GB690120A - Improvements in and relating to the starting of gas turbines - Google Patents

Abstract

690,120. Gas turbine plant; rotary pumps. ENGLISH ELECTRIC CO.. Ltd. July 13, 1951 [July 18. 1950]. No. 17930/50. Classes 110(ii) and 110(iii) [Also in Group XXVII] A gas turbine plant is driven up to its self starting speed by a hydraulic motor which is supplied with liquid under pressure by an independently driven auxiliary pump of the plant such as a lubricating oil or fuel pump. In the plant shown, Fig. 1, a gas turbine 2 drives a compressor 1, a load 3 and a lubricating oil pump 4. An auxiliary lubricating oil pump 5 driven by an electric motor 6 is provided to supply oil during the starting period and in the event of failure of the pump 4. Both pumps draw oil from a sump 10. A stop or non-return valve 11 is arranged between the sump 10 and the pump 4 which discharges through a non-return valve 12 to the bearings. A stop valve 15 is arranged between the delivery of the pump 5 and the inlet to the pump 4. A pressure relief valve 16, stop valve 17 and non- return valve 18 are arranged between the delivery of the pump 5 and the bearings. In normal operation. the valves 11 and 17 are open and the stop valve 15 closed and the pump 4 draws oil from the sump 10 and delivers it to the bearings. The non-return valve 18 is closed by the oil pressure and the pressure responsive capsule 13 keeps the switch 14 open. Should the pump 4 fail, switch 14 is closed by the capsule 13 and the relay 31 energised to close the switch 31<SP>1</SP> and start the motor 6. The pump 5 then delivers oil from the sump 10 to the bearings through the non-return valve 18. A latch 31<SP>11</SP> keeps the switch 31<SP>1</SP> closed when the oil pressure regains its normal value. For starting, the valves 11 and 17 are closed and the valve 15 opened. The pump 5 is then started and delivers oil under pressure to the pump 4 which acts as a hydraulic motor and drives the machines 1, 2, 3. As soon as the machines 1, 2, 3 are self-running, the valves 11, 17 are opened and the valve 15 closed. The relative sizes and speeds of the pumps 4, 5 are chosen that. at the self-running speed of the machines 1, 2. 3. the requirements of the pump 4 are 2 per cent to 25 per cent less than that of the pump 5. Above this speed, the requirements of the pump 4 should exceed the delivery of the pump 5 so that it commences to suck oil from the sump 10. In a modification, the valve 15 is replaced by a spring loaded valve in a cylinder which controls two sets of ports. One set is connected to the suction of the pump 4 and the other set to a return to the sump 10. The arrangement is such that when the valve 17 is closed, the pressure in the conduit 26 rises and the spring loaded valve opens the ports connected to the pump 4. Any further increase in pressure causes the valve to open the second set of ports and allows the excess oil to return to the sump. In this arrangement the relief valve 16 is placed in the conduit between the discharge of the pump 4 and the bearings. In another modification, the valve 15 is replaced by a two way cock which may connect the discharge of the pump 5 either to the suction conduit 8 of the pump 4 or to the conduit 26. In this arrangement, a pressure relief valve which can be set to two different loadings is placed between the discharge of the pump 5 and the two way cock. In normal operation, the two way cock is set to connect the discharge of the pump 5 with the conduit 26 and the relief valve set to the lower loading. For starting, the cock is set to connect the discharge of the pump to the conduit 8 and the relief valve set to the higher loading. The two way cock and the means for varying the loading of the relief valve may be coupled to one another but it is preferred to retain independent operation of these members so that the relief valve may be set to the lower loading and the pump 5 connected to the conduit 8 when it is desired to drive the machines 1, 2. 3 for a prolonged period below the self driving speed. In another plant, Fig. 4, comprising a low pressure compressor 27 driven by an intermediate pressure turbine 29, a high pressure compressor 1 driven by a high pressure turbine 2 and a useful output low pressure turbine 30, only the set consisting of the high pressure compressor 1 and turbine 2 is driven up to the self-driving speed. In this arrangement, the pump 5 driven by the electric motor 6 acts as the lubricating pump during normal operation and the unit 4 serves only as a hydraulic starter motor which is connected to the turbine-compressor unit 1. 2 by a free wheel or overdrive clutch 21 which automatically disengages itself when the turbine 1 reaches its self-driving speed. The pump 5 normally discharges through a valve 22 to the bearings. When it is desired to start the unit 1, 2, the valve 22 is closed, the pump discharge pressure rises and the motor 4 operated. A modification in which the pump 5 is the fuel pump is also described. The starting arrangements described with reference to Fig. 4 can be applied to the plant shown in Fig. 1.