JPS6343979B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a shaft voltage monitoring device for a rotating machine.

(Prior art) Turbine generators and other types of rotating machinery may generate shaft voltage due to electrical or mechanical causes, but if the value becomes excessive, the shaft may be directly or indirectly driven by the rotating shaft. This induces shaft current in the control device that is being used and the bearing that supports the rotating shaft.
There is a risk of electrical discharge and associated electrolytic corrosion.

In order to prevent such shaft voltage generation, conventionally,
A widely used method is to release the voltage generated in the rotating shaft to the ground using a shaft grounding device. This shaft grounding device is shown in FIG. A current collecting brush 3 is attached to a stationary part 2 of the rotating machine so as to be in contact with a rotating shaft 1 of the rotating machine. With this current collecting brush 3, the rotating shaft 1 and the stationary part 2 are brought to the same potential, and then connected to the ground 3 via the grounding wire 4 provided on the stationary part 2.
0 to ground point 5. Figure 2 also shows a conventional shaft grounding device, but the current collector brush 3 is connected to the stationary part 2.
An electrical insulating material 6 is interposed between the parts when the parts are attached to each other. For this reason, a grounding wire 8 is provided that directly connects the current collecting brush 3 to the grounding point 5. Therefore, the voltage generated on the rotating shaft is released from the current collector brush 3 to the ground 30 via the ground wire 4 (ground wire 8 in FIG. 2).

On the other hand, the shaft voltage itself has conventionally been measured by temporary wiring at the site using a portable DC voltmeter as part of regular site patrols approximately every week.

(Problems to be Solved by the Invention) The conventional shaft grounding device as described above has a drawback in that it is extremely difficult to determine whether or not the grounding function is being maintained normally during its use. In other words, the degree of wear on the current collector brush 3 is determined by periodic dimensional measurements and visual inspection, but this only estimates the grounding function as an indirect measure of the amount of wear, and is not useful for the purpose of functional monitoring. Sufficient accuracy cannot be expected. Furthermore, in order to make the determination, it is necessary to go to the actual installation location of the current collecting brush 3, which has the drawback of placing a large burden on the operator.

Furthermore, the shaft voltage monitoring method as described above has the following problems. Figure 3 shows the results of a long-term continuous recording test regarding the DC component shaft voltage of a large steam turbine, which is a typical rotating machine. As can be seen from Figure 3, the shaft voltage is normally relatively stable at a small value, but when some kind of stress is applied, it suddenly modulates and suddenly increases not only in absolute value but also in the width of fluctuation. It shows a tendency to This means that not only the DC component but also the AC component is increasing as the shaft voltage. Discharge phenomena in minute gaps occur both under DC voltage and AC voltage, and there is a lower limit voltage for generation. Taking these things into consideration, it is insufficient to monitor the DC component alone in shaft voltage, and it is necessary to monitor the AC component as well. Furthermore, as shown in FIG. 3, if the situation suddenly changes, intermittent monitoring has little meaning, and continuous monitoring is necessary.

In addition, "monitoring" as used in this specification means that when the state of the monitored object reaches a preset state, the device itself generates an alarm, etc., and proactively notifies operators who are not necessarily in a monitoring state. It is not only used in this sense, but if an operator is in a monitoring mode, it can be used to mean ``instruction in a manner that allows determination of whether or not the condition of the monitored object has become a predetermined abnormal condition'', It is used in a meaning that includes "measuring and recording so that it can be determined whether the state has reached a predetermined abnormal state or not."

The present invention has been made in consideration of the above circumstances, and allows an operator to easily determine whether there is an abnormality in the shaft grounding device by continuously monitoring the DC and AC components of the shaft voltage, and based on the indicated values. The purpose of the present invention is to provide a shaft voltage monitoring device that can be used.

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, the present invention includes a plurality of current collecting brushes that are in contact with a rotating shaft of a rotating machine, a grounding wire that grounds at least one of the current collecting brushes,
a separation circuit that separates an electric signal between an ungrounded brush and a grounded brush in the current collecting brush into a DC signal and an AC signal; and a DC signal and an AC signal separated by the separation circuit are each predetermined. The shaft voltage monitoring device is characterized in that it is equipped with a monitoring means for monitoring whether or not the voltage exceeds a set value.

(Example) Examples of the present invention will be described below with reference to FIGS. 4 to 9.

FIG. 4 shows a first embodiment of the present invention. A shaft grounding device consisting of a current collecting brush 3a and a grounding wire 8 is attached to one end of the rotating shaft 1. Further, a current collecting brush 3b is attached to the other end of the rotating shaft 1 with the same dimensions as the shaft grounding device, and an electric signal obtained thereby is transmitted to the monitoring device 15 via a cable 7. In the monitoring device 15, this signal is passed through a low pass filter 11 as a separation circuit to extract only the DC component, and the same signal is passed through a high pass filter 12 as a separation circuit to extract the DC component as well. The signal is separated into a DC signal and an AC signal, and each is input to the monitoring instrument 20. The monitoring instrument 20 has a DC signal detection end 16, an AC signal detection end 17, and a grounding wire 8 connected to the grounding point 5.
The voltage between the terminal and the ground terminal 18, which is the output terminal of the terminal, is monitored. Monitoring by the monitoring instrument 20 is performed, for example, by detecting whether the DC signal and the AC signal each exceed a predetermined value. 5 to 7 show embodiments of such a monitoring instrument 20. FIG. Figure 5 shows DC signal end 1
The DC signal at the AC signal end 17 is monitored by a DC voltmeter 21, and the AC signal at the AC signal end 17 is monitored by an AC voltmeter 22. In FIG. 6, an AC/DC converter 13 is connected to a high-pass filter 12 to convert an alternating current signal into a direct current signal. Reference numeral 23 denotes a scanner, which switches the input signals of the detection terminals 16 and 17 at appropriate time intervals and inputs them to the DC voltmeter 21. 7th
The figure shows a dot type with built-in scanner 23 shown in Figure 6.
An example using a DC voltage recorder 25 will be shown. In addition,
This dotting type DC voltage recorder 25 may be a continuous pen writing type voltage recorder. Further, the voltmeters 21 and 22 in FIGS. 5 and 6 may each be used as an alarm setting device, and may have only a monitoring function of issuing an alarm only when the shaft voltage reaches a certain value.

With such a configuration, the DC component and AC component of the shaft voltage can be continuously monitored. In particular, in the monitoring instrument shown in FIG. 6, the number of voltmeters can be reduced. Furthermore, voltmeters 21 and 2
If 2 is used as an alarm setting device, monitoring can be performed more easily.

FIG. 8 shows a second embodiment of the invention. Regarding the two current collecting brushes 3a and 3b, both have the same configuration for monitoring shaft voltage. That is, the signals from the current collecting brushes 3a and 3b are applied to low-pass filters 11a and 11b and high-pass filters 12a and 12b via cables 7a and 7b, and the outputs of these filters are input to the monitoring instrument 20. Switches 14a and 14b are interposed between the current collecting brushes 3a and 3b and the grounding wires 8a and 8b.
Therefore, it is possible to arbitrarily switch between the shaft grounding function and the shaft voltage monitoring function at both ends of the rotating shaft 1.

Because of this configuration, in this embodiment, when abnormal shaft voltage is observed on the shaft voltage monitoring side,
By closing the switch 14a or 14b of the system and grounding it to the earth 30, abnormal shaft voltage can be prevented and the operator can be provided with a specific method of handling when abnormal shaft voltage occurs. Furthermore, it is possible that the abnormal shaft voltage is caused by an abnormality in the current collecting brush, and a work instruction to inspect the current collecting brush can be given.

FIG. 9 shows a third embodiment of the present invention. There are two systems at each end of the rotating shaft 1.
That is, current collector brushes 3a and 3c are provided at one end of the rotating shaft.
in contact with the switches 14a and 14 respectively.
c, low-pass filters 11a, 11c, and high-pass filters 12a, 12c are connected, and their outputs are input to the monitoring instrument 20. Current collector brushes 3b and 3d are in contact with the other end of the rotating shaft, and are equipped with switches 14b and 14d, low-pass filters 11b and 11d, and high-pass filters 12b and 1, respectively.
2d are connected and their outputs are input to the monitoring instrument 20.

With this configuration, in this embodiment, it is possible to check the contact status of each current collection brush. That is, one current collecting brush 3 of the rotating shaft 1
a and 3c are installed at the same position with respect to the axial direction of the rotating shaft 1, and should exhibit equipotential.
Therefore, when there is an extreme difference in potential between the current collecting brushes 3a and 3c, it can be seen that either the current collecting brush 3a or 3c is abnormal. Which current collecting brush is abnormal can be determined by closing each switch 14a or 14c and observing the change. That is, when one switch 14a is closed, the system is connected to the ground point 5, so the voltage is zero, but if the current collector brush 3a is abnormal and there is a connection with the rotating shaft 1. If the contact is not good, the voltage of the current collecting brush 3c will not become zero. Therefore, it can be determined that the current collecting brush 3a is abnormal.

As described above, in this embodiment, not only can accuracy be improved by double measuring the shaft voltage at both ends of the rotating shaft, but also the contact status of the current collecting brush can be confirmed by operating a switch. In other words, inspection can be performed remotely without directly approaching the rotating machine. This is extremely important, especially in cases where access to the site is not easy, such as with nuclear turbines.

The above is an example applied to a single-axis rotating machine.
If the rotary machine is constructed of a multi-shaft system such as a large steam turbine, each shaft may be constructed as in the above embodiment. Although it is possible to provide a monitoring instrument for each axis, the same monitoring instrument may be used for monitoring.

〔Effect of the invention〕

As described above, the present invention brings a plurality of current collecting brushes into contact with the rotating shaft of a rotating machine, at least one of them is grounded, and electrical signals between the ungrounded current collecting brushes and the grounded current collecting brushes are transmitted. Since the DC and AC components are separated and monitored, continuous monitoring of the shaft voltage is possible, and operators can easily determine whether there is an abnormality in the shaft grounding device. Furthermore, compared to measurements made on-site using temporary wiring using a portable voltmeter, the burden on the operator can be significantly reduced. Furthermore, since safe operation of the rotating machine can be ensured, its reliability in long-term operation can be greatly improved.

[Brief explanation of the drawing]

Figures 1 and 2 are conventional shaft grounding devices, Figure 3 is a continuous shaft voltage record in a large steam turbine, and Figure 4 is a continuous shaft voltage record in a large steam turbine.
The figure shows a shaft voltage monitoring device that is a first embodiment of the present invention, Figures 5, 6, and 7 are examples of a monitoring instrument, and Figure 8 shows a shaft voltage monitor that is a second embodiment of the present invention. Voltage Monitoring Device FIG. 9 shows a withstand voltage monitoring device according to a third embodiment of the present invention. 1... Rotating shaft, 2... Stationary part, 3... Current collection brush, 4
...Ground wire, 6...Insulator, 8...Ground wire, 11...Low pass filter, 12...High pass filter, 1
3... AC/DC converter, 14... Switch, 1
5... Monitoring device, 20... Monitoring instrument, 21... DC voltmeter, 22... AC voltmeter, 25... Voltage recorder, 30
...Earth.

Claims (1)

[Claims] 1. A plurality of current collecting brushes in contact with a rotating shaft of a rotating machine, a grounding wire that grounds at least one of the current collecting brushes, and a non-grounded brush and a grounded brush among the current collecting brushes. a separation circuit that separates an electrical signal between the two into a DC signal and an AC signal, and a monitoring means that monitors whether the DC signal and AC signal separated by the separation circuit each exceed a predetermined value. An axial voltage monitoring device characterized by comprising: 2. In the device according to claim 1,
An axial voltage monitoring device comprising a switch configured to connect any one of the current collecting brushes to the grounding wire. 3. In the device according to claim 1,
A shaft voltage monitoring device characterized in that a plurality of current collecting brushes are brought into contact with each of the same locations on the rotating shaft, and electrical signals from each of these current collecting brushes are extracted. 4. The shaft voltage monitoring device according to any one of claims 1 to 3, wherein the monitoring means includes a voltmeter that measures the DC signal and the AC signal. 5. The shaft voltage monitoring device according to any one of claims 1 to 3, wherein the monitoring means includes a voltage recorder that measures and records the DC signal and the AC signal. Device. 6. In the device according to any one of claims 1 to 3, the monitoring means has an alarm setting that issues an alarm when the DC signal and the AC signal exceed the predetermined value. An axial voltage monitoring device comprising: