Rotary kinetic fluid motors or pumps – Selectively adjustable vane or working fluid control means – Upstream of runner
Reexamination Certificate
2000-11-16
2002-11-26
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
Selectively adjustable vane or working fluid control means
Upstream of runner
C251S058000
Reexamination Certificate
active
06485258
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electromechanical actuating drive for a valve, in particular of a turbine, with a push rod for setting an opening position of the valve and with an electric motor for driving the push rod. The invention relates, furthermore, to a steam turbine with a valve and with an associated actuating drive.
A turbine, in particular a steam turbine, usually has a considerable number of valves which may be used, for example, as fresh-steam, intercepting or bypass valves and also as scram valves. In such cases, the opening position of each of these valves serves for setting a respective material or steam stream and is capable of being set, for example, via a push rod assigned to the respective valve. Such a push rod is an integral part of an actuating drive assigned to the valve. In this context, the actuating drive may have to satisfy stringent requirements, particularly as regards actuating force and actuating speed. For the valve to have a high degree of reliability, it may be necessary, for example, that the actuating drive have an actuating force of about 200 kN and an actuating time of about 100 ms.
EP 0 040 732 A1 specifies an actuating drive for steam turbine valves which has a decentral hydraulic system. The hydraulic system of such an actuating drive is integrated to form a compact drive block arranged on the valve housing, so that only a cable system is still necessary for supplying energy to the actuating drive. If oil is used as hydraulic fluid, this may lead, under extremely unfavorable circumstances, to an ignition of the oil and therefore to a fire in the steam turbine.
DE 44 46 605 A1 specifies a valve for a steam turbine which has a valve spindle with a valve cone arranged thereon. The valve spindle is driven via an electric motor which is connected to the valve spindle via an electromagnetically actuated coupling. For automatic selfclosing of the valve, the latter comprises a cup spring system. The electromagnetic coupling is connected to a threaded bush which cooperates with the valve spindle guided fixedly in terms of rotation and which thus moves the latter axially. The threaded bush is designed as a spherical threaded bush, so that it acts upon the valve spindle with low play and low friction. Since the valve spindle is guided fixedly in terms of rotation, that is to say the latter can be moved up and down only axially when the threaded bush rotates, there is no need for a drive having a translational effect. Instead, an electric motor rotating in two different directions is sufficient for this purpose. However, the electric motor must have a torque safety device, in order thereby to prevent the situation where, for example during the closing of the valve, the valve cone adjoining the valve spindle at one end does not, when coming to bear against the sealing seat assigned to it, suffers damage or damages said sealing seat.
DE 36 18 479 A1 discloses a fitting for shutting off a flow, with a housing, in which a closing piece is movable between the open and shut end positions with the aid of a thread, with a rotary drive (drive motor) which is switched off with a time delay. A gear with two concentrically arranged ballscrew spindles is arranged between the rotary drive and the closing piece. A purely mechanical setting of a torque is achieved by means of this double-spindle system, the setting being carried out at a correspondingly high rotational speed without much effort.
SUMMARY OF THE INVENTION
An object on which the invention is based is, therefore, to specify an actuating drive for a valve, in particular of a turbine, in which, along with a particularly low risk of fire, fault-free operation of the valve is ensured. A further object of the invention is to specify a steam turbine with a low risk of operation being disrupted by a fire.
This and other objects are achieved by means of an electromechanical actuating drive with a push rod for setting an opening position of the valve, and with an electric motor for driving the push rod, the push rod and the electric motor being connected to one another via a transmission device, by means of which a changing torque can be generated, depending on the axial displacement of the push rod.
An electromechanical actuating drive with a transmission device, by means of which a changing torque can be generated, depending on the stroke of the push rod, is particularly advantageous in those valves in which the force to be exerted on the push rod during the closing or the opening of the valve changes as a function of the stroke of the push rod. This may occur in valves, for example in a steam turbine, in which a prevailing steam pressure is present on the valve cone and supports the latter during the closing operation or keeps the valve cone closed. In such a valve, initially a high force (steam pressure×effective valve cone surface) has to be overcome in order to open the valves to some extent. As soon as a particular opening cross section is afforded, pressure relief takes place, so that, during the further opening operation, in each case a lower force is necessary in order to displace the push rod. The transmission device may be designed appropriately, depending on the size, load and requirement of the valve, in particular the opening and closing operation (closing speed, etc.). Moreover, using an electric motor markedly reduces a risk of fire, as compared with actuating drives with oil hydraulics.
The electric motor is preferably designed as a variable-speed synchronous motor. A synchronous motor of this type makes it possible, particularly in conjunction with a power amplifier, to have highly accurate position regulation with a control accuracy of about 0.1 mm, along with a motor power up to about 30 kW. The power amplifier acts, in this case, as a frequency converter and allows a general or position-dependent reduction in the motor current and in the motor rotational speed. At the same time, all the drive powers and drive actuating speeds which are required in practice can be afforded by an appropriate adaption of the operating parameters.
In order to convert the rotational movement of the electric motor into a linear movement provided for driving the push rod, the transmission device is designed preferably as a crank mechanism, a planetary gear or the like.
Feed-dependent torque/force transmission is possible by means of a crank mechanism. Moreover, in the case of a quick closing of the valve, such as occurs, for example, during a quick-action closure of a valve in a turbine, necessary limit damping may already be achieved by means of the crank mechanism. Additional devices for speed reduction during the last stroke of the valve cone (sealing piece) into the valve seat may therefore be dispensed with, as required. In this case, a crank mechanism has a crank element, in particular a crank disk, which rotates about an axis of rotation and on which the push rod acts at a connection point, the connection point being at a distance from the axis of rotation of the crank element (crank disk). During a rotational movement of the crank disk, the push rod connected to it executes a linear movement along the main axis of the push rod between two maximum end positions. A very high torque can be generated in these end positions via the crank disk, since, during a rotation of the crank disk, only a very short linear distance is covered in the direction of the push axis in the respective end position.
The actuating drive is preferably designed in such a way that, when a closing position of the valve is reached, an angle in the range of between 5° and 20°, preferably about 10°, is formed between the main axis of the push rod and a connecting line between the connection point, at which the push rod acts on the crank disk, and the axis of rotation. Thus, when the valve is in the closing position, the connection point is located in the vicinity of a maximum end position, so that, during a rotation of the crank disk, a high torque and therefore a high force can be transmitted to the push
Ryznic John E.
Siemens Aktiengesellschaft
Staas & Halsey , LLP
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