Patent GB-598237-A (GB)
Title: Improvements in or relating to electrical consumption control equipment
IPC: G01R11/56
Filed: 1944-11-02
Abstract: 598,237. Electric control systems. STANDARD TELEPHONES & CABLES, Ltd., McWHIRTER, E. M. S., WARDEN, F. W., and WARD, H. J. Nov. 2, 1944, No. 21459. [Class 40 (i)]' [Also in Groups XXXV and XXXVI] In an arrangement for limiting a "flow"- consumption, e.g. electrical energy, so that its integral over a predetermined period will not exceed but will as nearly as possible equal a given maximum quantity (demand) for the period, an average permissible rate of consumption is calculated at predetermined equal intervals throughout the period by dividing the unused portion of the maximum quantity by the unexpired portion of the period. This permissible rate is, for each interval, compared with the actual consumption by means arranged to adjust the load automatically so that the maximum demand is not exceeded. It is shown in the Specification that where the period T is divided into equal intervals t, the permissible load Pn+1 at the beginning of the (n+1)th interval t is related to Pn, that for the nth interval, by Pn+1 + Pn+ Pn -#n.t/T - nt where #n is the average load consumption for the nth interval. Thus, at the beginning of any interval the new permitted load Pn+1 can be derived from the previous figure Pn by. measuring the actual consumption #n, subtracting this from Pn, then multiplying by t/T-nt, the reciprocal of the number-of-calculating intervals left in the period, and then adding to the permitted load Pn. As shown, applied to limiting an electrical energy flow, the maximum demand period of half-an-hour is divided into minute intervals and the load measuring unit consists of a triode V1 and the associated elements connected to the input thereof. X1, X2 are contacts closed periodically by the kW.H. meter in accordance with the energy consumption and the Specification shows that with the arrangement of C1, C2, R1, R2, R3 and the battery B the potential on the grid of V1 is proportional to #n, the actual consumption during the nth minute. At the beginning of each half-hour integrating period, a relay HA is operated for approximately one second. The driving magnet SAM of a multibank stepping switch SA is thus energized over contacts ha2 and t1. Switch SA stops until wiper Sa2 thereof reaches a position corresponding to the setting of a maximum demand switch wiper ms1 when relay T is energized to break the energizing circuit of switch SA drive magnet at t1. In this position of switch SA, the voltage on wiper sa1 from potentiometer POT corresponds to the permitted load P1 for the first interval as determined by the maximum demand given for the period. Wiper sa1 is connected through a resistance RS to the cathode of valve V1 so that the potential across RS is equal to P1-#1. This voltage is multiplied by t/T-nt, the reciprocal of the number of calculating intervals left in the period, by means of a tapping switch wiper sc1 of a switch SC. The switch SC is restored to its home position at the beginning of the halfhour integration period, the drive magnet SCM thereof being energized over contacts ha1 and homing bank sc2. In this position wiper sc1 1 engages the - tap on resistance RS so that 29 during the first interval condenser C3 is charged up over contacts ma1, ma2, to a voltage P1 - #1/29. At the end of the first minute, a 29 relay MA is operated for a short interval and the voltage across condenser C3 is connected over contacts ma1, ma2, ma3 to a balance detector consisting of valves V2, V3. A relay MB is operated over contacts ma4 to disconnect the homing circuit of a switch SB at contacts mb1. Over wiper sb1 of this switch the grid of valve V3 is earthed. As the grid of V2 is now at a greater potential (P1-#1/29), valve V2 only on the detector unit conducts to energize a relay P. Contacts p1 thereof now connect the driving magnets SAM, SBM to a source of impulses. Switches SA, SB are thus stepped until the voltage on the grid of V3 by way of wiper sb1 equals that on the grid of V2 when relay Q operates to open the stepping circuit at contacts q1. Thus, as the voltages per step of sa1 and sb1 are the same, the wiper voltage on sa1 has been increased by an amount equal to the voltage on C3 which is proportional to P1 - #1/29. Thus, the new setting of SA is 29 P1 + P1-#1/29 = P2. When relays MA, MB release, switch SB is restored to its home position and drive-magnet SCM, which has been energized over contact mb3, releases, so that SM is advanced one step and condenser C3 is connected to the 1/28 tap on resistance RS and charges up to a voltage proportional to P2-#2/28. which is added to P2 at the end of the second minute to give P2 + P2-#2/28 =P3. Thus, minute by minute the voltage on wiper sal is changed to a value proportional to Pn until at the end of the half-hour relay HA again operates, readjusting the voltage on wiper sa1 to a value corresponding to P1. Load detector unit.-This unit comprises valves V4, V5, the grids of which are biassed to #n and Pn, i.e. the actual and permitted loads respectively. Whichever of these values is greater causes the corresponding valve to conduct while the other valve is biassed back to cut-off. Thus, if the factory load #n is greater than the permitted load Pn, valve V4 conducts, and relay L operates. Similarly, if the factory load is less than the permitted load, V5 conducts and relay R operates. Load control units.-These may comprise any known method of varying the load under the control of relays L and R. In another embodiment, Fig. 2, which caters particularly for the case where the target consumption for any interval is not integral, two counters are used consisting of relay trains or as disclosed in Specifications 555,392 and 566,156, [both in Group XXXIX], cold cathode tube circuits. The first counter, the integral counter, is set according to the target Tp, i.e. the permissible load for the current interval, say, the pth. This number when considered as expressed in radix' (n-p+ 1) that is the number of unexpired intervals t in the period T, gives, together with the remainder rp, set up on the second (remainder) counter, the unexpired portion of the maximum quantity at the commencement of the pth interval. At the beginning of a half-hour period T, the quantities Tp and rp are set up from the maximum demand meter. The reading of the integral counter is fed at the beginning of each half-minute interval t to a target indicator and to an integer transfer chain, which are then rendered independent of the integer counter until the next interval. Under control of the transfer chain, an impulse generator feeds Tp impulses through an impulse absorber which absorbs the first impulse so that (Tp-1) impulses are fed additively to the remainder counter. Impulses from the KWH meter pass through a corrector to the remainder counter in a subtractive sense, any excess or deficiency in the remainder counter being accommodated by the reversible transfer mechanism to the integer counter. It is shown algebraically in the Specification that when, at the end of each half-minute interval t, an interval counter, synchronized from the maximum demand meter at each period, effects a reduction of one in the radix of the two counters, then the two counters automatically indicate respectively the appropriate target T(p+1) and remainder x(p+1) for the succeeding (p+1)th interval, at the end of which the target indicator and integer transfer chain are again operated as indicated above. A load-setting device compares the actual load with the target as set up on the integral counter and adjusts the load accordingly.