Patent GB-1408867-A (GB)
Title: Control system for a plurality of alternator units supplying a common electrical distribution system
IPC: H02P9/00
Filed: 1972-09-06
Abstract: 1408867 Controlling the connection of alternators to a distribution system CATERPILLAR TRACTOR CO 6 Sept 1972 [10 Sept 1971] 41414/72 Heading H2H A control system for selectively connecting engine driven alternators to a distribution system 7 comprises a master circuit, Fig. 1, a number of identical control circuits, Fig. 2, each associated with a respective one of the alternators, load sensing circuits 8, 9 for measuring the power supplied by the alternators to the distribution system, call circuits 17, 18; 17, 19; 17, 20 for energizing or de-energizing the respective alternator control circuit in dependence on the load measured by the sensing circuits, starting and shut down devices in each alternator control circuit for starting and stopping the associated engine, and a malfunction detector in each control circuit for operating the associated shut down device on detection of malfunction of an alternator to shut down the alternator. The described system relates to four engine driven alternator units labelled "base" and nos. 1, 2, 3. Initially the base unit is connected to the distribution system by closing a switch 28 to supply a positive voltage from a battery 29 to a positive rail 30 in the control circuit, a switch S2 being set to the AUTO position whilst the switches S2 of the units 1, 2, 3 are set to MANUAL until after starting the base unit whereupon they are switched to AUTO. A cranking relay 39 therefore starts the engine and a relay 38 is provided to shut down the engine if it fails to start within a certain time. When the alternator has reached a predetermined output voltage, relays controlling a circuit breaker 103 connect the alternator to the distribution system 7. If the load on the system requires a second alternator to be connected to the system, the circuit 17 operates the relay 18 to initiate synchronization of the alternators by comparing the phase of the alternator outputs using transformers 100, 101. When the second alternator has been synchronized its circuit breaker 103 is closed to connect the alternator output to the distribution system. Circuits 59, 60 provide a signal proportional to the power generated by the alternator, the signal being fed via an engine speed governor, computer control 71 to a governor actuator 74 which controls the engine throttle. Since the throttle position for the required alternator output power is known, if the input to an amplifier 77 is greater than that normally necessary for this power output, a governor relay 78 is energized to energize a malfunction relay 79. A relay 43 for shutting down the engine is also energized and the battery 29 is connected via a lead P1 to a relay 115 to start the next alternator unit. In the event of a sudden overload occurring the amplifier 77 triggers the relays 78 of each of the alternator units thereby closing contacts 78a in a circuit 12 and supplying the full voltage of the battery 29 to a lead 15. Since this voltage exceeds the threshold voltages set by potentiometers 16, all of the circuits 17 are operated to energize the relays 18-20 and switch on each of the alternators. After bringing up to speed and synchronizing, the alternators are connected to the distribution system. The voltage on lead 15 also energizes an overload timing relay 120 which, after 8 seconds, operates a relay 121 to enable a trip device 122 to open contacts 123 thereby disconnecting non essential loads from the distribution system.