Patent GB-884993-A (GB)
Title: Improvements in or relating to electrical generating plant
IPC: G06G7/635
Filed: 1958-01-07
Abstract: 884,993. Automatic control systems for power stations operating in parallel. BROWNLEE, W. R. Jan. 7, 1958 [Jan. 7, 1957], No. 674/58. Class 38 (4). [Also in Group XXXVI] An electrical distribution system having a number of generating plants connected thereto generally of the kind disclosed in Specifications 884,991 and 884,992 is characterized in that a computing apparatus is situated at each generating plant, the reference quantity, against which each computing apparatus functions, being common to all the plants but which is obtained externally of any of the plants connected to the system. In a system whereby an economic division of load is obtained each plant is provided with a computing and load assigning apparatus 3. A dispatching office 1 receives signals corresponding to the reference voltage 18, the desired system values 17 and the actual system values 16 and from these is derived a signal 15 used to control the computing apparatus at each plant, the control at each plant being governed by the difference between the phase angle of the control signal 15 and the phase angle of the voltage at each plant which is supplied to the computing apparatus at each plant by a connection such as 12, the control effected by each computing apparatus being a linear function of the phase angle difference. Thus the division of load can be maintained in an economic balance by maintaining a given phase angle in the common signal 15 and the load division may be regulated by variation of the phase angle of the signal 15. The common signal 15 is fed to each computer as shown in Fig. 2 where it is taken to a receiver 54 and a device 55 wherein its phase angle is compared with the generated voltage phase angle which is fed to the device 55 by a line 12. Should the comparison show any deviation from economic balance of the plant an output will appear at the device 55 which is fed to an amplifier 57 by way of a follow-up circuit 56, the resultant amplifier output causing a motor 58 to run to re-balance the follow-up circuit 56. At the same time movement of the motor 58 sets a moving contact 31 on a potentiometer 29 which forms part of the upper branch of a bridge circuit 22. The upper branch of the bridge circuit 22 thus computes the incremental transmission loss ratio, a ratio which is linearly dependent on the phase angle difference measured in the device 55. Potentiometers 28, 30 are provided in this branch to allow for the introduction into the computation of a constant quantity by manual adjustment of a control knob 37. The lower branch of the bridge circuit 22 is provided for computing the incremental generating cost ratio, a potentiometer 32 being provided to allow the introduction of a quantity dependent upon the cost of fuel into the computation. Thus any deviation from economic balance in the operation of the generating plant will cause an output from the bridge circuit 22 to run the motor 50 which adjusts the turbine governor to alter the output of the generator, the bridge being re-balanced by a potentiometer 33 controlled by a cam 42 on the turbine valve shaft. Should there be more than one generator at the plant each is provided with a bridge circuit such as 22. In the case where a generating plant is connected to an intermediate point in the system the computation is arranged in two stages, the first in which a comparison is made between the plant and the intermediate point, the second in which the comparison is between the intermediate point and the reference point. The apparatus at the dispatching office 1 comprises a self-balancing bridge wherein actual and desired conditions are compared, the bridge apparatus subsequently controlling a phase-shifting device which transmits the required signal over the line 15. Specifications 568,204 and 884,994 also are referred to.