GB938013A - Improvements in and relating to electric turbine-start control arrangements - Google Patents

Abstract

938,013. Gas turbine plant. GENERAL ELECTRIC CO. April 14, 1960 [April 27, 1959], No. 13456/60. Class 110 (3). A gas turbine type engine starter comprising a control system in which a main switch, when closed, begins a sequence of automatic operations, has a relay which is energized by a combustion chamber pressure responsive switch breaking a short circuit path around the relay containing normally closed contacts of the relay. The arrangement is such that the relay must be reset by opening the main switch before another sequence of operations can be initiated. A gas turbine type starter has a combustion chamber 11 to which fuel and air are supplied from containers 18, 24 through solenoid-operated valves 21, 28, 29. The turbine 12 drives the starter pinion 16 through a reduction gear 17. When switch 44 is closed, current flows through contacts B2, 43 and A3 to solenoids 30, 31 and also through contacts B3 to the solenoid 22 so that a flow of fuel and air is initiated to the combustion chamber 11. Current also flows through the contacts B3, pressure switch arm 37 and contacts A2 to the ignition unit 33. Relay coil A is not energized owing to the low resistance of the by-pass through contacts B2, 43, A3, B3, switch arm 37 and contacts A2. The relay coil B is not energized as contact B1 and switch 47 are open. After a brief interval, combustion occurs in the combustion chamber and the resulting pressure increase causes switch arm to move from contact 40 to contact 41. The shunt path around the relay coil A is now broken at contact 40 so that the coil A is connected in series with the ignition unit 33. The coil actuates the relay to open contacts A2, A3 and close contact A1. The closing of contact A1 locks in the relay coil A and de-energizes the ignition unit 33. The pressure switch 36 is of the snap action kind so as to ensure that the continued energization of the solenoids 22, 30, 31 through contacts B2, 43, arm 37 and contacts B3. The bus-bar 45 is connected now to the air and fuel solenoids through a circuit which at the return of the pressure switch to its low pressure position interrupts the current supply in the fuel and air control solenoids. When a preselected cut-out speed is attained the speed control mechanism 48 opens a switch 43 which breaks the connection between the bus-bar 45 and the air and fuel solenoids 30, 31 and 22, thereby closing the valves 21, 28, 29. This causes a drop in combustion chamber pressure and a return of arm 37 to contact 40. Interruption of combustion causes the speed of the turbine 12 to decrease and switch 43 to re-close. Since the relay coil remains energized, the contacts A2, A3 remain open and contacts A1 remain closed so that the closing of the switch 43 does not re-establish the circuit to the fuel and air solenoids. To re-open a starting sequence, switch 44 must be opened first to interrupt the power supply to the relay coil A to cause resetting of the contacts. If an air motoring form of operation is required, main switch 47 is closed. This energizes coil B and closes contacts B1 and opens contacts B2, B3. The motor 45 is then connected to solenoids 30, 31 so that air only is supplied to the combustion chamber 11. A diode 49 is provided to dissipate energy in the solenoids when the current is interrupted and to reduce arcing at the switch 43.