CN113311307B - Diode open-circuit fault detection method for three-phase brushless exciter rotating rectifier - Google Patents
Diode open-circuit fault detection method for three-phase brushless exciter rotating rectifier Download PDFInfo
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Abstract
The invention discloses a method for detecting open circuit fault of a diode of a rotating rectifier of a three-phase brushless exciter, which comprises the following steps: A. respectively installing vibration sensors in the horizontal direction and the vertical direction of shafts at two ends of an exciter, and receiving signals at the output end of the vibration sensors through a data acquisition and analysis system; B. determining an expression of air gap flux density after an open circuit fault of a diode of the rotating rectifier; C. determining the rotor stress and the vibration characteristic frequency caused by the open circuit fault of the diode of the rotating rectifier; D. determining a fault threshold value of the harmonic amplitude of the vibration characteristic of the rotor; E. and if the amplitude of the rotor vibration characteristic harmonic wave is larger than the fault threshold value, judging that the diode of the rotary rectifier has an open-circuit fault, otherwise, judging that the diode of the rotary rectifier is normal. The invention can improve the defects of the prior art and improve the diagnosis reliability of the open-circuit fault of the diode of the rotating rectifier of the brushless exciter.
Description
Technical Field
The invention relates to the technical field of brushless exciters, in particular to a method for detecting open-circuit faults of diodes of a rotating rectifier of a three-phase brushless exciter.
Background
Compared with the traditional brush excitation mode, the brushless excitation mode has the advantages of large output excitation current, low noise, small pollution, low failure rate, simple maintenance and the like, and is the preferred excitation mode of the current 1000 MW-level large generator set. The rotary rectifier is a key and weak link in a brushless excitation system, and the rectifier diode works with high rotating speed and high load of the generator for a long time and bears huge centrifugal force and electromagnetic action, so that open-circuit faults of the rectifier diode frequently occur. The open-circuit fault of the diode of the rotary rectifier is generally a single-tube fault at the initial stage, and if early warning and processing are not timely, the open-circuit fault may evolve to a vicious situation of multi-tube faults. In 2014, a main transformer C-phase high-voltage side of a machine of a No. 3 nuclear power station in China has a fault, so that an excitation system channel is switched, a rotating diode one-phase failure alarm occurs in the machine of No. 1 after about 3s, and a rotating diode two-phase failure tripping signal occurs after about 9 s. Because the capacity born by the rectifier diodes is larger when the brushless exciter normally operates, after a single diode in the rotary rectifier breaks down, other normal diodes are overloaded, so that the state deterioration speed of the normal diodes is accelerated, the vicious situation of multi-tube failure of the rotary rectifier in a short time is possibly caused, and the safe and stable operation of the unit is seriously influenced. Therefore, real-time monitoring on the open-circuit fault of the rotating diode of the brushless exciter is necessary, and the development of the on-line diagnosis method for the open-circuit fault of the rotating diode with high sensitivity and strong stability has important practical significance on safe operation of a large generator set.
The brushless excitation system consists of a pivot type alternating current generator and a rotary rectifier, and a pivot type alternating current generator rotor, the rotary rectifier and a main generator rotor are coaxially assembled to form the brushless excitation synchronous generator set commonly used in the current nuclear power station. Because the rotating rectifier rotates synchronously with the generator when the unit operates normally, the fault information of the diode in the rectifier cannot be directly acquired, which brings certain difficulty to the on-line diagnosis of the diode fault of the rotating rectifier. The diagnosis method for the open-circuit fault of the diode of the rotary rectifier is characterized in that experts and scholars at home and abroad carry out a great deal of research to obtain some achievements, and the detection method mainly proposed at present comprises the following steps: DNC (diode non-conduction detection system) method, neon indicator lamp frequency detection method, exciter exciting current harmonic method, generator end voltage spectrum analysis method and U-shaped detection coil method.
The DNC method is one of the diode open-circuit fault detection methods widely used in the present external rotor brushless exciter, the Hall probes (generally three probes are fixed) are fixed on the exciter stator side, the probes are close to the rectifier bridge arm and armature winding lead wire, when the armature branch connected with normal diode is passed through the Hall probes, the voltage pulse can be induced in the probes, so that it can be used for detecting the open-circuit fault of external rotor brushless exciterWhen an armature branch circuit connected with the barrier diode sweeps across the Hall probe, voltage pulse can not be induced in the probe, and the on-off state of the diode on the bridge arm connected with each lead wire is reversely deduced according to the quantity of the induced voltage pulse of the Hall probe. The DNC method has good applicability and a fault positioning function, can visually reflect the on-off state of the rotary rectifier, but the Hall sensor has poor stability, and is easy to have the problems of inaccurate measurement caused by the displacement of a unit due to vibration, signal distortion caused by oil stain or dust pollution and the like. According to the neon indicator lamp frequency detection method, a rectifier diode is connected with a fuse light-emitting tube in series, and the fault of the diode is identified according to the flash frequency of the fuse light-emitting tube. The method is a manual detection method, cannot be used as a real-time monitoring means, and is generally only used as an auxiliary monitoring means. The detection principle of the exciter exciting current harmonic method is as follows: in the brushless excitation generator set, an armature winding of an alternating current exciter, a rotating rectifier bridge and a main generator excitation winding form a closed loop, when an open-circuit fault occurs in a rotating rectifier bridge diode, armature branch current connected with a fault diode is zero, asymmetric armature current generates armature harmonic magnetic potential, the harmonic magnetic potential induces harmonic current in an excitation winding of the exciter, and the open-circuit fault of the rotating diode can be detected by utilizing specific harmonic components in the excitation current. Based on the method, the open-circuit fault characteristic analysis of the rotating diode of the nuclear power multi-phase angle type brushless excitation system published in 2019 in the automated journal of the power system researches the harmonic characteristics of the exciting current when one tube of the rotating diode of the nuclear power 11 phase angle type brushless excitation machine is open-circuit and one phase is open-circuit, and the researches show that fundamental wave and 2,3 and 4 … … harmonics appear in the exciting current when one tube of the rotating diode is open-circuit, 2, 4 and 6 … … even harmonics appear in the exciting current when one phase of the rotating diode is open-circuit, and the amplitude is 2 times of the component amplitude of the even harmonic of the exciting current when one tube of the rotating diode is open-circuit. The text "Study of branched excitation system estimation based on improved generation algorithm" uses the ratio R of fundamental frequency component to direct current component in the excitation current to determine the fault type of the rotating diode, R<10% rotating diode Normal, 10%<R<55% rotating diode is open circuit fault, R>A 55% rotating diode is a short circuit fault. The detection principle of the generator end voltage spectrum analysis method is as follows: after the rotating diode fails, harmonic current can be generated in exciting current of the main generator, further, harmonic magnetic potential is generated in air gap magnetic potential of the main generator, harmonic voltage is induced in an armature winding of a stator of the generator by the harmonic magnetic potential, and the fault of the rotating diode is detected through specific frequency harmonic components in terminal voltage of the generator. The text of protection of Brushless excitation Diodes surfaces by Spectral Analysis of Main Output Voltage researches terminal Voltage characteristic harmonics of the conditions of open-circuit fault and short-circuit fault of a Rotating diode respectively, and researches show that the terminal Voltage of a generator mainly contains (2k + 1) p omega harmonic component (wherein k is a constant, p is the pole pair number of the generator, and omega is the rotation frequency of a rotor of the generator) when the diode is normal; [ (2k + 1) p +/-p ] will appear in the generator terminal voltage after the diode has open circuit fault and short circuit fault ex ]Harmonic component of Ω (where p ex Pole pair number of exciter) and the fault frequency distinguishes the diode fault type by combining 6 harmonic amplitudes in the terminal voltage, the 6 harmonic amplitude is less than 20dB for diode open-circuit fault, and the 6 harmonic amplitude is more than 20dB for diode short-circuit fault. The text "Excitation control of a harmonic synchronous motor" determines the type of rotating diode according to the ratio R of the amplitudes of the 2 nd harmonic and the 9 th harmonic in the output voltage of the rotating rectifier, 20%<R<30% of rotating diodes are normal, 30%<R<40% of rotating diodes are short-circuit faults, 40%<R<A 50% rotating diode is an open circuit fault. The invention patent CN107843805A 'brushless exciter rotating diode open-circuit fault on-line diagnosis method' proposes that a U-shaped detection coil is installed at a branch position in a magnetic pole of an exciter stator yoke, when an open-circuit fault occurs in a rotating diode, armature incremental magnetic potential appears near an armature branch connected with the fault diode, the magnetic potential rotates synchronously with an armature, harmonic induction potential with the same rotating frequency as a rotor is induced in the U-shaped detection coil, and the open-circuit fault of the rotating diode can be identified by the harmonic potential. The article "Research on an online diagnostics for detecting diode faults in a three-phase short excitation with two coils" further proposes that the spatial positions on the exciter stator yoke differ by 1Two U-shaped coils are arranged at the position of 80 degrees, and the open-circuit fault of the diode is detected according to the difference condition of induced potentials of the two U-shaped coils.
The method is established on the electromagnetic characteristics of the exciter, in order to improve the utilization level and the diagnosis reliability of vibration information of faults of rotating diodes of the exciter, the vibration frequency characteristics of the rotor caused by the faults of the diodes are also emphasized, and the diagnosis level of the faults can be further improved by comprehensively considering the fault characteristics.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for detecting the open-circuit fault of the diode of the three-phase brushless exciter rotating rectifier, which can solve the defects of the prior art and improve the diagnosis reliability of the open-circuit fault of the diode of the brushless exciter rotating rectifier.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows.
A three-phase brushless exciter rotating rectifier diode open-circuit fault detection method comprises the following steps:
A. respectively installing vibration sensors in the horizontal direction and the vertical direction of shafts at two ends of an exciter, and receiving signals at the output end of the vibration sensors through a data acquisition and analysis system;
B. determining an air gap flux density expression after the diode of the rotating rectifier has an open circuit fault;
C. determining the rotor stress and the vibration characteristic frequency caused by the open circuit fault of the diode of the rotating rectifier;
D. determining a fault threshold value of the harmonic amplitude of the vibration characteristic of the rotor;
E. and if the vibration characteristic harmonic amplitude of the rotor is larger than the fault threshold value, judging that the diode of the rotary rectifier has open-circuit fault, otherwise, judging that the diode of the rotary rectifier is normal.
Preferably, in the step B, the step C,
when the rotating diode is normal, the air gap magnetic potential of the exciter is synthesized by the excitation magnetic potential and the armature magnetic potential to obtain a Fourier series expression of the excitation magnetic potential in a rotor coordinate system:
if the current of the armature winding keeps unchanged after the armature winding is conducted when the exciter normally runs, and the armature winding is conducted only in two phases at any time, the Fourier series expression of the armature magnetic potential in a rotor coordinate system is as follows:
according to the formula (2) and the formula (3), the air gap magnetic potential of the exciter when the diode is normal is obtained as follows:
a Fourier series expression of armature magnetic potential increment delta F in a rotor coordinate system:
theta in the above formula r ' by theta r +θ 0 Instead, the formula (4) and the formula (3) are located in the same coordinate system, and Δ F (θ) after coordinate conversion r ') is:
and (3) enabling the air gap magnetic potential of the exciter after the diode fault to be equivalent to the sum of the air gap magnetic potential when the diode is normal and the armature increment magnetic potential generated after the diode fault, wherein the air gap magnetic potential of the exciter after the diode fault is as follows:
F δ (θ r )＝F f1 cosP(θ r +γ)+F a1 cosP(θ r -α)+ΔF m cosm(θ r +θ 0 ) (6)，
air gap permeance lambda δ (θ r ) Expressed as:
the exciter air gap flux density after diode failure is:
the x-axis component and the y-axis component of the unbalanced magnetic pulling force of the rotor under the rotor coordinate system after the diode fails are as follows:
from the above formula, F +1, 3P-1, 3P +1, 5P-1, and 5P +1 are only present when m = P-1 x And F y The magnetic field is not equal to zero, namely only P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 subharmonics of armature magnetic potential increment can generate unbalanced magnetic pull force on the rotor after the diode fails; the method includes the steps that m = P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 are brought into the above two formulas, and the x-axis component and the y-axis component of unbalanced magnetic pull of the rotor are obtained and are respectively as follows:
as can be known from the above formula, the number of times of armature increment magnetic potential harmonic waves for changing the vibration state of the rotor is P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1, and P is the pole pair number of the brushless exciter.
As a preferenceIn step C, the characteristic frequency of the fault after the diode of the rotating rectifier is open-circuit fault is omega r /2π、(P±1)ω r /2π、(2P±1)ω r /2π、(3P±1)ω r N 2 pi, where ω is r Is the mechanical angular velocity, omega, of the rotor r In units of rad/s.
Preferably, in step D, the failure determination threshold is set to:
wherein A, B, C, D is ω of the diode of the rotary rectifier under normal state r /2πHz、(P±1)ω r /2πHz、(2P±1)ω r [ 2 ] π Hz and (3P. + -. 1) ω r The/2 pi Hz harmonic vibration amplitude, delta A, delta B, delta C and delta D respectively represent omega after the diode of the rotating rectifier fails r /2πHz、(P±1)ω r /2πHz、(2P±1)ω r [ 2 ] π Hz and (3P. + -. 1) ω r The increment of the vibration amplitude of the/2 pi Hz harmonic is considered to be zero when the increment is zero or negative.
Adopt the beneficial effect that above-mentioned technical scheme brought to lie in:
1. the fault characteristic harmonic frequency of the diagnosis method provided by the invention is only related to the mechanical angular speed of the unit and the pole pair number of the exciter, and the method is suitable for inner rotor type three-phase brushless exciters with different rotating speeds and pole pair numbers and has good applicability.
2. Based on the mechanical characteristics of the brushless exciter, the invention can complete the online diagnosis of the running state of the rotating rectifier diode only by installing the vibration sensor and the matched data online acquisition and real-time analysis system in the horizontal direction and the vertical direction of the external shaft of the exciter. The method is simple, flexible and convenient to operate, does not affect the normal operation of the unit, can be matched with other diagnosis methods to diagnose the state of the diode simultaneously, and improves the reliability of diagnosis.
Drawings
FIG. 1 is a schematic diagram of a three-phase brushless excitation system;
FIG. 2 is a diagram of the brushless exciter armature winding coupling;
FIG. 3 is a waveform diagram of excitation magnetic potential in a stator coordinate system;
FIG. 4 is a waveform of the magnetic potential of the armature A, B phase in the conduction period of the armature winding AB;
FIG. 5 is a current distribution and a magnetic potential waveform diagram of the armature winding commutation process when the rotating diode is normal, wherein FIG. 5a is the conduction state at time AB (-) 0 time, and FIG. 5b is the conduction state at time AC 0 (+) time;
FIG. 6 is a current distribution and a magnetic potential waveform diagram of the armature winding commutation process at the time of a rotary diode failure, wherein FIG. 6a is a conduction state at time AB (-) 0, and FIG. 6b is a conduction state at time AC (+) 0;
FIG. 7 is a graph of armature magnetic potential delta during the AB/AC conduction period after a spinning diode failure;
FIG. 8 is a distribution diagram of armature magnetic potential increments in a rotor coordinate system;
FIG. 9 is a schematic view of the unbalanced magnetic pull of the rotor shown in vector form;
FIG. 10 is the resulting unbalanced magnetic pull force F for both normal and fault conditions of the rotating diode;
FIG. 11 is the unbalanced magnetic pull X-axis component for both normal and fault conditions of the rotating diode;
FIG. 12 is the Y-axis component of unbalanced magnetic pull in normal and fault conditions for a rotating diode;
FIG. 13 is a graph showing the resulting unbalanced magnetic pull force F spectrum when the rotating diode is normal;
FIG. 14 is a graph of the X-axis component spectrum of the unbalanced magnetic pull force when the rotating diode is normal;
FIG. 15 is a graph of the Y-axis component spectrum of the unbalanced magnetic pull force when the rotating diode is normal;
FIG. 16 is a graph of the resulting unbalanced magnetic pull force F spectrum at a rotating diode failure;
FIG. 17 is a graph of the X-axis component spectrum of the unbalanced magnetic pull force at the failure of a rotating diode;
FIG. 18 is a graph of the Y-axis component spectrum of the unbalanced magnetic pull force at the failure of a rotating diode.
Detailed Description
Symbol list: p, pole pair number of the brushless exciter; eta, windingThe distance angle of the coil on a single pole; omega r The mechanical angular velocity of the armature rotation; gamma, the included angle of the axes of the stator and the rotor; theta.theta. r The rotor space mechanical angle; theta.theta. s Stator space mechanical angle; n is a radical of hydrogen f The number of turns of each pole of excitation winding; i is f Exciting current of the exciter; n is a radical of a The total number of turns of each slot winding of the armature; i is a Effective value of phase current; α, armature slot angle (mechanical angle); lambda [ alpha ] 0 The constant term of the air gap permeance; lambda 2n The amplitude of each harmonic of the air gap flux guide; f f1 Excitation magnetic potential fundamental wave amplitude; f a1 The amplitude of the armature magnetic potential fundamental wave; b n (θ r ) Radial magnetic flux density; b t (θ r ) Tangential magnetic flux density; mu.s 0 Vacuum magnetic conductivity; r, the outer diameter of the rotor; l, rotor axial effective length; σ, the direction of the unbalanced magnetic pull; theta 0 The position angle of the difference between the longitudinal axes of the coordinate systems of the formula (5) and the formula (4); Δ F m M-th harmonic amplitudes of armature magnetic potential increments, where m is equal to 1,2,3, …, respectively.
One embodiment of the present invention comprises the steps of:
A. respectively installing vibration sensors in the horizontal direction and the vertical direction of shafts at two ends of an exciter, and receiving signals at the output end of the vibration sensors through a data acquisition and analysis system;
B. determining an expression of air gap flux density after an open circuit fault of a diode of the rotating rectifier;
C. determining the rotor stress and the vibration characteristic frequency caused by the open circuit fault of the diode of the rotating rectifier;
D. determining a fault threshold value of the harmonic amplitude of the vibration characteristic of the rotor;
E. and if the amplitude of the rotor vibration characteristic harmonic wave is larger than the fault threshold value, judging that the diode of the rotary rectifier has an open-circuit fault, otherwise, judging that the diode of the rotary rectifier is normal.
In the embodiment, a 5.8MW internal rotor type three-phase brushless exciter in a certain domestic motor factory is taken as an example, the structure diagram of an excitation system of the exciter is shown in figure 1, the wiring diagram of an armature winding is shown in figure 2, and the unit parameters are shown in table 1.
TABLE 1 5.8MW internal rotor type three-phase brushless exciter parameters
The rotating diode of the brushless exciter is directly connected with the armature winding, when the diode is normal, the air gap magnetic field of the exciter is symmetrical, and the resultant force of the electromagnetic force borne by the rotor is zero theoretically; when the diode fails and the failed diode is in conduction, the armature circuit is asymmetric due to the fact that the failed diode cannot be conducted, further asymmetry of an air-gap magnetic field is induced, and asymmetric air-gap magnetic flux density enables the rotor to bear unbalanced electromagnetic force and causes change of the vibration rule of the rotor iron core.
As can be seen from fig. 1, each branch of the armature winding of the brushless exciter is connected to a rectifying bridge arm, and according to the characteristics of the rectifying circuit, when the difference between the induced potentials of two phase armature windings reaches the maximum, the corresponding diode on the bridge arm connected to the two phase armature winding branches will be in a conducting state, so that the two phase armature windings are in a conducting state, and the same current flows through the two phase armature windings, and the other phase winding is in a turning-off state. The conduction sequence of the exciter armature winding is as follows: AB → AC → BC → BA → CA → CB, each conducting at 60 ° electrical angle. According to the conduction rule of the armature winding and the displacement characteristic of the armature magnetic field, the air gap magnetic potential of the exciter in each conduction period of the armature winding is the same, and the air gap magnetic potential of the exciter and the stress condition of the rotor are analyzed by taking the AB conduction period as an example.
When the rotating diode is normal, the air gap magnetic potential of the exciter is synthesized by the excitation magnetic potential and the armature magnetic potential, and a Fourier series expression of the excitation magnetic potential in a rotor coordinate system is obtained according to the figure 3:
neglecting the phase change process, assuming that the current remains unchanged after the armature winding is conducted when the exciter operates normally, the armature winding is conducted only in two phases at any time, and making a A, B phase armature magnetic potential waveform diagram of the armature winding AB conduction period when the diode operates normally, as shown in fig. 4 (in the diagram, the A phase magnetic potential is represented by a dotted line, and the B phase magnetic potential is represented by a solid line). According to fig. 4, considering that the armature magnetic potential is the composition of the magnetic potential of the conducting phase winding, the fourier series expression of the armature magnetic potential in the rotor coordinate system in the AB conducting period when the diode is normal is:
according to the formulas (2) and (3), the air gap magnetic potential of the exciter when the diode is normal is as follows:
according to the space symmetry and the similarity of the conduction rules of the armature windings, diodes on bridge arms connected with any phase and any branch can be taken as representatives, and the air gap magnetic potential and the rotor stress condition of the exciter after the fault is researched by taking the diode of the positive half-bridge arm of the 5 th branch (A5) of the A phase as an example.
Fig. 5 and 6 are graphs of current distribution and armature magnetic potential of the armature winding during AB → AC commutation under normal diode and a fault condition of the positive half-bridge arm diode of the A5 branch, respectively, and comparing the two graphs, it can be found that armature magnetic potential increment occurs near the fault diode branch after the diode fault, as shown in fig. 7. According to fig. 8, a fourier series expression of the armature magnetic potential increment Δ F in the rotor coordinate system is obtained:
theta in the above formula r ' by theta r +θ 0 Instead, equation (4) and equation (3) are located in the same coordinate systemCoordinate-converted Δ F (θ) r ') is:
considering only the fundamental wave of the excitation magnetic potential and the armature magnetic potential, considering that the air gap magnetic potential of the exciter after the diode fault can be equivalent to the sum of the air gap magnetic potential when the diode is normal and the armature increment magnetic potential generated after the diode fault, the air gap magnetic potential of the exciter after the diode fault is:
F δ (θ r )＝F f1 cosP(θ r +γ)+F a1 cosP(θ r -α)+ΔF m cosm(θ r +θ 0 ) (6)
the magnetic pole of the brushless exciter is usually a salient pole structure with uneven air gap and magnetic conductance lambda of the air gap δ (θ r ) Can be expressed as:
only the constant term and the second harmonic of the air gap permeance are considered, and according to the air gap permeance method, the density of the air gap flux of the exciter after the diode fails is as follows:
according to Maxwell stress Zhang Liangfa, the x-axis component and the y-axis component of the unbalanced magnetic pulling force of the rotor under the rotor coordinate system after the diode fails are obtained as follows:
from aboveAs can be seen from the above two formulas, F +1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 are only used when m = P-1 x And F y Not equal to zero, namely only the P-1, P +1, 3P-1, 3P +1, 5P-1, 5P +1 subharmonics of armature magnetic potential increment can generate unbalanced magnetic pull force on the rotor after the diode fails. The components of the x axis and the y axis of the unbalanced magnetic pulling force of the rotor are respectively obtained by substituting m = P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 into the above two formulas:
it can be seen from the unbalanced magnetic pulling force analytic expression that theoretically, after the diode fails, the unbalanced magnetic pulling force applied to the exciter rotor contains two components, one is a 200Hz component with the same frequency as the armature potential, and the other is a constant component rotating synchronously with the rotor. The magnitudes of the two components mainly depend on the fundamental amplitude of the excitation magnetic potential, the fundamental amplitude of the armature magnetic potential and the P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 harmonic amplitudes of armature magnetic potential increment.
Every time the armature of the brushless exciter rotates a pair of magnetic poles, the three-phase armature winding carries out 6 phase changes. When the positive half-bridge arm diode of the A5 branch has an open-circuit fault, in the conduction time periods of the AB phase and the AC phase of the armature winding (the two time periods are continuous and occupy 120-degree electrical angle in one electrical cycle), the A5 branch cannot be conducted due to the disconnection of the anode diode, so that the armature current distribution and the main magnetic field of the exciter are asymmetric, and the rotor bears unbalanced magnetic pull force; the armature windings are normally conducted in the conducting time period of the BC phase, the BA phase, the CA phase and the CB phase of the armature windings, the main magnetic field of the exciter is symmetrical, and the rotor does not bear unbalanced magnetic pull force. It follows that unbalanced magnetic pull forces are only present during the AB, AC conduction period of the armature winding. The 5.8MW internal rotor type three-phase brushless exciter studied in this embodiment has 8 pairs of poles, in each electrical cycle 360 ° (360 °/8 mechanical cycles), the A5 branch positive half-bridge arm diode should be turned on but cannot occupy 120 ° electrical angle during the turn-on period, at this time, a pulse electromagnetic force is generated, and the exciter recovers to normal without pulse electromagnetic force at other 240 ° electrical angles, so the inner rotor will be acted by 8 times of unbalanced magnetic pull force successively in one rotation cycle. As can be seen from fig. 9, in a single rotation period, the directions of the unbalanced magnetic pull pulses at different time points are changed, and each time the fault diode branch rotates through a pair of magnetic poles, the rotor is subjected to one unbalanced magnetic pull pulse, so that 8 unbalanced magnetic pull clusters with pulse properties are generated in total, and the 8 unbalanced magnetic pull clusters are uniformly distributed along the circumference. It can also be seen from fig. 9 that the area with the pulsed magnetic pull clusters occupies approximately 1/3 of the space corresponding to 120 ° electrical angle at which the faulty diode should be switched on, and the area without the pulsed magnetic pull clusters occupies 2/3 of the space corresponding to the phase (240 ° electrical angle) at which the faulty branch should be switched off.
As can be seen from fig. 10, the unbalanced magnetic pulling force applied to the exciter rotor when the diode is normal is substantially zero, the mechanical angular velocity of the rotor of the 5.8MW internal rotor type three-phase brushless exciter studied in this embodiment is 25rad/s, the rotor is subjected to the action of unbalanced magnetic pulling force pulses for 8 times in one rotation period after the diode fails, and the frequency of the electromagnetic force pulses is 200Hz. Under the influence of the fault diode on the distribution of the current of each branch, in the stage that the fault diode is supposed to be turned off, the exciter still has slight magnetic field imbalance actually, and small unbalanced magnetic pull force is generated. Since the direction of the pulse electromagnetic force rotates as the armature rotates, its components in the X-axis and Y-axis directions exhibit sinusoidal wave properties, and as is apparent from fig. 11 and 12, the envelope of the unbalanced force pulse exhibits remarkable sinusoidal wave properties.
As can be seen from fig. 13, 14 and 15, the amplitudes of the harmonics in the resultant of unbalanced magnetic pull force of the rotor when the diodes are normal, the X-axis component and the Y-axis component frequency spectrum are all very low, and are all less than 50N.
As can be seen from fig. 16, the spectrum of the resultant unbalanced magnetic pull force after the diode fault contains significant dc component and 200Hz component, which is consistent with the analytical calculation result. At the same time, the unbalanced magnetic pull force frequency spectrum also contains harmonics of 400Hz, 600Hz, etc., which are respectively 200HzThe frequency is divided into 2 times and 3 times of frequency multiplication, which is necessary to be contained in the Fourier decomposition of the pulse type unbalanced magnetic pulling force. As can be seen from fig. 17 and 18, the frequency spectrums of the X-axis component and the Y-axis component of the unbalanced magnetic pulling force after the diode failure contain obvious frequency components of 25Hz, 175Hz, 225Hz, 375Hz, 425Hz, 575Hz, 625Hz, etc., wherein 25Hz corresponds to the dc component of the resultant unbalanced magnetic pulling force, the harmonics of 175Hz and 225Hz correspond to 200Hz of the resultant unbalanced magnetic pulling force, the harmonics of 375Hz and 425Hz correspond to 400Hz of the resultant unbalanced magnetic pulling force, and the harmonics of 575Hz and 625Hz correspond to 600Hz of the resultant unbalanced magnetic pulling force, which are the result of resolving the rotating unbalanced magnetic pulling force into the stationary coordinate system. The mechanical angular velocity of the rotor of the brushless exciter used in this example was 25rad/s, and according to the above analysis, when open circuit failure occurred in the rotating rectifier diode, a larger magnitude of ω occurred in the X-axis component and Y-axis component frequency spectra of the unbalanced magnetic pull of the rotor r /2πHz、(P±1)ω r /2πHz、(2P±1)ω r [ 2 ] π Hz and (3P. + -. 1) ω r And the/2 pi Hz harmonic components excite the vibration of the rotor with the same frequency according to the incidence relation between excitation and response, so that the vibration characteristics can be obtained by respectively installing vibration sensors in the horizontal direction and the vertical direction of shafts at two ends of the exciter, and the open-circuit fault of the diode of the brushless exciter is further judged.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience of description of the present invention, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (1)
1. A three-phase brushless exciter rotating rectifier diode open-circuit fault detection method is characterized by comprising the following steps:
A. respectively installing vibration sensors in the horizontal direction and the vertical direction of shafts at two ends of an exciter, and receiving signals at the output end of the vibration sensors through a data acquisition and analysis system;
B. determining an expression of air gap flux density after an open circuit fault of a diode of the rotating rectifier;
C. determining the rotor stress and the vibration characteristic frequency caused by the open circuit fault of the diode of the rotating rectifier;
D. determining a fault threshold value of the harmonic amplitude of the vibration characteristic of the rotor;
E. if the amplitude of the rotor vibration characteristic harmonic wave is larger than a fault threshold value, judging that the diode of the rotary rectifier has an open-circuit fault, otherwise, judging that the diode of the rotary rectifier is normal;
in the step (B), the step (A),
when the rotating diode is normal, the air gap magnetic potential of the exciter is synthesized by the excitation magnetic potential and the armature magnetic potential to obtain a Fourier series expression of the excitation magnetic potential in a rotor coordinate system:
if the current of the armature winding keeps unchanged after the armature winding is conducted when the exciter normally runs, and the armature winding is conducted only in two phases at any time, the Fourier series expression of the armature magnetic potential in a rotor coordinate system is as follows:
according to the formula (1) and the formula (2), the air gap magnetic potential of the exciter when the diode is normal is obtained as follows:
a Fourier series expression of armature magnetic potential increment delta F in a rotor coordinate system:
theta in the above formula r ' by theta r +θ 0 Instead, Δ F (θ) after coordinate conversion is performed by locating the formula (4) and the formula (3) in the same coordinate system r ') is:
and (3) enabling the air gap magnetic potential of the exciter after the diode fault to be equivalent to the sum of the air gap magnetic potential when the diode is normal and the armature increment magnetic potential generated after the diode fault, wherein the air gap magnetic potential of the exciter after the diode fault is as follows:
F δ (θ r )＝F fl cosP(θ r +γ)+F a1 cosP(θ r -α)+ΔF m cosm(θ r +θ 0 ) (6)，
air gap permeance lambda δ (θ r ) Expressed as:
the exciter air gap flux density after diode failure is:
the x-axis component and the y-axis component of the unbalanced magnetic pulling force of the rotor under the rotor coordinate system after the diode fails are as follows:
from the above formula, F +1, 3P-1, 3P +1, 5P-1 and 5P +1 are present only when m = P-1, P +1, 3P-1 and 5P +1 x And F y The magnetic field is not equal to zero, namely only P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 subharmonics of armature magnetic potential increment can generate unbalanced magnetic pull force on the rotor after the diode fails; the method includes the steps that m = P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1 are brought into the above two formulas, and the x-axis component and the y-axis component of unbalanced magnetic pull of the rotor are obtained and are respectively as follows:
as can be known from the formula, the number of times of armature incremental magnetic potential harmonic waves for changing the vibration state of the rotor is P-1, P +1, 3P-1, 3P +1, 5P-1 and 5P +1, and P is the pole pair number of the brushless exciter;
wherein the symbol list: p, pole pair number of the brushless exciter; η, the distance angle of the coil wound on a single pole; omega r The mechanical angular velocity of the armature rotation; gamma, the included angle of the axes of the stator and the rotor; theta r The rotor space mechanical angle; theta s Stator space mechanical angle; n is a radical of f The number of turns of each excitation winding; i is f Exciting current of the exciter; n is a radical of a Each armatureThe total number of turns of the slot winding; i is a Effective value of phase current; α, armature slot angle (mechanical angle); lambda [ alpha ] 0 The constant term of the air gap permeance; lambda [ alpha ] 2n The amplitude of each harmonic of the air gap flux guide; f f1 Excitation magnetic potential fundamental wave amplitude; f a1 The amplitude of the armature magnetic potential fundamental wave; b n (θ r ) Radial magnetic flux density; b t (θ r ) Tangential magnetic flux density; mu.s 0 Vacuum magnetic conductivity; r, the outer diameter of the rotor; l, rotor axial effective length; sigma, the direction of unbalanced magnetic pull; theta.theta. 0 The position angle of the difference between the longitudinal axes of the coordinate systems of the formula (5) and the formula (4); Δ F m M-order harmonic amplitudes of armature magnetic potential increments, wherein m is equal to 1,2,3 and … respectively;
in step C, the characteristic frequency of the fault after the diode of the rotating rectifier is opened and the fault is omega r /2π、(P±1)ω r /2π、(2P±1)ω r /2π、(3P±1)ω r N 2 pi, where ω is r Is the mechanical angular velocity, omega, of the rotor r The unit of (d) is rad/s;
in step D, the failure determination threshold is set to:
wherein A, B, C, D is ω of the diode of the rotary rectifier under normal state r /2πHz、(P±1)ω r /2πHz、(2P±1)ω r [ 2 ] π Hz and (3P. + -. 1) ω r The/2 pi Hz harmonic vibration amplitude, delta A, delta B, delta C and delta D respectively represent omega after the diode of the rotating rectifier fails r /2πHz、(P±1)ω r /2πHz、(2P±1)ω r A/2 π Hz and (3P. + -.1) ω r The increment of the vibration amplitude of the/2 pi Hz harmonic is considered to be zero when the increment is zero or negative.
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