CN1045661C - Turbine-medium flow monitor - Google Patents

Abstract

A method and device for detecting the fluid flow of a driving steam turbine, the fluid flows through a blade channel between a fluid inlet and a fluid outlet, by detecting the pressure value of the fluid at the fluid inlet and the fluid outlet; according to the detected pressure value , Calculate the fluid flow electronically; compare the calculated fluid flow with the maximum expected flow electronically; when the calculated flow exceeds the maximum expected flow, an indication is automatically issued.

Description

Steam turbine medium flow detection device and method

The present invention relates to the detection of media flow along the passage of a steam turbine blade.

Steam turbine blades are constructed to experience the flow of a propelling medium, which may be steam or gas, having a flow rate up to the maximum design value. If the flow rate of the propelling medium exceeds this maximum value, it may cause damage to the blades. Various abnormal operating conditions can cause the flow rate to exceed its maximum design value. Such abnormal operating conditions include steam turbines with feed water heaters not working. The potential for damage is particularly high in the case of low pressure turbine discharge end blades due to exceeding the maximum design flow.

In order to avoid generating flows that can cause blade damage, it is current practice to provide operators with specific operating instructions and/or precautionary instructions. However, there is currently no instrumentation provided to alert the operator that an excess of design flow is occurring.

A primary object of the present invention is to provide a reliable warning that the flow rate of the turbine drive medium flowing along the passage of the turbine blades is approaching or exceeding the maximum design value.

In view of this purpose, the present invention relates to a method of detecting the flow of a liquid driving a steam turbine, the fluid flowing through the blade passage of the turbine between the inlet of the fluid and the outlet of the fluid and the blade passage associated with a maximum desired flow rate, characterized by detecting The fluid pressure value at the inlet and fluid outlet, the fluid flow rate is calculated by electronic instruments based on the detected pressure value using the relationship $W\≈\sqrt{P^2\mathrm{ain}-P{a}^2\mathrm{out}}$ calculated.

where W is the fluid flow

Pain is the actual absolute pressure at the inlet of the vane channel

Paout is the actual absolute pressure at the outlet of the vane channel

Comparing the calculated flow rate with the maximum ideal flow rate, when the calculated flow rate exceeds the maximum ideal flow rate, an indication is automatically issued.

As a general rule, the maximum desired flow is the maximum design flow, which is the maximum flow that can be maintained without risking blade damage. According to engineering practice, a given maximum design flow rate may contain a selected safety factor. In the following description, the invention will refer to a system for detection based on the maximum design flow of the turbine section. However, it will be appreciated that the present invention may be applied to a test arrangement in which the reference pressure value is related to a maximum desired flow rate selected based on factors other than the maximum design flow rate.

1 and 2 are circuit diagrams illustrating two embodiments of a detection circuit according to the invention.

The detection method and device according to the present invention are realized based on the identification that the flow exceeds or is approaching the maximum design flow. This identification can be observed by measuring the absolute pressure of the propelling medium at the inlet and outlet of the turbine blade channel. Therefore, according to the equation derived from the stodola equation: $\frac{\mathrm{Wa}}{\mathrm{Wd}}=\sqrt{\frac{P^2\mathrm{ain}-P^2\mathrm{aout}}{P^2\mathrm{din}-P^2\mathrm{do\; out}}}$

Where: Wa is the actual flow

Pain is the actual absolute pressure at the inlet

Paout is the actual absolute pressure at the outlet

Pdin and Pdout are the design inlet and outlet absolute pressures relative to the maximum design flow.

The standard stodola equation establishes a single flow value as a function of inlet and outlet pressures and includes a term for the product of inlet pressure and steam specific volume. If the properties of the steam do not vary much over time, the above relation holds, ie this additional term can be ignored. This relationship is also generally valid for detecting different flow rates in the same steam turbine. However, under widely varying steam conditions, where the same blade is used for different turbines, this relationship is unreliable, and in this case it is necessary to introduce a reciprocal if the PV term becomes the numerator and denominator of the above relationship .

If Wa/Wd > 1, the design flow is being exceeded, which corresponds to $\sqrt{\frac{P^2\mathrm{ain}-P^2\mathrm{aout}}{P^2\mathrm{din}-P^2\mathrm{do\; out}}}>1$ Since Pdin and Pdout are known, then $\frac{1}{\sqrt{P^2\mathrm{din}-P^2\mathrm{do\; out}}}$ can be set to C, so when $C\sqrt{P^2\mathrm{ain}-P^2\mathrm{aout}}>1.0\…\…\left(1\right)$ Then the relationship can be expressed as $C\sqrt{(\mathrm{Pain}-\mathrm{Paout})(\mathrm{Pain}+\mathrm{Paout})}>1.0-----\left(2\right)$ Thus by measuring the absolute pressure values at the inlet and outlet of the turbine blade passage and processing the measurements in a simple circuit, flow rates greater than selected design values can be detected. The circuit may be an analog circuit that provides a warning if the calculated result is greater than a threshold equal to one. However, when the relation on the left side of each of inequalities (1) and (2) is itself greater than 1, then the square of the relation will also be greater than 1, so the circuitry used to generate the warning does not include components for square root calculations.

A first embodiment of a circuit for generating such a warning is depicted in FIG. 1 , which circuit is connected to the signal outputs of the two pressure sensors 2 and 4 . Sensors 2 and 4 may be of any conventional type configured to produce an output pressure representative of the absolute pressure of the fluid associated with the sensors. The sensor 2 is arranged at the inlet of the passage of the steam turbine blade, and the sensor 4 is arranged at the outlet of the passage.

The output signal Vpin from the sensor 2 is sent to the signal input terminal of the first diode operational amplifier squaring circuit 6 , while the output signal Vpout of the sensor 4 is connected to the input terminal of the second diode operational amplifier squaring circuit 8 . Circuits 6 and 8 are basically the same except that the output signal of sensor 2 is sent to the inverting input terminal of operational amplifier circuit 6, and the output of sensor 4 is sent to the positive input terminal of operational amplifier 8, so that the signals from the two circuits 6 and 8 output signals will have respective opposite polarities.

However the output signals from circuits 6 and 8 are fed to an analog summing circuit 10 which, like circuits 6 and 8, is based on conventional operational amplifiers.

The output signal from summing circuit 10 is proportional to the difference between the square of the voltage produced by sensor 2 and the square of the voltage supplied by sensor 4 . An output signal from circuit 10 is supplied to one input of comparator 12 . A signal proportional to 1/C ² is supplied to the other input of comparator 12 . The output of the comparator 12 is connected to the input of a warning device 14 to generate a warning when the above inequality (1) holds.

If one wishes to base the generation of the warning signal on the square root of the squared difference between the input and output pressures, a square root function generator can be inserted between the summing circuit 10 and the relevant input of the comparator 12, and the comparison input of the comparator 12 can receive A signal proportional to 1/C, or a square root function generator can be inserted between the output of the comparator 12 and the input of the warning device 14 . This square root function generator can be formed by a further operational amplifier connected in its feedback path to a squaring circuit, eg circuit 6 .

A second embodiment of the present invention for generating a warning signal according to the above inequality (2) is shown in FIG. 2 . In this embodiment, the output signals Vpin and Vpout are sent to the addition circuit 20 and the subtraction circuit 24, and the resulting sum and difference signals are sent to the corresponding input terminals of an analog multiplier 26, and the output signal of the multiplier 26 is Indicates (Pin-Pout)(Pin+Pout).

The output signal from multiplier 26 is again supplied to comparator 12 where it is compared with a signal representing 1/ ^C2 . When the inequality (2) holds, the output signal from the comparator 12 is sent to the warning device 14 to generate a warning. Here again, the square root function is realized by the square root function generator described above between the output of the multiplier 26 and the input of the comparator 12, or between the output of the comparator 12 and the input of the warning device 14 .

Each of the analog circuits described in FIGS. 1 and 2 can be constructed from known conventional circuits to be an essential standard part of an analog signal processor.

In a detection system of the type contemplated by the present invention, the inequality generating a warning can use the maximum design flow or a flow value slightly less than the maximum as a reference value, thereby providing a reliable safety factor.

Since the invention is basically concerned with providing a warning when a given flow rate is exceeded, reliable results can be obtained with a simulation system of the type described in the accompanying drawings. Such circuits are advantageous because they are inexpensive to manufacture and can be altered for a particular application. However, it will be apparent to one of ordinary skill in the art that the type of system contemplated by the present invention may also include digital means or be implemented by programming a provided digital system to perform other control or detection functions, if desired.

From the foregoing description of specific embodiments of the invention it will be apparent that many modifications may be made without departing from the spirit of the invention. It is intended by the appended claims to cover all such modifications as are within the true scope and spirit of the invention.

Accordingly, the presently disclosed embodiments are to be considered in all respects as illustrative and non-restrictive, the scope of the invention being otherwise indicated by the appended claims, meaning and equivalents of the claims All changes coming within the scope are to be embraced in the claims.

Claims (5)

1. be used to detect the method for flow of the liquid of driving steam turbine, the turbine blade passage between fluid flows body inlet and the fluid egress point, and blade path is relevant with a greatest hope flow, and described method is characterised in that and may further comprise the steps:

The fluid pressure value of test fluid porch and fluid outlet;

Utilize the following relationship formula according to the force value that detected with electronics method Fluid Computation flow: $W\≈\sqrt{{P_{\mathrm{ain}}}^2-{P_{\mathrm{aout}}}^2},$ Wherein, W is a fluid flow,

P _AinBe actual absolute pressure in the blade path porch, and

P _AoutBe actual absolute pressure in the blade path exit;

The flow and the greatest hope flow that calculate are compared; And

When the flow that calculates surpasses the greatest hope flow, send an indication automatically.

2. according to the method for claim 1, it is characterized in that: calculating and comparison step are undertaken by analog signal processing device.

3. according to the method for claim 1, it is characterized in that: send an indication and comprise warning of generation.

4. be used to detect the device of flow of the fluid of driving steam turbine, turbine blade passage between fluid flows body inlet and the fluid egress point, and blade path is relevant with a greatest hope flow, described device comprises: be used to detect the pressure sensor device (2 in the force value of fluid intake place and exit fluid, 4), described device is characterised in that also and comprises:

First circuit arrangement that links to each other with described pressure sensor device (6,8,10), be used to utilize the following relationship formula according to detected force value with electronics method Fluid Computation flow: $W\≈\sqrt{{P_{\mathrm{ain}}}^2-{P_{\mathrm{aout}}}^2},$ Wherein, W is a fluid flow,

P _AinBe actual absolute pressure in the blade path porch, and

P _AoutBe actual absolute pressure in the blade path exit;

With the second circuit device (12) that described first circuit arrangement (6,8,10) links to each other, the flow and the greatest hope flow that are used for calculating with electronics method compare; And

The indicating device (14) that links to each other with described second circuit device (12) is used for sending automatically an indication when the flow that calculates surpasses the greatest hope flow.

5. according to the device of claim 4, it is characterized in that: described first circuit arrangement (6,8,10) and described second circuit device (12) are analog signal processing devices.

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