A method for detecting inter-turn short circuit fault diagnosis of stator homophasic double-branch current

Abstract

The present application belongs to the field of motor fault diagnosis, and discloses a kind of detection stator same-phase double branch current inter-turn short circuit fault diagnosis method, the present application is aimed at long-term network operation of phase modifier, and operation condition is complex and poor, leading to stator inter-turn short circuit or rotor inter-turn short circuit often occurs, and the stator winding of phase modifier is parallel double branch design, the present application detects stator side same-phase double branch current, and according to the amplitude difference and phase difference of double branch current under the analysis of fault state and normal state, carries out fault diagnosis, effectively solves the problem of difficult fault diagnosis of phase modifier stator and rotor inter-turn short circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of motor fault diagnosis, and particularly relates to a method for diagnosing inter-turn short circuit fault of stator homophase double-branch current. BACKGROUND

[0002] In recent years, with the rapid popularization of extra-high voltage direct current transmission projects, the problems of insufficient dynamic reactive power supply and weak voltage support capacity at the sending and receiving ends are increasingly prominent, and objective requirements for large-scale active power transmission of direct current must be matched with large-scale dynamic reactive power, that is, "large direct current transmission and strong reactive power support". Therefore, a new type of phase modifier for meeting the new requirements of power transmission has become one of the research hotspots.

[0003] The single-machine capacity of a new generation of large-capacity phase modifier is increased to 300 Mvar, which can comprehensively improve the dynamic reactive power reserve of the system, and can solve various types of voltage stability problems such as insufficient dynamic reactive power at the receiving end of the power grid and insufficient short-circuit capacity support at the weak sending end of the power grid. In addition, when a fault occurs in the system, the new type of phase modifier can also improve the dynamic reactive power response characteristics of the system, reduce the number of commutation failures, quickly make up for the lack of reactive power during short-circuit faults, and thus strengthen the voltage support and operational flexibility of the system.

[0004] The new type of large-capacity synchronous phase modifier will be affected by the strong impact current of the power grid during the solution of the power grid fault, and will cause local temperature to be too high, insulation to be damaged, mechanical vibration and the like after a long time. Although the synchronous phase modifier has a relay protection device inside, it is only used to protect the phase modifier from being further damaged after the fault occurs, and the type, degree and position of the fault cannot be distinguished.

[0005] The inter-turn short circuit fault of the stator and rotor windings is a very common fault of synchronous motors. The impact current during the power grid fault, the aging and wear of the stator and rotor winding coils and the like can cause the inter-turn short circuit fault of the stator and rotor windings, which can cause local overheating of the motor, damage to the mechanical structure, and even serious accidents such as burning, and has great harm to the system. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for diagnosing the inter-turn short circuit fault of the stator homophase double-branch current, which solves the effective diagnosis of the inter-turn short circuit fault of the stator and rotor of the phase modifier in the prior art.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] A method for diagnosing the inter-turn short circuit fault of the stator homophase double-branch current, comprising the following steps:

[0009] (1) install current transformers in the three-phase six-branch stator of the synchronous phase modifier to detect the branch current and phase, and use the current transformers to detect and obtain the branch current amplitude and phase.

[0010] (2) according to the current amplitude and phase in step (1), obtain the in-phase two-branch current amplitude difference and phase difference.

[0011] (3) compare the three sets of phase differences of the phase modifier in the normal operation state (record the maximum amplitude difference as i1 and the maximum phase difference as ) with the three sets of phase differences of the phase modifier in the fault condition state, so as to perform fault diagnosis.

[0012] Further, the current amplitude and phase in step (1) are

[0013] Further, the current amplitude difference and phase difference in step (2) are

[0014]

[0015] Further, the judgment basis of the fault diagnosis in step (3) is specifically as follows:

[0016] all the three sets of phase differences are less than or equal to and all the three-phase amplitude differences are greater than i1, then the synchronous phase modifier has a rotor winding turn-to-turn short circuit fault.

[0017] one of the three sets of phase differences is greater than and the amplitude difference is greater than i1, then the synchronous phase modifier has a stator winding turn-to-turn short circuit fault.

[0018] The rotor winding turn-to-turn short circuit fault diagnosis method of the rotor side mounted detection coil judges the rotor winding fault or the stator winding fault by detecting the in-phase branch current, and the stator turn-to-turn short circuit fault can be located to the branch where the fault occurs.

[0019] The beneficial effects of the present application are as follows:

[0020] The present application detects the in-phase two-branch current of the stator, compares the branch current amplitude difference and phase difference in the normal state with those in the fault state for fault diagnosis. The stator and rotor turn-to-turn short circuit faults often occur in the phase modifier, and the problem of online fault diagnosis difficulty of the phase modifier stator and rotor winding turn-to-turn short circuit can be effectively solved. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0022] Figure 1 is a stator inter-turn short circuit fault diagnosis flow chart;

[0023] Figure 2 is a rotor winding schematic diagram;

[0024] Figure 3 is a stator double branch winding schematic diagram;

[0025] Figure 4 is a simulation model rotor inter-turn short circuit in-phase double branch current difference iD1 line graph;

[0026] Figure 5 is a simulation model stator inter-turn short circuit in-phase double branch current difference iD2 line graph;

[0027] Figure 6 is a rotor winding inter-turn short circuit fault when the short circuit coil generates excitation magnetic motive force waveform diagram;

[0028] Figure 7 is a rotor winding inter-turn normal state excitation magnetic motive force waveform diagram;

[0029] Figure 8 is a stator A phase double branch circuit model diagram;

[0030] Figure 9 is a stator winding inter-turn short circuit fault equivalent circuit diagram. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0032] The application pre-sets a fault scene, in which fault diagnosis is carried out. The synchronous phase modifier simulation model has a rated capacity of 300 Mvar, a stator rated voltage of 20 kV, a rated frequency of 50 Hz, a stator rated current of 8660 A, a rated excitation voltage of 415 V, a rated excitation current of 1835 A, 48 stator slots, 2 conductors per slot, 2 parallel branch numbers, 32 rotor slots, and 12 turns of winding per slot. Now, it is set that turn-to-turn short circuit fault of 6 turns of winding occurs in a stator or rotor slot, the phase modifier is always in turn-to-turn short circuit fault after the fault, and the fault degree can become larger with time growth. The following describes the fault diagnosis.

[0033] As shown in Figures 1-5 , the application provides a technical solution, a turn-to-turn short circuit fault diagnosis method for detecting stator in-phase double-branch current, which comprises the following steps:

[0034] (4) The branch current and phase are detected by installing current transformers in the three-phase six-branch stator of the synchronous phase modifier, and the current transformer is used to detect and obtain the branch current amplitude and phase as

[0035] (5) According to the parameters in step (1), the in-phase two-branch current amplitude difference and phase difference are obtained as

[0036] (3) The three sets of phase difference values of the phase modifier in the normal operation state (the maximum amplitude difference in the normal state is i1, and the maximum phase difference is ) are compared with the three sets of phase difference values of the phase modifier in the fault condition state , and then the fault diagnosis is carried out.

[0037] Further, the basis for judging the fault diagnosis is specifically as follows:

[0038] All the three sets of phase differences are less than or equal to , and the amplitude difference of each three-phase is greater than i1, then the synchronous phase modifier has a rotor winding turn-to-turn short circuit fault.

[0039] One of the three sets of phase differences is greater than , and the amplitude difference is greater than i1, then the synchronous phase modifier has a stator winding turn-to-turn short circuit fault.

[0040] Further, when the rotor winding turn-to-turn short circuit fault occurs in a rotor slot at a certain moment, the excitation magnetic motive force waveform generated by the short circuit coil is as shown in Figure 6 , and the excitation magnetic motive force waveform in the normal state is as shown in Figure 7 by the dashed line.

[0041] The magnetic motive force Ffd (α) Fourier analysis yields:

[0042]

[0043] Where n is a positive integer, I f N is the excitation current. fd Let W be the number of turns in the short-circuit coil, γ be the rotor tooth circumferential angle, β be the rotor slot angle, d be the d-th slot, and α be the rotor electrical angle. To simplify the calculation, let the variable W be... dn for:

[0044]

[0045] At this point, taking phase A as an example, the stator phase A dual-branch circuit model diagram is as follows: Figure 8 As shown. After a fault occurs, the voltage difference Δu′ between the two branches will be:

[0046]

[0047] Among them, e a1 e a2 For the induced electromotive force of branches a1 and a2, I a1 I a2 R is the induced current in branches a1 and a2. a1 R a2 Let jωL be the resistance of branches a1 and a2. a1 、jωL a2 For the reactances of branches a1 and a2, I′ f The excitation current after the fault is given, Nc represents the number of turns per phase winding, and k ω1 ν represents the fundamental winding factor, l represents the air gap length, ν represents the magnetic flux density cutting winding linear velocity, and Λ represents the vacuum permeability.

[0048] At this time, even harmonic circulating currents will appear in the parallel branches, and there will be an amplitude difference between the currents in the two branches, but no phase difference.

[0049] Therefore, the rotor winding inter-turn short circuit fault diagnosis method with a detection coil installed on the rotor side can determine the rotor winding fault or stator winding fault by detecting the current of the same phase branch, and the stator inter-turn short circuit fault can be located to the branch where the fault is located.

[0050] When a stator winding inter-turn short circuit fault occurs, taking phase A as an example, the equivalent circuit diagram is as follows: Figure 9 As shown. Before the fault, the two branches were symmetrical, with no voltage difference and equal impedance. After the fault, only the fundamental and odd harmonic magnetomotive forces remained in the air gap, and no voltage difference was generated between the two branches. However, since the short-circuit resistance of branch a1 was much smaller than the impedance of the short-circuited coil, i.e.:

[0051] r << jωL ff This results in two branch impedances being unequal, i.e.:

[0052]

[0053] where Z a1 , Z a2 are the equivalent impedances of the a1 and a2 branches, are the impedance angles of the a1 and a2 branches, L A is the inductance of the A phase under normal conditions, L ff is the inductance of the faulted section. According to the above formula, the two branch currents will have a difference in amplitude and a difference in phase.

[0054] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0055] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only illustrative of the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application.

Claims

1. A method of detecting a turn-to-turn short circuit fault diagnosis of a stator phase balanced dual branch current, characterized by, comprising the steps of: (1) install current transformers in the three-phase six-branch stator of the synchronous phase modifier to detect the branch current and phase, and use the current transformers to detect and obtain the branch current amplitude and phase 、 、 、 、 、 ; (2) According to the current amplitude and phase in step (1), the in-phase two-branch current amplitude difference and phase difference are obtained , , ; (3) the three sets of phase difference of the regulating phase machine in normal operation state are recorded, the maximum amplitude difference in normal state is , and the maximum phase difference is , which are compared with the three sets of phase difference of the regulating phase machine in fault state, so that fault diagnosis is performed, and the judgment basis of fault diagnosis is as follows: The phase difference of the three groups is less than or equal to The amplitude difference of the three phases is greater than The synchronous phase modifier has a rotor winding turn-to-turn short circuit fault. The phase difference of the three groups is greater than a certain phase , and the amplitude difference is greater than , and the synchronous phase modifier has a stator winding turn-to-turn short circuit fault.

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