Patent GB-1328228-A (GB)
Title: Ward-leonard drive system
IPC: H02P7/34
Filed: 1970-11-26
Abstract: 1328228 Electric motor control systems SIEMENS AG 26 Nov 1970 [26 Nov 1969] 56323/70 Heading H2J In a Ward-Leonard speed control for a D.C. motor 5 driving a crane or hoist, an asynchronous motor 2 drives a generator 4 which is interconnected with and supplies the motor 5 as shown. The generator has a compensating winding 10 in series with pole coils 6, 7 and 8, 9 of the generator and motor respectively. A field winding 11 of the generator is supplied with variable voltage, whereby to vary the speed of motor 5, from the rectified output of an autotransformer regulator 13 connected across main supply phases R, S. The regulator tap 14 is driven by a D.C. shunt motor 17 to a position depending upon the setting of a master selector switch M, to give two speed values on "lift" (HE) and two on "lower" (SE) operations, at which values the motor 5 runs below the rated speed. For speeds above the I and II settings of the switch M there is provided a further cam 37 on an extension 38 of the cam shaft and which controls a switch 41. When switch 41 is closed it causes a field winding 20 of the motor 5 to be energized from the rectified output of an autotransformer regulator 22, the tap 23 of which is driven by a D.C. shunt motor 25. Movement of the selector switch M opens or closes, by means of cams, selected ones of switches b3, b4, b5, &c. to energize respective relays D1-D4. For instance, with selector M in position I "lift" (HE), the contact b3 closes, relay D1 is energized closing d1, d11 thereby energizing a relay C1 so that contacts C1 close and connect the generator field winding to the regulator 13 output. Also a "speed up" relay C3 is energized via d1 and cam switch contacts al, so that contacts C31, C32 close and adjusting motor 17 is energized. The motor 17 will run in the direction of solid arrow, driving a cam-shaft 16 and the tap 14 until the contact a1 is opened by its cam causing C3 to drop out and stop the motor 17. The tap position will then correspond to the selected position I of the switch M. At the next higher speed position II the relay D3 is energized and relay C3 is energized via a5 and d3, and so on. To reduce the speed of motor 5 the selector switch M is moved from II to I whereupon a "slow down" relay C4 is caused to be energized if the motor 17 is connected to D.C. supply via c41, c42 whereby it will run in the reverse direction. To avoid overloading the crane drive motor 5 when running at light loads and higher than nominal rated speed, the voltage applied to field winding 20 of the motor 5 is varied in a manner whereby the torque remains within a predetermined limit curve. To effect this, relays 30-32 act as current sensing means and each responds to a different value of armature current of motor 5 to produce outputs at terminals 34, 35, 36 respectively of a device 33. Thereby the relay C3 is energized and the tap adjusting motor 25 is switched on to effect a reduction in the motor 5 field according to which of the terminals 34, 35, 36 have outputs. When motor 5 is required to run in the reverse or lowering direction (SE) step I, the contact b4 is closed thus energizing relay D2 so that a change-over relay C2 is energized via d2 causing contacts c2 to close. Thereby voltage is applied to generator winding 11 in the reverse polarity to previously.