Patent GB-547081-A (GB)
Title: Automatic turbine control system
IPC: F01K9/00
Filed: 1941-04-10
Abstract: 547,081. Fluid-pressure servomotor-control systems. BRITISH THOMSON-HOUSTON CO., Ltd. April 10, 1941, No. 4804. Convention date, April 10, 1940. [Class 135] [Also in Group XXVI] An automatic control system for a steam turbine driving an electric generator brings the turbine up from cold to full speed and connects the generator to the line. The various auxiliaries are brought into operation and connections made and broken at the proper places in the sequence of operations by electrically-operated devices and each step in the sequence is possible only if the various checks are favourable. The system also provides automatic control for the normal shutting down of the turbine. If at any time, during running, a pre-emergency condition obtains, e.g. a too low steam pressure, the system automatically shuts the turbine down in normal fashion. In the event of a more serious defect, e.g: loss of condenser vacuum, the generator will be immediately disconnected from the line and the turbine shut down. Upon the occurrence of an extreme emergency, e.g. an excessive generator or bearing temperature, the main circuit breaker will be tripped, the throttle valve shut and the various auxiliaries except the oil pump shut down. The steam connection is provided with an emergency stop valve 14, a speed-governor controlled throttle valve 16 and a starting throttle valve 15 by which the turbine is controlled up to the point when it commences to take load. Up to this point, the governor control is held by a latch 78 in the full speed no load position. The throttle valve 15 is operated by an electric motor 33 through a servomotor 23. The servomotor is byepassed by a cylinder 51 when a latch 59 is removed and the valve 15 is then closed by a spring. The latch is re-set and the byepass closed by a reversal of the motor 33 to cause the rod 35 to push the piston 52 to its lower position. A number of switches 41 to 46 operated with the throttle valve are included in the control circuits. The starting sequence is initiated by hand and is carried through by a motor-operated rotary drum controller which is moved from one stage to another as the circuit is made which indicates the completion of the operations in that stage. The closing of the starting switch, if the contacts of the various protective devices are closed, causes the controller to move from the " off " position to " start ". In this position, circuits are closed for energizing the air pump, water pump, condensate pump, stop valve, vacuum breaker valve and the oil pump. When the oil pressure is built up, a circuit is closed for operating the throttle valve to admit steam sufficient for warming but not moving the turbine. The warming period is measured by a time switch which finally causes the further opening of the throttle to starting or rolling position. When the turbine starts to roll a lowspeed governor switch closes its contacts causing the throttle valve to close and the turbine to stop. At the same time the controller moves to the first " check" position. On the closing of a second manual switch, the controller moves to the position to bring the turbine to speed. The throttle valve trip is re-set and the throttle opened, to warming position. After a time delay, the throttle is slowly tapped further until the turbine is making, say, 400 r.p.m. At this time, the lubricating-oil cooling water is started and water admitted to the high and low pressure turbine packings. After a further time delay, the throttle is opened to bring the turbine up to speed. When the exciter voltage is sufficient the generator field shunt is broken and the exciter, with full normal resistance in its shunt field, is connected to the generator field slip rings. If, after a predetermined time, the necessary exciter voltage is not reached, an auxiliary source of excitation current is switched in, and contacts are opened to preclude a later connection of the exciter. At the same time, the supply of cooling water to the generator ventilating air cooler is initiated. At about 98 per cent turbine speed, a speed switch closes contacts which put in a contact-making voltmeter which commences the adjustment of the generator voltage and a time delay relay is energized which allows time for the turbine to reach full speed and then causes the rapid movement of the throttle to fully open position. This closes contacts which cause the drum controller to move to the second " check " position. The throttle valve is shut and the turbine slows down. If everything is in order, a button is pressed and the drum controller moves to "synchronizing" position. If the progress of the cycle up to this point has been unduly delayed, a time delay relay energizes a signal bell or the like. With the drum controller in "synchronizing" position, the throttle valve mechanism is re-set and the valve is opened rapidly to the 400 r.p.m. position and thereafter tapped open to fully open position. The turbine is now under the control of the speed governor 70 (within the limit imposed by the latch 78) and the speed matcher, which may be as described in Specification 347,066, [Group XXXV] , is put into operation and by means of the motor 76 brings the turbine to correct speed and the synchronizer will, when the frequency difference and the phase difference are suitably small, cause the closing of the circuit breaker. Contacts closed thereby cause the drum controller to move to " running " position and there follow the cutting off of steam to the high-pressure packing, the closing of the high-pressure packing leak of 125, and the turbine drain valve 127 and the releasing of the governor latch 78. The voltage and load control are also connected to push-buttons in the supervisor's cabinet. The tapping open of the throttle valve 15 and the slow unloading of the turbine by means of the motor 76 are obtained by including in the circuits motor driven intermittent contacts as shown in Fig. 4. The duration of the contacts is varied by relative movement between the brushes 362, 363.