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Speed measurement system for turbine power plant

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system speed Turbi Measurement

Description

CROSS REFERENCE TO RELATED APPLICATION

Ser. No. 468,972, which is a continuation of Ser. No. 247,877, now abandoned, which is a continuation-in-part of Ser. No. 246,900, now abandoned, said original application being filed on Apr. 24, 1972, and all entitled "General System and Method For Starting, Stopping, Synchronizing, and Operating a Steam Turbine with Digital Computer Control" and assigned to the present assignee is incorporated by reference herein for the purpose of disclosing the details of the turbine system generally referred to herein.

BACKGROUND OF THE INVENTION

The present invention relates broadly to an improved system for controlling the operation of a turbine power plant; and more particularly to an improved speed measurement system, for controlling the rotational speed of the turbine which provides rapid updating and high resoluting capability for direct digital input of turbine speed to a digital processor of the system.

In systems for controlling the operation of a turbine power plant, the rotational speed of the turbine shaft is considered in a control loop either as an end controlled or intermediate controlled system variable. Various systems for determining turbine speed have been developed over the years in order to provide an accurate speed signal for positioning the speed inlet valves to control the outlet of the turbine.

For example, an analog control system is described in U.S. Pat. No. 3,098,176, ELECTRIC LONG RANGE SPEED GOVERNOR, by M. A. Eggenberger, P. H. Troutman and J. F. Sauter, whereby a tachometer generator, which is connected to the turbine shaft generates a DC signal having a magnitude proportional to the actual speed of the turbine. In U.S. Pat. No. 3,097,488, TURBINE CONTROL SYSTEM, by M. A. Eggenberger, P. H. Troutman and E. C. Callan, there is described a system with a permanent magnet generator that is attached to the turbine shaft which generates an AC signal having a frequency proportional to actual turbine speeds. This AC signal is converted to a DC signal by saturable magnetic cores to provide a feedback voltage signal proportional to the frequency of the AC signal; and therefore, the speed of the turbine. The more recently developed turbine control systems, utilize a toothed wheel connected to the turbine shaft; and pulses generated by a reluctance pick-up adjacent to the toothed wheel are translated into a DC voltage which is utilized in an analog control circuit. A typical circuit for accomplishing the desired translation from a pulse frequency to a DC voltage is shown in U.S. Pat. No. 3,090,929, CONTROLLER CIRCUITRY WITH PULSE WIDTH MODULATOR by F. P. Thompson, assigned to the same assignee as this application. The frequency to voltage conversion technique described in the Thompson patent has operated satisfactorily in an electrohydraulic control system such as is described in an article by M. Burnbaum and E. G. Noyes presented to ASME-IEEE NATIONAL POWER CONFERENCE in Albany, N.Y., Sept. 19-23, 1965. In applying the frequency to voltage conversion technique to this type of system, the speed voltage may be applied directly to a control network of the general type described in U.S. Pat. No. 3,452,258, DIGITAL ANALOG FEEDBACK CONTROL SYSTEM EMPLOYING SOLID STATE DIGITAL POTENTIOMETER, by F. P Thompson, also assigned to the same assignee as this application.

With the advent of the turbine control systems of the digital-electrohydraulic type rendered the frequency to voltage conversion technique impractical. A system of this type is described in great detail in copending U.S. patent application Ser. No. 408,972, which is a continuation of Ser. No. 247,877, now abandoned, which is a continuation-in-part of Ser. No. 247,440, now abandoned, and entitled GENERAL SYSTEM AND METHOD FOR STARTING, SYNCHRONIZING AND OPERATING A STEAM TURBINE WITH DIGITAL COMPUTER CONTROL, all filed by Theodore C. Giras and Robert Uram and assigned to the present assignee; said original application being filed on Apr. 24, 1972. This is a consequence of the fact that digital equipment, without an analog or digital converter, operates only in response to digital input signals. For example, the central processing unit of a digital computer continuously performs digital routines under the control of programmed instructions. However, since a computer can perform only one operation at a time, externally generated data can only be accepted by the computer by interrupting the routine in process or by waiting until the routine which is running has been completed. Determinations of this nature are made by the executive program which establishes priorities for the various routines including the input routines.

In real time control, various systems status signals are generated independently in the computer cycle time. System conditions which can be expressed in terms of yes or no, or on or off, can be monitored by switches or relays which by their very nature generates signals in binary form. The states of the variable being monitored is stored by the condition of the switch or relay until the central processing unit of the computer is ready to accept the stored data. Such inputs are known as contact inputs. Numerous schemes for multiplexing and paralleling contact inputs have been developed to improve the efficiency of the computer system. Where analog functions are input to the computer, they must be transformed into digital signals before they can be accepted. Many types of analog to digital converters have been developed to form this transformation. Such transformation may typically be performed by converting the DC voltage into pulses having a frequency which is a function of the analog voltage level in a voltage to frequency converter. The pulses so generated are indicated in a digital counter and the resultant signal is fed into the central processing unit of the computer. Such conversion takes time, and as frequent sampling of the variable being monitored is central to proper dynamic control of the system, the converter may be engaged for a considerable period of its operating time merely monitoring a single analog signal. Economic considerations dictate the number of analog to digital converters that can be provided in a system.

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