GB2079987A

GB2079987A - Turbine control and protection system

Info

Publication number: GB2079987A
Application number: GB8120009A
Authority: GB
Original assignee: Simmering Graz Pauker AG; MAN Maschinenfabrik Augsburg Nuernberg AG; Voith Getriebe KG
Current assignee: Simmering Graz Pauker AG; Voith Getriebe KG; MAN AG
Priority date: 1980-07-07
Filing date: 1981-06-29
Publication date: 1982-01-27
Also published as: IT8122786A0; IT1167548B; IT8122786A1; DE3126069C2; CH657184A5; AT370851B; ATA353880A; FR2486144A1; FR2486144B1; DE3126069A1; GB2079987B

Abstract

A turbine control and protection system includes one or more control valves (52) and an emergency shutdown (start-up) valve (51) in a line carrying a working fluid to the turbine. Two substantially identical but separate speed controllers (63, 62) are coupled respectively to each control valve and the emergency shutdown valve, the speed controllers each having a pair of independent inductive pick-ups monitoring the speed of the turbine. In addition to providing emergency shutdown when the turbine speed exceeds a set value the controllers may be energised to stop turbine operation in response to external signals. Checking means are provided enabling tests of operation of the system to be carried out without effecting the operation of the turbine. In the event of failure of one controller, the second can take over its function. <IMAGE>

Description

SPECIFICATION Turbine control and protection system The invention relates to a turbine control and protection system with one or more control valves and an emergency shut down valve in a line carrying a working medium to the turbine, with speed sensors and a control and protection arrangement connected to these and actuating the valves.

It has been customary to effect control of turbines, including emergency control, using mechano-hydraulic systems. For normal operation, these have a speed controller which effects actuation of control valves by a mechanohydraulic system. To protect against overspeeds, an overspeed emergency trip is usually provided, essentially comprising a pin let into the turbine shaft which, mainly through the action of centrifugal forces, when a certain speed is exceeded, actuates a pawl which in turn acts through a reversible drive to cause release of hydraulic oil to operate emergency shutdown valves. A solenoid valve is also provided in the hydraulic oil supply to permit emergency shutdown by electrical means from another source, e.g. by systems having priority, such as generator protection, electrical emergency shutdown buttons and the like.

However, this kind of arrangement has a series of shortcomings. Firstly, the mechanical parts are very sensitive and the risk af impairment through dirt, resinification of the oil, long-term aging or material fatigue is high.

Again checking the equipment is difficult. This is done either by artificially induced overspeeds while interrupting routine turbine operation or without interruption -- by simulating an overspeed and simultaneously suppressing the overspeed trip. Simulation involves either registering the real value or actuating the overspeed trip mechanically by pumping in oil under the emergency shutdown pin.

The operational control system and the protection system are different in both design and mode of operation so that neither system can take over the function of the other if one of the two systems should fail. Finally the cost of the system is high, as if a reserve is desired, the entire arrangement has to be duplicated, at correspondingly increased expense.

It is also known for an overspeed -- emergency shutdown trip to be produced using electronichydraulic systems. In this case, the turbine speed is measured inductively and monitored by electronic evaluation circuitry and as a rule emergency shutdown is tripped using a solenoid valve. To test the system during normal running, it is necessary to switch over to a parallel monitoring system to protect the turbine, and a corresponding test circuitry is simultaneously activated. This test circuit has the disadvantage that the tripping circuit is broken and correct tripping while running is only guaranteed when the test circuit is switched back to the normal state, which cannot always be checked ultimately.

Electronic-hydraulic control systems are also known; such systems are separate from the protection systems, however, and act solely on the control valves.

An object of the invention is to provide a turbine control and protection system overcoming or alleviating the difficulties of the known systems.

According to the invention there is provided a turbine control and protection system, including one or more control valves and an emergency shutdown valve in a line feeding a working medium to the turbine, speed sensors and a control and protection arrangement connected to the valves for actuating the valves, wherein there are provided for the control system and for the protection system two substantially identical but independent speed controllers, one of which speed controllers is effectively coupled with the or each control valve and the other of which speed controllers is effectively coupled with the emergency shutdown valve, each of said speed controllers having two independent pick-ups monitoring the speed of the turbine.

An advantage of this design, providing identical systems for the control function and the protection function is that one controller can temporarily take over the function of the other, e.g. if one controller fails. Thus, even when the most stringent safety requirements apply, there is no longer any need to duplicate all the equipment.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is an illustrative diagram of a single turbine control circuit, Fig. 2 is an illustrative diagram of an emergency shutdown valve which may be tested during operation, and Fig. 3 is a block circuit diagram of a system embodying the invention and equipped with a speed controller and an emergency shutdown and start-up controller.

Fig. 1 shows the turbine 1 coupled to a working medium line (e.g. steam line) 2 which incorporates a number of control valve(s) 3 actuated by means of a setting drive 6 connected to a control oil line 4 and an actuating oil line 5.

A disk 8 with grooves or teeth on its circumference is mounted on the turbine shaft 7.

Disk 8 works with two induction pick-ups 9 and 9' each of which generate an electrical impulse fed via lines 10 and 10' respectively to a controller 11 whenever a tooth of the disk passes them. The controller 11 may be fed externally with a reference input, e.g. a direct current in the range of O to approximately 20 mA via line 12, from a higher controller (a cascade control system or the like).

An external signal to trip the emergency shutdown may be fed to controller 11 via line 13, that is to say emergency shutdown can be tripped externally for example manually or by the generator protection system.

The 'set value' adjustment of controller 11 is illustrated at 14; and keys 1 6 and 1 7 coupled to controller 11 via lines 1 8 and 1 9 as shown are used for remote adjustment of the speed setting.

The three lines 20, 21 and 22 lead from the controller to display units 23, 24 and 25 which give the actual speed of the turbine, the 'set value' and the magnitude of the controller output signal.

The outputs 26 to 29 are coupled to interlock and signalling equipment and transmit signals for standstill n = 0, minimum speed nmin, maximum speed n max or indicate an emergency shutdown nss.

Line 30 carries the controller output signal and connects a pressure regulating unit 31 to the controller 1 the control-oil line 4 runs from the pressure regulating unit 31 which acts as an electronic-hydraulic transducer.

The turbine's speed is measured by the two magnet-induction pick-ups 9 and 9' and the controller 11 always selects the greater of the two pick-up signals. This ensures that, even if one measuring channel (10 or 10') fails, for example, through a break in the cable, the turbine may still be aperated without problem. For this purpose pick-ups having a generative action are chosen which, by virtue of the system, may only emit signals in the direction of lower frequency when a fault or failure occurs.

The controller output signal is fed to the pressure regulating unit 31 as an impressed current in the range of, say, 0 to 20 mA, and unit 31 converts the electrical signal into an impulse oil pressure which is passed directly to the control mechanism -- here the setting drive 6 - of the control valve(s) 3.

The pressure regulating unit 31 employed may preferably take the form of the immersed armature solenoid described in Austrian Patent Specification 306 171 acting as an electro hydraulic transducer.

The oil pressure set by the pressure regulating unit 31 is fed directly to the setting units (setting drive 6) as a setting variable.

An emergency shutdown arrangement is built into the control system. This trips the turbine emergency shutdown through the pressure regulating unit 31 by switching off the auxiliary power as soon as one of the two real-value measuring channels (lines 10 and 10') indicates an overspeed, if both real values show any undue temporary change or if one real-value channel fails and the second shows an undue temporary change. External emergency shutdown, via line 13, may also be effected.

The required setting forces may be obtained without servo-systems by using a powercontrolled electromagnet in the pressure regulating unit 31. As a result, the response time is considerably reduced and the normally narrow cross-sections of the servo-systems and the attendant risk of clogging eliminated.

The control system includes an emergency shutdown system that may be tested while in operation. The block circuit diagram of such a system is shown in Fig. 2.

In Fig. 2 test lines 32 and 32' are shown to be directly connected to respective ones of lines 10 and 10'. Each test lines include a pulse generator (33 and 33' respectively) which can supply a sequence of impulses.

The pulse repetition rate of the signals generated by the generators 33 and'33' depends upon the magnitude of the D.C. voltage fed thereto, via lines 34 and 34' as shown, from a D.C.

voltage selector 35 having a selector switch 36, the maximum p.r.r. being generated when the maximum D.C. voltage is applied. The maximum D.C. voltage corresponds to a maximum speed that can be handled, greater than the turbine emergency shutdown speed.

Only one of the lines 34 and 34' can be fed with a D.C. voltage by the selector switch 36 at a time. In addition, the voltage selector or integrato? 35 can only supply a D.C. voltage when, or as long as, it is enabled so to do by a blocking element 37 (a kind of AND-gate with one negating input) the two inputs of which are connected to a tripping line 38 and a test switch 39.

The signal supplied by the pulse generator 33 or 33' when activated by the D.C. voltage is superimposed on the signal produced by the pickup 9 or 9'. The transducers are not switched over to "pick-up" or "generator".

The lines 10 and 10' run respectively to transducers 40 and 40' which supply a D.C.

voltage (dependent upon the frequency of the pulse sequence fed thereto) to limit stages 41 and 41' as shown. The outputs of the limit stages 41 and 41' trigger emergency shutdown via comparator OR-elements 42 and 43 by deenergising a relay 48. Emergency shutdown may also be triggered by an external emergency shutdown signal on line 13 or by a system monitor 45. The operation of the system monitor may be tested by means of a test key 47 and a blocking AND-element 46.

Testing is effected such that with the response of the tripping signal (the output of the limit stages 41 and 41' or output of the system monitor 45) the mergency shutdown relay 48 is de-energised.

As a result, auxiliary power to the pressure regulating unit 31 is switched off and blocking line 38 is connected to a 24 V source. By this the blocking AND-elements 46 and 37 block, the test is ended and the emergency shutdown relay 48 returns to its original position.

The output of the comparator OR-element 43 is connected to the emergency shutdown relay 48 and to an indicating relay 49 used solely for external indicating purposes such as display or revertive communication.

The pressure regulating unit 31 is fed with auxiliary power e.g. +24 volt D.C. voltage, via the emergency shutdown relay 48.

When the emergency shutdown relay 48 switches over to the position shown in Fig. 2, the direct voltage is absent and the valves 3 are shut immediately -- emergency shutdown.

As shown in Fig. 2, each of the two speed measuring channels 10 and 10' contains an emergency shutdown speed monitor which switches the auxiliary power away from the pressure regulating unit 31 by means of a relay when the set limit is attained. As a result the magnet can no longer attract and the impulse oil pressure is reduced. The steam control valves close and the turbine is shut down. The parallel relay 49 is available for use in an external control system.

The emergency shutdown system is the most important protection system of a turbine installation. Therefore, the components should be checked at regular intervals. This control system permits active checking of all the components involved in any phase of operation without effecting the turbine speed. For this, each of the two speed measuring pick-ups may be subjected to a constantly rising "test speed". During such a check, the other measuring channel effects control on its own. When the emergency shutdown speed is reached, the protection system responds. The emergency shutdown relay 48 is switched over, i.e. de-energised, and cuts the auxiliary power supply to the pressure regulating unit 31. The closing contact of the emergency shutdown relay 48 indicates "emergency shutdown tripped".With this, the test speed is re-set to zero, the emergency shutdown relay pulls up again and the pressure regulating unit 31 can carry on working again.

The emergency shutdown relay 48 is only deenergised for a maximum of 20 milliseconds. This is roughly equivalent to one control cycle of the magnetic force control circuit in the pressure regulating unit 31. This ensures that the position of the steam control valves is not changed.

The operation of the control valves can easily be checked by a slight change in the speed setting. Maximum protection and reliability are achieved by also fitting the emergency shutdown valve with a speed controller.

All the functional units (controller, pressure regulating unit, setting drives) are designed so that the installation is shut down (i.e. fails safe) when the auxiliary power (electrical, hydraulic) fails.

The block circuit diagram of such an installation in accordance with the invention is depicted in Fig. 3.

As in Fig. 1 , the turbine 1, its shaft 7 and the pick-up disk 8 are shown. Numeral 50 denotes a working machine (in particular a generator or compressor) driven by turbine 1. An emergency shutdown valve 51 and one or more control valves 52 are located one behind the other in sequence as shown in the working medium line 2 leading to turbine 1. Valves 51 and 52 are actuated by setting mechanisms 53 and 54 which are connected by means of lines 55, a coupling valve 56, a line 57 and a manually operated emergency cut-off valve 58 together or in parallel with one another to an actuating oil source. Control oil lines 60 and 61 run to the working cylinders 53 and 54 as shown from respective pressure regulating units 31 and 31'.

In the event of an emergency shutdown, coupling valve 56 directs the actuating oil to the valve control mechanisms 53 and 54.

Two completely identical controllers are provided with the system shown in Fig. 3, namely the emergency shutdown controller 62 and the speed controller 63. Each of these two controllers is connected to two pick-ups 9 and 9' by means of two lines 10 and 10'. Both controllers 62 and 63 are linked to the emergency cut-off switch 65, an interlock 66 and the external control system 67 by means of an intermediate circuit (linking circuit) 64. An external display 68 and facilities for external communications, shown at 69, are also connected to the intermediate circuit 64. Each pressure regulating unit 31 and 31' can be provided with a manual actuator 31" to set it in an end or open position.

From each controller 62 (63) a line 30 (31') carrying its output signal goes to the pressure regulating unit 31(31') associated with the particular controller. Between the controllers 31 and 31' there is a signal link 59 which also switches off the second system when only one protection system responds.

Furthermore, the 'set value' selector at both controllers is zeroed in such an event.

The lines 70,71, and 71' are provided to supply electrical auxiliary power (or hydraulic auxiliary power as appropriate) from a source (current or hydraulic) not shown to the linking circuit 64 and from this to the pressure regulating units 31 and 31'.

The emergency shutdown valve 51 is actuated in the same way as the control valve(s) 52.

It will be seen that the described embodiments provide a control and protection system which is composed of identical but independent assemblies and offers the possibility of complete checking of every function, both when the turbine is stopped and when the turbine is running without disturbing the turbine in any way. An advantage of the identical composition is to ensure that if one circuit (or an assembly) fails, the protection function may be taken over by the other circuit and, in certain circumstances, emergency operation may also be maintained, while minimising the cost of components. This means a high level of availability (very low probability of failure); naturally, high quality of control and maximum machine protection and the organisation of redundant systems and optimum adaptability to other (priority) control systems are enabled.

A system embodying the invention has the following advantages.

Such a system enables: speed-controlled remote start-up by means of the start-up and emergency shutdown controller; emergency control function by the emergency shutdown controller if the speed controller fails; by linking the emergency shutdown signals of both controllers quadruple redundancy is obtained on the signal side and double redundancy on the setting element side. As a result the mechanical emergency shutdown trip needed until now can be eliminated; higher emergency shutdown tripping systems, e.g. generator protection, emergency cut-off and the like, are fully integrated into the system.

Consequently, it will be seen that we now provide an electronic turbine speed control and emergency shutdown tripping system consisting of real-value pick-ups, set-value/real-value comparators, setting elements for turbine control valves with multiple speed limit monitoring.

Particularly advantageous features of this arrangement are that a second, completely identical turbine speed control and emergency shutdown tripping system acts on the turbine start-up valve (emergency shutdown valve) through an identical associated setting element, that this second turbine speed control and emergency shutdown tripping system, just like the first, can be fully functionally checked while operational without interruption or interference with the turbine operation, the setting elements cut the turbine energy flow in the absence of the auxiliary power and/or that the actual control functions can also be taken over by the start-up control system. Higher protection systems can act on the system and trigger emergency shutdown.

Claims

1. A turbine control and protection system, including one or more control valves and an emergency shutdown valve in a line feeding a working medium to the turbine, speed sensors and a control and protection arrangement connected to the valves for actuating the valves, wherein there are provided for the control system and for the protection system two substantially identical but independent speed controllers, one of which speed controllers is effectively coupled with the or each control valve and the other of which speed controllers is effectively coupled with the emergency shutdown valve, each of said speed controllers having two independent pick-ups monitoring the speed of the turbine.

2. A system according to claim 1, wherein pressure regulating units are provided with a manual adjustment mechanism by which one control valve may be driven into an end or open position at any time.

3. A system according to claim 1 or claim 2, wherein a coupling valve is provided to cut off auxiliary power for the emergency shutdown valve and the or each control valve at the time of an emergency shutdown,

4. A system according to any one of the preceding claims, wherein a pressure regulating unit serves both as a control element and as a tripping element for emergency shutdown, the tripping of the emergency shutdown being effected by cutting off the auxiliary power.

5. A system according to any one of the preceding claims, wherein to test the emergency shutdown, a test signal is superimposed on the pick-up, the real-value signal alone is suppressed by the superimposed test signal and the rest of the protection system remains operational, auxiliary power supply to a pressure regulating unit is cut, and the test is completed after this interruption and the auxiliary power supply reactivated.

6. A system according to any one of the preceding claims, wherein the system is linked to a higher control system, the higher control circuits can be superimposed on both of the emergency shutdown valve controller and the controller of the or each control valve.

7. A system accprding to claim 6, wherein an operation controller is provided to control operation of the speed controller.

8. A system according to claim 6 or claim 7, wherein a further controller is provided to control operation of the start-up controller.

9. A turbine control and protection system substantially as herein described with reference to the accompanying drawings.