-con erably of a non-linear type, such as an incan nected rectifiers connected in parallel with said descent lamp flament which has a low resistance winding to limit the excitation voltage across said when the voltage impressed on the resistor is low winding to a predetermined maximum value. and a relatively high resistance when the in CHARLES A THOMAS. pressed voltage is high. This embodiment of my 40 invention may be incorporated in any dynamo REFERENCEs CITED electric machine and is not necessarily limited The following references are of record in the to . Resistor if alternatively may be file of this patent: connected to current collector 2 instead of out UNITED STATES PATENTS put terminal 4. This connects the compensator 45 circuit directly across current collectors 2 and 3. Number Name Date It will be seen from the above that this inven 1855,736 White ------Apr. 26, 1932 tion provides a simple, low-cost, maintenance 2,151,678 Blankenbuehler free structure for the elimination of undesired et al. ------Mar. 28, 1939 residual magnetic fields in a dynamoelectric ma 50