Patent GB-673856-A (GB)
Title: Method and apparatus for limiting the acceleration of the motor of a ward leonard set
IPC: H02P7/34
Filed: 1949-07-04
Abstract: 673,856. Control of D.C. motors. MATERIEL ELECTRIQUE, S. W. July 4, 1949. [July 5, 1948] No. 17651/49. Class 38 (iii). [Also in Group XXXV] In order to limit the acceleration or deceleration of the motor of a Ward Leonard set, wherein the generator is excited by a selfenergizing exciter having a series field winding the ampere-turns of self-excitation of which produce an E.M.F. which compensates the ohmic voltage drop in the field circuit of the generator, the ampere-turns produced by the sole control field winding of the exciter or the algebraic sum of the ampere-turns produced by the control field windings and a supplementary acceleration-limiting field winding of the exciter are limited, so that the E.M.F. which these windings would produce without the series field winding is in turn limited to a stipulated value, this value being such as to provide the maximum acceleration of the motor, the limitation of said ampere-turns limiting the rate of change with respect to time of the flux of the generator field. A motor M (Fig. 4) is supplied from a Ward-Leonard generator G having a field winding g fed from exciter E. The exciter has a self-excited series field winding e which is adapted to compensate for the ohmic drop in the circuit of the winding g, the arrangement being such that the rate of change of flux produced by the generator field winding is substantially proportional to any additional voltage provided at the exciter terminals due to the excitation of supplementary control winding or windings of the exciter. The control winding e1 is energized in accordance with the difference between a reference voltage derived from potentiometer P and a speed-measuring voltage obtained from tachometer generator T. Excessive acceleration due to rapid adjustment of the potentiometer is prevented by bridge rectifier ABCD which is connected to a direct-current source and resistor r2. The voltage applied to the winding e<SP>1</SP> never greatly exceed that of the source F, even when the difference-voltage is large. The acceleration of the motor may be also limited by the provision of an exciter field winding which opposes the winding e<SP>1</SP> and is shunted across it through a rectifier bridge having two terminals connected to a source of constant voltage, Fig. 5 (not shown). The exciter may have control field windings energized respectively in accordance with a reference voltage, the motor armature voltage, and the armature current, Figs. 6, 7 (not shown). The rate of change of motor speed is limited by an additional exciter field winding which is energized by an auxiliary generator having field windings connected respectively in series with the three control windings of the exciter. The auxiliary generator becomes effective to energize the limiting field winding of the exciter only when the resultant flux produced by the three exciter control windings tends to exceed a given value, and, when effective, it limits the resultant flux to substantially that value. In a further modification, Fig. 10 (not shown), the limiting field winding of the exciter is fed from the auxiliary generator through a resistor and rectifier bridge two terminals of which are connected to a constant voltage source opposing the voltage of the generator. In Fig. 11 the exciter is provided with a field winding e2 which is adapted to limit the acceleration of the motor and is supplied from resistor-inductor bridge ABCD. Terminals B, D, are supplied through rectifier X1 from transformer secondary winding S1, and terminals A, C, through rectifier X2 from secondary winding S2. Transformer primary windings P1, P2, are supplied in series from a constant source S. The exciter control windings e<SP>1</SP>, e<SP>11</SP>, e<SP>111</SP>, are respectively energized in accordance with a reference voltage, the motor voltage, and the motor current, and are each connected in series with saturating windings of transformers T1, T2. The transformers have polarising windings C1, C2, supplied through rectifier X3. When the resultant flux of the windings e<SP>1</SP>, e<SP>11</SP>, e<SP>111</SP>, reaches a given magnitude the transformer T, or T2, according to the sense of the resultant flux, becomes saturated, the balance of the bridge ABCD is distributed, and the winding e2 is energized to limit the acceleration of the motor.