Patent GB-481938-A (GB)
Title: Improvements relating to control systems for electrical winding equipments for mine hoists and the like
IPC: H02P7/34
Filed: 1936-09-16
Abstract: 481,938. Master control of D.C. motors; actuating controllers. SMITH, G. D., LOYNES, E., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. Sept. 16, 1936, Nos. 25261/36 and 4501/37. [Class 38 (iii.)] [Also in Group XXIX] Varying E.M.F. ; regenerative braking.-In an electric winding or hoisting equipment with Ward-Leonard control, an emergency trip causes the resistance previously cut out of the . generator field circuit for accelerating the motor to be progressively reinserted by means of over-riding the normal means controlling the generator excitation, and the mechanical brakes are applied at or towards the end of the period of regenerative braking thus produced. The generator field resistance may be controlled normally by a face-plate regulator and reinserted after a trip by sequentially operated delay-action relays or relays responsive to current, voltage or the distance moved by the hoist, subsequent to the emergency condition arising. The regulator may alternatively be controlled by a servomotor and biassed to the weak field position to which it is automatically returned after a trip by venting of the servomotor. The regenerative braking energy may be absorbed by the supply mains feeding the motor driving the Ward-Leonard generator, or, where this is not possible, as described in Specification 481,939. The Ward- Leonard generator field GF, Fig. 1, is supplied through forward or reverse contactors F, R, from an exciter EX with field EF mechanically coupled to the generator, and the winding motor (not shown) is accelerated by cutting resistance 2 out of the generator field circuit by a face plate rheostat. In the event of an emergency trip a safety circuit SC is opened to de-energize a safety contactor S, whereupon, over back-contacts Sb of relay S one of the relays M1 .... M6 is energized, depending on the position of the bridging contact 3 of the face plate rheostat. If the bridging contact rests on rheostat contact bar 8, for example, then relay M5 is energized over contacts Xg, 8, 3, 1, Xa, and the preceding relays M4 .... M1 are energized sequentially over contacts M5a .... M2a. Relays M1 .... M6 are such that they operate immediately upon energization, but upon de-energization do not revert to normal until after an adjustable time delay. When M1 is energized, therefore, normally closed contacts M1c open to de-energize contactor X which opens contacts Xa to Xh, the generator field circuit being maintained over contacts M1b, M2b .... of the operated relays M1, M2 .... M5. Relays M5 .... M1 now revert to normal in succession and thereby reinsert the resistance 2 in the generator field circuit in steps at contacts M5b, M4b .... with a time delay between each reinsertion, until finally contacts M1b open to cut off the supply to the generator field and de-energize a brake solenoid B to apply the mechanical brakes. " Suicide " contacts (not shown) would also be closed at this time. The mechanical brakes could, alternatively, be applied earlier, for example, when contacts M2b or M3b open, and the relays M1 .... M6 may have contactors associated therewith so that their contacts do not have to pass the full field current. Motoring conditions are re-established by a reset button RS. In an arrangement similar to that of Fig. 1, the relays M1, M2 .... are energized successively as the bar 3 of the rheostat moves from the weak field position and when the normal control of the generator field is over-ridden at an energizing trip the field circuit is maintained over contacts of the relays M1, M2 .... in series with back-contacts of the safety relay S. In another embodiment, Fig. 3, the generator field, GF is regulated by a drum controller which successively operates contactors 22.... 27 in parallel with the relays M1 .... M6 to cut out the field resistance 2 to accelerate the motor. Upon a trip occurring, normal operation of the controller is over-ridden by opening of contacts Xc .... Xh, and the operative relays M6, M5 .... open sequentially to release the contactors 27, 26 .... 22 in turn to reinsert the resistance 2 in the generator field circuit, the brake solenoid B being released to apply the mechanical brakes as contacts M1a, open. The forward and reverse contacts f, r, for the generator field GF are controlled by contactor coils F, R, in series with interlock contacts Ra, Fa and overwind limit switches L1, L2. The pairs of coils M1, 22 ; M2, 23 ; .... may be replaced by a single coil. In a further embodiment, the regulator REG, Fig. 5, for the generator field GF is mechanically coupled to the piston 31 of a fluidpressure servomotor, Fig. 4, and biassed to the weak field position corresponding to the lowermost position of the piston 31. The driver's control lever DL, and depth indicator cams if these are employed for automatic operation, are connected by links 34, 33 to the piston-rod 32 and to a double-acting pilot valve 35, lowering of which from the position shown permits pressure fluid to flow from supply P through the ducts 36, 38 to the cylinder 30 where it lifts the piston to operate the regulator to increase the generator excitation, and accelerate the motor. Raising of the valve 35 connects the ducts 38, 36 to the exhaust E and the piston falls to decrease and finally break the generator field circuit. When an emergency trip occurs, a normally energized trip solenoid TS is de-energized and a trip valve 39 falls to connect the cylinder to the exhaust E through a duct 37 independently of the position of the pilot valve 35. Needle valves 41, 42 serve to adjust the fluid flow through the ducts 36, 37, the valve 41 being retracted bodily from duct 36 by a projection 44 on piston-rod 32 in opposition to a biassing spring 45, to permit more rapid operation of the regulator at slow motor speeds. The valve 42 may be automatically adjusted by depth cams or overwind members so as to vary the deceleration with depth. In operation, a reset key RS is operated to close a relay RC, Fig. 6, contacts of which RCb, RCc close to energize safety relays S1, S2 over safety circuits SC1, SC2. The safety relays lock over contacts S1a, S2a, de-energize relay RC at contacts S2c, and at contacts S1b, S2b energize the brake solenoid BS. Trip solenoid TS on the servomotor is energized over S2a. Operation of the driver's lever DL, Fig. 4, also operates the controller MC, Fig. 5, forward or reverse movement of which energizes over interlock contact 48a or 49a, a relay 48 or 49 which energizes the generator field GF over contacts 48b, 48c or 49b, 49c. If an emergency trip causes a break in the safety circuit SC2, relay S2 releases to de-energize the trip solenoid TS whereupon the regulator REG is returned to reinsert resistance in the generator field, back contacts 47a, 47b of a relay 47 closing to shortcircuit the controller MC so that the generator field cannot be broken thereby by release of relay 48 or 49 which remains energized over contacts Y until the regulator arm approaches the weak field position when contacts Y are opened and the mechanical brakes are applied by de-energization of BS. Emergencies which necessitate the immediate removal of the supply to the winding motor cause a trip in the safety circuit SC1 to de-energize relay S1, the generator field circuit being immediately opened at contacts S1b, and the mechanical brakes applied by release of solenoid BS. A suicide circuit is then connected at 52 to remove the residual magnetism of the field GF after a time delay sufficient to allow the winder motor to stop.