JPH0121322B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for protecting a steam turbine by stress management, which may be operated in a humid region, and is particularly applicable to the rotor of a nuclear steam turbine. The present invention relates to a turbine protection method suitable for controlling and managing generated stress to protect the steam turbine.

[Prior Art] Conventionally, rotor stress management due to changes in the load of a nuclear power turbine has generally been performed using a control chart as shown in FIG. 1, without directly measuring the stress. In the figure, the horizontal axis represents the amount of change in the load factor, and the vertical axis represents the minimum time required for the load change, and the four curves A, B, C, and D are the smaller ones before and after the load change, respectively. The load factor of is 0%,
The curves are for 10%, 20%, and 30%. For example, a 20% curve is used both when the load factor increases from 20% and above, and when the load factor decreases to 20%.

However, in recent years, in power plants using nuclear power turbines, there has been a demand for temporary isolated operation within the plant in the event of a failure in the outside line system. In-plant isolated operation cuts off the load from the outside line system and covers only the power consumption within the plant, and is a significantly lighter load operation than rated operation.

When the plant enters isolated operation and when normal operation is restored, a large thermal stress is applied to the turbine rotor due to the sudden load change, which shortens the life of the rotor. Furthermore, the frequency of normal startups and shutdowns as well as unplanned shutdowns and startups in nuclear power plants tends to increase, and these also generate thermal stress in the rotor and shorten its lifespan. Furthermore, in the future,
It is expected that nuclear power plants will require intermediate load operation, which will also create thermal stress on the rotor and reduce rotor life. Under these circumstances, there is an increasing need for stress management of nuclear turbine rotors.

FIG. 2 is a chart showing an example of temperature changes and stress changes in the turbine rotor when the load on the steam turbine changes. The upper half of this chart represents temperature;
1 is the high pressure first stage steam temperature, 2 is the rotor surface temperature,
3 is the rotor center hole temperature. The lower half of this diagram represents stress; 4 is the rotor center hole stress, 5 is the rotor surface stress, 6 is the rotor residual stress, and 7 is the compressive yield point. Now, we will explain the case of cold start, that is, the case where the rotor temperature is approximately equal to room temperature and high temperature steam flows in. First, with the inflow of steam, the rotor surface temperature 2 shown by the broken line increases, and the rotor surface stress 5 also shown by the broken line produces compressive stress. Here, the thermal stress is highest at a portion where stress is concentrated, such as the base of the disk, and the stress exceeds the minus yield point 7 and causes plastic deformation in the compression direction. As a result, a tensile residual stress 6 is generated when the steady state is reached. On the other hand, in this process, due to the change in the rotor center hole temperature 3 shown by the dashed line, a rotor center hole stress 4 is generated in the tensile direction opposite to the rotor surface, as shown by the solid line. When the turbine is stopped, the steam temperature 1 falls more rapidly than the rotor temperature. At this time, the rotor surface stress 5
The rotor center hole pressure 4 (solid line) produces a compressive stress as shown in point E, and the rotor center hole pressure 4 produces compressive stress as shown in point E.

To deal with the occurrence of such thermal stress, conventional nuclear power turbines have adopted a method of monitoring rotor stress by ensuring an allowable load change range and time using the curve shown in FIG.

In a conventional thermal power turbine, a stress management system as shown in FIG.
At the same time, the detection signal of the steam temperature detector 26 is input to the thermal stress calculator 10 via the ΔT calculator 9, and in parallel with the above, the detection signal of the rotor rotation speed measuring device 11 is input to the centrifugal stress calculator. input into the device 12. The calculation result of the above thermal stress calculator 10,
The calculation results of the centrifugal stress calculator 12 are input to the composite stress calculator 13 to obtain the composite stress, and based on the results, the creep wear calculator 15 and the rotor stress determiner 16 make a situation determination and continue. Decide either operation 17 or valve adjustment 18.
When adjusting the valve, the adjustment valve 25 is controlled to open or close via the valve opening/closing device 19 in response to the adjustment command signal 18a.

[Problems to be Solved by the Invention] If a nuclear power turbine is managed by the rotor stress monitoring method as described above, there are the following drawbacks.

One of the drawbacks is that when the monitoring system shown in FIG. 3 performs control based on the chart shown in FIG.
It has not been possible to manage stress in response to various operational change modes in actual operation, particularly rapid load changes and rotational speed changes such as load shedding in the event of an accident or the above-mentioned isolated operation within the plant. In addition, due to the poor accuracy of rotor temperature control, it may take longer than necessary to respond to restarts and load increases after such accidents, or to load increases after isolated operation within the plant, or if the load increases under normal load. There was a risk of excessive stress due to control based on the change curve.

Another shortcoming of traditional rotor stress monitoring methods is that nuclear turbines are often operated in wet steam, so the steam thermometer is also in the wet steam range, making it difficult to handle sudden load changes and thermal stress problems. This is a problem in that the thermometer reading cannot fully follow changes in steam temperature, making it impossible to perform highly accurate stress management.

[Object of the Invention] An object of the present invention is to reduce the thermal stress of the rotor of a steam turbine, which is operated mainly with wet steam, such as a nuclear turbine, regardless of the wet state of the steam, and to reduce the time delay. It is possible to perform highly accurate stress management by determining the stress with high accuracy without any stress. To provide a method of protecting nuclear power turbines.

[Means for Solving the Problems] In order to achieve the above object, the present invention detects the pressure in the humid area and calculates the pressure from this pressure in a steam turbine that is often operated in a humid area such as a nuclear turbine. The saturation temperature uniquely determined by the steam table is determined, the thermal stress of the steam turbine rotor is calculated, and it is determined whether or not the steam is wet steam. When it is determined that the steam is wet steam, the above calculation is performed. The stress of the rotor is managed based on the saturation temperature.

[Operation] According to the method described above, the thermal stress generated in the rotor can be determined with high accuracy without any time delay, regardless of the wet state of the steam, so that the stress can always be kept within the specified value. It is possible to perform precise control so that the turbine can be operated safely.

[Example] Next, an example of the present invention will be described with reference to FIGS. 4 to 6.

FIG. 4 is an i-s diagram of a nuclear power turbine.
The reactor generated steam is located at point A, and the high pressure turbine inlet is at point B at rated load. By performing work within the high pressure turbine, the high pressure turbine outlet becomes point C. The enthalpy (vertical axis) of the steam at point C increases by the moisture separator and reaches point D at the inlet of the low pressure turbine. Then, it performs work in the low-pressure turbine, and reaches a point E on the exhaust pressure line e at the outlet of the low-pressure turbine.

In the case of partial load, the pressure at each stage decreases due to the decrease in the amount of steam at the steam turbine inlet, and the
Points D and E move to points B1, C1, D1, and E1, respectively.

Typically, the minimum load for nuclear turbines is 25% of the rating
It is. In addition, during station isolated operation where the pressure of each stage of the steam turbine decreases rapidly, the station load is small at about 3%, but the reactor side requires about 40% of the water supply flow rate, so the high pressure turbine extraction amount is large; During operation, the high-pressure turbine inlet flow rate is relatively large compared to the station load, and the area after the high-pressure first stage is in a wet region. That is, except when the rotational speed increases or decreases, the stage on the lower pressure side than after the high pressure first stage is in the wet region.

Figure 5 shows the relationship between pressure and saturation temperature in wet steam. As is clear from this figure, when the stage is in the wet steam region, the steam temperature of the stage is uniquely determined from the steam table if the stage pressure is detected.

As stated above, in most load changes in nuclear power turbines, the stages after the high-pressure first stage are operated in the wet steam region, so it is necessary to perform stress control specific to operational changes in wet steam. In other words, the thermometer has a poor ability to follow temperature changes in wet steam due to the humidity, and cannot follow sudden changes like in the case of dry steam. In order to solve this problem, the method of the present invention has the following features: (a) Only when the steam is wet steam, by detecting the pressure in the paragraph, it is possible to unambiguously convert the pressure to the saturation temperature as described in FIG. to calculate the steam temperature with high accuracy and good followability.

(b) If the steam is in the superheated range, it is not possible to convert pressure to temperature using the steam table, so if the steam is in the superheated range (for example, when the rotation speed is increasing during startup), use a thermometer to measure the steam temperature. Monitor. When moving to the humid area, after confirming that the steam is in the humid area with a hygrometer, the steam temperature is monitored by converting the detected pressure to temperature (method (a) above). Perform stress management.

Therefore, the stress management of the rotor is carried out by applying the method of the present invention under the above-mentioned conditions.The stage pressure detection positions are the high-pressure first stage inlet, after the high-pressure first stage, the high-pressure exhaust part, and the low-pressure Possible locations include the first stage inlet, after the low pressure first stage, before and after the low pressure final stage, etc.

FIG. 6 shows a block diagram of a stress management system constructed to implement the method of the present invention based on the above basic idea. This embodiment is intended for use after the high pressure first stage.

High-pressure first stage post-pressure detector 8, ΔT, with the same drawing reference number as in FIG. 3 showing a stress management system configured for turbine monitoring according to the prior art.
Computing unit 9, rotor thermal stress computing unit 10, rotation speed measuring unit 11, rotor centrifugal stress computing unit 12, composite stress computing unit 13, operating time measuring unit 14, creep wear computing unit 15, rotor stress determining unit 16, continuous operation 1
7, valve regulator 18, valve switch 19, control valve 25,
and high pressure first stage temperature detector 26 are similar components to the prior art stress management system (FIG. 3).

A feature of the system configuration of an example of a stress management system (FIG. 6) configured to carry out the method of the present invention is the addition of a Q portion shown by a phantom line. That is, the signal output detected by the high-pressure first-stage post-pressure detector 8 is input to the steam temperature selector 22 via the temperature converter 20. The temperature converter 20 mentioned above has a saturated steam pressure as shown in FIG.
It has a function of storing temperature curves and converting input steam pressure into temperature. The above conversion may be performed using a steam table. In the present invention, the steam table includes a steam pressure-temperature curve.

The signal output of the temperature detector 26 which detects the steam temperature after the high pressure first stage is also input to the steam temperature selector 22.

Furthermore, a humidity detector 21 is provided to detect the humidity of the steam after the high-pressure first stage, and its signal output is input to the steam temperature selector 22.

The steam temperature selector 22 is the humidity detector 21.
The device is configured to receive the signal output from the device and operate as follows based on the signal output. That is, when the humidity is >0, a signal representing the steam temperature converted by the temperature converter 20 is given to the ΔT calculator 9. Also,
When the humidity level is 0, a signal indicating the steam temperature detected by the temperature detector 26 is given to the ΔT calculator 9.

The steam temperature selector 22 described above has a structure that also has a comparison calculation function, and compares the converted steam temperature obtained by the temperature converter 20 described above with the actual steam temperature measured by the temperature detector 26, and records the comparison result on the recorder 24. record it. Furthermore, when the humidity detector 21 detects a humid steam state, the steam temperature selector 22 determines that the deviation between the temperature calculated by the temperature converter 20 and the actual temperature measured by the temperature detector 26 is determined in advance. It is configured so that an alarm 23 is activated when a given reference value is exceeded.

Next, an example in which the turbine protection method of the present invention is implemented using the above-mentioned management system shown in FIG. 6 will be described.

The pressure P ₁ , temperature T ₁ , and humidity M ₁ after the high-pressure first stage detected by the pressure detector 8, temperature detector 26, and humidity detector 21 installed in the high-pressure first stage are determined by the steam temperature selector 22. will be judged and selected. In other words, when the humidity level M ₁ > 0, the temperature T ₁₀ obtained by converting the pressure P ₁ detected by the pressure detector using the steam table is the temperature after the high pressure first stage, and when the humidity level M ₁ = 0, the temperature is detected. The temperature T ₁ detected by the device is selected as the temperature after the high pressure first stage.

The heat transfer coefficient of the rotor surface is calculated from the thus selected post-first stage temperature T ₁₀ or T ₁ and the post-first stage pressure P ₁ , and the temperature change ΔT is calculated by the calculator 9.
The thermal stress σ _T is calculated by the thermal stress calculator 10. If the thermal stress σ _T is calculated in this way, stress management of the rotor can be performed based on the thermal stress σ T . That is, it is possible to manage the stress of the rotor at each point in time so that it does not exceed the allowable stress, and to perform inspection and maintenance by calculating the degree of thermal fatigue of the rotor during long-term use.

In the above embodiment, rotor stress management was performed by calculating the rotor temperature based on the steam temperature converted from the steam table. Similarly, the turbine casing temperature was calculated based on the steam temperature converted from the steam table. It is also possible to calculate rotor stress management from changes in either or both of the calculated rotor temperature and the calculated casing temperature.

Regarding the above-mentioned embodiment, a more detailed stress management method will be described below.

The centrifugal stress σ _F is calculated by the rotor centrifugal stress calculator 12 from the rotation speed determined by the rotation speed measuring device 11, and the combined stress σ _F +σ _T with the previously calculated thermal stress σ _T is calculated by the operating time measuring device 14. The rotor stress determiner 16 compares and determines the stress calculated in advance by the creep wear calculator 15 based on the operating time stored in the rotor stress judger 16, taking into account creep wear as the allowable value, and determines whether the resultant stress is below the allowable value If so, continue operation instruction 1
7, and if the combined stress exceeds the allowable value, the centrifugal In addition to adjusting the stress and thermal stress, the amount of wear and tear over the life of the rotor is accumulated and stored based on the operating time measured by the operating time measuring device 14. By calculating the lifetime wear and tear of the rotor in this manner, the remaining service life can be estimated with high accuracy, so that inspection and maintenance can be performed at an appropriate time and the steam turbine can be completely protected without waste.

As in the above example, if stress management is performed by finding the resultant force of the thermal stress calculated by applying the present invention and the centrifugal stress calculated from the rotation speed, stress management that accurately simulates the actual conditions becomes possible. .

Further, by integrating the above-mentioned calculated thermal stress with respect to the operating time, it is possible to perform appropriate and precise stress management that takes the creep life of the rotor into consideration.

As mentioned above, in addition to monitoring long-term wear and tear, calculate the ratio of rotor stress to allowable stress at each point in operation, and control so that this ratio does not exceed 100%. is also an effective protection measure, and if it is automatically controlled, stress management can be done unmanned.

Also, like the management system shown in Figure 6,
If the humidity detector 21 is provided and the stress is managed by calculating the stress using the converted steam temperature when the steam is wet steam and using the measured steam temperature when the steam is dry steam, for example, Appropriate management can be carried out even when the steam conditions become dry, such as when the rotational speed is increasing during startup of a nuclear steam turbine.

As explained in the management system diagram of Fig. 6, when the saturated steam temperature converted from the steam pressure and the steam temperature directly detected by the temperature detector are A device is installed that automatically records or alarms when a deviation above a certain value occurs, and when the above deviation exceeds a certain value, it is determined that some abnormality has occurred, and the pressure and temperature are controlled. Abnormalities in the detector or computing unit can be detected early.

Also, as described in the previous embodiment,
Detection of steam pressure, detection of steam temperature, and detection of whether steam is wet steam or dry steam are as follows:
Respectively, at least one of the high-pressure first stage inlet, after the high-pressure first stage, high-pressure exhaust section, low-pressure first stage inlet, after the low-pressure first stage, before the low-pressure final stage, after the low-pressure final stage, and at the intermediate stage. , rotor temperature and stress can be calculated appropriately.

Furthermore, in the management system shown in Figure 6,
It is also possible to omit the installation of the humidity detector 21 and determine the humidity of the steam by comparing a preset turbine plan value with the actual operating output.

To determine humidity using this method, at the design stage of the relevant steam turbine, set as a planned value how the humidity of steam in each stage will change as the turbine load factor changes. .

That is, the planned humidity level for the load factor is set in advance.

Then, the planned humidity corresponding to the actual measured output value during operation of the steam turbine is calculated,
The wetness of the working steam can be estimated.

As a result of the estimation, if the humidity level is >0, the above-mentioned converted temperature _T10 is selected as the steam temperature, and if the humidity level is 0, the actually measured temperature _T1 is selected as the steam temperature.

Estimating humidity in this way inevitably lowers the accuracy compared to actually measuring humidity using a hygrometer, but this method (humidity estimation)
By using the humidity sensor 21, the humidity detector 21 becomes unnecessary, and the configuration of the turbine protection system becomes simple and inexpensive.

[Effects of the Invention] As explained above, the nuclear turbine protection method of the present invention detects the steam pressure of the steam turbine,
Convert the above pressure to saturated steam temperature using the steam table, and if the steam is wet steam, calculate the temperature of the main components that come into contact with the steam, such as the rotor of the steam turbine, based on the above converted temperature. However, in the case of dry steam, by controlling the stress of the turbine rotor based on the temperature detected by a thermometer, the thermal stress of the rotor of a steam turbine that has the opportunity to be operated with wet steam can be reduced depending on the humidity of the steam. Regardless of how
It is particularly suitable for protecting nuclear power turbines because it is possible to obtain stress with high accuracy and perform highly accurate stress management to protect steam turbines.

[Brief explanation of drawings]

Figure 1 is a control chart used for stress management in conventional nuclear power turbines, Figure 2 is a diagram showing the state of rotor stress generation due to changes in steam temperature, and Figure 3 is a diagram used in conventional thermal turbines. A management system diagram, Fig. 4 is an I-S diagram of a nuclear turbine, Fig. 5 is a steam diagram showing the relationship between wet steam pressure and saturation temperature, and Fig. 6 is a nuclear turbine protection method of the present invention. 1 is an example of a diagram of a steam turbine management system configured for implementation. 1...Temperature after high pressure first stage, 2...Rotor surface temperature,
3... Rotor center hole temperature, 4... Rotor center hole stress,
5...Rotor surface stress, 6...Residual stress, 7...Minus yield point, 8...High pressure first stage post-pressure detector, 9...
ΔT calculator, 10... Rotor thermal stress calculator, 11...
Rotation speed measuring device, 12... Rotor centrifugal stress calculator, 1
3...Synthetic stress calculator, 14...Operation time measuring device, 1
5... Creep wear and tear calculator, 16... Rotor stress determiner, 17... Continuous operation, 18... Valve adjuster, 19... Valve opener, 20... Converter that converts pressure to saturation temperature, 21... Humidity detector, 22...Steam temperature selector, 23...Alarm, 24...Recorder, 25...Adjustment valve, 26...High pressure first stage post-temperature detector.

Claims (1)

[Claims] 1. (a) Detects the steam pressure of the steam turbine and converts the pressure to a saturation temperature using a steam table; (b) Detects whether the steam of the steam turbine is wet steam or dry steam. (c) If the above steam is wet steam, calculate the rotor stress based on the saturated steam temperature converted from the steam pressure; (d) If the above steam is dry steam, calculate the stress on the rotor based on the saturated steam temperature converted from the steam pressure. 1. A nuclear turbine protection method, characterized in that rotor stress is calculated on the basis of steam temperature, which in some cases is directly detected by a temperature detector. 2. When the saturated steam temperature calculated from the steam pressure and the steam temperature directly detected by the temperature detector differ by a certain value or more when the steam of the steam turbine is wet steam, The nuclear turbine protection method according to claim 1, characterized in that it is determined that an abnormality has occurred. 3. Detection of the steam pressure and steam temperature as described above;
In addition, whether steam is wet steam or dry steam is determined at the high-pressure first stage inlet of the steam turbine, after the high-pressure first stage, high-pressure exhaust section, low-pressure first stage inlet,
The nuclear power plant according to claim 1 or 2, characterized in that the process is carried out for steam at at least one of the following: after the first low-pressure stage, before the final low-pressure stage, after the final low-pressure stage, and at an intermediate stage. Turbine protection methods. 4 The above-mentioned determination of whether steam is wet steam or dry steam is made by setting the relationship between the turbine load factor and steam humidity at the design stage of the steam turbine, and then determining whether the steam is wet steam or dry steam while the turbine is in operation. 3. The nuclear turbine protection method according to claim 1 or 2, wherein the load factor is actually measured and estimated by comparing it with the above relationship.