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    • 专利摘要:
    Procedure and measurement system of lack of symmetry in three-phase induction motors. The invention relates to a method and measurement system for lack of symmetry in three-phase induction motors. The method comprises calculating at least one parameter selected from the group consisting of the symmetry defect intensity (ID), the lack of symmetry index (IFS) and the symmetry factor (FS). The system comprises means for measuring and acquiring electrical signals; processor means; a program for measuring the displacement power of neutral; and visualization means. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2712350A1
    申请号:ES201831104
    申请日:2018-11-14
    公开日:2019-05-10
    发明作者:Martinez Vicente Leon；Romeu Joaquín Montanana；Lopez Elisa Penalvo
    申请人:Universidad Politecnica de Valencia；
    IPC主号:
    专利说明:

    [0001] PROCEDURE AND METHOD OF MEASUREMENT OF LACK OF SYMMETRY IN
    [0002]
    [0003] Field of the invention
    [0004] The present invention relates to the field of monitoring devices and protection of three-phase induction motors against phase failures and lack of symmetry, caused both by breakages or accidental disconnections and manufacturing defects of their windings.
    [0005]
    [0006] Background of the invention
    [0007] The accidental cutting or disconnection of a stator phase is a well-known failure in industrial practice, which affects the good functioning of the three-phase induction motors, causing important thermal and mechanical effects, which are responsible for the breakage and putting out of service of these machines. Also, the breakage of the rotor bars can cause the paralyzation of the production process in all kinds of activities in which these engines are used, with important economic consequences.
    [0008] From the above it follows the need to protect three-phase induction motors against phase failures, in particular, and against any failure of symmetry (such as bus breakage), in general. Currently, the protection measure most used in the industry against these defects is the use of motor protectors, of which you can find a large number of ranges and manufacturing companies. These devices have a thermal relay and a magnetic relay, but only the thermal relay is effective for protection against phase faults, since it is activated by the overcurrents caused for the failure. Other protection devices against phase faults currently available are the relays of phase failure, which cause the opening of a contactor when any of the power supply lines of the motor are disconnected.
    [0009] However, the relays of phase failure are not effective when the fault is internal to the motor, as occurs with eccentricities or breaks of the rotor bars and in accidental cuts of the stator windings. In addition, the motor protectors are also not useful for the protection against accidental breakage of the rotor bars or when the phase failure is not abrupt, but is caused by a slow and progressive deterioration of the motor windings. In these cases, the motor protectors and the relays of lack of phase based on the current technologies are totally insensitive, because the increase in value experienced by the currents of the stator is usually well below the detection threshold of these devices.
    [0010] In addition, the motor protectors and the phase fault relays act once the phase failure or the symmetry defect has already occurred. Therefore, with these protective devices it is not possible to perform a preventive maintenance of the motor against these defects.
    [0011] In the patent ES 2588260 B2 of the present applicant, a formulation of the displacement power of the neutral was used to determine the state of conservation of the neutral conductor in the electric distribution networks. The formulation of the neutral power that was used in these patents is only applicable to three-phase star connections, but not for triangle connections; therefore it is not useful for its application to the monitoring of three-phase motors in general.
    [0012] It would therefore be desirable to have a procedure and system that allow the monitoring, monitoring and protection of three-phase induction motors, regardless of whether its stator winding is connected in a triangle or star.
    [0013]
    [0014] Summary of the invention
    [0015] The object of the present invention is to provide a three-phase induction motors protection system and method against any symmetry defect, which overcome at least some of the limitations of the phase failure motor protectors and relays of the prior art. In particular, one objective is to provide a method and system that can be used in the protection of conventional phase faults, both by disconnection of the power supply lines of the motor and by breakage of the stator coils or of the rotor bars. Additionally, one objective is to provide a procedure and system that allows to carry out prevention tasks, reporting in real time the deterioration of the coils or the motor rods before the complete breakage occurs.
    [0016] Any of the above-mentioned defects gives rise to symmetry faults in the motor, which cause neutral displacement phenomena. Therefore, the method and system disclosed herein are based on the measurement of the energetic effects of displacement of the neutral that are manifested in the stator coils of the motor as a consequence of the failure. These effects can be quantified by the displacement power of the neutral or, simply, power of the neutral.
    [0017] According to a first aspect, the present invention discloses a measurement method of lack of symmetry in three-phase induction motors, which comprises calculating at least one parameter selected from the group constituted by the symmetry defect intensity (ID), the symmetry lack index (IFS) and the symmetry factor (FS), according to the following equations :
    [0018]
    [0019]
    [0020] where
    [0021] Sn is the displacement power of neutral,
    [0022] S! ^ Is the initial neutral displacement power, and
    [0023] S is the apparent power of the motor.
    [0024] According to a second aspect, the present invention discloses a measurement system of lack of symmetry in three-phase induction motors, comprising:
    [0025] - Means of measurement and acquisition of electrical signals;
    [0026] - processor means;
    [0027] - a program for measuring the neutral displacement power; Y
    [0028] - visualization means.
    [0029]
    [0030] Brief description of the drawings
    [0031] The present invention will be better understood with reference to the following drawings which illustrate preferred embodiments of the present invention, provided by way of example, and which are not to be construed as limiting the invention in any way:
    [0032] Figures 1A and 1B form a diagram showing the operational sequence of the procedure according to a embodiment of the invention, applicable to systems of surveillance and protection of three-phase induction motors against lack of symmetry and phase failures. Figure 1A shows the operational sequence of the procedure corresponding to three-phase induction motors with the star-connected stator. Figure 1B shows the operational sequence of the procedure corresponding to three-phase induction motors with the stator connected in a triangle.
    [0033] Figure 2 is a diagram representing a possible embodiment of the monitoring and protection system, as well as its connection to a three-phase induction motor with the star-connected stator.
    [0034] Figure 3 is a diagram representing a possible embodiment of the monitoring and protection system, as well as its connection to a three-phase induction motor with the stator connected in a triangle.
    [0035] Figure 4 is a diagram representing the programming modules for the monitoring and protection system against symmetry failures of three-phase induction motors with the star-connected stator according to an embodiment of the invention.
    [0036] Figure 5 is a diagram representing the programming modules for the monitoring and protection system against symmetry failures of three-phase induction motors with the stator connected in a triangle according to an embodiment of the invention.
    [0037] Figures 6A and 6B form a diagram showing the operational sequence of the method of the invention for systems of preventive maintenance and quality control of three-phase induction motors according to an embodiment of the invention. Figure 6A shows the operational sequence of the procedure corresponding to three-phase induction motors with the star-connected stator. Figure 6B shows the operational sequence of the procedure corresponding to three-phase induction motors with the stator connected in a triangle.
    [0038] Figure 7 is a diagram representing a possible embodiment of the system of preventive maintenance and quality control, as well as its connection to a three-phase induction motor with the stator connected in star.
    [0039] Figure 8 is a diagram representing a possible embodiment of the system of preventive maintenance and quality control, as well as its connection to a three-phase induction motor with the stator connected in a triangle.
    [0040] Figure 9 is a diagram representing the programming modules for the preventive maintenance and quality control system of three-phase induction motors with the star-connected stator according to an embodiment of the invention.
    [0041] Figure 10 is a diagram representing the programming modules for the system of preventive maintenance and quality control of three-phase induction motors with the stator connected in a triangle according to an embodiment of the invention.
    [0042] Figure 11 shows a possible embodiment of the means of visualization of the monitoring and protection system, in the face of lack of symmetry, and of the system of preventive maintenance and quality control of the symmetry of three-phase induction motors, with indication of the values of the displacement power of the neutral, the intensity of the defect and the coefficients that inform about the symmetry of the motor, as well as the type of connection of the motor (star or triangle) and the signal of activation of the protection or of the alarm.
    [0043] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The systems object of the present invention are based on the measurement of the energetic effects caused by the displacement of the neutral point (real or virtual) of the stator of the motor, using for it the displacement power of the neutral. The monitoring and protection systems disclosed in the present invention can be applied to all types of three-phase induction motors, rotor winding or short-circuited (cage) rotor, with the stator windings connected in both star and triangle, and are able to open the stator circuit in the event of an untimely phase failure, as well as preventive and predictive maintenance tasks, informing the user of any possible defect of symmetry in the stator and rotor coils, or in the bars of the rotor, as well as eccentricities in the motor.
    [0044] The invention relates to a method and a measurement system for lack of symmetry in three-phase induction motors for their monitoring and protection against all types of symmetry defects, such as phase faults or bus breakage, among others. The present invention is based on the fact that the decrease in the symmetry, caused by these defects in the stator or in the rotor of the motor, gives rise to neutral displacement phenomena, whose effects can be measured in the stator winding using the displacement power of the neutral.
    [0045] Two cases are distinguished, depending on whether the motor stator coils are connected in star or triangle.1
    [0046]
    [0047] 1) Motors with stator coils connected in star.
    [0048] In this type of connection, the final ends of the motor stator coils are connected at a neutral point, physically real, but there is no homopolar sequence current flow in the absence of a neutral conductor. In the ideal case in which the motor is symmetrical, there are no homopolar sequence voltages in the stator coils, according to Fortescue's theorem. However, the lack of symmetry of the real motors results in the presence of homopolar sequence voltages in the stator coils, whose value is, according to Fortescue:
    [0049]
    [0050]
    [0051]
    [0052] VRN , VSN and VTN being the phasors of the simple stresses of the stator, at the fundamental frequency, Vh being the effective value of the homopolar voltages and being ah the argument of said voltages. These voltages Vh identify the phenomenon of the displacement of the neutral point, whose energetic effects on the motor are determined by the displacement power of the neutral (SnY ), of equation:
    [0053]
    [0054]
    [0055]
    [0056] being
    [0057]
    [0058]
    [0059]
    [0060] the apparent power of the motor connected in star, according to the formulation of F. Buchholz, and being
    [0061]
    [0062]
    [0063]
    [0064] the apparent power of the generator, also connected in star, where VRNg , VSNg and VTNg are the effective values of the simple voltages, of fundamental frequency, of the generator. The fundamental frequency currents ( lR, ls, lT) in the phases of the motor and the generator are equal, since both are directly connected; so that:
    [0065]
    [0066]
    [0067]
    [0068] According to Fortescue's theorem, the above equation can be reduced to the following:
    [0069]
    [0070]
    [0071] In industrial practice, the homopolar sequence voltage and fundamental frequency of the generator can be considered negligible (Vhg ~ 0), and therefore the displacement power of the neutral in the star-connected motor can be obtained as:
    [0072]
    [0073]
    [0074] If there are no symmetry faults in the motor, Vh = 0 and SnY = 0. However, any symmetry defect that occurs in the motor (phase failure, bus break, etc.) leads to the presence of sequence voltages homopolar in the stator windings ( Vh ^ 0) and, therefore, that values for the displacement power of the neutral ( SnY ) can be recorded. For this reason, the intensity of the symmetry defect of the star motors (IDY ) is established in the present invention, a parameter that defines the relationship between the value of the power of the neutral at any instant of operation of the motor ( SnY ) and the value of said power registered in the engine manufacturing process
    [0075]
    [0076]
    [0077]
    [0078] This parameter is of the greatest importance for determine the severity of any failure of motor symmetry with the stator connected in star.
    [0079] Another important parameter to know the symmetry defects present in the three-phase induction motors are the lack of symmetry index ( IFSY ), defined by the relation between the displacement power of the neutral ( SnY ), obtained according to the equation [7], and the apparent power ( SY ), measured according to equation [3], both determined at the fundamental frequency and with the stator of the motor connected in star:
    [0080]
    [0081]
    [0082]
    [0083] If the motor is perfectly symmetric, then IFSY = 0. However, in the real motors there are faults of symmetry resulting from its manufacturing process; therefore, IFSy is always greater than zero. High power motors have values of lack of symmetry between 0.001 < IFSY <0.01, while small and medium power motors have higher IFSy values, comprised between 0.02 < IFSY <0.05. When a phase failure occurs, indices of lack of symmetry higher than 0.4 may be recorded.
    [0084] The symmetry factor of the star-connected motors (FSY ), defined as:
    [0085]
    [0086]
    [0087]
    [0088] is another useful parameter to know the proximity of any three-phase induction motor to its ideal conditions, of perfect symmetry. The symmetry factor ( FSY ) can be expressed as a percentage.
    [0089]
    [0090] 2) Motors with stator coils connected in triangle.
    [0091] Neutral displacement phenomena can also occur in three-phase induction motors whose stator winding is arranged in a triangle, although in these connections the neutral point is virtual and not physically real, as in the case of star connections. The magnitude that identifies the displacement phenomenon of the neutral in the triangle connections is a homopolar sequence current, unlike what happens in motors with the stator windings connected in star, in which the phenomenon of the displacement of the neutral is observe for the presence of a homopolar sequence voltage.
    [0092] When the three-phase induction machine is constructively symmetrical, there is no circulation of homopolar sequence currents, at the fundamental frequency, in the stator winding, whether it is connected in a star (because there is no neutral conductor) or connected in a triangle, even when the stresses of the source are unbalanced. This result has its justification in the first Kirchhoff law and Fortescue's theorem. However, when the three-phase induction machine ceases to be symmetrical, either due to constructive defects (eccentricities, differences between the coils or between the stator and rotor magnetic couplings) or due to accidental defects, such as phase faults, homopolar sequence currents and fundamental frequency in the stator winding. Its value in a fasorial form is determined by Fortescue's theorem:
    [0093]
    [0094]
    [0095]
    [0096] where I RS, lST and ITR are the phasors corresponding to the currents in the stator phases of the motor, to the fundamental frequency.
    [0097] The effects of the neutral displacement phenomenon, indicated by the presence of this homopolar sequence current, can also be determined by a displacement power of the neutral for motors connected in a triangle ( SnA ), which can be expressed, similar to the motors in star, like:
    [0098]
    [0099]
    [0100]
    [0101] being SA the apparent power of the three-phase induction motors with the stator winding connected in a triangle, whose formulation according to F. Buchholz is:
    [0102]
    [0103]
    [0104]
    [0105] and SgA is the apparent power of the three-phase generator directly connected to the motor, whose equation, according to F. Buchholz, is:
    [0106]
    [0107]
    [0108]
    [0109] In these equations ( VRS, VST, VTR ) are the effective values of the line (composite) voltages applied by the generator to the motor stator windings, connected in triangle, ( I rs , I st , I tr ) are the effective values of the currents in said motor stator coils, and ( iRsgJsrg ^ TRg ) are the effective values of the currents in the generator phases. All these magnitudes are measured at the fundamental frequency.
    [0110] These two ultimasecuaciones determine that the displacement power of the neutral for three-phase induction motors with the stator coils connected in triangle is expressed as:
    [0111]
    [0112]
    [0113]
    [0114] In the absence of phase failure or any other defect that causes a lack of symmetry in the motor, the currents in the stator phases of the motor and in the generator phases are equal and, therefore, the apparent powers of the motor and the generator are the same:
    [0115]
    [0116]
    [0117]
    [0118] and the neutral displacement phenomenon (SnA = 0) does not manifest itself.
    [0119] However, when there is a lack of symmetry in the motor, as in the case of a phase failure, the currents in the motor and in the generator have different values. According to Fortescue's theorem, the difference is only found in the homopolar sequence currents of the motor ( I h) and the generator (I hg), since the direct and inverse sequence currents are equal in the motor and in the generator ( / <2 = Idg, h = kg '). Likewise, if the generator is symmetric, consideration that can be accepted without serious error, in the vast majority of cases, there are no homopolar sequence currents in the generator ( lhg = 0); therefore, it is true that:
    [0120]
    [0121]
    [0122]
    [0123] being the effective value of the homopolar sequence currents and fundamental frequency recorded in the motor stator, and the equation of the displacement power of the neutral for triangle connections is reduced to the following:
    [0124]
    [0125]
    [0126]
    [0127] where (Vrs, Vst, Vtr ) are the effective values of the line voltages applied to the motor stator coils, at the fundamental frequency.
    [0128] The value of the travel power of the neutral for three-phase induction motors with the winding statoric connected in triangle ( S nA), obtained according to the equation [18], determines the energetic impact that any lack of symmetry (such as a phase failure or breakage of rods in the rotor, among others) causes on the motor, but the increase of the value of this magnitude, measured at any instant ( SnA ), with respect to its value corresponding to the asymmetry of the motor's manufacture (S ° a ), determines the intensity of any symmetry defect in the three-phase induction motors connected in triangle:
    [0129]
    [0130]
    [0131]
    [0132] Parameter that informs about the importance of the defect.
    [0133] The quotient between the displacement power of the neutral ( SnA ), determined according to the equation [18], and the apparent power of the motor ( S a ), obtained according to the equation [13], to the fundamental frequency, defines the fault index of symmetry of three-phase induction motors with stator coils connected in triangle:
    [0134]
    [0135]
    [0136]
    [0137] which is another useful parameter to determine the lack of symmetry in the engine and inform about its danger.
    [0138] The smaller the value of IFS a , the closer the motor is to its ideal construction behavior, totally symmetrical. If the motor was symmetric IFS a = 0 . However, this theoretical value is never reached. Due to constructive defects, generally caused in the manufacturing process, values of 0.001 < IFS a < 0.01, for high power motors, and from 0.02 < IFS a < 0.05, for small power motors are observed . Faced with a phase failure, the lack of symmetry index ( IFS a ) reaches values between 0.4 and 0.5.
    [0139] Likewise, the symmetry factor of three-phase induction motors with the stator winding connected in a triangle (FSA) is defined as:
    [0140] FSa = 1 - IFS a [21]
    [0141] This parameter is also important to determine the symmetry conditions of the three-phase induction motors connected in a triangle and it is very useful to know the manufacturing quality of the three-phase motors.
    [0142] Therefore, according to a first aspect, the invention relates to a method for determining the effects of the lack of symmetry that occurs in the operation of three-phase induction motors (such as phase faults, bus breakage, eccentricities, among others), based on the measurement of the displacement power of the neutral (Sn ) and the use of derived parameters of this magnitude, such as the intensity of the defect ( ID ) and the lack of symmetry index ( IFS ), for perform a preventive surveillance against defects of lack of symmetry, as well as allow the activation of a means of protection, when the defect reaches dangerous levels for the engine. Additionally, the procedure allows to know the structural symmetry faults of the motor, produced in its manufacture, using the symmetry factor (FS).
    [0143] According to a preferred embodiment of the present invention, the method of measurement of lack of symmetry (for symmetry defects such as phase faults, bus breakage, etc.) in three-phase induction motors connected in star comprises:
    [0144] i) measure the voltages and currents in the coils of the engine stator in charge, in an initial trial, and get its phasors
    [0145] corresponding to the fundamental frequency;
    [0146] ii) calculate the phasor corresponding to the homopolar sequence component and the fundamental frequency of the voltages
    [0147] iii) determine the displacement power of the star motor neutral in the initial test
    [0148] applying the equation [7],
    [0149]
    [0150]
    [0151]
    [0152] and the structural phase failure or manufacture of the star motor ( IFS °), applying equation [9],
    [0153]
    [0154]
    [0155]
    [0156] or, the factor of structural symmetry or of manufacture of the motor, according to the equation [10],
    [0157]
    [0158]
    [0159]
    [0160] iv) obtain the phasors of the tensions
    [0161] v calculate the phasor
    [0162]
    [0163] vi) determine the phasor
    [0164]
    [0165]
    [0166]
    [0167] vii) calculate the value of the displacement power of the total neutral, at each instant of operation of the motor connected in star, as:
    [0168]
    [0169]
    [0170]
    [0171] viii) to know the level of danger for the integrity and good functioning of the three-phase induction motors connected in star, before any defect of lack of symmetry, from the values at any moment of the intensity of the defect
    [0172]
    [0173]
    [0174]
    [0175] where SnY is obtained by the equation [7] and
    [0176] ix: calculate the specific impact of any defect of lack of symmetry, such as a phase failure or a break of a rotor bar, in addition to the structural asymmetry, of the motor, using the effective value of the homopolar sequence voltage and frequency fundamental characteristic of the failure
    [0177]
    [0178]
    [0179]
    [0180] x: obtain the index of lack of total symmetry of the motor at each instant of star operation such as:
    [0181]
    [0182]
    [0183]
    [0184] where the value of IFS °, which measures the asymmetry of manufacture of the engine is known from [23], in the step iii), as well as the factor of total symmetry of the star motor ( FSY ) using equation [24];
    [0185] xi) determine the importance of the lack of symmetry characteristic of any defect that has arisen during the operation of the motor, such as phase faults or breaks in the rotor bars, based on the lack of symmetry index:
    [0186]
    [0187]
    [0188]
    [0189] In the case of three-phase induction motors connected in triangle, the measurement procedure of lack of symmetry includes:
    [0190] i) measure the voltages and currents in the stator coils of the motor under load, in an initial test, and obtain its phasors
    [0191] corresponding to the fundamental frequency;
    [0192] ii) calculate the phasor corresponding to the homopolar sequence component and fundamental frequency of said currents (1 %), according to equation [11];
    [0193] iii) determine the displacement power of the motor neutral (S ° A), applying equation [18],
    [0194]
    [0195]
    [0196]
    [0197] and the structural phase failure or triangle engine manufacturing index (I FS £), applying equation [20],
    [0198]
    [0199]
    [0200]
    [0201] or, the factor of structural symmetry or of manufacture of the motor in triangle, according to the equation [21],
    [0202]
    [0203]
    [0204]
    [0205] iv) obtain the phasors of the tensions (
    [0206] v) calculate the phasor I h of the homopolar sequence currents and fundamental frequency at each moment of operation of the motor connected in a triangle, applying equation [11] to the currents measured in the previous step;
    [0207] vi) determine the phasor
    [0208]
    [0209]
    [0210]
    [0211] vii) calculate the value of the displacement power of the total neutral, at each instant of operation of the engine in a triangle, such as:
    [0212]
    [0213]
    [0214]
    [0215] viii) to know the level of danger for the integrity and good functioning of the three-phase induction motors connected in a triangle, before any defect of lack of symmetry, from the values of the intensity of the defect, obtained at any instant by the relationship:
    [0216]
    [0217]
    [0218]
    [0219] where SnA is obtained by equation [18] and S ° A is known from the initial characterization of the motor, according to [31];
    [0220] ix) calculate the specific impact of any failure of symmetry of the motor connected in a triangle, in addition to the structural asymmetry, of the motor, using the effective value of the homopolar current and the fundamental frequency of the fault f
    [0221] (Ih ), that is:
    [0222]
    [0223]
    [0224]
    [0225] x) obtain the index of lack of total symmetry of the engine, at each instant of operation in a triangle, such as:
    [0226]
    [0227]
    [0228]
    [0229] where the value of IFS £, which measures the asymmetry of manufacture of the motor is known from [32], in step iii), as well as to determine also the factor of total symmetry of the motor in triangle by means of equation [33];
    [0230] Xi, determine the importance of the lack of symmetry characteristic of defects that have arisen during the operation of the motor in a triangle, such as phase failures or breaks in the rotor bars, based on the lack of symmetry index:
    [0231]
    [0232]
    [0233]
    [0234] Referring now to the attached figures, FIGS. 1A and 1B show an embodiment of the method for the measurement of symmetry defects (such as phase faults, bus breakage, eccentricities, among others) in three-phase induction motors and their application to the realization of surveillance and protection systems (figure 1A shows the operational sequence for motors connected in star, figure 1B shows the operational sequence for motors connected in triangle), which comprises the following operations:
    [0235] - Selection of the connection of the motor coils (1), receiving information from a mechanical sensor located in the terminal reserved for the connection of the neutral, in such a way that if there is a cable connected to that terminal, it is determined that the connection of the The motor is a star, and if the terminal is disconnected, it is determined that the connection is in a triangle.
    [0236] - Digital processing (2) of the sampled signals obtained by physical means of measurement and acquisition of electrical signals (D) of the system (see figures 2 and 3), obtaining (in 3) the matrices of effective values and initial phases of voltage and intensity at fundamental frequency for each phase of the motor stator, in total six matrices for each voltage and current phase.
    [0237] - With these matrices, the effective values and initial phases of the homopolar sequence components of the stator voltages of the motor, connected in star, to the fundamental frequency, according to equation [1], are obtained (in 4).
    [0238] - From the matrices of effective values of the voltages for the fundamental frequency (in 3) and the homopolar sequence voltage and fundamental frequency (in 4), registered in the first operation of the motor, the (in 5) displacement powers of the neutral of motor manufacturing, connected in star, according to equation [22], as well as of the lack of structural symmetry index of the star motor (in 6), according to equation [23], and the factor of structural symmetry of the star motor (in 7), according to the equation [24].
    [0239] - From the homopolar sequence and fundamental frequency voltages measured at any time and in the first operation of the motor, by applying equation [1], the sequence voltage is obtained (in 8) homopolar specifies the defect of symmetry produced in the motor, according to the equation [25].
    [0240] - From the effective values of the homopolar sequence and fundamental frequency voltages measured in the previous step and in the first operation of the motor, the displacement powers of the total neutral and the symmetry defect of the connected motor are obtained (in 9) in star, according to equations [26] and [28], respectively, as well as the indices of lack of total symmetry of the motor and produced by the failures of symmetry (in 10), according to equations [29] and [30], respectively.
    [0241] - From the values of the displacement power of the neutral measured at any instant, according to the equation [26], and in the first operation of the motor, according to the equation [22], we obtain (in 11), the intensity of the defect of symmetry of the motor connected in star, in any instant, according to the equation [27]; if the values of this parameter exceed a certain threshold value, comprised between 3 and 5, it is understood that the defect is dangerous for the motor and protection must be activated.
    [0242] - From the matrices of voltages and currents of the phases, measured (in 3) for the motor connected in a triangle, the effective values and initial phases of the components of homopolar sequence and fundamental frequency of the currents are obtained (in 14) of the stator of the motor connected in a triangle, according to the equation [11].
    [0243] - From the matrices of effective values of the phase voltages of the fundamental frequency (in 3) and of the homopolar sequence current (in 14), recorded in the first operation of the motor connected in a triangle, they are obtained (in 15). ) the displacement powers of the manufacturing (or structural) neutral of the motor connected in a triangle, according to equation [31], as well as the index of lack of structural symmetry of the engine (in 16), according to the equation [32], and of the structural symmetry factor of the engine in triangle (in 17), according to the equation [33].
    [0244] - From the registered homopolar sequence current (at 15) in the first motor operation and the measured homopolar sequence current (at 14) in the stator windings at any time, the current of homopolar sequence in the stator specifies the lack of symmetry produced in the motor, as a consequence of a phase failure or break of bars, according to the equation [34].
    [0245] - From the homopolar sequence currents corresponding to structural and produced symmetry faults, the displacement powers of the total neutral are obtained (in 19), according to equation [35], and specific to the lack of symmetry produced in the motor connected in a triangle, according to the equation [37], as well as (in 20) the indices of lack of total and proper symmetry of each defect, according to equations [38] and [39], respectively.
    [0246] - From the displacement power values of the structural (manufacturing) neutral of the motor connected in a triangle, determined according to the equation [31], and the displacement power of the neutral measured at each instant, according to the equation [35] , we obtain (in 21), the intensity of the defect at any instant of operation of the motor connected in a triangle, according to the equation [36].
    [0247] - Starting from a threshold value of the defect intensity, the opening of an interruption means (static or mechanical) will be activated (in 12). In practice, this threshold value, which when exceeded can become dangerous for the integrity and good functioning of the engine, it is between 3 and 5.
    [0248] - The graphical and numerical information of the values of the displacement power of the neutral in motors connected in star or triangle, as well as the monitoring and protection coefficients, obtained according to the procedure, are shown (in 13) in a visualization means .
    [0249] In another preferred embodiment of the invention, the method for measuring symmetry defects can be applied to the realization of systems of preventive maintenance and quality control of three-phase induction motors, connected both in star and in triangle, as shown in Figures 7 and 8, according to the operational sequence shown in Figures 6A and 6B (Figure 6A shows the operational sequence for star-connected motors, Figure 6B shows the operational sequence for motors connected in triangle), which comprises the same operations that the surveillance and protection systems, indicated above, with the only difference that:
    [0250] - From a threshold value of the intensity of the defect, between 3 and 5, a visual and / or acoustic alarm will be activated (in 22), instead of activating the opening of a three-phase switch, when the defect is dangerous for the integrity of the engine.
    [0251] According to an embodiment of the present invention, the system (A) for the measurement of lack of symmetry in three-phase induction motors (B) connected in star (see figure 2) and connected in a triangle (see figure 3), is formed by physical means of measuring and acquiring electrical signals (D) (hardware), processor means (E), a program for measuring the displacement power of the neutral and of the factors that measure the motor symmetry (P), display means (V), and activation means (F) of disconnect switches (S), internal or external.
    [0252] The physical means of measuring and acquiring electrical signals (D) comprise signal conditioners and a data acquisition card. The signal conditioners adapt the instantaneous values of the secondary voltages and currents of voltage and current measurement sensors (C), in such a way that the voltages in their outputs can be applied to the analog inputs of the acquisition card or equivalent system, which converts the analog signals of voltage and intensity into a series of discrete samples that are used as input in the measurement program. There is also a processor means (E) with a base plate on which the acquisition card is placed so that the discrete samples of the voltage and intensity signals can be exchanged with the measurement program (P), which has a threshold value of the defect intensity, between 3 and 5, whose exceeding can be dangerous for the integrity of the motor. In the display means (V), which in a preferred embodiment can be a screen, all the information on the values of the displacement power of the neutral and of the monitoring and protection parameters against motor symmetry defects is displayed. Figure 11 shows a possible arrangement of the screen and the presentation of these magnitudes therein.
    [0253] According to another embodiment of the invention, the system (A) for the measurement of lack of symmetry in three-phase induction motors (B) connected in star (see figure 7) and connected in a triangle (see figure 8), it lacks the activation means of disconnect switches, and is therefore formed by a physical means of measuring and acquiring electrical signals (D) (hardware), a processor means (E), a program for measuring the power of displacement of the neutral and of the factors that measure the symmetry of the motor (P), and a means of visualization (V).
    [0254] The processor means (E) for the symmetry measurement system in three-phase induction motors connected in a star according to an embodiment of the present invention are composed of the following modules (FIG. 4):
    [0255] - Digital signal processing module (23), which acquires tension and intensity samples, and stores them in a vector for each of them.
    [0256] - Analysis module (24), in which the effective values and the initial phase of the fundamental frequency voltages and currents are obtained, from the samples acquired in the digital signal processing module (23).
    [0257] - Symmetry module (25), which obtains the matrices of the homopolar sequence components, in effective value and in phase, from the voltages of the motor stator coils to the fundamental frequency, from the matrices obtained in the module previous.
    [0258] - Power displacement module of the neutral (26), in charge of obtaining the values of the displacement powers of the structural neutral (of manufacture) and produced, caused by eventual motor symmetry defects, according to equations [22], [26] ] and [28], from the matrices of voltages and currents of the two previous modules.
    [0259] - Module of fault indices and symmetry factors (27), in which the coefficients that determine the symmetry of manufacture of the motor or its lack of symmetry are obtained, caused by defects produced, such as phase failures, among others, and which allow to monitor the dangerousness of said defects, based on to the values of voltages, currents and powers, obtained in the previous modules, after applying equations [27], [29] and [30].
    [0260] - Protection module (28), responsible for deciding the application of the switch signal (S), internal or external, taking into account the value of the defect intensity and the other failure coefficients, determined by the equations [27] ], [29] and [30].
    [0261] - Visualization module (29), responsible for displaying on a screen the graphical and numerical information of the displacement powers of the neutral and of the monitoring and protection coefficients of the motor, as shown in figure 11.
    [0262] The processor means (E) for the symmetry measuring system in three-phase induction motors connected in a triangle according to an embodiment of the present invention are composed of the following modules (FIG. 5):
    [0263] - Digital signal processing module (23), which acquires tension and intensity samples, and stores them in a vector for each of them.
    [0264] - Analysis module (24), in which the effective values and the initial phase of the fundamental frequency voltages and currents are obtained, from the samples acquired in the digital signal processing module (23).
    [0265] - Symmetry module (30), which obtains the matrices of the homopolar sequence components, in effective value and in phase, of the currents in the stator coils of the motor at the fundamental frequency, from the matrices obtained in the previous module.
    [0266] - Modulus of displacement powers of the neutral (31), in charge of obtaining the values of the displacement powers of the structural neutral (of manufacture) and produced, caused by eventual defects of symmetry of the motor, according to equations [31], [35] ] and [37], from the matrices of voltages and currents of the two previous modules.
    [0267] - Module of failure indices and symmetry factors (32), in which the coefficients that determine the symmetry of the motor's manufacture or its lack of symmetry are obtained, caused by defects produced, such as phase failures, among others, and they allow to monitor the dangerousness of said defects, based on the values of voltages, currents and powers, obtained in the previous modules, after applying the equations [36], [38] and [39].
    [0268] - Protection module (28), responsible for deciding the application of the switch signal (S), internal or external, taking into account the value of the defect intensity and the other failure coefficients, determined by the equations [36] ], [38] and [39].
    [0269] - Visualization module (29), responsible for displaying on a screen the graphical and numerical information of the displacement powers of the neutral and of the monitoring and protection coefficients of the motor, as shown in figure 11.
    [0270] According to another preferred embodiment of the present invention, the processor means (E) for the measurement system of lack of symmetry in three-phase induction motors, are already connected in star or in triangle (see figures 9 and 10, respectively), they comprise in place of the protection module (28) (or additionally at the same), an alarm module (30), responsible for activating a light and / or acoustic alarm, taking into account the value of the intensity of the defect and of the other failure coefficients, determined by the equations [27], [29] and [30] in the case of motors connected in star, or by equations [36], [38] and [39] in the case of motors connected in a triangle.
    [0271] The invention has been described above according to preferred embodiments thereof. However, a number of variations will occur to the person skilled in the art which would be apparent from the teachings disclosed herein and which are intended to be included within the scope of the appended claims.
    权利要求:
    Claims (1)
    [0001]
    Measurement procedure of lack of symmetry in three-phase induction motors, which comprises calculating at least one parameter selected from the group constituted by the symmetry defect intensity (ID), the lack of symmetry index (IFS) and the symmetry factor ( FS), according to the following equations:

    where
    Sn is the displacement power of neutral,
    S! ^ Is the initial neutral displacement power, and
    S is the apparent power of the motor.
    The method according to claim 1, wherein the three-phase induction motor comprises coils connected in a selected configuration of star configuration and triangle configuration, characterized in that the apparent power of the motor and the neutral displacement power are respectively calculated according to the equations [3] and [7]

    for the star configuration,
    and according to equations [13] and [18]

    for the configuration in triangle.
    Procedure according to any of the claims above, characterized in that the initial neutral displacement power is provided by the motor manufacturer.
    4. Process according to any of claims 1 and 2, characterized in that the displacement power initial neutral is measured in the first operation performed by the motor.
    Method according to any one of the preceding claims, characterized in that at least one parameter selected from the group consisting of the symmetry index (IFS) and the symmetry factor (FS) at the time of manufacture of the engine is calculated and used as manufacturing quality control parameters.
    Method according to any one of the preceding claims, comprising calculating the symmetry defect intensity (ID), characterized in that it also comprises activating protection means when the ID value exceeds a threshold value.
    Method according to claim 6, characterized in that the threshold value of ID from which protection means are activated is between 3 and 5.
    Method according to any of claims 6 and 7, characterized in that the protection means comprise the opening of interruption means.
    9. Method according to any of the preceding claims, characterized in that it also comprises the visualization of the calculated parameters.
    10. Measurement system of lack of symmetry in three-phase induction motors, comprising:
    - Means of measurement and acquisition of electrical signals (D);
    - processor means (E);
    - a program for measuring the displacement power of neutral (P); Y
    - visualization means (V).
    11. System according to claim 10, characterized in that the means for measuring and acquiring electrical signals (D) comprise:
    - signal conditioners, and
    - a data acquisition card.
    System according to any of claims 10 and 11, characterized in that the measurement program (P) comprises:
    - a digital signal processing module (23);
    - an analysis module (24);
    - a symmetry module (25);
    - a modulus of displacement powers of the neutral (26);
    - a module of fault indices and symmetry factors (27); Y
    - a display module (29).
    System according to any one of claims 10 to 12, characterized in that it also comprises means for activating (F) the motor disconnect switch (S), and in addition the measuring program (P) comprises a protection module ( 28) to decide the activation of the switch (S) through the switch activation means (F) (S) in case the symmetry defect intensity value exceeds an ID threshold value stored in the program.
    14. System according to any of claims 10 to 13, characterized in that the measurement program (P) further comprises an alarm module (30) to emit an alarm in case the intensity value of symmetry defect exceeds an ID threshold value stored in the program.
    System according to any of claims 13 and 14, characterized in that the threshold value of ID stored in the program is between 3 and 5.
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    同族专利:
    公开号 | 公开日
    WO2020099709A1|2020-05-22|
    ES2712350B2|2019-09-12|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    WO2017212088A1|2016-06-07|2017-12-14|Universitat Politècnica De València|Method and device for determining the state of the neutral conductor in an electrical installation|
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    ES201831104A|ES2712350B2|2018-11-14|2018-11-14|PROCEDURE AND SYSTEM OF MEASUREMENT OF LACK OF SYMMETRY IN THREE-PHASE INDUCTION MOTORS|ES201831104A| ES2712350B2|2018-11-14|2018-11-14|PROCEDURE AND SYSTEM OF MEASUREMENT OF LACK OF SYMMETRY IN THREE-PHASE INDUCTION MOTORS|
    PCT/ES2019/070779| WO2020099709A1|2018-11-14|2019-11-13|Method and system for measuring the lack of symmetry in three-phase induction motors|
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