CN112557899A - Independent-judgment double-fed motor slip ring fault monitoring method - Google Patents
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Abstract
The invention discloses an independently judged doubly-fed motor slip ring fault monitoring method, which comprises the following steps: selecting a slip ring ignition judgment threshold value K according to the structural characteristics and the resistance characteristics of the slip ring carbon brush; collecting a rotor current waveform with a certain duration at equal time intervals in real time in a T period when the rotating speed of the generator is basically unchanged; carrying out frequency identification on the three-phase rotor current sequence obtained by sampling through local linearization; calculating to obtain fault characteristic time length delta t; according to the identification result, performing rotation coordinate transformation on the three-phase rotor current sequence obtained by sampling; and performing morphological analysis on the transformation result to diagnose the early faults of the slip ring and the electric brush. According to the technical scheme, the slip ring fault monitoring effect is realized through morphological analysis of the processed signal result, additional equipment is not needed, the method is simple to realize, simple and convenient to install, strong in directivity, small in calculated amount and clear in mechanism, and the early fault waveform with strong transient randomness can be judged.
Description
Technical Field
The invention relates to the technical field of wind power faults, in particular to an independent-judgment double-fed motor slip ring fault monitoring method.
Background
For a megawatt double-fed wind generating set, the exciting current is large, a plurality of electric brushes are distributed on the same phase, and the mutual current equalizing effect is difficult to ensure. In actual operation, the change of resistance between the electric brush and the slip ring easily causes secondary distribution of electric brush current, so that part of the electric brush is overloaded, if the ambient air humidity is high or the resistance of the electric brush changes, the probability of sparking between the slip ring and the electric brush is obviously increased, the slip ring is slightly corroded by pitting, and the slip ring electric brush of the generator is damaged seriously, so that the normal operation of the generator is influenced.
The reasons for the occurrence of electrical sparks between brushes and slip rings in engineering applications are many, such as: the vibration of the whole machine is too large, so that the vibration of the electric brush is too large; the surface of the slip ring is burnt or rough, so that the slip ring and the slip ring are in poor contact; the electric brush is overheated during operation and the ambient environment has high humidity; the pressure of the constant-pressure spring is insufficient to cause the electric brush to swing in the brush holder, and the like; the connection resistance of the electric brush and the brush braid changes; the brush is stuck in the brush box to cause poor contact. If the early-stage slip ring/electric brush ignition can be diagnosed, the electric brush is replaced in time, the planned maintenance is carried out on the equipment, the shutdown loss is avoided, and the method has very important engineering significance.
At present, the electric brush and slip ring sparks of the double-fed wind generating set can be monitored by means of a photoelectric tube monitoring method, electric brush current, contact voltage peak values and the like, but most of the methods need equipment, so that the cost is high, the reliability is low, and the adaptability is poor. Research institutions and wind turbine manufacturers have also recently conducted relevant research on spark monitoring between the two, and some articles and patents have been published, but most of them are from the perspective of brush current. For example, the resistance change theory and simulation research of the electric brush slip ring of the doubly-fed asynchronous generator are realized, and the method is characterized in that the equivalent resistance of the electric brush and the slip ring is analyzed, the current of each electric brush is measured, Fourier transform is carried out, and characteristic components are extracted.
The method needs to carry out statistics and complex calculation of a large amount of data in the implementation process, and is difficult to carry out real-time judgment, but has the problems that the actual slip ring ignition faults all occur instantaneously and have no periodically repeated characteristic, so that the frequency domain characteristics are difficult to obtain through Fourier transform; or overcurrent protection based on a power electronic switch at the converter side is carried out, effective relevance with faults is lacked, the detection requirements of transient property and strong randomness of early faults of the electric brush/slip ring are difficult to meet, and the detection objects are more, so that the detection is difficult to realize on the basis of hardware of the existing wind turbine generator without transformation and installation of equipment.
Chinese patent document CN106918452A discloses a method for diagnosing faults of a slip ring device of a doubly-fed asynchronous generator based on vibration. The method comprises the following steps: a vibration signal acquisition system structure is built by adopting a Nigh data acquisition instrument, a direct current voltage source and a PC signal processor; sampling a slip ring vibration signal of a slip ring surface; carrying out four-layer small-packet wave decomposition on the obtained vibration signal according to a small-packet wave decomposition principle to obtain 16 sub-frequency bands; performing energy statistical analysis on the vibration signals under different frequency bands after the wavelet 4-layer decomposition by adopting a wavelet energy spectrum-based method; and judging the operation conditions of the armature slip ring according to the energy concentration frequency band, namely four operation conditions of normal operation, the slip ring surface integral scratch damage fault, the slip ring surface local superficial damage fault and the slip ring surface ring roundness damage fault. The technical scheme needs to carry out statistics and complex calculation of a large amount of data, and is difficult to judge in real time, but the problem is that the actual slip ring ignition faults all occur instantaneously and have no periodically repeated characteristic, so that the rapid judgment is difficult.
Disclosure of Invention
The invention mainly solves the technical problems of complex calculation and difficult real-time judgment of the original technical scheme, and provides an independent judgment double-fed motor slip ring fault monitoring method.
The technical problem of the invention is mainly solved by the following technical scheme: the invention comprises the following steps:
a. selecting a slip ring ignition judgment threshold value K according to the structural characteristics and the resistance characteristics of the slip ring carbon brush;
b. collecting a rotor current waveform with a certain duration at equal time intervals in real time in a T period when the rotating speed of the generator is basically unchanged;
c. carrying out frequency identification on the three-phase rotor current sequence obtained by sampling through local linearization;
d. calculating to obtain fault characteristic time length delta t;
e. according to the identification result, performing rotation coordinate transformation on the three-phase rotor current sequence obtained by sampling;
f. and performing morphological analysis on the transformation result to diagnose the early faults of the slip ring and the electric brush.
Preferably, the threshold value K in the step a is selected according to the resistance jump quantity during ignition,
the essential reason that the electric brush and the slip ring generate sparking in the working process is that the contact failure of the contact surface of the electric brush and the slip ring under high current load causes air breakdown discharge between the electric brush and the slip ring, local high temperature is generated, and therefore the roughness of the contact surface of the slip ring and the electric brush is further increased, and vicious circle is formed.
Preferably, in step b, during a period T when the rotating speed of the generator is basically unchanged, the actual rotor current sequence measured by one phase of the three-phase currents is
{ia}＝[i1a i2a ... ina] (2)
Rotor electricityStream sample value sequence i1a、i2a、...、inaBy expression of (3)
In the above formula, δ1、δ2、...、δnFor error, effective amplitude I of three-phase rotor currentrThe phases are the same and differ by 120 degrees. Real-time acquisition of three-phase current i of generator rotor during grid-connected operation of unitA、iB、iC. When sparking occurs between the brushes and the slip rings, this is reflected in the rotor current.
Preferably, the concrete step of the step c comprises the steps of further restricting the rotor current frequency to 8Hz-16Hz, obtaining effective rotor current information of a plurality of periods through sampling of the fixed time window width T, and determining the peak value I of the sine fitting current according to the average value of three-phase current peak values in the sampling of the fixed time window widthmFurther, the ideal form of the three-phase current of the rotor is
Because the rotating speed range of the doubly-fed wind generator is limited, the rotor current frequency range is also limited and cannot exceed 1/3fs(about 16 Hz). In addition, it is considered that the clearer brush sparking characteristic occurs only when the rotor load exceeds 50%, and then the rotor current frequency can be further constrained to be about 8Hz to 16Hz according to the characteristics of the doubly-fed wind generator.
Preferably, in the step c, in the vicinity of the zero-crossing region, the sine value is approximately linear to the derivative of the angle, a certain amount of data is taken before and after the zero-crossing region for local linearization, the current zero-crossing point is obtained according to the linearization result, the frequency of the current is obtained according to the analysis of the three-phase rotor current zero-crossing point, and the average value is taken as the final identification result f2。
Preferably, the specific step of step d comprises an electric arcThe arc migration between the slip ring and the electric brush is not characterized in the early stage of the fault, and the duration is longer than the time when a specific position on a slip ring loop passes by twice the width of the electric brush, namely when L is the effective length of a carbon brush contacting the slip ring, r is the radius of the slip ring, and omegamAt a mechanical speed, the arc lasts for a period of time of about
The mechanism of the ignition of the slip ring brush is that the sliding contact is not uniform over the entire circumference, and the behavior of the failure is that the contact point progresses to the contact surface. At the moment of lighting of the slip ring electric brush, the microscopic current state is arcing-arc breaking, and a specific objective rule exists.
Preferably, step d performs Park transformation of a three-phase rotating coordinate system on the rotor current as follows,
preferably, the step e extracts the average value of the d-axis current and the q-axis current in the time interval after the rotation coordinate transformation, performs least square comparison of the transformation result to the average value on the data after the transformation in a time interval with delta t as a characteristic time interval, n sampling points are arranged in the time interval with delta t, and when the comparison difference between the d axis and the q axis in the same time interval with delta t is greater than a certain threshold value K, the early ignition phenomenon of the carbon brush slip ring occurs.
Preferably, the stator frequency f is based on the principle of doubly-fed power generationsRotor frequency frAnd a mechanical rotational speed omegamThe following relationship is maintained
In the above formula, p is the pole pair number of the generator, frAdjusted following the change in rotational speed, fsThe stator frequency is the grid frequency and keeps basically unchanged, and f is within a certain control periodrIs not changed. The essence of the electric brush slip ring ignition lies in the instant reduction of the contact point number and the pressure, namely the instant increase of the contact resistance of the electric brush slip ring, but the voltage source type converter adopted by the double-fed unit has the natural property of maintaining the output voltage stable.
Preferably, the contact resistance of the brush slip ring in operation is composed of a shrinkage resistance and a film resistance, and the expression is
Where rhol、ρrResistivity of carbon brush and slip ring; epsilon is the deformation coefficient of the material; hl、HrThe Brinell hardness of the carbon brush and the slip ring contact material; n and F are the number of contact points and the contact pressure respectively; rhoaThe resistivity of the film layer.
The invention has the beneficial effects that:
1. only the rotor current information in the doubly-fed wind power generation system needs to be acquired, so that the instantaneous and random slip ring/electric brush early fault can be reflected more intuitively and quickly
2. The three-phase rotor current is collected for polymerization analysis, and the judgment is carried out by utilizing the characteristic morphology principle, so that the mechanism is clear, and the accuracy is high.
3. The method adopted by the invention has small calculation amount, can achieve the effects of real-time acquisition and real-time analysis, and realizes leakage-free capture of dynamic data in the running detection process.
4. The method of the invention has simple installation and low cost of upgrading and reconstruction.
Drawings
FIG. 1 is a flow chart of the present invention.
Fig. 2 is a schematic view of a slip ring and brush according to the present invention.
Fig. 3 is a schematic diagram of a slip ring resistor according to the present invention.
Fig. 4 is a diagram of equivalent resistance of a slip ring resistor in accordance with the present invention.
Fig. 5 is a graph of sampled values of a rotor current of the present invention.
Fig. 6 is a linearization diagram of a zero crossing region of a rotor current sample according to the invention.
Fig. 7 is a d, q, 0 axis characteristic diagram of rotor current when a slip ring brush of the present invention is fired.
Detailed Description
The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings.
Example (b):
for the current doubly-fed wind generator, one electric brush is not enough to carry the required current, and a plurality of electric brushes are generally connected in parallel. According to the principle of doubly-fed generation, the stator frequency fsRotor frequency frAnd a mechanical rotational speed omegamThe following relationship is maintained
In the above formula, p is the pole pair number of the generator, frAdjusted following the change in rotational speed, fsThe stator frequency is the grid frequency and keeps basically unchanged, and f is within a certain control periodrAnd is not changed.
The method for monitoring the slip ring fault of the doubly-fed motor by independent judgment in the embodiment is shown in fig. 1, and comprises the following steps:
a. selecting a slip ring ignition judgment threshold value K according to the structural characteristics and the resistance characteristics of the slip ring carbon brush, selecting the threshold value K according to the resistance jump variable during ignition,
the essential reason that the electric brush and the slip ring generate sparking in the working process is that the contact failure of the contact surface of the electric brush and the slip ring under high current load causes air breakdown discharge between the electric brush and the slip ring, local high temperature is generated, and therefore the roughness of the contact surface of the slip ring and the electric brush is further increased, and vicious circle is formed.
As shown in fig. 2, a contact resistance exists between the contact surfaces of the brush and the slip ring, and according to the theory of electrical contact, the contact resistance of the brush slip ring in operation is composed of a shrinkage resistance and a film resistance, and the expression is
Where rhol、ρrResistivity of carbon brush and slip ring; epsilon is the deformation coefficient of the material; hl、HrThe Brinell hardness of the carbon brush and the slip ring contact material; n and F are the number of contact points and the contact pressure respectively; rhoaThe resistivity of the film layer.
The resistance of a single brush/slip ring is composed of two parts, one is contact resistance, and the other is brush + slip ring resistance, and the equivalent diagrams are shown in fig. 3 and 4.
The contact resistance exists between the contact surfaces of the electric brush and the slip ring, and according to the electric contact theory, the contact resistance of the electric brush slip ring in operation consists of a contraction resistance and a film resistance, and the expression is
Where rhol、ρrResistivity of carbon brush and slip ring; epsilon is the deformation coefficient of the material; hl、HrThe Brinell hardness of the carbon brush and the slip ring contact material; n and F are the number of contact points and the contact pressure respectively; rhoaThe resistivity of the film layer.
The brush resistance is determined by its own characteristics, and there are individual differences. When the slip ring rotates, the resistance of the slip ring changes periodically, and for a single electric brush, the current of the electric brush flows to the slip ring through 2 paths, wherein one path is L as shown in figure 31And the other path is L2The slip-ring resistance can then be expressed as a parallel connection of two circuits, for which the slip-ring resistance varies periodically for the three brushes in fig. 2, which can be expressed as
In the above formula, RringBeing the resistance of the whole loop of the slip-ring, omegamα and β are mounting angles of the brushes 2 and 3 with respect to the brush 1, which are rotational angular speeds of the slip ring, that is, the generator.
Then, for each brush's independent circuit, it is known
According to the circuit principle, the equivalent resistance of a brush slip ring is R under the normal condition1(t)、R2(t)、R3(t) parallel connection. When the electric brush 1 is contacted with the slip ring to strike fire, the equivalent resistance of the slip ring of the electric brush is suddenly changed into R due to the high-resistance characteristic of the electric arc2(t)、R3(t) parallel connection.
The slip ring loop is negligible and simplified in use because it uses stainless steel or copper rings capable of carrying large currents in the doubly-fed wind generator, which are typically much less resistive than carbon brushes and contact resistances. Slip ring R according to generator brushcAnd Rbrush、RringCan obtain the jump variable of the equivalent resistance of the brush slip ring structure.
The essence of the electric brush slip ring ignition lies in the instant reduction of the contact point number and the pressure, namely the instant increase of the contact resistance of the electric brush slip ring, but the voltage source type converter adopted by the double-fed unit has the natural property of maintaining the output voltage stable.
b. And in a T period when the rotating speed of the generator is basically unchanged, acquiring the rotor current waveform of a certain time length at equal time intervals in real time.
In the T period when the rotating speed of the generator is basically unchanged, the actual rotor current sequence measured by one phase in the three-phase currents is
{ia}＝[i1a i2a ... ina] (2)
Rotor current sampling value sequence i1a、i2a、...、inaBy expression of (3)
In the above formula, δ1、δ2、...、δnFor error, effective amplitude I of three-phase rotor currentrThe phases are the same and differ by 120 degrees. Real-time acquisition of three-phase current i of generator rotor during grid-connected operation of unitA、iB、iC. When sparking occurs between the brushes and the slip rings, this is reflected in the rotor current.
c. And carrying out frequency identification on the three-phase rotor current sequence obtained by sampling through local linearization.
Because the rotating speed range of the doubly-fed wind generator is limited, the rotor current frequency range is also limited and cannot exceed 1/3fs(about 16 Hz). In addition, it is considered that the clearer brush sparking characteristic occurs only when the rotor load exceeds 50%, and then the rotor current frequency can be further constrained to be about 8Hz to 16Hz according to the characteristics of the doubly-fed wind generator. Obtaining effective rotor current information of a plurality of periods through sampling of the fixed time window width T, and determining the peak value I of sine fitting current according to the average value of three-phase current peak values in the sampling of the fixed time window widthmAnd, furthermore,the ideal form of the three-phase current of the rotor is
As shown in fig. 5 and 6, in the vicinity of the zero-crossing region, the sine value is approximately linear to the derivative of the angle, a certain amount of data is taken before and after the zero-crossing region for local linearization, the current zero-crossing point is obtained according to the linearization result, the frequency of the current is obtained according to the analysis of the three-phase rotor current zero-crossing point, and the average value is taken as the final identification result f2。
d. And calculating to obtain fault characteristic time length delta t, wherein in terms of a mechanism of sparking of the slip ring electric brush, the sliding contact of the whole circumference is uneven, and the fault property is that the fault develops from a contact point to a contact surface. At the moment of lighting of the slip ring electric brush, the microscopic current state is arcing-arc breaking, and a specific objective rule exists. The arc occurs between the slip ring and the brushes and is not characterized by arc migration early in the fault, i.e., the duration is approximately the time to pass twice the width of the brushes at a particular location on the slip ring track. That is, when L is the effective length of the carbon brush contacting the slip ring, r is the radius of the slip ring, omegamAt a mechanical rotational speed, the arc then lasts for a period of time of about
e. And according to the identification result, performing rotation coordinate transformation on the three-phase rotor current sequence obtained by sampling. The Park transformation of a three-phase rotating coordinate system is carried out on the rotor current, see formula (6),
at the moment when the slip ring brush is ignited, the d-axis and q-axis conversion results of the three-phase rotor currents can obtain characteristic waveforms similar to those in fig. 7, and the waveforms of the three-phase rotor currents change to a certain extent according to the relative relation among a rotating coordinate system, the three-phase currents and the fault positions, but all the waveforms deviate from stable d and q areas, and the time length is delta t.
f. And performing morphological analysis on the transformation result to diagnose the early faults of the slip ring and the electric brush. Therefore, according to the mechanism of the slip ring electric brush ignition, when the doubly-fed generator operates, the rotor current is sampled with the period of T, the rotating speed of the generator is basically kept unchanged within the time of T, and the generator is judged to be in a high-load working condition according to the rotating speed. And carrying out rotation coordinate transformation on the three-phase rotor current in the time interval, extracting the average value of d-axis and q-axis currents in the time interval, carrying out least square comparison of the transformation result on the average value by taking delta t as a characteristic time interval on the transformed data, and having n sampling points in the delta t time interval. And when the comparison difference of the d axis and the q axis in the same delta t time period is greater than a certain threshold value K, the phenomenon of early sparking of the carbon brush slip ring can be considered to occur.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Although the terms rotor current waveform, frequency identification, etc. are used more herein, the possibility of using other terms is not excluded. These terms are used merely to more conveniently describe and explain the nature of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.
Claims (10)
1. An independently judged doubly-fed motor slip ring fault monitoring method is characterized by comprising the following steps:
a. selecting a slip ring ignition judgment threshold value K according to the structural characteristics and the resistance characteristics of the slip ring carbon brush;
b. collecting a rotor current waveform with a certain duration at equal time intervals in real time in a T period when the rotating speed of the generator is basically unchanged;
c. carrying out frequency identification on the three-phase rotor current sequence obtained by sampling through local linearization;
d. calculating to obtain fault characteristic time length delta t;
e. according to the identification result, performing rotation coordinate transformation on the three-phase rotor current sequence obtained by sampling;
f. and performing morphological analysis on the transformation result to diagnose the early faults of the slip ring and the electric brush.
2. The slip ring fault monitoring method of the doubly-fed machine with independent judgment of claim 1, wherein the threshold value K in the step a is selected according to a resistance jump variable during ignition,
3. the slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 2, wherein in the step b, in the T period when the rotating speed of the generator is basically unchanged, the actual rotor current sequence measured by one phase of three-phase currents is
{ia}＝[i1a i2a ... ina] (2)
Rotor current sampling value sequence i1a、i2a、...、inaBy expression of (3)
In the above formula, δ1、δ2、...、δnFor error, effective amplitude I of three-phase rotor currentrThe phases are the same and differ by 120 degrees.
4. The slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 1, wherein the concrete step of the step c comprises the steps of further restricting the current frequency of the rotor to be 8Hz-16Hz, and obtaining effective slip rings of a plurality of cycles through sampling of the width T of a fixed time windowDetermining the peak value I of sine fitting current according to the average value of three-phase current peak values in the fixed time window width samplingmFurther, the ideal form of the three-phase current of the rotor is
5. The slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 4, wherein in the step c, in the vicinity of the zero-crossing region, the sine value is approximately linear to the derivative of the angle, a certain amount of data is taken before and after the zero-crossing region for local linearization, the current zero-crossing point is obtained according to the linearization result, the current frequency is obtained according to the analysis of the current zero-crossing point of the three-phase rotor, and the average value is taken as the final identification result f2。
6. The slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 1, wherein the concrete step d includes that an arc occurs between the slip ring and the brush, the arc migration is not characterized in the early stage of the fault, and the duration is the time when a specific position on a slip ring loop passes by twice the width of the brush, namely when L is the effective length of the carbon brush contacting the slip ring, r is the radius of the slip ring, and ω is the effective length of the carbon brush contacting the slip ringmAt a mechanical speed, the arc lasts for a period of time of about
7. The slip ring fault monitoring method of the doubly-fed machine with independent judgment of claim 1, wherein the step e performs Park transformation on a three-phase rotating coordinate system on the rotor current as follows,
8. the slip ring fault monitoring method of the doubly-fed motor with the independent judgment of claim 7, wherein the step e is used for extracting the average value of currents of d and q axes in the time period after the rotating coordinate transformation, carrying out least square comparison of the transformation result to the average value on the data after the transformation in the time period with delta t as a characteristic time period, wherein n sampling points exist in the time period with delta t, and when the comparison difference between the d and q axes in the same time period with delta t is larger than a threshold value K, an early ignition phenomenon of the carbon brush slip ring occurs.
9. The slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 1, wherein the stator frequency f is determined according to the principle of doubly-fed power generationsRotor frequency frAnd a mechanical rotational speed omegamThe following relationship is maintained
In the above formula, p is the pole pair number of the generator, frAdjusted following the change in rotational speed, fsThe stator frequency is the grid frequency and keeps basically unchanged, and f is within a certain control periodrAnd is not changed.
10. The slip ring fault monitoring method for the doubly-fed motor with independent judgment of claim 9, wherein the contact resistance exists between contact surfaces of the electric brush and the slip ring, and according to an electric contact theory, for each electric brush, the contact resistance of the slip ring of the electric brush in operation consists of a shrinkage resistance and a film resistance, and the expression is
Where rhol、ρrResistivity of carbon brush and slip ring; epsilon is the deformation coefficient of the material; hl、HrThe Brinell hardness of the carbon brush and the slip ring contact material; n isF is the contact point number and the contact pressure respectively; rhoaThe resistivity of the film layer.
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| CN116953414A (en) * | 2023-09-15 | 2023-10-27 | 无锡同康工程技术有限公司 | Intelligent monitoring method and system for slip ring |
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| CN103427397A (en) * | 2013-07-23 | 2013-12-04 | 大唐华银电力股份有限公司 | Fire protection method and system of slip ring of generator rotor |
| CN110687446A (en) * | 2019-07-15 | 2020-01-14 | 浙江运达风电股份有限公司 | Double-fed wind driven generator electric brush and slip ring early fault diagnosis method |
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