JPH0155334B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for monitoring torsional vibration of a rotating shaft system of a turbine generator when a series capacitor is inserted into a power transmission system from the turbine generator.

It is well known that torsional vibrations occur in rotating shaft systems such as turbine generators and compressors due to the delicate balance of the shaft systems as they rotate.

Moreover, a rotating shaft system usually has a plurality of natural frequencies, and when the rotational frequency approaches one of the natural frequencies, resonance occurs, producing extremely large vibrations.

However, during normal rotation, torsional vibration occurs in the rotating shaft system as a combination of vibration mode components corresponding to each of the above-mentioned natural frequencies, but it is not very large.

On the other hand, when some external force acts on these rotating shaft systems, a resonance phenomenon occurs at one of the natural frequencies of this rotating shaft system, and when the shaft system begins to generate automatic vibration, the vibration increases rapidly, and sometimes It may also destroy the shaft system.

A series capacitor is often inserted into the power transmission system of a turbine generator, but since the power transmission line is transformer-coupled, there is a phase delay between the input and output sides, and there is a power loss, so it is necessary to compensate for this. It is inserted. However, this series capacitor is also the source of external force acting on the shaft system,
This is caused by changes in the frequency of the power transmission system, which varies with its capacity.

In other words, when the vibration of the power flowing through the power transmission line and the torsional vibration of the turbine generator shaft system double resonate, automatic vibration of the electromechanical system occurs, and this is particularly important for SSR.
(Sub-Synchronus Resonance). This phenomenon occurs when the natural frequency fe of the power transmission system and the torsional natural frequency fm of the rotating shaft system including the turbine generator become fe + fm = power transmission system frequency (50 or 60Hz)...(1), and when a small disturbance is added to this, the frequency suddenly increases. It occurs in

As mentioned earlier, there is a risk that the rotating shaft system will be destroyed due to the rapid growth of self-excited vibrations, so the occurrence of such vibrations must be constantly monitored. Conventionally, torsional vibration monitoring as shown in Figure 1 has been used. equipment was provided.

The output power of a generator 02 rotated by a turbine 01 is connected to a power transmission system via a generator output power transmission line 03.

04 is a measurement current transformer (measured value C Ti),
05 is a measurement voltage transformer (P Ti), which is connected to the generator output power transmission line 03,
The generator output power P is calculated by multiplying the measured current CTi and voltage PTi by the wattmeter 06 for each phase, and adding the values of these three phases by the adder 07. P= 〓 ⁱ CTi・PTi... (2) Pass the generator output power P obtained in this way through the filter 08 to remove the steady portion (DC component) and the component above the transmission system frequency to obtain the fluctuating component ΔP below the transmission system frequency.

As can be seen from equation (1) above, self-excited vibration occurs when the vibration of the power transmission system is lower than the power transmission system frequency, so the fluctuation component of power below the power transmission system frequency △
Its occurrence can be detected by monitoring the amplitude of P. In other words, when self-excited vibration occurs, the fluctuation component increases, so input the set value △P' into the setting device 09 in advance, compare it with the fluctuation component ΔP in the comparator 010, and set the set value △P'. If the limit is exceeded, a warning will be issued and
Appropriate processing is performed, such as removing the series capacitor and disconnecting the generator 02 from the power transmission system.

As already mentioned, self-excited vibration generates excessive torsional vibration in the rotating shaft system of the turbine generator, and the torsional vibration generates stress in the shaft system, causing it to break.
Although it is possible to detect the occurrence of self-excited vibration based on the magnitude of the power fluctuation component △P, it is difficult to accurately estimate the stress on each part of the rotating shaft system, and therefore the set value △P' may vary considerably. The value had to be set with some margin, and conventional devices had no choice but to become overly cautious monitoring devices.

The present invention eliminates this drawback and is a device for monitoring the rotating shaft system of a turbine generator connected to a power transmission system equipped with a series capacitor, which detects torsional vibrations at a fixed position of the rotating shaft system. A vibration detection device to be detected and a vibration waveform obtained by the device that decomposes and extracts only the mode component having a frequency lower than the power transmission system frequency of the turbine generator among the natural frequencies of the rotating shaft system. The stress for each mode component at the above arbitrary position is determined from the relationship between the vibration of the rotating shaft system at a fixed position and the vibration at an arbitrary position in the decomposition device and the above mode component determined in advance, and the relationship between the vibration and stress at the same arbitrary position. It is characterized by a comparator that compares the calculated stress with a preset value and issues a command when the stress exceeds the set value.The purpose of the comparator is to Torsional vibration monitoring of a rotating shaft system that reliably and appropriately detects self-excited vibrations caused by inserting a rotary shaft system into a power transmission system in relation to stress at any position on the rotating shaft system. It provides equipment.

First, torsional vibration of the rotating shaft system and its stress will be explained.

As mentioned above, the torsional vibration of the rotating shaft system has a plurality of natural frequencies, and it vibrates as a composite of the vibration mode components of each of the natural frequencies.

Number the natural frequencies from the smallest to the first and second, and define the frequency as fi and the vibration mode shape of each as Gi.
(x) Let the mode component be Ai. This vibration mode type
Gi(x) is as shown by the solid line in Figure 2, and is the i-th vibration Yi(x,
t) is expressed as Yi(x, t)=Gi(x)・AiC _ps (2πfit+ei)...(3), and the synthesized vibration Y(x, t) is expressed as Y(x, t)=ΣYi(x , t) ...(4), and vibrations are usually measured (observed) in this form.

The relationship between the position X _p and X is expressed using the upper vibration mode form as follows: Yi (x, t) = Gi (x) Y (x _p , t) / Gi (x _p ) (5).

On the other hand, stress is proportional to the amplitude of vibration, so if the next mode proportionality constant at position x is αi (x) and stress is Vi (x), as shown by the dotted line in Figure 2, then Vi (x) = αi (x) Yi (x, t) ...(6), and from the relationship of equation (5), the i-th stress at position x is x _p
Vi (x) = αi (x) Gi (x) Y (x _p , t) / Gi (x _p ) using
...(7).

Although the rotating shaft system has a plurality of natural frequencies, this invention focuses only on those below the commercial frequency of the turbine generator.

Now, let's talk about series capacitors, which are increasingly used as the demand for electricity increases these days, and are installed to increase the power transmission capacity of power transmission lines.

Since the power transmission capacity is inversely proportional to the reactance of the power transmission system, as shown in equation (8), the inductive reactance ωL is canceled out by the capacitive reactance (-1/ωc),
Processes have begun to be taken to increase power transmission capacity by reducing reactance x.

X=ωL−1/ωc …(8) Since the resistance specific to the power transmission line is sufficiently small compared to the inductive reactance and can be ignored, if L is the inductance of the power transmission system and C is the capacity of the series capacitor, then the resistance of the power transmission system is The natural frequency fe is expressed as fe=1/2π√ (9), and as the degree of compensation by the series capacitor increases, the natural frequency fe of the power transmission system also increases.

In other words, as can be seen from equation (1), the natural frequency fe
As increases, the sum fe +
fm becomes the transmission system frequency and is exposed to the risk of self-excited vibration. At that time, if a small external force acts and the self-excited vibration expands, its natural frequency
If the vibration mode component for fm increases and the stress increases, the shaft system will be destroyed.
The allowable stress differs depending on the position of the shaft system.

Therefore, the present invention does not only detect fluctuations in the natural frequency of the power transmission system, but also detects the torsional vibration of the corresponding natural frequency of the rotating shaft system caused by the fluctuation, and the torsional vibration can reduce stress at any position. The shaft system is monitored by determining whether the value exceeds a certain value.

That is, the monitoring device of the present invention includes a vibration detection device that detects torsional vibration Y (x _p , t) at a fixed position x _p of the rotating shaft system. In addition, the obtained torsional vibration Y (x _p , t) is expressed as the natural frequency of the rotating shaft system.
Frequencies lower than the grid frequency (e.g. f ₁ and
f ₂ ) with first and second order modal components Y ₁ (x _p ,
t) and Y ₂ (x _p , t).

Next, we will find the stress in the rotating shaft system at this mode component Yix ( _p , t)i = 1, 2.
As shown by the dotted line in the figure, the proportionality constant αi(x) of stress to amplitude changes depending on the position x.

In other words, if you want to find the stress with high accuracy, it is sufficient to find the stress at the position x where its absolute value is maximum. (α ₁ in Figure 2
(x ₁ ), α ₂ (x ₂ )) Therefore, it would be quick to install a vibration detection device at that position and detect torsional vibration, but the position differs depending on the mode and the rotation axis system In some cases, it may not be possible to physically install it.

Therefore, the torsional vibration at an arbitrary position is estimated from the fixed position x _p and the stress is determined, and the stress at an arbitrary position is calculated by a mode-specific arithmetic unit using the relationship in equation (7).

Through the above procedure, the i-th stress Vi(x) at an arbitrary position x is determined. When this stress increases, it means that self-excited vibration has begun to be induced, so it is best to constantly compare it with a certain value and take various measures as soon as it exceeds a certain value.

In the present invention, stress is constantly monitored by a comparator.

As described above, according to the monitoring device of the present invention, it is possible to protect the rotating shaft system of a turbine generator connected to the power transmission system in which the series capacitor is installed from failures caused by the development of self-excited vibrations. Moreover, it is also possible to efficiently operate the series capacitor.

The present invention will be described below with reference to an embodiment shown in FIG.

Reference numeral 1 denotes high-pressure and low-pressure turbines, which are connected to a generator 2, and whose rotating shafts form a straight line and constitute a rotating shaft system Z. Note that the output of the generator 2 is connected to a power transmission system (not shown), and a series capacitor is inserted.

Reference numeral 11 indicates a tooth ring disposed at a fixed position x _p of the rotation axis system Z. Reference numeral 12 indicates a pick-up disposed opposite the tooth ring 11.

That is, the tooth ring 11 has, for example, 60 tooth profiles formed at equal intervals, and the pick-up 12 generates one pulse each time one of the tooth profiles passes. Reference numeral 13 denotes a torsional vibration meter which receives the output of the pickup 12 and measures the torsional vibration at a fixed position x _p , and calculates the torsional vibration Y (x _p , t) by differentiating the pulse interval emitted by the pickup 12.
can be obtained. These tooth rings 11 and pick-up 1
2. The torsional vibration detecting device is composed of the torsional vibration meter 13, but in order to improve the detection accuracy, the tooth ring 11 is
It is also possible to increase the number of .

Reference numeral 14 denotes a first filter, which is a mode component having a frequency lower than the commercial frequency of the turbine generator, among the natural vibration modes of the rotating shaft system _Z , of the torsional vibration Y (x _p t) at the fixed position x p. (for example, the first-order and second-order mode components), 〓 ⁱ⁼³ Yi(x _p , t) is removed.

15 and 15' are band pulse filters,
The sum of torsional vibrations that have passed through the first filter 14 and have a frequency lower than the power transmission system frequency.
It allows only corresponding ones of Y ₁ (x _p , t) + Y ₂ (x _p , t) to pass through, and those that have passed through the band pulse filter 15 are primary mode components.
Y ₁ (x _p , t) and band pulse filter 15'
The one passing through is the second-order mode component Y ₂ (x _p , t)
It is. The first filter 14 and the two band pulse filters 15, 15' constitute a decomposition device.

16, 16' are multipliers, 17, 17' are setters, and constant αi is used to obtain the i-th stress Vi (xi) at an arbitrary position xi (i=1, 2) shown in equation (7). (xi) Gi(xi)/Gi(x _p ) (i=1, 2) are stored in the setters 17, 17', respectively, and the output Yi(x _p ,
t) in multipliers 16 and 16'.

These multipliers 16, 16' and setters 17, 7
1' constitutes a mode-specific arithmetic unit, but
The arbitrary position xi for one vibration mode is not limited to one, but may be calculated at a plurality of positions.

Reference numerals 18 and 18' are peak detectors that detect the peak values of stress obtained by the multipliers 16 and 16'. If the stress waveform V ₁ (x ₁ ) at the position x ₁ is obtained, then its peak value V ^k ₁ (x ₁ )K=1·2 is detected.

19 to 21 and 19' to 21' are comparators, and 22 to 24 and 22' to 24' are setters _.
The values δ ₁ to δ ³ ₁ of the stress caution, warning, and danger inspection levels are respectively set in the setting devices 22' to 24', and similar values δ ¹ ₂ to δ ³ ₂ at the position x ₂ are set, respectively. The outputs of the peak detectors 18, 18' and their set values are compared by a comparator 19 or the like. For example, the comparator 19 outputs when the Kth peak V ^k ₁ (x ₁ ) is larger than δ ₁ ' and V ^K+1 ₁ (x ₁ ) is also larger than δ ₁ ', thereby eliminating error movements due to spike noise, etc. It is prevented.

The outputs of comparators 19 and 19' are sent to alarm A.
The outputs of the comparators 20, 20' also generate a signal T ₁ which eliminates the series capacitor, and furthermore the outputs of the comparators 21, 20'
The output of 21' generates a trip signal _T2 for disconnecting the generator output from the power grid.

When self-excited vibration occurs due to the double resonance of the vibration of the power transmission system in which the series capacitor is inserted and the torsional vibration of the rotating shaft system of the turbine generator, it will last from several seconds to several seconds, depending on the damping rate of the torsional vibration of the rotating shaft system. There is a possibility that the vibration will grow to such a huge extent that the rotating shaft system will break down within ten seconds, but in the monitoring device according to one embodiment of the present invention, all measurements, calculations, and judgments are performed electrically. It has a fast response speed and functions well as a monitoring device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional monitoring device, FIG. 2 is a diagram showing primary and secondary mode shapes and proportionality constants, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is the stress diagram obtained at position x ₁ . 1: Turbine, 2: Generator, 11: Tooth ring, 1
2: Pickup, 13: Vibration meter, 14: First filter, 15: Band pass filter, 16: Multiplier, 17: Setting device, 18: Peak detector, 19
to 21: comparator, 22 to 24: setting device,
Z: Rotation axis system.

Claims (1)

[Claims] 1 A device for monitoring the rotating shaft system of a turbine generator connected to a power transmission system equipped with a series capacitor, which includes a vibration detection device that detects torsional vibration at a fixed position of the rotating shaft system, and a vibration detection device that detects torsional vibration at a fixed position of the rotating shaft system. A decomposition device that decomposes and extracts only the mode component having a frequency lower than the commercial frequency of the turbine generator out of the natural frequencies of the rotating shaft system of the obtained vibration waveform, and a rotation at the above mode component determined in advance. A mode-specific calculation device that calculates the stress for each mode component at the arbitrary position from the relationship between the vibration at a fixed position of the shaft system and the vibration at an arbitrary position, and the relationship between the vibration and stress at the same arbitrary position, and the calculated stress A rotating shaft system torsional vibration monitoring device comprising a comparator that compares the stress with a preset value and issues a command when the stress exceeds the set value.