A system and method for calculating the moment of inertia of a steam turbine shaft system

Abstract

The present invention relates to a system and method for measuring the moment of inertia of a steam turbine shaft system. The system comprises a rotating shaft, a gear plate, a magnetoresistive sensor, an oscilloscope, and a computer. The system calculates the shaft system's rotational speed change based on the alternating signal transmitted by the magnetoresistive sensor during turbine load rejection, thereby calculating the shaft system's acceleration and further calculating the turbine shaft system's moment of inertia. The present invention has the following beneficial effects: The system uses a high-precision, high-frequency oscilloscope to collect instantaneous signals from the gear plate teeth passing through the magnetoresistive sensor, thereby improving the resolution of the speed signal acquisition. By rationally dividing the speed clusters, it overcomes signal voltage fluctuations during speed measurement and enables batch signal processing. The system offers advantages such as simple operation, high data accuracy, and clear physical concepts.

Description

Technical Field

[0001] The present invention belongs to the field of steam turbine generator set measurement, and in particular relates to a system and method for measuring the rotational inertia of a steam turbine shaft system. Background Art

[0002] In classical mechanics, the moment of inertia is a measure of the inertia of a rigid body when it rotates around an axis. It is represented by the letter I or J and its unit is kg·m 2 For a point mass, I = mr 2 , where m is its mass and r is the perpendicular distance between the particle and the axis of rotation. The moment of inertia in rotational dynamics is equivalent to mass in linear dynamics. It can be formally understood as an object's inertia with respect to rotational motion. The moment of inertia can be used to establish relationships between quantities such as angular momentum, angular velocity, torque, and angular acceleration.

[0003] The calculation formula for the moment of inertia of the steam turbine generator set is:

[0004]

[0005] Where J is the rotor moment of inertia, P0 is the generator load value at the moment of load rejection, ω0 is the initial angular velocity at the moment of load rejection, a is the speed acceleration at the moment of load rejection, and η is the generator efficiency. The speed acceleration a is calculated based on the dynamic speed measurement value. However, in the currently commonly used method for calculating the moment of inertia of steam turbine generator sets, the speed value is the speed signal secondary-transmitted by the steam turbine generator set DCS system. This speed signal is distorted and has limited accuracy. Therefore, the speed output response cannot meet the millisecond-level speed signal accuracy requirements at the moment of load rejection, resulting in low measurement accuracy of the speed acceleration a, and thus the inability to accurately measure the moment of inertia of the steam turbine generator set. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a system and method for measuring the moment of inertia of a steam turbine shaft system.

[0007] The steam turbine shaft system rotational inertia measurement system includes a rotating shaft, a gear plate, a magnetoresistive sensor, a wave recorder and a computer;

[0008] The system for measuring the rotational inertia of the turbine shaft system is installed on the turbine through a rotating shaft; the other end of the rotating shaft is connected to the center of the gear plate, a magnetoresistive sensor is fixed on the radial direction of the gear plate, the magnetoresistive sensor is connected to a recorder, and the recorder is connected to a computer.

[0009] The calculation method of the steam turbine shaft system moment of inertia calculation system comprises the following steps:

[0010] S1. Start the steam turbine, causing the shaft to drive the gear plate to rotate. Use an oscilloscope to sample the voltage data obtained by the magnetoresistive sensor and transmit it to a computer. Use the generator off-grid signal as a reference signal to intercept the data.

[0011] S2. According to the characteristics of the alternating signal with peaks and valleys, search for the peak points of the alternating signal and establish the peak point sequence P = (P1, P2...P n ); Divide the signal according to the peak point and establish the gear plate single tooth signal sequence;

[0012] S3, merge the adjacent k single tooth signals into a set, according to the sampling period t o Calculate the time interval of the collection, time interval t i =(P i+k -P i )×t0, the speed S at time i i =60k / t i , calculate the speed time series S=(s1,s2……s n );

[0013] S4. Draw a speed curve according to the speed time series;

[0014] S5. Calculate the speed acceleration according to the speed time series, speed acceleration a i =s i+1 -s i , calculate the speed acceleration sequence A=(a1,a2……a n ), take the maximum acceleration value before the speed reaches the peak value as the instantaneous acceleration of load rejection, and then calculate the moment of inertia according to the formula.

[0015] Preferably, in step S1: a load rejection test is performed using an operating condition with an initial load of 20%-30%, the speed of the steam turbine is v0 during normal operation, and when the generator is disconnected from the grid, data of a period of time before the disconnection signal is intercepted; the sampling rate of the recorder is set to a times the frequency of the tooth signal, the number of teeth of the gear plate is n, and the sampling rate of the recorder is set to a·v0·nHz.

[0016] Preferably, in step S1: a is greater than 3.

[0017] Preferably, step S2 is specifically as follows:

[0018] S2.1 Searching for the peak point: When the voltage value V P At the same time, it is greater than the previous sampling point V P-1 and the next sampling point V P+1 When the value of is , the point is defined as the peak point of the signal, that is, V P -V P-1>0 and V P -V P+1 The point p > 0 is the peak point;

[0019] S2.2 Establish a peak point sequence P = (P1, P2...P n ), where P n The value of is the sequence number of the nth peak point in the original sampling data;

[0020] S2.3 Verify the sequence: Let T i =P i+1 -P i , we get the sequence T=(T1,T2……T n ), if the deviation of the unit values ​​in sequence T is greater than or equal to 10%, it indicates that the sampling rate is set too high, and the original data needs to be processed by interval sampling, and a new sequence P needs to be obtained and re-verified according to the method described in steps S2.1 and S2.2 until the deviation of the unit values ​​in sequence T is less than 10%;

[0021] S2.4 Establish a signal sequence of a single tooth of the gear plate: After verification, divide the signal with the peak points as the discontinuity points. After division, the data between adjacent peak points are the signals of a single tooth of the gear plate passing through the sensor.

[0022] Preferably, in step S4: observe whether the speed curve is smooth and whether it has step-like features; if the curve is not smooth, reduce the k value; if the curve has step-like features, increase the k value until a smooth speed curve without step-like features is obtained.

[0023] As an example, in step S5: the calculation formula of the moment of inertia is:

[0024]

[0025] Where:

[0026] J is the rotor moment of inertia, unit is kg×m 2 ;

[0027] n0 is the initial speed at the moment of load rejection, which is the first value of the speed time series before the reference signal;

[0028] P0 is the generator load value at the moment of load rejection, obtained through measurement;

[0029] ω0 is the initial angular velocity at the moment of load rejection, which is obtained based on n0;

[0030] a is the instantaneous acceleration of load rejection;

[0031] η is the generator efficiency, and the change in electromagnetic loss at the initial load rejection is neglected, which is calculated as 99%.

[0032] The beneficial effects of the present invention are:

[0033] 1) The present invention proposes a system and method for measuring the rotational inertia of a steam turbine shaft system. With the help of a high-precision, high-frequency oscilloscope, the alternating signal generated by each tooth on the turbine gear plate when passing through a magnetoresistive sensor is collected. The time interval between the peak-to-peak values ​​of the alternating signal is used to determine the time it takes for a single tooth to pass through the magnetoresistive sensor, thereby obtaining the rotational speed value. The calculated rotational speed value is used to plot a dynamic speed curve during the load rejection period, and then the precise values ​​of n0, ω0, and a are calculated based on the speed curve, effectively improving the measurement accuracy of the rotational inertia.

[0034] 2) The present invention performs a load rejection test on a working condition with an initial load of 20%-30% and calculates the moment of inertia; thereby effectively avoiding the safety risks in conventional 100% and 50% load rejection tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the assembly diagram of the steam turbine shafting moment of inertia measurement system proposed by the present invention;

[0036] Figure 2 This is the flow chart for calculating the moment of inertia of the turbine shaft system;

[0037] Figure 3 This is the signal fluctuation diagram obtained by the oscilloscope when the sampling rate is moderate;

[0038] Figure 4 This is the signal fluctuation diagram obtained by the oscilloscope when the sampling rate is too high.

[0039] Description of the accompanying symbols: steam turbine 1, rotating shaft 2, gear plate 3, magnetoresistive sensor 4, wave recorder 5, computer 6. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the following examples. The following examples are provided only to facilitate understanding of the present invention. It should be noted that, without departing from the principles of the present invention, it is possible for a person skilled in the art to make various modifications to the present invention, and such improvements and modifications fall within the scope of the claims of the present invention.

[0041] Example 1

[0042] As an example, Figure 1 The system for measuring the moment of inertia of a steam turbine shaft system is characterized by comprising: a rotating shaft 2, a gear plate 3, a magnetoresistive sensor 4, a wave recorder 5 and a computer 6;

[0043] The system for measuring the moment of inertia of the turbine shaft system is mounted on the turbine 1 via a rotating shaft 2. The other end of the rotating shaft 2 is connected to the center of a gear plate 3. A magnetoresistive sensor 4 is fixed directly above the gear plate. The magnetoresistive sensor 4 is connected to an oscilloscope 5, which is connected to a computer 6. The oscilloscope 5 is a high-precision, high-speed sampling device with a 16-bit sampling bit and a maximum sampling frequency of 200kHz. It can automatically collect and save data based on rising or falling edge signals. During a load rejection test, the system can collect the voltage signal output by the gear plate through the magnetoresistive sensor and calculate the turbine shaft system speed, acceleration, and moment of inertia based on the signal changes.

[0044] Example 2

[0045] According to the first embodiment, the present invention provides another embodiment, such as Figures 1 to 4 As shown, the measurement method of the steam turbine shafting moment of inertia measurement system includes the following steps:

[0046] S1. Conduct a load rejection test using an initial load of 20%-30%. Start the steam turbine 1. During normal operation, the speed of the steam turbine 1 is stabilized at 3000 r / min. The rotating shaft 2 drives the gear plate 3 to rotate. The voltage data obtained by the magnetoresistive sensor 4 is sampled using an oscilloscope 5 and transmitted to a computer 6.

[0047] During the turbine load rejection test, the oscilloscope collects the alternating signal generated by the gear plate passing the magnetoresistive sensor and the generator disconnection signal, and automatically saves the signal for the required time period. The sampling frequency of the oscilloscope is determined by the turbine shaft speed and the number of gear plate teeth. Since the turbine unit has a stable speed of 3000r / min (50Hz) during normal operation, the sampling rate of the oscilloscope is 4 times the tooth signal frequency. The number of gear plate teeth is n, and the sampling rate of the oscilloscope is set to 4×50×n=200nHz. When the generator disconnects from the grid, the generator disconnection signal is used as the reference signal, and the oscilloscope 5 is used to intercept the data 60s before the disconnection signal for sampling.

[0048] S2. Based on the characteristics of the alternating signal, which has peaks and valleys, searching for peak points in the alternating signal, dividing the signal according to the peak points, and establishing a single tooth signal sequence of the gear plate;

[0049] S2.1 Searching for the peak point: When the voltage value V P At the same time, it is greater than the previous sampling point V P-1 and the next sampling point V P+1 When the value of V P -V P-1 >0 and V P -V P+1 When >0, point p is defined as the peak point of the signal;

[0050] S2.2 Establish a peak point sequence P = (P1, P2...P n ), where P n The value of is the sequence number of the nth peak point in the original sampling data;

[0051] S2.3 Verify the sequence: Let T i =P i+1 -P i , we get the sequence T=(T1,T2……T n ); observe the unit values ​​in sequence T. If the deviation of the unit values ​​in sequence T is greater than or equal to 10%, it indicates that the sampling rate is set too high. Figure 4 As shown in FIG1 , if the sampling rate is set too high, multiple peak voltages with similar voltage values ​​will be collected. In actual use, these peak points have no actual physical meaning, and the original data needs to be processed by interval sampling. The new sequence P is obtained and re-verified according to the method described in steps S2.1 and S2.2 until the deviation of the unit value in the sequence T is less than 10%, as shown in FIG1 . Figure 3 As shown;

[0052] S2.4 Establish a single gear tooth signal sequence: After verification, divide the signal using the peak points as discontinuity points. After division, the data between adjacent peak points is the signal of a single gear tooth 3 passing through the sensor;

[0053] S3, merge the adjacent k single tooth signals into a set, according to the sampling period t o Calculate the time interval of the collection, time interval t i =(P i+k -P i )×t0, the speed S at time i i =60k / t i , calculate the speed time series S=(s1,s2……s n );

[0054] S4. Draw a speed curve based on the speed time series; observe whether the speed curve is smooth and whether it has step-like features; if the curve is not smooth, reduce the k value; if the curve has step-like features, increase the k value until a smooth speed curve without step-like features is obtained;

[0055] S5. Calculate the speed acceleration according to the speed time series, speed acceleration a i =s i+1 -s i , calculate the speed acceleration sequence A=(a1,a2……a n ), take the maximum acceleration value before the speed reaches the peak value as the instantaneous acceleration of load rejection, and then calculate the moment of inertia according to the formula;

[0056] The calculation formula for the moment of inertia is

[0057]

[0058] Where:

[0059] J is the rotor moment of inertia, unit is kg×m 2 ;

[0060] n0 is the initial speed at the moment of load rejection, which is the first value of the speed time series before the reference signal;

[0061] P0 is the generator load value at the moment of load rejection, obtained through measurement;

[0062] ω0 is the initial angular velocity at the moment of load rejection, which is obtained based on n0;

[0063] a is the instantaneous acceleration of load rejection;

[0064] η is the generator efficiency, and the change in electromagnetic loss at the initial load rejection is neglected, which is calculated as 99%.

Claims

1. A method for calculating the moment of inertia of a steam turbine shaft system, characterized in that: include: A rotating shaft (2), a gear plate (3), a magnetoresistive sensor (4), an oscilloscope (5) and a computer (6); The system for measuring the moment of inertia of the turbine shaft system is installed on the turbine (1) via a rotating shaft (2); the other end of the rotating shaft (2) is connected to the center of a gear plate (3); a magnetoresistive sensor (4) is fixed radially on the gear plate; the magnetoresistive sensor (4) is connected to a wave recorder (5); and the wave recorder (5) is connected to a computer (6); The method comprises the following steps: S1, start the steam turbine (1), so that the rotating shaft (2) drives the gear plate (3) to rotate, use the wave recorder (5) to sample the voltage data obtained by the magnetoresistive sensor (4), and transmit it to the computer (6); use the generator off-grid signal as a reference signal to intercept the data; S2. According to the characteristics of the alternating signal with peaks and valleys, search for the peak points of the alternating signal and establish the peak point sequence P = (P1, P2...P n ); dividing the signal according to the peak point and establishing a single tooth signal sequence of the gear plate (3); S3, merge the adjacent k single tooth signals into a set, according to the sampling period t o Calculate the time interval of the collection, time interval t i =(P i+k -P i )×t0, the speed S at time i i =60k / t i , calculate the speed time series S=(s1,s2……s n ); S4. Draw a speed curve according to the speed time series; S5. Calculate the speed acceleration according to the speed time series, speed acceleration a i =s i+1 -s i , calculate the speed acceleration sequence A=(a1,a2……a n ), take the maximum acceleration value before the speed reaches the peak value as the instantaneous acceleration of load rejection, and then calculate the moment of inertia according to the formula.

2. The method for calculating the moment of inertia of a steam turbine shaft system according to claim 1, wherein: In step S1: a load rejection test is performed under the operating condition of an initial load of 20%-30%, the speed of the steam turbine (1) is v0 during normal operation, and when the generator is disconnected from the grid, data of a period of time before the disconnection signal is intercepted; the sampling rate of the recorder (5) is set to a times the frequency of the tooth signal, the number of teeth of the gear plate (3) is n, and the sampling rate of the recorder is set to a·v0·nHz.

3. The method for calculating the moment of inertia of a steam turbine shaft system according to claim 2, wherein: In step S1: a is greater than 3.

4. The method for calculating the moment of inertia of a steam turbine shaft system according to claim 1, wherein: Step S2 is specifically as follows: S2.1 Searching for the peak point: When the voltage value V P At the same time, it is greater than the previous sampling point V P-1 and the next sampling point V P+1 When the value of is , the point is defined as the peak point of the signal, that is, V P -V P-1 >0 and V P -V P+1 The point p > 0 is the peak point; S2.2 Establish a peak point sequence P = (P1, P2...P n ), where P n The value of is the sequence number of the nth peak point in the original sampling data; S2.3 Verify the sequence: Let T i =P i+1 -P i , we get the sequence T=(T1,T2……T n ), if the deviation of the unit values ​​in sequence T is greater than or equal to 10%, it indicates that the sampling rate is set too high, and the original data needs to be processed by interval sampling, and a new sequence P needs to be obtained and re-verified according to the method described in steps S2.1 and S2.2 until the deviation of the unit values ​​in sequence T is less than 10%; S2.4 Establishing a signal sequence of a single tooth of a gear plate: After verification, the signal is divided with the peak point as the discontinuity point. After division, the data between adjacent peak points are the signals of a single tooth of the gear plate (3) passing through the sensor.

5. The method for calculating the moment of inertia of a steam turbine shaft system according to claim 1, wherein: In step S4: observe whether the speed curve is smooth and whether it has step-like features; if the curve is not smooth, reduce the k value; if the curve has step-like features, increase the k value until a smooth speed curve without step-like features is obtained.

6. The method for calculating the moment of inertia of a steam turbine shaft system according to claim 1, wherein: In step S5: the calculation formula of the moment of inertia is Where: J is the rotor moment of inertia, unit is kg×m 2 ; n0 is the initial speed at the moment of load rejection, which is the first value of the speed time series before the reference signal; P0 is the generator load value at the moment of load rejection, obtained through measurement; ω0 is the initial angular velocity at the moment of load rejection, which is obtained based on n0; a is the instantaneous acceleration of load rejection; η is the generator efficiency, and the change in electromagnetic loss at the initial load rejection is neglected, which is calculated as 99%.

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