Patent GB-1519174-A (GB)
Title: Computerized peak-shaving system for alleviating electric utility peak loads
IPC: H02J3/14
Filed: 1975-06-09
Abstract: 1519174 Supply systems with load-shedding control MEGATHERM CORP 9 June 1975 [16 Aug 1974] 24597/75 Heading H2H A system for lowering peak demand on an electrical distribution network to alleviate a power emergency while minimizing the effect of service disruption comprises a plurality of energy-storing loads supplied by the network and divided into mutually exclusive groups each composed of loads having similar reservecapacity-versus-time characteristics, a plurality of receiver control means to disconnect the loads of respective groups in response to corresponding signals, central transmitting means to generate the signals on command, first control means to cause the transmitting means to generate the signals to simultaneously disconnect at least some of the groups from the network in response to a peak power demand, means to determine, for each group, a respective permissible off-time based on characteristic anticipated energy consumption profiles established from past statistical records, and means to automatically reconnect the respective groups one at a time in accordance with the respective permissible off-times thereof. In the described embodiment the loads are thermal storage water heaters 12 in buildings having different user characteristics, e.g. hotels, schools, offices, houses and factories, Fig. 1 (not shown), the heaters 12 of the various user load groups A-E each being controlled by respective relay units 42, 44 responsive to corresponding radio receivers 38-40 (one per group) associated with a common transmitter 36, which receives from a frequency selector 32 a plurality of different frequencies for controlling the receivers of groups A-E to cause their heaters 12 to be simultaneously disconnected when a sensor 28 (or company personnel) detects a predetermined load peak on the network, such detection causing a relay 30 at a computer load control centre (26), Fig. 1 (not shown), to pass a control signal to the selector 32, which thereupon produces its output of different frequencies, and also to a data storage unit 34, which contains information of the permissible off-times for the heaters 12 of the groups A-E based on past usage statistics. When the unit 34 is enabled by the control signal, a clock 46 applies a digital signal indicative of the current time (i.e. when heaters 12 are disconnected) to the unit 34 and to respective comparators 48 each associated with a group A-E, the unit 34 having outputs corresponding to these groups and connected to the corresponding comparators, whereby production of sequential signals at these outputs causes the comparators 48 to sequentially produce signals applied to group inputs A-E of selector 32, which emits signals of corresponding frequency to transmitter 36 to cause the groups of heaters to be sequentially reconnected according to the user requirements. The data in unit 34 may be periodically updated to take account of such factors as time of year and change of user requirements. Reconnections of a heater 12 at a time outside off-peak hours may be prevented by a load limiter (31) at the heater, Fig. 1 (not shown), this limiter effecting reconnection at a subsequent suitable time. The receivers 38-40 may be responsive to coded signals transmitted by telephone or power distribution line and further equipment may be located at each heater to perform load calculations and signal manipulation relevant to the heater. Instead of storage heaters, the loads may comprise conventional water heaters. Members 34, 46, 48 may comprise a computer unit 50 and member 34 may be replaced by a calculator. Reconnection of the loads in ways other than by remote control is envisaged.