A multi-band passive filter loop shaft voltage diagnosis and suppression device and method

Abstract

A multi-band passive filtering circuit shaft voltage diagnosis and suppression device and method, which relates to the technical field of electrical equipment state detection and diagnosis, and solves the problem of how to measure and suppress abnormal shaft voltage under different operating conditions during the operation of a large generator; one end of an electrostatic effect discharge switch is connected in parallel with one end of multiple filtering frequency selection switches, the other end of the electrostatic effect discharge switch is connected to one end of a current-limiting resistor, and the other end of the current-limiting resistor is grounded; one end of a fuse is connected to the large shaft of the generator's excitation end, and the other end of the fuse is connected to the common point of the parallel connection of the electrostatic effect discharge switch and multiple filtering frequency selection switches; the other ends of multiple filtering frequency selection switches are respectively connected to the input ends of multiple passive band-pass filters, and the output ends of multiple passive band-pass filters are respectively connected to the common point of the connection between the electrostatic effect discharge switch and the current-limiting resistor; a voltmeter is connected in parallel across the current-limiting resistor; the circuit structure is simple, the measurement range is wide, it is convenient to find out the cause of abnormal shaft voltage, and the effective management of shaft voltage is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment state detection and diagnosis, and in particular to a multi-band passive filter circuit shaft voltage diagnosis and suppression device and method. Background Art

[0002] When a rotor shaft of a high-speed rotating electrical machine is operating normally, a certain shaft voltage will be generated. If the shaft voltage suppression and protection measures are not appropriate, once a circuit is formed, shaft current will be generated. A strong shaft current will generate electric arcs, rapidly deteriorate lubrication, and cause electro-corrosion of the shaft neck and bearing alloy, resulting in failures. At the same time, a strong shaft current will also cause serious equipment magnetization, leading to failures such as vibration, resulting in shutdown accidents.

[0003] During the operation of the unit, the main reasons for the possible generation of shaft voltage mainly include the following three aspects:

[0004] 1. Shaft voltage and its hazards caused by electrostatic effects

[0005] The shaft voltage generated by electrostatic effects is mainly in the form of a high potential on the rotor large shaft caused by the accumulation of static charges. When the steam end grounding brush is in good contact, the static charges can transfer the potential to the ground potential through the steam end grounding brush; due to insufficient tightness after the brush wears, oil stains or other impurities interference, it may cause the large shaft at the steam end to be unable to be grounded well, thus causing a significant increase in the shaft voltage of the rotor large shaft.

[0006] Due to the friction between dry steam and turbine blades in the low-pressure cylinder of a large steam turbine generator set, high-speed steam generates static charges on the turbine rotor, or due to poor shaft seals of the steam turbine connected coaxially with the generator, high-speed steam leaks along the shaft or steam jets at high speed in the cylinder, etc., causing the shaft to carry static charges. The static charges charge the shaft capacitance related to the grounding condition, thereby generating shaft voltage. The shaft voltage induced by the accumulation of static charges. The large shaft of a steam turbine generator set is often composed of many sections of rotating shafts, such as the high-pressure rotor, intermediate-pressure rotor, low-pressure rotor, generator rotor, exciter rotor, and sub-exciter rotor of the steam turbine. These rotors are connected into a whole, called the shafting. The entire shafting is supported by several radial bearings (journal bearings) and axial bearings (thrust bearings). The support points on the shaft are called journal bearings. When the steam turbine generator is running at full speed, the entire large shaft floats on the oil film between all journal bearings and bearing bushes. Therefore, the potential of the large shaft is a floating potential.

[0007] According to the basic theory of electrical engineering, when a metal in a floating potential state rubs against other media, positive or negative static charges will accumulate; when a metal in a floating potential state generates charges and it is difficult to release them (because the oil film of the bearing bush has a high insulation resistance), a high potential may be accumulated. The large shaft of a steam turbine generator set exactly meets these two conditions. Because the high-speed rotation of the steam turbine blades rubs against the steam, the last 1-2 stages of blades rub against the air, the main oil pump impeller of the steam turbine rubs against the lubricating oil, the fan on the generator rotor rubs against hydrogen or air, etc., static electricity will accumulate on the large shaft. The accumulated static charges, whether positive or negative, are concentrated at the tips of the steam turbine blades and rotate at high speed with the steam turbine rotor. Also according to the basic theory of electrical engineering, the static charges rotating at high speed will generate eddy currents on the cylinder wall of the steam turbine. Because the cylinder wall of the steam turbine is made of thick metal and the eddy currents are large, the large eddy currents not only cause energy loss, but also burn the upper and lower joint surfaces of the cylinder and the fastening bolts of the joint surfaces, damaging the equipment. In addition, the high voltage generated by the accumulation of static charges on the large shaft is most likely to generate discharges on the oil film, because the gap size of the oil film is the smallest, which causes the bearing bush to burn and also gradually deteriorates the quality of the lubricating oil.

[0008] The method to solve the above problems is to ground the large shaft. After grounding, the large shaft is no longer a metal body with a floating potential, and the charges are released to the ground through the grounding point, so that the large shaft cannot accumulate charges. The grounding point of the large shaft is generally installed on the shaft section between the low-pressure cylinder of the steam turbine and the generator, because this section of the general steam turbine generator set is the only exposed shaft section.

[0009] 2. Shaft voltage caused by asymmetry of the generator magnetic circuit and its hazards

[0010] The shaft voltage caused by asymmetry of the generator magnetic circuit is mainly composed of a 50Hz fundamental frequency voltage component, accompanied by some 3rd harmonic components of 150Hz and 5th harmonic components of 250Hz.

[0011] Due to the shaft voltage caused by asymmetry of the generator magnetic circuit, according to the reasons for the asymmetry of the magnetic circuit, it can be divided into the following three types:

[0012] 1) Shaft voltage caused by flux asymmetry: It is impossible to ensure absolute symmetry of the magnetic circuit during the manufacture of the generator. Therefore, during the operation of the generator, the magnetic flux linked by the loop formed by the large shaft, bearing, and platen alternates, and an alternating potential will be generated on the large shaft, and this potential has the characteristics of the fundamental wave. When the loop formed by the large shaft, journal, bearing bush, bearing housing, and platen is connected for some reason, due to the very low loop resistance, a large shaft current will be generated, causing damage to the components of the relevant shaft current loop.

[0013] 2) Axial voltage generated by inter-turn short circuit of generator rotor winding: If an inter-turn short circuit occurs, the axial magnetic fluxes generated by the two sets of coils cannot be completely cancelled out, resulting in an axial unbalanced magnetic flux. The more turns short-circuited, the greater the unbalanced axial magnetic flux. When this magnetic flux is superimposed on the axial magnetic flux or the value of the axial magnetic flux itself reaches a certain level, a relatively high monopole voltage will be generated between the journal and the oil film. Once the oil film is broken down, it is very likely to cause damage to the bearing bush.

[0014] 3) Axial voltage generated by magnetization of the motor shaft: After the steam turbine generator set is magnetized for some reason, there are circumferential and axial residual magnetic fields, and monopole voltages are induced by the residual magnetic fields in the rotor and bearing components. As described above, this induced voltage will exist in the bearings and shaft seals, that is, from the blades through the diaphragm, diaphragm sleeve, cylinder, bearings with damaged oil film, and the shaft back to the blades. Thus, a large current can cause damage to the corresponding components, and the magnetic flux generated by this current may also magnetize the steam turbine circumferentially.

[0015] 3. Axial voltage and its hazards caused by external voltage

[0016] The axial voltage caused by external voltage is mainly 300 Hz, that is, the 6th harmonic, and is accompanied by some 50 Hz fundamental frequency voltage components.

[0017] 1) Influence of static excitation device: The high-frequency voltage pulses generated during the commutation of thyristors in the self-excited excitation system will generate high-frequency voltage pulses between the bearing bush and the oil film of the journal. Once the oil film is broken down, it is very likely to cause damage to the parts where the corresponding shaft current flows through.

[0018] 2) Axial voltage generated by the active rotor winding protection device: In the generator rotor protection device, rotor grounding protections such as one-point grounding protection with superimposed DC, one-point grounding excitation protection with superimposed AC voltage admittance principle, and one-point grounding protection of the excitation circuit with superimposed square wave voltage are adopted. In the principle design, axial voltage will be generated between the bearing bush and the oil film of the journal through the coupling of the insulation capacitance and resistance related to the grounding condition. Once the oil film is broken down, it is very likely to cause damage to the parts where the corresponding shaft current flows through.

[0019] In summary, the key to preventing the harm of shaft voltage lies in preventing the formation of a path for shaft current. As long as an effective loop interruption can be achieved, the above problems can be prevented. Therefore, insulation must be used between the bearing at the excitation end of the motor and the generator and the base plate, and between the bearing and the oil pipe to interrupt the path. Since the shaft voltage is usually very small (not higher than 10V), only very low insulation conditions are required to prevent current generation. To limit the shaft voltage and interrupt the loop composed of the shafting, bearing bush, and base, current small units generally install insulating gaskets under the bearing seat on the excitation side of the generator, and large units generally install two layers of insulating gaskets on the bearing ring to let this high-strength insulating material bear the shaft voltage, so as to avoid the oil film being broken down due to excessive voltage. During the operation of the generator, due to installation or other reasons, the insulating gasket may be damaged, aged, or have oil stains accumulated, and then lose its insulating function. Then the entire shaft voltage is applied to the oil film. The oil film during the high-speed rotation of the generator is very thin and is easily broken down and spark discharged. Since the discharge loop resistance composed of the generator shafting, bearing bush, and base is very low, and the voltage energy is large, a relatively large shaft current will be generated, resulting in the burning of the bearing bush babbit and the rapid deterioration of the sealing oil quality.

[0020] In the prior art, Wang Yu (North China Electric Power University) disclosed a measure for preventing and controlling the shaft voltage of a generator in the literature "Research on Shaft Voltage and Electrical Corrosion of Bearing Bush of Large Steam Turbine Generator". The prevention and control of the shaft voltage of the generator is achieved by grounding the RC circuit on the excitation side. However, only 1 group of RC passive filter circuits is set in this literature, and only the monitoring of a single frequency component (300Hz) of the shaft voltage can be realized, that is, the interference of high-frequency pulse signals generated by the thyristor commutation of the static excitation system is excluded; the monitored shaft voltage frequency range is narrow.

[0021] Therefore, for large generators, during operation, due to improper measures for suppressing and protecting the shaft voltage, harmful shaft currents are generated at components such as the generator bearings, bearing bushes, and gears, which can cause oil film breakdown, electrical corrosion of the bearing bushes, and electrochemical corrosion. In severe cases, it may cause a significant increase in the vibration of the generator bearing bushes, accelerate the deterioration of the lubricating oil quality, hydrogen leakage from the unit, and even shutdown accidents. How to measure abnormal shaft voltage and how to suppress shaft voltage is an urgent problem to be solved. Summary of the Invention

[0022] The purpose of the present invention is to solve the problem of how to measure and suppress abnormal shaft voltage under different working conditions during the operation of large generators.

[0023] The present invention solves the above technical problems through the following technical solutions:

[0024] A multi - band passive filtering circuit shaft voltage diagnosis and suppression device, comprising an electrostatic effect discharge switch (K0), multiple filtering frequency selection switches, multiple passive band - pass filters, a voltmeter (26), a current - limiting resistor (r), and a fuse (F); one end of the electrostatic effect discharge switch (K0) is connected in parallel with one end of the multiple filtering frequency selection switches, the other end of the electrostatic effect discharge switch (K0) is connected to one end of the current - limiting resistor (r), and the other end of the current - limiting resistor (r) is grounded; one end of the fuse (F) is connected to the generator excitation end large shaft (16), and the other end of the fuse (F) is connected to the parallel common point of the electrostatic effect discharge switch (K0) and the multiple filtering frequency selection switches; the other ends of the multiple filtering frequency selection switches are respectively connected to the input ends of the multiple passive band - pass filters, and the output ends of the multiple passive band - pass filters are respectively connected to the connection common point of the electrostatic effect discharge switch (K0) and the current - limiting resistor (r); the voltmeter (26) is connected in parallel across both ends of the current - limiting resistor (r); the center frequencies of the multiple passive band - pass filters are continuously adjustable between 50 Hz and 300 Hz; the diagnosis and suppression of the shaft voltage generated by the electrostatic effect are achieved by switching on and off the electrostatic effect discharge switch (K0); by sequentially switching on and off the multiple filtering frequency selection switches, the multiple passive band - pass filters with corresponding different circuit parameters are switched on and off, so as to realize the spectrum analysis, abnormal diagnosis, and harmonic suppression of the shaft voltage of the generator excitation end large shaft to the ground.

[0025] The device of the present invention aims at the influencing factors and respective signal amplitude characteristics of shaft voltage anomalies caused by different working conditions. By switching on and off filtering circuits with different circuit parameters and cooperating with the current - limiting resistor (r), the fuse (F), and the voltmeter (26), multiple passive band - pass filters that are continuously adjustable between 50 Hz and 300 Hz are used to realize the spectrum analysis, abnormal diagnosis, and harmonic suppression of the shaft voltage of the generator excitation end large shaft (16) to the ground. The circuit structure is simple and the measurement range is wide.

[0026] As a further improvement of the technical solution of the present invention, the circuit structures of the multiple passive band-pass filters are the same, and each includes a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth variable resistor (R4), a fifth variable resistor (R5), a sixth variable resistor (R6), a first operational amplifier (D1), a second operational amplifier (D2), a first capacitor (C1), and a second capacitor (C2); one end of the first resistor (R1) is a voltage input terminal, the other end of the first resistor (R1) is connected in series with one end of the second resistor (R2), and the other end of the second resistor (R2) is grounded; one end of the third resistor (R3) is connected to the series common terminal of the first resistor (R1) and the second resistor (R2), and the other end is connected to the non-inverting input terminal of the first operational amplifier (D1), the inverting input terminal of the first operational amplifier (D1) is connected to the output terminal of the first operational amplifier (D1), one end of the sixth variable resistor (R6) is connected to the output terminal of the first operational amplifier (D1), and the other end is connected in series with one end of the second capacitor (C2), and the other end of the second capacitor (C2) is connected to the inverting input terminal of the second operational amplifier (D2); one end of the fourth variable resistor (R4) is connected to the series common point of the sixth variable resistor (R6) and the second capacitor (C2), and the other end is grounded; one end of the first capacitor (C1) is connected to the series common point of the sixth variable resistor (R6) and the second capacitor (C2), and the other end is connected to the output terminal of the second operational amplifier (D2); one end of the fifth variable resistor (R5) is connected to the inverting input terminal of the second operational amplifier (D2), and the other end is connected to the output terminal of the second operational amplifier (D2); the non-inverting input terminal of the second operational amplifier (D2) is grounded.

[0027] As a further improvement of the technical solution of the present invention, the multiple filter frequency selection switches include a first filter frequency selection switch (K1), a second filter frequency selection switch (K2), a third filter frequency selection switch (K3), a fourth filter frequency selection switch (K4), a fifth filter frequency selection switch (K5), and a sixth filter frequency selection switch (K6); the multiple passive band-pass filters include a first RC passive band-pass filter (20), a second RC passive band-pass filter (21), a third RC passive band-pass filter (22), a fourth RC passive band-pass filter (23), a fifth RC passive band-pass filter (24), and a sixth RC passive band-pass filter (25);

[0028] One ends of the described electrostatic effect discharge switch (K0), first filter frequency selection switch (K1), second filter frequency selection switch (K2), third filter frequency selection switch (K3), fourth filter frequency selection switch (K4), fifth filter frequency selection switch (K5), and sixth filter frequency selection switch (K6) are connected together; the other end of the electrostatic effect discharge switch (K0) is connected to one end of the current-limiting resistor (r); the other end of the first filter frequency selection switch (K1) is connected to the input end of the first RC passive band-pass filter (20), and the output end of the first RC passive band-pass filter (20) is connected to one end of the current-limiting resistor (r); the other end of the second filter frequency selection switch (K2) is connected to the input end of the second RC passive band-pass filter (21), and the output end of the second RC passive band-pass filter (21) is connected to one end of the current-limiting resistor (r); the other end of the third filter frequency selection switch (K3) is connected to the input end of the third RC passive band-pass filter (22), and the output end of the third RC passive band-pass filter (22) is connected to one end of the current-limiting resistor (r); the other end of the fourth filter frequency selection switch (K4) is connected to the input end of the fourth RC passive band-pass filter (23), and the output end of the fourth RC passive band-pass filter (23) is connected to one end of the current-limiting resistor (r); the other end of the fifth filter frequency selection switch (K5) is connected to the input end of the fifth RC passive band-pass filter (24), and the output end of the fifth RC passive band-pass filter (24) is connected to one end of the current-limiting resistor (r); the other end of the sixth filter frequency selection switch (K6) is connected to the input end of the sixth RC passive band-pass filter (25), and the output end of the sixth RC passive band-pass filter (25) is connected to one end of the current-limiting resistor (r).

[0029] As a further improvement of the technical solution of the present invention, the center frequency of the first RC passive band-pass filter (20) is 50 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.2 uF.

[0030] As a further improvement of the technical solution of the present invention, the center frequency of the second RC passive band-pass filter (21) is 100 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 4 kΩ, R5 = 100 kΩ, R6 = 5 kΩ, C1 = C2 = 0.1 uF.

[0031] As a further improvement of the technical solution of the present invention, the center frequency of the third RC passive band-pass filter (22) is 150 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 6 kΩ, R5 = 95 kΩ, R6 = 5 kΩ, C1 = C2 = 0.067 uF.

[0032] As a further improvement of the technical solution of the present invention, the center frequency of the fourth RC passive band-pass filter (23) is 200 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 3 kΩ, R5 = 130 kΩ, R6 = 6 kΩ, C1 = C2 = 0.05 uF.

[0033] As a further improvement of the technical solution of the present invention, the center frequency of the fifth RC passive band-pass filter (24) is 250 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.04 uF.

[0034] As a further improvement of the technical solution of the present invention, the center frequency of the sixth RC passive band-pass filter (25) is 300 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 1.5 kΩ, R5 = 190 kΩ, R6 = 10 kΩ, C1 = C2 = 0.033 uF.

[0035] An axial voltage diagnosis and suppression method using the multi-band passive filtering loop axial voltage diagnosis and suppression device described above includes the following:

[0036] (1) Diagnosis and suppression of axial voltage generated by electrostatic effect;

[0037] 1) Diagnosis: Close the electrostatic effect discharge switch (K0), a good path is formed between the large shaft of the generator excitation end (16) and the ground, and static charges are injected into the ground through the excitation end grounding loop. Use a voltmeter (26) to measure that the amplitude of the axial voltage drops rapidly; disconnect the electrostatic effect discharge switch (K0), after the unit runs for a period of time, use a voltmeter (26) to measure that the axial voltage rises again, and it is judged that the abnormal increase in axial voltage is caused by the electrostatic effect;

[0038] 2) Suppression: Such abnormal increase in axial voltage is usually caused by poor grounding of the large shaft at the steam end of the unit, and it is treated by replacing the constant voltage spring, replacing the carbon rod or multi-point grounding at the steam end, etc.;

[0039] (2) Diagnosis and suppression of axial voltage caused by asymmetry of the generator magnetic circuit;

[0040] 1) Diagnosis: After the multiple filter frequency selection switches are turned on and off in sequence, and the band-pass filtering is performed through multiple passive band-pass filters respectively, at this time, the voltmeter (26) is used to measure the corresponding shaft voltage respectively. When the amplitude of the fundamental frequency voltage component is large and contains the 3rd harmonic and 5th harmonic components, it is judged that the abnormal increase in the shaft voltage is caused by the asymmetry of the generator magnetic circuit;

[0041] 2) Suppression: Such abnormal increase in the shaft voltage is usually caused by the factor of short circuit fault in the rotor turn. Therefore, it is necessary to combine the unit shutdown and maintenance to carry out timely treatment;

[0042] (3) Diagnosis and suppression of the shaft voltage and its hazards caused by external voltage;

[0043] 1) Diagnosis: After the multiple filter frequency selection switches are turned on and off in sequence, and the shaft voltage passes through multiple passive band-pass filters for band-pass filtering respectively, at this time, the voltmeter (26) is used to measure the corresponding shaft voltage respectively. When the amplitude of the 6th harmonic component is large and contains some fundamental frequency voltage components, it is judged that the abnormal increase in the shaft voltage is caused by external voltage;

[0044] 2) Suppression: Such abnormal increase in the shaft voltage is caused by the factor that the high-frequency voltage pulse generated during the thyristor commutation of the self-excited static excitation system is coupled to the rotor shaft. The instantaneous amplitude is relatively high, and it has a greater impact on the oil film and bearing insulation; for such defects, by keeping the corresponding filter frequency selection switch normally closed, the circuit between the generator excitation end shaft (16) and the ground is kept conducting, and the 6th harmonic component is eliminated to achieve the treatment of such abnormal shaft voltage.

[0045] The advantages of the present invention are as follows:

[0046] (1) The device of the present invention aims at the influencing factors and their respective signal amplitude characteristics of the abnormal shaft voltage caused by different working conditions. By turning on and off the filter circuits with different circuit parameters and cooperating with the current-limiting resistor (r), fuse (F), and voltmeter (26), multiple passive band-pass filters continuously adjustable between 50Hz and 300Hz are used to realize the spectrum analysis, abnormal diagnosis, and harmonic suppression of the shaft voltage of the generator excitation end shaft (16) to the ground. The circuit structure is simple and the measurement range is wide.

[0047] (2) The method of the present invention can not only realize the monitoring of the 50Hz - 300Hz components, but also further judge the possible reasons for the abnormal shaft voltage through the magnitude of the different frequency component amplitudes of the actually monitored shaft voltage. In addition, after finding out the reason for the abnormal shaft voltage, if the unit maintenance window period has not arrived, the effective treatment of the shaft voltage can also be realized by closing the selection switch of the corresponding filter frequency. Description of the Drawings

[0048] Figure 1Schematic circuit diagram of an axial voltage diagnosis and suppression device for a multi-band passive filter circuit according to an embodiment of the present invention;

[0049] Figure 2 Schematic circuit diagram of a passive band-pass filter of an axial voltage diagnosis and suppression device for a multi-band passive filter circuit according to an embodiment of the present invention. Specific embodiments

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0051] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0052] Embodiment 1

[0053] As Figure 1 shown, a large generator system includes a steam turbine rotor shaft 10, a steam turbine 11, a coupling 12, a grounding carbon brush 13, a generator rotor shaft 14, a generator 15, and a generator excitation end shaft 16; the steam turbine rotor shaft 10, the steam turbine 11, the coupling 12, the grounding carbon brush 13, the generator rotor shaft 14, the generator 15, and the generator excitation end shaft 16 are connected in sequence.

[0054] As Figure 1 shown, a multi-band passive filter circuit axial voltage diagnosis and suppression device includes an electrostatic effect discharge switch K0, a first filter frequency selection switch K1, a second filter frequency selection switch K2, a third filter frequency selection switch K3, a fourth filter frequency selection switch K4, a fifth filter frequency selection switch K5, a sixth filter frequency selection switch K6, a first RC passive band-pass filter 20, a second RC passive band-pass filter 21, a third RC passive band-pass filter 22, a fourth RC passive band-pass filter 23, a fifth RC passive band-pass filter 24, a sixth RC passive band-pass filter 25, a voltmeter 26, a current-limiting resistor r, and a fuse F.

[0055] One ends of the described static electricity effect discharge switch K0, the first filter frequency selection switch K1, the second filter frequency selection switch K2, the third filter frequency selection switch K3, the fourth filter frequency selection switch K4, the fifth filter frequency selection switch K5, and the sixth filter frequency selection switch K6 are connected in parallel together; One end of the fuse F is connected to the large shaft 16 at the excitation end of the generator, and the other end of the fuse F is connected to the parallel common point of the static electricity effect discharge switch K0 and multiple filter frequency selection switches; The other end of the static electricity effect discharge switch K0 is connected to one end of the current-limiting resistor r; The other end of the first filter frequency selection switch K1 is connected to the input end of the first RC passive band-pass filter 20, and the output end of the first RC passive band-pass filter 20 is connected to one end of the current-limiting resistor r; The other end of the second filter frequency selection switch K2 is connected to the input end of the second RC passive band-pass filter 21, and the output end of the second RC passive band-pass filter 21 is connected to one end of the current-limiting resistor r; The other end of the third filter frequency selection switch K3 is connected to the input end of the third RC passive band-pass filter 22, and the output end of the third RC passive band-pass filter 22 is connected to one end of the current-limiting resistor r; The other end of the fourth filter frequency selection switch K4 is connected to the input end of the fourth RC passive band-pass filter 23, and the output end of the fourth RC passive band-pass filter 23 is connected to one end of the current-limiting resistor r; The other end of the fifth filter frequency selection switch K5 is connected to the input end of the fifth RC passive band-pass filter 24, and the output end of the fifth RC passive band-pass filter 24 is connected to one end of the current-limiting resistor r; The other end of the sixth filter frequency selection switch K6 is connected to the input end of the sixth RC passive band-pass filter 25, and the output end of the sixth RC passive band-pass filter 25 is connected to one end of the current-limiting resistor r; The other end of the current-limiting resistor r is grounded; The voltmeter 26 is connected in parallel across both ends of the current-limiting resistor r.

[0056] The described grounding carbon brush 13 is in direct contact with the large shaft at the excitation end of the rotor, and is composed of a constant voltage spring, a carbon rod, and a brush holder. Its function is to achieve a reliable connection between the large shaft of the rotor and the filter detection circuit under the condition of rotation of the large shaft, and form a path with the monitoring and diagnosis device; The fuse F is used to protect the entire monitoring circuit and prevent the filter circuit from being broken down or causing personal safety risks due to excessive shaft voltage when the carbon brush contacts the large shaft of the rotor; The current-limiting resistor r is used to limit the current magnitude of the entire shaft voltage monitoring circuit and avoid the capacitor breakdown that may be caused by the peak shaft voltage; The voltmeter 26: is connected in parallel across both ends of the current-limiting resistor r. By reading the value of the voltmeter, the magnitude of the voltage of the large shaft 16 at the excitation end of the generator with respect to the ground and the amplitudes of different frequency components from 50 Hz to 300 Hz are determined.

[0057] As Figure 2As shown, the circuit structures of the first RC passive band-pass filter 20, the second RC passive band-pass filter 21, the third RC passive band-pass filter 22, the fourth RC passive band-pass filter 23, the fifth RC passive band-pass filter 24, and the sixth RC passive band-pass filter 25 are the same, and each includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth variable resistor R4, a fifth variable resistor R5, a sixth variable resistor R6, a first operational amplifier D1, a second operational amplifier D2, a first capacitor C1, and a second capacitor C2.

[0058] One end of the first resistor R1 is a voltage input terminal, the other end of the first resistor R1 is connected in series with one end of the second resistor R2, and the other end of the second resistor R2 is grounded; one end of the third resistor R3 is connected to the series common terminal of the first resistor R1 and the second resistor R2, and the other end is connected to the non-inverting input terminal of the first operational amplifier D1. The inverting input terminal of the first operational amplifier D1 is connected to the output terminal of the first operational amplifier D1. One end of the sixth variable resistor R6 is connected to the output terminal of the first operational amplifier D1, and the other end is connected in series with one end of the second capacitor C2. The other end of the second capacitor C2 is connected to the inverting input terminal of the second operational amplifier D2; one end of the fourth variable resistor R4 is connected to the series common point of the sixth variable resistor R6 and the second capacitor C2, and the other end is grounded; one end of the first capacitor C1 is connected to the series common point of the sixth variable resistor R6 and the second capacitor C2, and the other end is connected to the output terminal of the second operational amplifier D2; one end of the fifth variable resistor R5 is connected to the inverting input terminal of the second operational amplifier D2, and the other end is connected to the output terminal of the second operational amplifier D2; the non-inverting input terminal of the second operational amplifier D2 is grounded.

[0059] Parameter design: For the voltage with a frequency of 50 Hz, the parameters of the first RC passive band-pass filter 20 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.2 uF; for the voltage with a frequency of 100 Hz, the parameters of the second RC passive band-pass filter 21 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 4 kΩ, R5 = 100 kΩ, R6 = 5 kΩ, C1 = C2 = 0.1 uF; for the voltage with a frequency of 150 Hz, the parameters of the third RC passive band-pass filter 22 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 6 kΩ, R5 = 95 kΩ, R6 = 5 kΩ, C1 = C2 = 0.067 uF; for the voltage with a frequency of 200 Hz, the parameters of the fourth RC passive band-pass filter 23 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 3 kΩ, R5 = 130 kΩ, R6 = 6 kΩ, C1 = C2 = 0.05 uF; for the voltage with a frequency of 250 Hz, the parameters of the fifth RC passive band-pass filter 24 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.04 uF; for the voltage with a frequency of 300 Hz, the parameters of the sixth RC passive band-pass filter 25 are designed as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 1.5 kΩ, R5 = 190 kΩ, R6 = 10 kΩ, C1 = C2 = 0.033 uF.

[0060] The parameter settings of the band-pass filter are as follows in the table:

[0061] Center frequency R1 (Ω) R2 (Ω) R3 (Ω) R4 (Ω) R5 (Ω) R6 (Ω) C1 = C2 (uF) 50 Hz 50k 10k 10k 2k 160k 8k 0.2 100 Hz 50k 10k 10k 4k 100k 5k 0.1 150 Hz 50k 10k 10k 6k 95k 5k 0.067 200 Hz 50k 10k 10k 3k 130k 6k 0.05 250 Hz 50k 10k 10k 2k 160k 8k 0.04 300 Hz 50k 10k 10k 1.5k 190k 10k 0.033

[0062] An axial voltage diagnosis and suppression method for an axial voltage diagnosis and suppression device of a multi-band passive filtering circuit using the above is specifically as follows:

[0063] 1. Diagnosis and suppression of axial voltage generated by electrostatic effect

[0064] 1) Diagnosis: Close the electrostatic effect discharge switch K0, a good path is formed between the large shaft 16 at the excitation end of the generator and the ground, and the static charge is injected into the ground through the grounding circuit at the excitation end. Use a voltmeter 26 to measure that the amplitude of the axial voltage drops rapidly; disconnect the electrostatic effect discharge switch K0, after the unit operates for a period of time, use a voltmeter 26 to measure that the axial voltage rises again, and it is judged that the abnormal increase in axial voltage is caused by the electrostatic effect.

[0065] 2) Suppression: Such abnormal increase in axial voltage is usually caused by poor grounding of the large shaft at the steam end of the unit. It is treated by replacing the constant voltage spring, replacing the carbon rod or multi-point grounding at the steam end, etc.

[0066] 2. Diagnosis and Suppression of Shaft Voltage Caused by Asymmetry of Generator Magnetic Circuit

[0067] 1) Diagnosis: Successively turn on and off the first filter frequency selection switch K1, the second filter frequency selection switch K2, the third filter frequency selection switch K3, the fourth filter frequency selection switch K4, the fifth filter frequency selection switch K5, and the sixth filter frequency selection switch K6. After the shaft voltage passes through the first RC passive band-pass filter 20, the second RC passive band-pass filter 21, the third RC passive band-pass filter 22, the fourth RC passive band-pass filter 23, the fifth RC passive band-pass filter 24, and the sixth RC passive band-pass filter 25 for band-pass filtering respectively, use the voltmeter 26 to measure the corresponding shaft voltage at this time. When the amplitude of the fundamental frequency voltage component is large and contains the third harmonic and fifth harmonic components, it is judged that the abnormal increase in shaft voltage is caused by the asymmetry of the generator magnetic circuit.

[0068] 2) Suppression: Such abnormal increase in shaft voltage is usually caused by the factor of short circuit fault in the rotor turn. Therefore, it is necessary to combine the unit shutdown for maintenance and timely treatment.

[0069] 3. Diagnosis and Suppression of Shaft Voltage and Its Harm caused by External Voltage

[0070] 1) Diagnosis: Successively turn on and off the first filter frequency selection switch K1, the second filter frequency selection switch K2, the third filter frequency selection switch K3, the fourth filter frequency selection switch K4, the fifth filter frequency selection switch K5, and the sixth filter frequency selection switch K6. After the shaft voltage passes through the first RC passive band-pass filter 20, the second RC passive band-pass filter 21, the third RC passive band-pass filter 22, the fourth RC passive band-pass filter 23, the fifth RC passive band-pass filter 24, and the sixth RC passive band-pass filter 25 for band-pass filtering respectively, use the voltmeter 26 to measure the corresponding shaft voltage at this time. When the amplitude of the sixth harmonic component is large and contains some fundamental frequency voltage components, it is judged that the abnormal increase in shaft voltage is caused by external voltage;

[0071] 2) Suppression: Such abnormal increase in shaft voltage is caused by the factor that the high-frequency voltage pulse generated during the thyristor commutation of the self-excited static excitation system is coupled to the rotor shaft. The instantaneous amplitude is relatively high, which has a greater impact on the oil film and bearing insulation. For such defects, by keeping the sixth filter frequency selection switch K6 normally closed and keeping the circuit between the generator excitation end shaft 16 and the ground conducting, the sixth harmonic component is eliminated, and the treatment of such abnormal shaft voltage is realized.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for diagnosing and suppressing shaft voltage using a multi - band passive filter circuit shaft voltage diagnosis and suppression device, the multi - band passive filter circuit shaft voltage diagnosis and suppression device comprising: Electrostatic effect discharge switch (K0), multiple filter frequency selection switches, multiple passive band-pass filters, voltmeter (26), current-limiting resistor (r), fuse (F); One end of the electrostatic effect discharge switch (K0) is connected in parallel with one end of multiple filter frequency selection switches, the other end of the electrostatic effect discharge switch (K0) is connected to one end of the current-limiting resistor (r), and the other end of the current-limiting resistor (r) is grounded; One end of the fuse (F) is connected to the large shaft of the generator excitation end (16), and the other end of the fuse (F) is connected to the parallel common point of the electrostatic effect discharge switch (K0) and multiple filter frequency selection switches; The other ends of the multiple filter frequency selection switches are respectively connected to the input ends of multiple passive band-pass filters, and the output ends of the multiple passive band-pass filters are respectively connected to the connection common point of the electrostatic effect discharge switch (K0) and the current-limiting resistor (r); The voltmeter (26) is connected in parallel across both ends of the current-limiting resistor (r); The center frequencies of the multiple passive band-pass filters are continuously adjustable between 50 Hz and 300 Hz; The diagnosis and suppression of the shaft voltage generated by the electrostatic effect are carried out by switching on and off the electrostatic effect discharge switch (K0); By sequentially switching on and off multiple filter frequency selection switches, the multiple passive band-pass filters with corresponding different circuit parameters are switched on and off to realize the spectrum analysis, abnormal diagnosis and harmonic suppression of the shaft voltage between the generator excitation end large shaft and the ground; It is characterized in that the shaft voltage diagnosis and suppression method includes the following contents: (1) Diagnosis and suppression of the shaft voltage generated by the electrostatic effect; 1) Diagnosis: Close the electrostatic effect discharge switch (K0), a good path is formed between the large shaft of the generator excitation end (16) and the ground, and the static charge is injected into the ground through the excitation end grounding loop. Use the voltmeter (26) to measure that the amplitude of the shaft voltage drops rapidly; Disconnect the electrostatic effect discharge switch (K0), and after the unit runs for a period of time, use the voltmeter (26) to measure that the shaft voltage rises again, and it is judged that the abnormal increase in the shaft voltage is caused by the electrostatic effect; 2) Suppression: Such abnormal increase in the shaft voltage is caused by poor grounding of the large shaft at the steam end of the unit, and it is treated by replacing the constant voltage spring, replacing the carbon rod or multi-point grounding at the steam end; (2) Diagnosis and suppression of the shaft voltage caused by the asymmetry of the generator magnetic circuit; 1) Diagnosis: After sequentially switching on and off multiple filter frequency selection switches and respectively performing band-pass filtering through multiple passive band-pass filters, at this time use the voltmeter (26) to measure the corresponding shaft voltage respectively. When the amplitude of the fundamental frequency voltage component is large and contains the 3rd harmonic and 5th harmonic components, it is judged that the abnormal increase in the shaft voltage is caused by the asymmetry of the generator magnetic circuit; 2) Suppression: Such abnormal increase in the shaft voltage is usually caused by the factor of short circuit fault between rotor turns. Therefore, it is necessary to combine the shutdown and maintenance of the unit for timely treatment; (3) Diagnosis and suppression of the shaft voltage and its hazards caused by external voltage; 1) Diagnosis: The multiple filter frequency selection switches are turned on and off in sequence. After the shaft voltage passes through multiple passive band-pass filters for band-pass filtering respectively, the voltmeter (26) is used to measure the corresponding shaft voltage at this time. When the amplitude of the 6th harmonic component is large and contains some fundamental frequency voltage components, it is judged that the abnormal increase in the shaft voltage is caused by the external voltage. 2) Suppression: The abnormal increase in such shaft voltage is caused by the factor that the high-frequency voltage pulse generated during the thyristor commutation of the static excitation system with self-excitation and constant excitation is coupled to the large shaft of the rotor. The instantaneous amplitude is high, and it has a great impact on the oil film and bearing insulation. For such defects, by keeping the corresponding filter frequency selection switch normally closed and keeping the circuit between the large shaft (16) of the generator excitation end and the ground conducting, the 6th harmonic component is eliminated, and the governance of such abnormal shaft voltage is realized.

2. The method for diagnosing and suppressing shaft voltage according to claim 1, wherein, The circuit structures of the multiple passive band-pass filters are the same, and each includes a first resistor (R1), a second resistor (R2), a third resistor (R3), a fourth variable resistor (R4), a fifth variable resistor (R5), a sixth variable resistor (R6), a first operational amplifier (D1), a second operational amplifier (D2), a first capacitor (C1), and a second capacitor (C2); one end of the first resistor (R1) is the voltage input end, and the other end of the first resistor (R1) is connected in series with one end of the second resistor (R2), and the other end of the second resistor (R2) is grounded; one end of the third resistor (R3) is connected to the series common end of the first resistor (R1) and the second resistor (R2), and the other end is connected to the non-inverting input end of the first operational amplifier (D1). The inverting input end of the first operational amplifier (D1) is connected to the output end of the first operational amplifier (D1). One end of the sixth variable resistor (R6) is connected to the output end of the first operational amplifier (D1), and the other end is connected in series with one end of the second capacitor (C2). The other end of the second capacitor (C2) is connected to the inverting input end of the second operational amplifier (D2); one end of the fourth variable resistor (R4) is connected to the series common point of the sixth variable resistor (R6) and the second capacitor (C2), and the other end is grounded; one end of the first capacitor (C1) is connected to the series common point of the sixth variable resistor (R6) and the second capacitor (C2), and the other end is connected to the output end of the second operational amplifier (D2); one end of the fifth variable resistor (R5) is connected to the inverting input end of the second operational amplifier (D2), and the other end is connected to the output end of the second operational amplifier (D2); the non-inverting input end of the second operational amplifier (D2) is grounded.

3. The method for diagnosing and suppressing shaft voltage according to claim 1, wherein, The multiple filtering frequency selection switches include a first filtering frequency selection switch (K1), a second filtering frequency selection switch (K2), a third filtering frequency selection switch (K3), a fourth filtering frequency selection switch (K4), a fifth filtering frequency selection switch (K5), and a sixth filtering frequency selection switch (K6); the multiple passive band-pass filters include a first RC passive band-pass filter (20), a second RC passive band-pass filter (21), a third RC passive band-pass filter (22), a fourth RC passive band-pass filter (23), a fifth RC passive band-pass filter (24), and a sixth RC passive band-pass filter (25). One ends of the electrostatic effect discharge switch (K0), the first filtering frequency selection switch (K1), the second filtering frequency selection switch (K2), the third filtering frequency selection switch (K3), the fourth filtering frequency selection switch (K4), the fifth filtering frequency selection switch (K5), and the sixth filtering frequency selection switch (K6) are connected together; the other end of the electrostatic effect discharge switch (K0) is connected to one end of the current-limiting resistor (r); the other end of the first filtering frequency selection switch (K1) is connected to the input end of the first RC passive band-pass filter (20), and the output end of the first RC passive band-pass filter (20) is connected to one end of the current-limiting resistor (r); the other end of the second filtering frequency selection switch (K2) is connected to the input end of the second RC passive band-pass filter (21), and the output end of the second RC passive band-pass filter (21) is connected to one end of the current-limiting resistor (r); the other end of the third filtering frequency selection switch (K3) is connected to the input end of the third RC passive band-pass filter (22), and the output end of the third RC passive band-pass filter (22) is connected to one end of the current-limiting resistor (r); the other end of the fourth filtering frequency selection switch (K4) is connected to the input end of the fourth RC passive band-pass filter (23), and the output end of the fourth RC passive band-pass filter (23) is connected to one end of the current-limiting resistor (r); the other end of the fifth filtering frequency selection switch (K5) is connected to the input end of the fifth RC passive band-pass filter (24), and the output end of the fifth RC passive band-pass filter (24) is connected to one end of the current-limiting resistor (r); the other end of the sixth filtering frequency selection switch (K6) is connected to the input end of the sixth RC passive band-pass filter (25), and the output end of the sixth RC passive band-pass filter (25) is connected to one end of the current-limiting resistor (r).

4. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the first RC passive band-pass filter (20) is 50 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.2 uF.

5. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the second RC passive band-pass filter (21) is 100 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 4 kΩ, R5 = 100 kΩ, R6 = 5 kΩ, C1 = C2 = 0.1 uF.

6. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the third RC passive band-pass filter (22) is 150 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 6 kΩ, R5 = 95 kΩ, R6 = 5 kΩ, C1 = C2 = 0.067 uF.

7. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the fourth RC passive band-pass filter (23) is 200 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 3 kΩ, R5 = 130 kΩ, R6 = 6 kΩ, C1 = C2 = 0.05 uF.

8. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the fifth RC passive band-pass filter (24) is 250 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 2 kΩ, R5 = 160 kΩ, R6 = 8 kΩ, C1 = C2 = 0.04 uF.

9. The method for diagnosing and suppressing shaft voltage according to claim 3, wherein, The center frequency of the sixth RC passive band-pass filter (25) is 300 Hz; the parameter design is as follows: R1 = 50 kΩ, R2 = 10 kΩ, R3 = 10 kΩ, R4 = 1.5 kΩ, R5 = 190 kΩ, R6 = 10 kΩ, C1 = C2 = 0.033 uF.

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