Patent GB-866271-A (GB)
Title: Improvements in electric power control system
IPC: H02J3/06
Filed: 1957-07-26
Abstract: 866,271. Automatic generation control systems. GENERAL ELECTRIC CO. July 26, 1957 [July 31, 1956], No. 23716/57. Class 38 (4). In a power network comprising a plurality of interconnected generating stations for supplying adjacent and distant areas according to preselected load schedules and a control station with means whereby a continuous control signal varying in frequency in accordance with deviation between actual and desired conditions of frequency and tie-line loads is produced, means are provided to modify the control signal supplied to at least one station in accordance with a penalty factor assigned to that station and based on transmission losses to the distributed load points, and to vary the power generated at each station to produce equal incremental costs of delivered power in response to the control signal. The basic control signal for stations in the local area is produced by a differential selsyn 28, Fig. 1, driven through a mechanical differential gear 23 in response to the sum of the frequency deviation #f and a multiple of the deviation from schedule K #W of tie-line power, the former being injected by a shaft 24 from a servo-amplifier 25 fed with the system frequency and a standard frequency, and from oscillator 26, and the latter by a shaft 22 from a servo-amplifier in which the actual tie-line load as fed to a summing amplifier 20 by telemeter receivers (not shown) is compared with the scheduled tie-line load. A multiplier K which is determined by the amplifier gain is arranged so that for changes of load in the remote area when frequency deviation and the line load deviation are opposite in sign #f and K #W are substantially equal and no local area control is effected. The control signal from differential selsyn 28 having a frequency fa + #f + K #W is passed to the local stations through a penalty factor unit 31 comprising a motor 30 driving a selsyn 29 whereby the signal frequency is modified, the motor being driven in accordance with the difference between the incremental cost of power delivered from the respective stations and the average incremental cost of power delivered by all the areas. The incremental cost dF/dP  ¸ I/L, where F is fuel input in cost per hr., P is the input power in megawatts/h., and L is a loss factor obtained from a loss factor computer 32 fed with plant loading and tie-line loading signals and delivering a loss factor 1/L to serve as a divisor in a dividing circuit 34 to which dF/dP is fed from a function generator 33 also fed with plant loading signals. The outputs of the respective dividing circuits are averaged in an amplifier 35 and compared individually with the average in balancing amplifiers 36 which provide the modifying signal to the penalty factor units. The signals are divided in frequency before being transmitted by conventional means to receivers 40 (Fig. 2) in the area stations in which the signal is reconstituted in a multiplier 41 and applied with the system frequency to a servo amplifier 42. The output shaft 43 drives differential selsyns 51-55 through gear-box 44 at ratios varying from 1-1 for selsyn 51 to 10-1 for selsyn 55 producing output signals representative of fα (the system frequency) + the area requirement to fα + <SP>1</SP>/ 10  of the area requirement which may be selected by a threebank control rate selector 56 to adjust the governors 80 of respective generators through a comparator 76 and servomotor 78. An integral function is introduced by driving control transformer selsyn 77 from the servomotor 78 through a reduction gearing 81. The correcting signal is modified in accordance with economic consideration by a selsyn 65 of a load proportioning unit 67 the motor 66 of which is driven in accordance with the difference between the generator output and the desired output corresponding to the incremental heat rate, the latter being obtained by multiplying in a potentiometer 73 a voltage proportional to incremental cost derived from a potentiometer 68 connected across a standard cell 70 the wiper of which is driven by a shaft 71 from the gear-box 44. The multiplier set up in potentiometer 73 is the fuel cost factor and if a common fuel is used a single potentiometer will suffice. In a modification, Fig. 3, providing proportional and reset control a servomotor 102 drives a tachometer generator 104 in accordance with the deviation of the system frequency from that of a standard 101, and a fraction of the tachometer output i.e. the frequency deviation signal applied to terminals 112, 113, Fig. 4, of unit 105, determined by potentiometer 117, is added to the difference between a signal representative of the actual tie-line load at terminals 120, 121 and a signal representative of the scheduled load set by the wiper on a potentiometer 123 to produce at output terminals 118, 119 an area requirement signal which is applied both to reset balancing amplifier 108 and to a balancing amplifier 106 for proportional control. Network 114, 115, 116 is effective against cumulative errors. The output of the balancing amplifier 106 to the proportional controller 107 is an alternating voltage whose amplitude and phase are related to the difference between the input from 105 and the signal fed back from the proportional controller, and it is applied in the controller to one phase of a two-phase motor 126, Fig. 5, the other phase of which is supplied from the network. The motor 126 drives, through a slipping clutch and reduction gearing 127, a selsyn 128 the rotor of which energizes the stator of a control selsyn 110 to produce a control signal, a tachometer generator 129, and a wiper of a potentiometer 130, the last named members causing a D.C. signal to be fed back from terminals 132, 133 to the balancing amplifier 106 for comparison with the input. The input from unit 105 to the reset balancing amplifier 108 is compared with the output of a tachometer 111 driven through a reduction gearing by a motor 109 having inherent speed limitation, the tachometer output being proportional to the rate of rotation of the motor and thus to the area requirement signal. The final control signal is thus modified by the limitation of motor 109 according to whether the area requirement signal is large or small. A penalty factor is introduced by a selsyn 145 driven by a motor 146 in response to the difference between the 1 output of a loss factor (-) computer 150 and a L 1 voltage proportional to log - from a potentio- L meter 147. Insofar as this system does not employ function generators it is not necessary for generators to be added to the line or removed therefrom in a predetermined order. An alternative system in which the penalty factor is determined by the difference between a computed predicted load and the actual load is described with reference to Fig. 6 (not shown). The Specification refers also to systems in which the central control station responds to frequency or load.