Patent GB-441514-A (GB)
Title: Improvements in or relating to electrical transient-anticipator protective mechanisms
IPC: H02H3/44
Filed: 1934-12-08
Abstract: 441,514. Fluid-pressure servomotorcontrol systems. SHEPHERD, G. R., 2, Norfolk Street, Strand, London.-(Westinghouse Electric & Manufacturing Co. ; East Pittsburg, Pennsylvania, U.S.A.) Dec. 8, 1934, No. 35332. [Class 135] An electric control mechanism comprises a force producing member responsive quickly to a sudden change in an electrical quantity, a second similar member responsive sluggishly to the same sudden change and balancing means responsive to a temporary inequality between the two forces whereby a control operation is effected in anticipation of the change of conditions which would result from the change in the electrical quantity. In the system shown a generator 2 is driven by a steam turbine 3 supplied through a valve 5 controlled by an overspeed device 10 and a valve 6 controlled by a speed governor 7 of the type in which oil is received and discharged through pipes 8, 9 and variations in pressure open or close the valve 6. The governor is provided with an additional low pressure outlet 41 by which an anticipated, but not yet effective increase of speed is counteracted in response to a sudden decrease of load on the transmission lines 1. A solenoid plunger 47 pushes downwardly for a predetermined interval of time a valve 43 which allows the low pressure oil to escape from the outlet pipe 41, the solenoid being operated through electric relays from the control apparatus responsive to the sudden decrease of load. This apparatus includes a beam 12 normally slightly biassed to engage a fixed pin 27, but adapted, on decrease of load, to close contacts 13 connected in an independent D.C. operating circuit 54. The beam 12 is controlled by solenoids 31, 32, 33, 34 through springs 14, 15, a dashpot 25 being also provided to effect slow closing while allowing quick opening of the contacts 13. The solenoids are provided with identical current and voltage windings. When the contacts are closed, a circuit is completed through the operating coil 56 of a holding relay 55, the circuit including resistance 60, and the normally closed push button 61. When contacts 13 open again, relay 55 is held by a connection to the negative lead through conductors 64, 63. The relay 55 completes a circuit through the solenoid 40 of the plunger 47 operating the valve 43, this circuit being completed from positive lead 54, through lead 70, contacts 68, lead 67, coil 40, resistance 66, lead 65, relay 55 and lead 63 to negative lead of source 54. Contacts 68 are normally closed by auxiliary relay 69 energized across source 54 by contact member 72 closed by a normally energized magnetizing coil 74. When relay 55 is operated, coil 74 is short circuited and a demagnetizing winding 77 assists opening of contacts 72 after a predetermined interval such as three seconds. The consequent opening of contacts 68 breaks circuit through winding 40 and restores normal oil governor operation. A discharge resistor 80 checks arcing at the contacts 68. With the double throw switch 81 in the position shown engaging the lower row of contacts, the relay 55 remains closed so that the above controlling operation cannot be repeated until push button 61 is depressed. But if switch 81 is adjusted to engage the upper row of contacts, the relay 55 is opened thus resetting the apparatus automatically after each operation.