Patent GB-650579-A (GB)
Title: Improvements in a control for direct current generators
IPC: B66B1/52
Filed: 1948-02-26
Abstract: 650,579. Exciting dynamo-electric machines. WAYGOOD-OTIS, Ltd. Feb. 26, 1948, No. 5750. Convention date, April 11, 1947. [Class 35] [Also in Groups XXXVII and XXXVIII] A direct-current generator has an armature, a separately-excited field winding, and a selfexcited shunt field winding, the separatelyexcited field winding having a circuit for connecting it to a source of direct-current for a given polarity of generator excitation, and uni-directional current-conducting means are provided for preventing the flow of current in the self-excited shunt field winding in a direction for self-excitation of the generator of a polarity opposite to said given polarity. The generator is shown as having an armature GA (Fig. 3), a series field winding SRF, a separatelyexcited field winding SEF, and a self-excited field winding SLF. A motor having armature MA is supplied from the generator. A motor field winding MF is energized by exciter EA (Fig. 2). A Ward-Leonard control system for a lift is referred to, the lift-car serving three floors. Push-buttons, provided on the landings and in the car, act through floor relays which have operating and release coils. These relays are latched in the operated position thereby registering a call. When the call is answered the latch is released. The picking-up and cancelling of calls is effected through brushes carried on the crosshead of a floor controller and co-operating stationary contacts. Direction mechanism comprises a number of hook switches, one for each floor, which are adapted to be engaged by a direction cam. Insulated rollers on the cam lift the hook switches off the cam surface. The circuits are illustrated for the condition with the car standing at the lowest floor and with the lift gates and car door closed. If a landing pushbottom 2UB is actuated, a relay 2UF is latched up and an up direction relay XU is energized through a circuit comprising hook switch 2HS and a section of direction arm DRC. A switch K closes to start the motor which drives the Ward-Leonard generator and the exciter EA. As the motor field winding approaches full excitation a relay MC operates to energize a switch SS. A pawl magnet PM is then excited to disengage pawl 18 from stopping-collar 20 (Fig. 1), so closing switches SLS1 and SLS2. An up direction relay U is energized, brushes UCPB and ULPB are connected to the supply, and a time-delay relay NT is energized. The switch U engages contacts U8, U9, to energize field winding SEF through resistor RS. A coil BR is excited to release the brake, and the lift is started upwardly. Upon operation of the switch U, contacts U10, U13, open to change the connection of the field winding SLF to the armature GA, the circuit to the field winding now being through resistor RSC, rectifiers SR1, SR4, contacts U11, U12, and series field winding SRF. The excitation of winding SLF assists that of the winding SEF. Switch U also engages contacts which complete the circuit to the coil of a switch E. Contacts E1, E2 close to short circuit portions of resistors RS and RSC respectively and, as a result, the car reaches full speed. Contacts E3 close to connect the coil of voltage relay VR across the armature GA. Upon operation of this relay, contacts VR2, VR3 close to connect winding SLF directly across the generator armature and series field winding. As the car approaches the second floor, brush ULPB engages contact 2US to energize the release coil of the switch SS which drops out. At substantially the same time roller IR opens switch 2HS to deenergize XU. The pawl magnet PM is deenergized to release the pawls for co-operation with the stopping-collars. When pawl 17 engages collar 19, switch SLS1 opens to deenergize switch E and break the circuit of relay VR. The byepass for the rectifiers SR1, SR4 and contacts U11, U12 is removed and resistors RS, RSC are fully restored, so reducing the speed of the car. As the car arrives at the second floor, switch SLS2 opens and deenergizes switch U to disconnect generator field winding SEF and apply the brake. The winding SLF is connected across the generator armature with reversed polarity to counteract the effect of residual magnetism. The brush ULGB engages contact 2US to energize the release coil of the relay 2UF thereby cancelling the call. The relay NT contacts NT1 after a certain time to break the circuit to coil K and shut down the motor-generator set. Calls that are registered on car button floor relays 1CF, 2CF and 3CF are answered as the car reaches the appropriate floor, regardless of the direction of travel, brushes UCPB and DCPB being effective during upward and downward travel respectively for co-operation with stationary contacts 1CS, 2CS or 3CS. Calls registered on landing button floor relays 1UF, 2UF, 2DF, 3DF are generally answered only during travel in the direction called for. However, if the highest call is a down landing call, it is answered during upward travel, or if the lowest call is an up landing call, it is answered during downward travel. During upward travel, with the contacts U11 and U12 closed, if the polarity of the generator armature GA tends to build up in the opposite direction to that desired, rectifiers SR4 and SR1 block the reverse flow of current through the field winding SLF, and rectifiers SR2, SR3 allow excitation of that winding in the proper direction. The winding SLF opposes the series field winding SRF and reduces the generator voltage to a value preventing downward travel. Similar operation is obtained during normal downward operation. If one of the rectifiers becomes short-circuited, a fuse FU prevents faulty energization of the winding SLF. False operation in the event of one or more of the rectifiers becoming open-circuited is also avoided. Due to the relay VR, the rectifiers are not subjected to the heavy currents obtaining during full speed operation. In the modification of Fig. 4 (not slown), the relay VR is omitted and the self-excited generator field winding is connected directly across the armature of the generator. Specification 297,801, [Class 40 (i)], is referred to.