US3470691A

US3470691A - Automatic starting and protection system for a gas turbine

Info

Publication number: US3470691A
Application number: US737743A
Authority: US
Inventors: Emile G Smith
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1968-06-17
Filing date: 1968-06-17
Publication date: 1969-10-07
Anticipated expiration: 1986-10-07

Description

Oct. 7, 1969 E. G. SMITH 3,470,691

AUTOMATIC STARTING AND PROTECTION'SYSTEM FOR A GAS TURBINE Filed June 17, 1968 2 Sheets-Sheet 2 R f .1. I T Q 88 United States Patent 3,470,691 AUTOMATIC STARTING AND PROTECTION SYSTEM FOR A GAS TURBINE Emile G. Smith, Bethe], C0nn., assignor to Avco Corporation, Stratford, Conn., a corporation of Delaware Filed June 17, 1968, Ser. No. 737,743 Int. Cl. F02g 3/00; F02c 7/26; F16p 7/00 U.S. Cl. 6039.09 6 Claims ABSTRACT OF THE DISCLOSURE A gas turbine engine having variable power turbine stator vanes is automatically started by means of a pushbutton operated control unit which serves to energize the starter motor and the ignition unit. The starter motor and ignition unit are de-energized after a successful start is indicated by a compressor speed comparator, or an attempted start is aborted by de-energizing the starter motor and ignition unit after a predetermined elapsed time. During operation, automatic protection is provided against a power turbine overspeed condition by automatically varying the stator vane position, and against an overtemperature condition by automatically bleeding main fuel.

BACKGROUND OF THE INVENTION In the starting of a gas turbine engine it is necessary for the operator to manipulate several controls over critical time periods. In starting and operating any gas turbine engine certain parameters are critical, and in the ordinary system the operator must carefully monitor his instruments to make certain that no damaging conditions exist. The particular gas turbine engine, in which the present invention was reduced to practice, utilized a free power turbine with variable power turbine stator vanes and a main fuel bleed valve. The present invention provides automatic monitoring and controlling of these devices and, in addition, provides means for automatically shutting down the starting procedure after a successful start, or aborting an unsuccessful start after a predetermined elapsed time.

The invention provides: a high pressure compressor speed (N pick-up for providing a pulse train whose pulse repetition rate is proportional to compressor speed; a power turbine speed (N pick-up for developing a pulse train having a repetition rate proportional to power turbine speed; a thermocouple harness for sensing engine gas temperature to the power turbine section which is used to prevent an overtemperature condition; and a timer for developing output pulses after a predetermined period of elapsed time if the engine has not yet started.

In the starting cycle, the operator depresses a starting button which serves to energize a starting relay, closing the circuits to the ignition unit and to the starter solenoid, and thereby to the starter motor. If the engine does not start, i.e., attain idle speed, within a predetermined time, the output from a delay timer serves to de-energize the starting relay, opening the circuits to the starter motor and the ignition unit and notifies the operator to abort the starting attempt. If a successful start is accomplished prior to the completion of the delay time, the output from the N comparator upon attaining a predetermined compressor speed, de-energizes the starting relay and thereby the starting accessories. After a successful start is made, operation is monitored by the power turbine, N speed pick-up and by the thermocouple harness. If the free power turbine speed exceeds a predetermined level, output pulses generated by the N comparator are used to control the stator vanes so as to slow the turbine down. In the event an overtemperature condition is sensed by the temperature comparator, an output is generated by the overtemperature comparator, and this serves to open the main fuel bleed valve which reduces the amount of fuel supplied to the combustion chamber and hence reduce operating temperatures.

THE DRAWINGS FIGURE 1 is a block diagram showing the overall configuration of the system while FIGURES 2 and 3 are schematics of the particular circuits utilized within the system.

DESCRIPTION OF THE INVENTION The overall system includes a starter motor 10 energized by means of a battery 12 through the contacts 14 of a starter solenoid 16, a starting relay 24, and through a master power switch S1 and transmission mode switch S2. In addition the system includes an ignition unit 18 which functions to energize the spark plugs in the engine when connected to the battery 12. The starter solenoid 16 and the ignition unit 18 are each energized through the

contacts

20 and 22 of a starting relay 24. The starting relay 24 is in turn energized by connecting the battery 12 through a transmission mode switch 52, which is closed when the engine transmission is in neutral, and through a pushbutton momentary start switch S3. Closing of the master power switch S1 also applies the battery 12 to a voltage regulator 25, the regulated voltage output of which appears at a terminal R. The regulated voltage appearing at the terminal R supplies the power for several subsystems within the system. For purposes of clarity, the connections from the voltage regulator 25 to the various circuits have been omitted, it being understood that all of the terminals R are interconnected.

With switches S1 and S2 closed, the momentary closing of the starting switch S3 applies the voltage from the battery 12 to an ignition and starter power control circuit 26. This causes the energization of the starting relay 24 and the closing of the

contacts

20 and 22. When the contacts 20 are closed, the starter solenoid 16 is energized, causing the contacts 14 to be closed and energizing the starter motor 10. When the contacts 22 are closed, the ignition unit is energized and functions to ignite the engine fuel.

The compressor speed N pick-up 28 is conventional and in a practical case may comprise a magnetic device producing pulses of a repetition rate proportional to the speed of the high pressure compressor. The output pulses from the N pick-up 28 are analyzed by an N speed comparator circuit 30 which serves to produce a series of output pulses when the speed of the high pressure compressor exceeds a predetermined level. In a successful start this will occur before output pulses are developed by a delay timer 32 and, when applied to the ignition and starter power control circuit 26, will serve to de-energize the starting relay 24 and open the circuits to the starter solenoid 16 and the ignition unit 18.

In the event that the N comparator does not develop output pulses prior to the expiration of a predetermined time due to a failure to start, an output is developed from the delay timer 32 and is applied to the ignition and starter power control circuit 26. This also serves to deenergize the starting relay 24, thereby disconnecting the starter solenoid 16 and ignition unit 18.. However, since a start has not been accomplished in this case, the attempt is aborted by this reaction and by ordering the operator to abort this attempt.

Therefore, during starting the ignition and starter power control circuit 26 can be supplied with pulses from two sources, the N comparator 30 or the delay timer 32. If supplied from the N comparator 30 through line 31 prior to the application of a pulse from the delay timer 32 through line 33, the engine has started and operation of the starter motor and the ignition unit 18 are no longer required. Therefore, the starting relay 24 is deenergized and the delay timer deactivated through line 35. However, if the delay timer operates before the compressor has reached the desired speed, the starter motor 10 and ignition 18 are turned off, but in this case the engine is not running, and the starting attempt is aborted.

In the event of any malfunction within the ignition and starter power control 26 or elsewhere in the starting power cycle, the operator can manually override the automatic system by means of depressing the start switch a second time. This will deenergize the automatic system and he may control the engine with a manual starter motor switch S4 and a manual ignition switch S5. These connect the battery directly to the starter solenoid 16 and the ignition unit 18 and must, of course, be monitored by the operator.

The battery 12 is also connected through switch S1 via a line 36 to a variable power turbine stator vane solenoid 38 and via a line 40 to a main fuel bleed solenoid 42. The circuit to ground for the stator vane solenoid 38 is completed through a line 44 and a stator vane power control circuit 46. Similarly, the circuit to ground for the main fuel bleed solenoid 42 is completed through a line 48 and a main fuel bleed control circuit 50.

Each of the connections to ground through the

control circuits

46 and 50 are normally open, and therefore the

solenoids

38 and 42 are normally de-energized. The power turbine stator vane control circuit 46 completes the connection of the solenoid 38 to ground when an output is developed from the N comparator 52. This occurs when the speed of the high pressure compressor, as measured by an N pick-up 54, exceeds a predetermined level. Similarly, the main fuel bleed control circuit 50 completes the connection to ground in response to output from an overtemperature comparator circuit 56. This occurs when thermocouples 58 measure a temperature considered eX- cessive by the comparator. This temperature level is modified by means of manual switches 60 and 61 which are set for particular operating conditions. When the stator vane power control circuit 46 completes the connection to ground, the stator vane solenoid 38 is energized and serves to change the position of the variable stator vanes 62 in the power turbine inlet and hence reduce the power turbine speed. When the main fuel bleed control circuit 50 completes the connection to ground, the main fuel bleed solenoid 42 is energized to open the main fuel bleed valve 64 in the fuel supply system so as to reduce the amount of fuel being delivered to the combustion chamber.

IGNITION AND STARTER POWER CONTROL UNIT The ignition and starter power control unit is shown in FIGURE 2. It comprises two silicon controlled rectifiers Q1 and Q2 which operate as a flip-flop. The rectifier Q1 controls the power applied to the relay 24 which in turn controls the starter solenoid 16 and the ignition unit 18. Power is applied to the ignition and starter power control unit 26 by the closing of switch S1. This supplies regulated D.C. voltage from the battery 12 to the voltage regulator 25 which serves to develop a regulated DC. voltage at the various terminals R throughout the system.

The silicon controlled rectifier Q1 is comprised of a cathode 68 connected to ground, an anode 70 connected to the terminal R through a diode 727 and the windings of relay 24, and a control electrode 74 connected to ground through a resistor 76. The silicon controlled rectifier Q2 is comprised of a cathode 77 connected to ground, an anode 78 connected to the terminal R through a resistor 80, and a control electrode 82 connected to ground through a resistor 84. The

anodes

70 and 78 of controlled rectifiers Q1 and Q2 are interconnected by means of a commutating capacitor 85.

The control electrode 82 of the rectifier Q2 is connected to the terminal R through a diode 86 and a capacitor 88, the junction of diode 86 and capacitor 88 being connected to ground through a resistor 90. The control electrode 74 of rectifier Q1 is connected to a start-stop terminal T1 through a capacitor 92 and a diode 94, capacitor 96, and a resistor 98. One side of the capacitor 96, is connected to ground through a resistor 100, while the other side is connected to ground through a resistor 102. The junction of capacitor 92 and diode 94 is con nected to the anode 78 of rectifier Q2 through a resistor 104.

When the master power switch S1 is closed, unregulated power is coupled through capacitor 88 and diode 86 to the control electrode 82. This will cause controlled rectifier Q2 to conduct and .assure that controlled rectifier Q1 is not conducting, having been commutated off by capacitor 85. Setting the flip-flop up into this initial turn-on state will assure the proper logic sequence preparation.

When the starting switch S3 is momentarily closed, the unregulated D.C. supply is connected to the terminal T1 and a pulse is applied to the control electrode 74 of rectifier Q1 through the resistor 98, capacitor 96, diode 94, and capacitor 92. It will be noted that a diode 103 is connected to the anode 70 of rectifier Q1 through a resistor 106; however, current flow through the diode 103, resulting from a voltage applied at T1, is blocked because of the high voltage at the anode 70 when it is not conducting which supplies a back voltage to diode 103 preventing it from conducting. However, the pulse applied to the control electrode 74 turns on rectifier Q1, energizing coil 24 and also connecting the commutating capacitor to ground and across the rectifier Q2. This serves to cut off rectifier Q2.

The rectifier Q2 will stay off and the rectifier Q1 will stay on until another pulse is applied to the control electrode 82 of rectifier Q2. This pulse can be applied manually by a second closing of the momentary start switch S3 which applies a second pulse to the terminal T1. A second pulse will flow. through the resistor 98 and capacitor 96. It will be blocked from flowing through the diode 94 since it is connected to the high voltage at anode 78 of the nonconducting rectifier Q2. However, current can now flow through the diode 103, then through a capacitor 108 and a diode 110 also connected to the control electrode 82 of rectifier Q2. This pulse serves to start the conduction of rectifier Q2. This conduction connects commutating capacitor 85 to ground across the rectifier Q1, and shuts Q1 off, de-energizing coil 24.

The rectifier Q2 can also be turned on by a pulse applied through a diode 112 supplied with a pulse at terminal T2 from the N comparator 30 or through a diode 114 supplied with a pulse at terminal T3 from the delay timer 32.

When the rectifier Q2 is first turned off, by application of the first start pulse through the closure of S3, the voltage developed at its anode 78 is applied to the delay timer 32 via terminal T4 and line 35 to start the timing cycle. At the end of a predetermined time delay, the delay timer 32 provides the pulse to the diode 114 necessary to again start the conduction of rectifier Q2 which will dc-energize coil 24 and abort the start attempt.

STATOR VANE AND MAIN FUEL BLEED SOLENOID CONTROL CIRCUITS The stator vane control circuit 46 and the main fuel bleed control circuit 50 are identical, the one serving to complete the circuit from the main fuel bleed solenoid to ground and the other serving to complete the circuit of the stator vane solenoid 38 to ground. The circuit for performing these functions is shown in FIGURE 3.

Each circuit has two input terminals T4 and T5. The terminal T4 represents the connection from either the stator vane solenoid 38 (at line 44) or the main fuel bleed solenoid 42 (at line 48), depending on whether the circuit is used for completing the connection of. the stator vane solenoid 38 to ground or for completing the connection of the main fuel bleed solenoid 42 to ground. Similarly,

the input terminal T5 represents either the connection from the N comparator 52 or the overtemperature comparator 56. The outputs from the N comparator 52 and the overtemperature comparator 56 comprise continuous trains of pulses which are developed during either an overspeed or an overternperature condition.

Each

circuit

46 and 50 comprises a silicon controlled rectifier Q3 having a cathode 120 connected to ground, an anode 122 connected to the terminal T4, and a control electrode 124 connected to ground through a resistor 126. The train of pulses at terminal T5 is connected to the control electrode 124 through a diode 128. The train of pulses renders the rectifier Q3 conductive and thereby completes the connection of the terminal T4 to ground. The grounding of terminal T4 completes the energization circuit of the stator vane solenoid or the main fuel bleed solenoid, as the case may be.

The train of input pulses applied at terminal T5 is also connected through a resistor 130 to the base 132 of a transistor Q4 having a grounded emitter 134 and a collector 136 connected to the regulated voltage terminal R through

resistors

138 and 140. A timing capacitor 142 is connected across the collector 136 and the emitter 134. So long as a train of input pulses is applied to the base 132 of transistor Q4, transistor Q4 is maintained in a state of current conduction at each input pulse and this prevents the build up of a steady state voltage on the capacitor 142. However, when the train of pulses terminates, the transistor Q4 stops conducting and the voltage applied from the regulated supply at terminal R begins to build up on the capacitor 142.

The voltage charge developed across capacitor 142 is applied to the base electrode 144 of a unijunction transistor Q5, the base two electrode 146 being connected to the regulated voltage terminal R through a resistor 148, the base one electrode 150 being connected to ground through a resistor 152. When the charge on the capacitor 142 reaches the peak point voltage level necessary to fire the unijunction transistor Q5, the current then flows through transistor Q5 and through a capacitor 154 into the control electrode 158 of rectifier Q6.

The resistor 156 is connected between the control electrode 158 and the cathode 160 of a silicon controlled rectifier Q6, the anode 162 being connected to the terminal R through resistor 140. The voltage developed across the resistor 156 causes the silicon controlled rectifier Q6 to conduct, thereby eifectively connecting its anode 160 to ground. It will be noted that the anode 162 of silicon controlled rectifier Q6 is connected to the anode 122 of rectifier Q3 through a capacitor 164. The grounding of the anode 162 discharges the capacitor 164 across the anode and cathode of the rectifier Q3, shutting Q3 ofif.

Thus, a train of pulses applied at T5 turns on the rectifier Q3 and energizes the associated load. The discontinuance of the train of pulses causes the timing capacitor 142 to charge, turning transistor Q5 on, and causing rectifier Q6 to conduct. Conduction of rectifier Q6 discharges the capacitor 164, shutting off rectifier Q3. The circuit will stay in this condition until a succeeding train of pulses is applied at T5.

OTHER COMPONENTS The remaining circuits and components are conventional and need not be described in detail. It suifices to point out that the N comparator 30, the N comparator 52, and the overtemperature comparator 56 each generates a train of pulses when its respective input exceeds a predetermined level. The reference level of the overtemperature comparator 56 is alterable for various throttle lever positions by means of manual switches 60 or 61 which are mounted on the throttle lever linkage. These switches are used to insert or take out one or more resistors from the comparator reference circuit to change the level at which an output is generated.

The delay timer 32 is also conventional and utilizes two unijunction transistors. Application of DC voltage from the ignition and starter power control unit 26 through line 35 starts the charging of an RC. network. When the RC. network is charged, the unijunction transistor conducts, delivering an output pulse at line 33 aborting the start attempt.

Obviously the system is capable of various modifications and adaptations. In a practical case, the system was supplemented by various additional outputs which were used to energize warning devices indicating an aborted starting attempt or an overspeed or overtemperature condition.

I claim:

1. In a system for automatically starting and controlling the operation of a gas turbine engine having a free power turbine, a compressor turbine and adjustable power turbine stator vanes, said system having a lurality of accessories including a starter solenoid for con-trolling the energization of a starter motor for rotating the compressor of said engine during starting, an ignition unit for igniting the fuel flowing into the combustion chamber of said engine during starting, an electromagnetic fuel bleed valve actuator for controlling fuel flow to said combustion chamber, an electromagnetic stator vane actuator for adjusting the position of the power turbine stator vanes of said free power turbine engine, a source of energization for said motor and accessories, each of said accessories and said motor being in an initial energization state wherein said starter motor and ignition unit are de-energized, said bleed valve is closed and said stator vanes are positioned for maximum power turbine speed, the combination comprismg:

first switch means for establishing connections between said source and said starter solenoid and said ignition unit, respectively;

first means controlling said first switch means to change the state of energization of said starter solenoid and ignition unit to a second state whereby said starter motor and ignition unit are energized;

means responsive to an engine operating parameter for generating a first control voltage;

second means controlling said switch means, said second means being responsive to said first control voltage above a predetermined level for changing the energization states of said ignition system and said starter solenoid to their respective initial energization states, said level representng a successful start to said engine;

timer means responsive to a predetermined lapse of time for generating a second control voltage, the occurrence of said second control voltage prior to the generation of said first control voltage controlling said first switch means for changing the energization state of said starter solenoid and said ignition system to their respective initial energization states whereby an attempted engine start is aborted;

second and third switch means for estbablishing connections between said source and said stator vane actuator and said fuel bleed solenoid, respectively; means responsive to the speed of rotation of said power turbine for generating a third control voltage;

third means controlling said second switch means, said third means being responsive to said third control voltage above a predetermned level, said level representing an overspeed condition of said power turbine for changing the energization state of said stator vane actuator for adjusting said stat-or vanes to reduce the speed of rotation of said power turbine;

means responsive to a predetermined measured gas temperature for generating a fourth control voltage; and fourth means controlling said third switch means,

said fourth means being responsive to said fourth control voltage above a predetermined level for changing the energization state of said fuel bleed solenoid whereby fuel is bled from said combustion chamber of said engine to reduce the temperature of said gas, said level representing an overtemperature condition.

2. The invention as defined in claim 1 wherein said third means controlling said second switch means and said fourth means controlling said third switch means each comprises:

a signal responsive electric conduction device having a first and second conduction state, the presence or absence of a third or fourth control voltage determining the state of a respective device, said second and third switch means being responsive to the state of a respective device.

3. The invention as defined in claim 2 wherein each of said second and third switch means comprises a first silicon controlled rectifier having an anode, a grounded cathode and a control electrode, said anode and cathode being connected in the energization path of a respective actuator, said actuators being energized when a respective rectifier is conductive, and wherein said third and fourth control means each comprises:

a transistor having a base, a grounded emitter and a collector connected to a regulated voltage supply through a resistor;

a timing capacitor connected between said collector and ground;

a unijunction transistor having a first electrode connected to said supply, a second electrode connected to ground through an output resistor, and a control electrode connected to said collector;

a second silicon controlled rectifier having a grounded cathode, an anode connected to said supply and a control electrode;

a commutating capacitor connected between the anodes of said first and second silicon controlled rectifiers;

a respective one of said third and fourth control voltages being applied simultaneously to the base of said transistor and to the control electrode of said first silicon controlled rectifier to render said first rectifier conductive, said control voltages comprising a train of pulses whereby said timing capacitor is maintained in a state of conduction When said control voltages are applied to said base to prohibit the development of a charge on said capacitor, and whereby in the absence of a control voltage a charge develops on said timing capacitor after a period determined by the time constants in circuit with said timing capacitor, a predetermined charge on said timing capacitor causing said unijunction transistor to conduct and rendering said second rectifier conductive effectively connecting said commutating capacitor across the anode and cathode of said first rectifier to stop conduction of said first rectifier.

4. The invention as defined in claim 1 wherein said engine operating parameter is compressor turbine speed, and wherein said gas temperature is measured at the inlet to said power turbine.

5. The invention as defined in claim 1 wherein said first switch means is a relay having energizable windings and first and second initially open contacts, said first contacts serving when closed to complete the connections from said source to said starter solenoid, said second contacts serving when closed to complete the connections from said source to said ignition unit;

a regulated voltage supply;

and a silicon controlled rectifier connected in series wih said windings, said regulated voltage supply being connected across said rectifier and said windings, said silicon controlled rectifier being rendered conductive by said first means, said silicon controlled rectifier being rendered non-conductive in response to said first control voltage above a predetermined level or in response to said second control voltage, whichever occurs first.

6. The invention as defined in claim 1 wherein said first switch is a relay having energizable windings and first and second initially open contacts;

a regulated voltage supply;

first and second silicon controlled rectifiers, each of said rectifiers having a grounded cathode, an anode, and a control electrode, the anode of said first rectifier being connected to said regulated voltage supply through said windings, the anode of said second rectifier being connected to said regulated voltage pp y;

a commutating capacitor connected between said anodes, said first means comprising a manually operated switch for connecting said source through a capacitor to the control electrode of said first rectifier for rendering said first rectifier conductive and effectively connecting said commutating capacitor across the anode and cathode of said second rectifier whereby said second rectifier is cut off;

said second means controlling said switch means comprising the connection of said first control voltage to the control electrode of said second rectifier to render said second rectifier conductive;

said timer means being initiated in response to the non-conduction of said second rectifier, said second control voltage being applied to the control electrode of said second rectifier to render said rectifier conductive at the end of said predetermined lapse of time;

the conduction of said second rectifier effectively connecting said commutating capacitor across the anode and cathode of said first rectifier whereby said first rectifier is cut off.

References Cited UNITED STATES PATENTS 2,866,385 12/1958 Miller 6039.14 XR 3,310,937 3/1967 Smith 6039.14 3,365,881 1/1968 McKenzie 60-39.14

CARLTON R. CROYLE, Primary Examiner ALLAN D. HERRMANN, Assistant Examiner US. Cl. X.R.