Patent GB-1236120-A (GB)
Title: Electric energy distribution control system
IPC: H02J3/14
Filed: 1969-09-25
Abstract: 1,236,120. Switching systems for heating apparatus. MINNESOTA MINING & MFG. CO. 25 Sept., 1969 [26 Sept., 1968], No. 47338/69. Heading H2H. An electrical energy distribution system comprises means whereby energy is distributed to a load or loads in a first mode in a series of intermittent pulses, the ON and OFF times of which pulses are controlled so that the load or each load receives a precise amount of energy during a predetermined period, further means being provided whereby at the end of the predetermined period, the system is switched to a second mode of operation during which period the load or loads are again supplied in a series of intermittent pulses. During the period of the second mode the energy level is lower than that during the predetermined period and is an interminable period. The system may also be switchable to operate in the second mode only. Five loads 40-44, which may be cooking utensils, are supplied from two phases of a three-phase supply N, C, B, A, by way of contactors 50, 51 and stepping switches 47, 48 the arrangement being such that the contactors are open whilst the switches are stepping and closed whilst the switches are stationary. Operation of the switches 47, 48 is effected by a coil 63 which coil is energized, when a switch 55 is closed from one phase of the three-phase supply by way of rectifier bridge 56, a further rectifier bridge 57 being provided to energize a recycling timer circuit 49, a pulse generator 52, a selector switch 53 and a stepping switch 54. To operate the system in the first mode followed by the second mode, switch 55 is closed and switch 53 moved to position d. Switches 59, 60, 61, 62 ganged to switch 53 are all moved correspondingly to position d. Stepping of the switches 47, 48 by the coil 63 then commences whilst the opening and closing of contactors 50, 51 is controlled by a coil 67 in the recycling timer circuit 49. The coil 67 is timed in its energized and de-energized states by a pair of transistors 86, 86 which are controlled by unijunction transistors 91, 92 and capacitors 99, 105 in conjunction with the resistors selected by switches 59, 60. The coil 67 opens and closes contact 66 which is in series with coil 63 thus stepping of switches 59, 60. The coil 67 also opens and closes contact 66 which is in series with coil 63 thus stepping of switches 47, 48 is effected to energize the loads 40-44 in pulses, the arrangement of these switches being such that only two of the loads 40-44 are energized at any one time. At the same time a coil 72 is energized closing contacts 73, 75 and opening contacts 74, 76. Closure of contact 73 energizes the pulse generator 52 which controls a coil 68 to close a contact 69 by means of which a coil 70 is controlled to step the switch 54, the switch 54 forming a counting device for the periods during which the loads 40-44 have been energized. When the switch 54 arrives at position j coil 72 is de-energized opening contact 73 to de-energize pulse generator 52 and placing contacts 74-76 into their original position. Thereupon the second mode of operation begins wherein the loads are intermittently supplied under control of the recycling timer circuit 49 which periods are not counted by switch 54, the second mode of operation being terminable only by the opening of switch 55. Thus, when the loads 40-44 are cooking utensils, the first mode is a cooking mode and the second mode a keep warm mode. A keep warm mode of operation only may be selected by placing switch 53 in position b or c. If desired the connections of switches 47, 48 may be modified to supply the loads from a single-phase supply.