Patent GB-884991-A (GB)
Title: Improvements in or relating to electrical generating plant
IPC: G06G7/635
Filed: 1958-01-02
Abstract: 884,991. Automatic control systems for power stations operating in parallel. BROWNLEE, W. R. Jan. 2, 1958 [Jan. 7, 1957], No. 210/58. Class 38 (4). [Also in Group XXXVI] An electrical distribution system having a number of generating plants connected thereto is provided with computing apparatus which equates the generating costs of the stations against the transmission losses so as to ensure that the generating plants share the load on the distribution system in the most economical manner. The computer apparatus shown in Fig. 1 equates the transmission losses against the generating costs of pairs of plants and uses one of the plants, say No. 1, as a reference ; that is, plants Nos. 1 and 2 are compared; plants Nos. 1 and 3 and plants Nos. 1 and 4, such that when each pair of plants is working at an economic balance the whole system is economically balanced. Should any deviation from economic balance occur it will be indicated by devices 266, 366 and 466 and the sharing of the load by the plants may be readjusted either manually or automatically to restore the. balance. If the adjustment is made automatically, the deviation signals are fed into control apparatus shown in Fig. 4 to which apparatus are supplied generation raising and lowering impulses which are routed to the generating plant to adjust the generation according to the dictates of the deviation signals. The computer shown in Fig. 1 is in three similar sections and is arranged to equate the incremental fuel costs against the incremental transmission loss ratio for each pair of generating plants, the incremental transmission loss being reduced to a function which is dependent upon the sine and cosine of the phase angle between the voltages at the plants in each pair. Taking plants Nos. 1, 2 there are fed to the receivers 117, 217 voltages representing the phase angles of the voltages at the bus-bars thereof, the outputs of the receivers 117, 217 being fed to a wattmeter 101 adapted to compare two voltages so that at the output terminals 113, 114 of the wattmeter there appears a voltage proportional to the cosine of the angle between the voltages of plants Nos. 1 and 2. This voltage is fed to a self-balancing bridge comprising fixed resistors 104, 105 and potentiometer 107. The outputs of the receiver 117, 217 are fed also to a varmeter 102 which compares the two voltages such that at its output terminals 124, 125 appears a voltage proportional to the sine of the angle between the voltages of plant Nos. 1 and 2; and this voltage is connected in series with the voltage across the bridge diagonal to feed the amplifier 103 which causes the motor 108 to balance the bridge and thus position a slider 144 in accordance with the existing value of the incremental transmission loss ratio for plants Nos. 1 and 2. Voltages which are representative of the fuel prices at plants Nos. 1 and 2 are set on potentiometers 132, 232 respectively by control knobs 136, 236, these voltages being fed to potentiometers 138, 238 respectively, the positions of the movable contacts 139, 239 representing the existing incremental generating costs of plants Nos. 1 and 2. A ratio between these costs is effected by means of a potentiometer 143 the movable contact 144 of which is positioned according to the incremental transmission loss ratio for the two plants. Thus when economic balance between plants Nos. 1 and 2 is attained no deviation will be indicated on the device 266. Should a deviation from economic balance occur it will be shown on the device 266, and the outputs of the plants Nos. 1 and 2 will need readjustment which may be done either manually or automatically thus the signals which represent these outputs fed to receivers 141, 241 will cause repositioning of the movable contacts 139, 239 whereby the incremental transmission losses and the incremental generating costs are re-equated to re-establish optimum economic balance. Plants Nos. 3 and 4 are similarly compared with plant No. 1 whereby the complete system is maintained in economic balance. As an alternative to the use of receivers 117, 217, 317, 417 the voltages to be fed to the wattmeters and varmeters may be derived by a network analyser. Specifications 537,938, 884,992, 884,993 and 884,994 are referred to.