Phase modifier stator winding turn-to-turn short circuit fault diagnosis method based on electromagnetic torque

Abstract

The invention discloses a phase modifier stator winding turn-to-turn short circuit fault diagnosis method based on electromagnetic torque, particularly relates to the technical field of electrical fault diagnosis, and solves the problems that in the prior art, in the operation process of a phase modifier, excitation current needs to be adjusted according to the actual demand of a power system; and the change of the exciting current often causes the reduction of the diagnosis effect of the fault characteristic quantity. According to the technical scheme, the method comprises the steps that firstly, three-phase stator currents Ia (t), Ib (t) and Ic (t), three-phase stator voltages Ua (t), Ub (t) and Uc (t), exciting current If (t) and rotating speed n (t) of the phase modifier are synchronously collected on line; the electromagnetic torque T (t) of the phase modifier is calculated; then calculating a fault characteristic quantity; and finally, setting a fault threshold value, and when the characteristic quantity is greater than the threshold value, determining a stator winding turn-to-turn short circuit fault. According to the invention, the interference of the excitation current change of the phase modifier on fault diagnosis can be suppressed, and the robustness of fault diagnosis is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical fault diagnosis, and particularly relates to a method for diagnosing inter-turn short circuit faults in the stator winding of a synchronous condenser based on electromagnetic torque. Background Art

[0002] With the large-scale grid connection of renewable energy and the continuous improvement of the voltage level and capacity of the power transmission system, the structure and operation mode of long-distance UHV DC transmission systems have become increasingly complex, and the problem of insufficient reactive power has become increasingly prominent. To address this challenge, a new generation of large synchronous condensers can provide effective reactive power support for the power transmission system with higher capacity, stronger dynamic voltage regulation ability, and higher reliability. In recent years, a new generation of large-capacity synchronous condensers has been widely used in HVDC transmission to effectively improve the operation stability of the system. As a key reactive power compensation device, once a synchronous condenser fails, not only is the repair cycle long, but it may also cause serious economic losses and system operation risks. To ensure the safe and stable operation of the power grid, it is imperative to conduct research on fault diagnosis for synchronous condensers.

[0003] Inter-turn short circuit faults in the stator winding are common and prone to occur in synchronous condensers. Once an inter-turn short circuit fault occurs in the stator winding of a synchronous condenser, it will cause a sharp increase in the winding current, leading to local overheating, and even damaging the winding insulation in severe cases. Therefore, studying inter-turn short circuit faults in the stator winding is of great significance for ensuring the healthy operation of synchronous condensers and even the power system. During the operation of a synchronous condenser, the excitation current needs to be adjusted according to the actual needs of the power system, and the change in the excitation current often leads to a decrease in the diagnostic effect of fault characteristic quantities. In order to improve the robustness of the method for diagnosing inter-turn short circuit faults in the stator winding, the present invention proposes a method for diagnosing inter-turn short circuit faults in the stator winding based on electromagnetic torque. Summary of the Invention

[0004] Therefore, the present invention solves the technical problem in the prior art that during the operation of a synchronous condenser, the excitation current needs to be adjusted according to the actual needs of the power system, and the change in the excitation current often leads to a decrease in the diagnostic effect of fault characteristic quantities; the method for diagnosing inter-turn short circuit faults in the stator winding of a synchronous condenser based on electromagnetic torque provided by the present invention can suppress the adverse effects of changes in the excitation current on fault diagnosis and improve the effectiveness of fault diagnosis.

[0005] The method for diagnosing inter-turn short circuit faults in the stator winding of a synchronous condenser based on electromagnetic torque provided by the present invention includes the following steps:

[0006] Step 1: Online synchronously collect the three-phase stator currents I a (t), I b (t) and I c (t) of the synchronous condenser, and the three-phase stator voltages U a (t), Ub (t) and U c (t), the exciting current I f (t) and the rotational speed n(t);

[0007] Step 2: Calculate the electromagnetic torque T(t) of the synchronous condenser;

[0008] Step 3: According to the analytical models of the air-gap magnetic field energy and the resultant magnetomotive force, obtain the relationship between the electromagnetic torque and the exciting current, and thereby set the fault characteristic quantity T 2th (t) represents the harmonic component with a frequency of 2ω in the electromagnetic torque;

[0009] Step 4: Set the fault threshold δ, and when T FI >δ, it is determined as a stator winding inter-turn short circuit fault.

[0010] In the said Step 1, the three-phase stator current, the three-phase stator voltage, the exciting current and the rotational speed are all instantaneous values at the same moment.

[0011] In the said Step 2, the electromagnetic torque T(t) can be obtained by the following formula:

[0012]

[0013] In the formula, is the voltage-current phase angle of the phase with the lowest current amplitude among the three phases.

[0014] The air-gap magnetic field energy in the said Step 3 can be expressed by the following formula:

[0015]

[0016] In the formula, l represents the axial length of the stator core, and R0 represents the inner surface radius of the air-gap magnetic field. Based on the principle of virtual displacement, when the rotor magnetomotive force has a small displacement △ψ, a damping-type electromagnetic torque will be generated, which is expressed as:

[0017]

[0018] After a stator winding inter-turn short circuit fault occurs, the resultant magnetomotive force f(α,t) and the magnetic permeability per unit area Λ0 of the synchronous condenser can be respectively expressed by the formulas:

[0019] f(α,t) = F r1 cos(ωt - pα + π / 2 + ψ) + F s1 cos(ωt - pα)

[0020] =(I f1 - I f2 cos2ωt)Ncos(ωt - pα + π / 2 + ψ)

[0021] +η(I f1 -I f2 cos2ωt)Ncos(ωt - pα)

[0022] Λ0 = μ0 / g0

[0023] Wherein, p represents the number of pole pairs, F r1 and F s1 respectively represent the stator magnetomotive force and the rotor magnetomotive force under the stator winding inter-turn short-circuit fault. I f1 represents the exciting current under no-fault condition, I f2 represents the peak value of the circulating current generated under the stator winding inter-turn short-circuit fault, N represents the number of turns per pole of the exciting winding, ω represents the electrical angular frequency, α represents the stator mechanical angle, ψ represents the internal attack angle, and η represents the ratio of the stator magnetomotive force to the rotor magnetomotive force.

[0024] The electromagnetic torque after the stator winding inter-turn short-circuit fault can be expressed by the formula:

[0025]

[0026] Wherein, n m represents the number of shorted turns, k = 1 / w c , w c represents the number of turns of each phase coil of the stator. It can be seen from the above formula that when the synchronous condenser has a stator winding inter-turn short-circuit fault, additional pulsating components with frequencies of 2ω and 4ω appear in the electromagnetic torque. The severity of the short-circuit fault is closely related to the amplitudes of these harmonic components. Therefore, the electromagnetic torque can be used as a characteristic index for the stator winding inter-turn short-circuit fault. In order to meet the different reactive power demands of the power system, it is necessary to adjust the exciting current of the synchronous condenser, and the change of the exciting current will affect the magnitude of the electromagnetic torque. Therefore, when using the electromagnetic torque as the characteristic of the stator winding inter-turn short-circuit fault, it is necessary to suppress the interference of the change of the exciting current on the fault recognition result, and thus the fault characteristic quantity

[0027] Furthermore, the step 3 includes: calculating the electromagnetic torque according to the real-time measured three-phase voltage, three-phase current and rotational speed, extracting the 2ω component in the electromagnetic torque, and calculating the fault characteristic quantity according to

[0028] The step 4 includes: the more severe the stator winding inter-turn short-circuit fault is, the larger the fault characteristic quantity T FI is. According to the structural performance and actual diagnosis requirements of the synchronous condenser, a fault threshold δ is set.

[0029] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0030] ​1. The method for diagnosing the inter-turn short circuit fault of the synchronous condenser stator winding based on electromagnetic torque provided by the present invention takes into account the actual working conditions of the synchronous condenser, where the excitation current needs to be frequently adjusted according to the grid demand. The fault characteristic quantity proposed by the present invention can suppress the adverse effects of the excitation current change on the fault diagnosis and improve the effectiveness of the fault diagnosis.

[0031] 2. The method for diagnosing the inter-turn short circuit fault of the synchronous condenser stator winding based on electromagnetic torque provided by the present invention is simple to apply, without the need for additional sensor devices or modification of the synchronous condenser, and can realize online monitoring according to the sensor data built into the synchronous condenser itself. Description of the Drawings

[0032] 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 required for use in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings.

[0033] Figure 1 It is a flow chart of the method for diagnosing the inter-turn short circuit fault of the synchronous condenser stator winding involved in the present invention;

[0034] Figure 2 It is a schematic diagram of the inter-turn short circuit fault of the synchronous condenser stator winding involved in the present invention;

[0035] Figure 3 It is a simulation model of the inter-turn short circuit fault of the stator winding;

[0036] Figure 4 It is the amplitude of the 2ω component of the electromagnetic torque during the inter-turn short circuit fault of the stator winding involved in the present invention;

[0037] Figure 5 It is the fault characteristic quantity T FI of the fault diagnosis result. Detailed Embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present application more clear, the following further details the present application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] Embodiment 1:

[0040] This embodiment provides a method for diagnosing the inter-turn short circuit fault of the synchronous condenser stator winding based on electromagnetic torque, including the following steps:

[0041] Step 1: Online synchronously collect the three-phase stator currents I a (t), I b(t) and I c (t), the three-phase stator voltage U a (t), U b (t) and U c (t), the exciting current I f (t) and the rotational speed n(t);

[0042] Step 2: Calculate the electromagnetic torque T(t) of the synchronous condenser;

[0043] Step 3: According to the analytical models of the air-gap magnetic field energy and the resultant magnetomotive force, obtain the relationship between the electromagnetic torque and the exciting current, and thus set the fault characteristic quantity T 2th (t) represents the harmonic component with a frequency of 2ω in the electromagnetic torque;

[0044] Step 4: Set the fault threshold δ. When T FI >δ, it is determined as a stator winding inter-turn short circuit fault.

[0045] In the said Step 1, the three-phase stator current, the three-phase stator voltage, the exciting current and the rotational speed are all instantaneous values at the same moment.

[0046] In the said Step 2, the electromagnetic torque T(t) can be obtained by the following formula:

[0047]

[0048] In the formula, is the voltage-current phase angle of the phase with the lowest current amplitude among the three phases.

[0049] The air-gap magnetic field energy in the said Step 3 can be expressed by the following formula:

[0050]

[0051] In the formula, l represents the axial length of the stator core, and R0 represents the inner surface radius of the air-gap magnetic field. Based on the principle of virtual displacement, when the rotor magnetomotive force has a small displacement △ψ, a damping-type electromagnetic torque will be generated, which is expressed as:

[0052]

[0053] After a stator winding inter-turn short circuit fault occurs, the resultant magnetomotive force f(α,t) and the permeability per unit area Λ0 of the synchronous condenser can be respectively expressed by the formulas:

[0054] f(α,t) = F r1 cos(ωt - pα + π / 2 + ψ) + F s1 cos(ωt - pα)

[0055] =(I f1 -I f2cos2ωt)Ncos(ωt - pα + π / 2 + ψ)

[0056] + η(I f1 - I f2 cos2ωt)Ncos(ωt - pα)

[0057] Λ0 = μ0 / g0

[0058] In the formula, p represents the number of pole pairs, F r1 and F s1 respectively represent the stator magnetomotive force and the rotor magnetomotive force under the stator winding inter-turn short circuit fault. I f1 represents the exciting current under no-fault condition, and I f2 represents the peak value of the circulating current generated under the stator winding inter-turn short circuit fault. N represents the number of turns per pole of the exciting winding, ω represents the electrical angular frequency, α represents the stator mechanical angle, ψ represents the internal attack angle, and η represents the ratio of the stator magnetomotive force to the rotor magnetomotive force.

[0059] The electromagnetic torque after the stator winding inter-turn short circuit fault can be expressed as the formula:

[0060]

[0061] In the formula, n m represents the number of shorted turns, k = 1 / w c , and w c represents the number of turns of each phase coil of the stator. It can be seen from the above formula that when the synchronous condenser has a stator winding inter-turn short circuit fault, additional pulsating components with frequencies of 2ω and 4ω appear in the electromagnetic torque. The severity of the short circuit fault is closely related to the amplitudes of these harmonic components. Therefore, the electromagnetic torque can be used as a characteristic index for the stator winding inter-turn short circuit fault. In order to meet the different reactive power requirements of the power system, it is necessary to adjust the exciting current of the synchronous condenser, and the change of the exciting current will affect the magnitude of the electromagnetic torque. Therefore, when using the electromagnetic torque as the characteristic of the stator winding inter-turn short circuit fault, it is necessary to suppress the interference of the exciting current change on the fault identification result, and thus the fault characteristic quantity

[0062] Furthermore, step 3 includes: calculating the electromagnetic torque according to the real-time measured three-phase voltage, three-phase current and rotational speed, extracting the 2ω component in the electromagnetic torque, and calculating the fault characteristic quantity according to

[0063] Step 4 includes: the more severe the stator winding inter-turn short circuit fault is, the larger the fault characteristic quantity T FI is. According to the structural performance and actual diagnosis requirements of the synchronous condenser, a fault threshold δ is set.

[0064] Embodiment 2: ​

[0065] Based on the above method, in this embodiment, a TTS-300-2 type 300 Mvar double-water-cooled synchronous condenser produced by Shanghai Electric Machinery Works Co., Ltd. is selected for diagnosis, and the specific parameters are shown in Table 1:

[0066] Table 1: Parameter Table of TTS-300-2 Type Synchronous Condenser

[0067]

[0068] The schematic diagram of the inter-turn short circuit fault of the stator winding of the synchronous condenser is as Figure 2 shown. According to the parameters of the synchronous condenser in Table 1, a simulation model is established as Figure 3 shown. When the synchronous condenser operates in the over-excited state, the simulated excitation currents are 1500 A, 1600 A, and 1700 A respectively, and the severity of the fault is divided into the following three types:

[0069] (1) When there is no fault, it is denoted as N1;

[0070] (2) One turn short circuit in branch a1, denoted as F2;

[0071] (3) Two turns short circuit in branch a1, denoted as F3.

[0072] The 2ω (100 Hz) component of the electromagnetic torque of the synchronous condenser under different excitation currents and fault severities is as Figure 4 shown. As Figure 4 can be seen, the increase in the severity of the fault and the increase in the excitation current will both lead to an increase in the amplitude of the 2ω component of the electromagnetic torque. Therefore, it is easy to misjudge the inter-turn short circuit fault of the stator winding only by using the amplitude of the harmonic component of the electromagnetic torque. Obtain the 2ω component of the electromagnetic torque and the excitation current value of the synchronous condenser, and calculate the fault characteristic quantity T FI = T 2th (t) / I f 2 (t), and get Figure 5 . As Figure 5 can be seen, the fault characteristic quantity T FI is only affected by the severity of the fault, and the change in the excitation current hardly affects the value of T FI . Therefore, the method for diagnosing the weak inter-turn short circuit fault of the stator winding of the synchronous condenser based on the electromagnetic torque proposed by the present invention can diagnose the inter-turn short circuit fault of the stator winding and is not affected by the change in the excitation current.

[0073] The specific embodiments described above further elaborate on the objective, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for diagnosing inter-turn short-circuit fault of a phase-converter stator winding based on electromagnetic torque, characterized in that: The steps include: S1: Online synchronous acquisition of the three-phase stator current Ia(t), Ib(t) and Ic(t) of the phase regulator, the three-phase stator voltage Ua(t), Ub(t) and Uc(t), the excitation current If(t) and the speed n(t); S2: Calculate the electromagnetic torque T(t) of the phase regulator; S3: Based on the analytical model of air gap magnetic field energy and synthetic magnetomotive force, the relationship between electromagnetic torque and excitation current is obtained, and the fault characteristic quantity is set accordingly. T 2th (t) represents the harmonic component with a frequency of 2ω in the electromagnetic torque; S4: Set the fault threshold δ, when T FI When >δ, it is determined as a stator winding turn-to-turn short circuit fault.

2. The method for diagnosing inter-turn short-circuit fault of a phase modulator stator winding based on electromagnetic torque according to claim 1, characterized in that: In step S1, the three-phase stator current, the three-phase stator voltage, the excitation current and the rotation speed are all instantaneous values ​​at the same moment.

3. The method for diagnosing inter-turn short-circuit fault of a phase modulator stator winding based on electromagnetic torque according to claim 1, characterized in that: In step S2, the electromagnetic torque T(t) is obtained by the following formula: In the formula, It is the voltage and current phase angle of the phase with the lowest current amplitude among the three phases.

4. The method for diagnosing inter-turn short-circuit fault of stator winding of phase modulator based on electromagnetic torque according to claim 1, characterized in that: In step S3: The air gap magnetic field energy is expressed as follows: In the formula, l represents the axial length of the stator core, and R0 represents the inner surface radius of the air gap magnetic field; Based on the virtual displacement principle, when the rotor magnetomotive force undergoes a small displacement △ψ, a damping electromagnetic torque will be generated, which can be expressed as: ψ After a stator winding inter-turn short circuit fault occurs, the synthetic magnetomotive force f(α, t) and the permeability per unit area Λ0 of the phase regulator are expressed as follows: Λ0=μ0 / g0; Where p represents the number of pole pairs, F r1 and F s1 They are respectively represented as the stator magnetomotive force and rotor magnetomotive force under stator winding interturn short circuit fault, I f1 Indicates the excitation current under no fault condition, I f2 It represents the peak value of circulating current generated under stator winding inter-turn short-circuit fault, N represents the number of turns per pole of excitation winding, ω represents the electrical angular frequency, α represents the stator mechanical angle, ψ represents the internal attack angle, and η represents the ratio of stator magnetomotive force to rotor magnetomotive force.

5. The method for diagnosing inter-turn short-circuit fault of stator winding of phase modulator based on electromagnetic torque according to claim 4, characterized in that: The electromagnetic torque after the stator winding interturn short circuit fault can be expressed as follows: Where n m Indicates the number of short-circuit turns, k = 1 / w c , w c Indicates the number of turns of each phase coil of the stator.

6. The method for diagnosing inter-turn short-circuit fault of stator winding of phase modulator based on electromagnetic torque according to claim 1, characterized in that: In the expression of electromagnetic torque, when a short-circuit fault occurs between turns of the stator winding of the phase regulator, additional pulsating components with frequencies of 2ω and 4ω appear in the electromagnetic torque; the severity of the short-circuit fault is closely related to the amplitude of these harmonic components, and the electromagnetic torque is used as a characteristic indicator of the short-circuit fault between turns of the stator winding; when the excitation current of the phase regulator is adjusted, the change of the excitation current will affect the magnitude of the electromagnetic torque in the expression. When the electromagnetic torque is used as the characteristic of the short-circuit fault between turns of the stator winding, the fault characteristic quantity is proposed 7. The method for diagnosing inter-turn short-circuit fault of stator winding of phase modulator based on electromagnetic torque according to claim 1, characterized in that: The step S3 comprises: calculating the electromagnetic torque according to the three-phase voltage, three-phase current and speed measured in real time, extracting the 2ω component in the electromagnetic torque, and calculating the electromagnetic torque according to the three-phase voltage, three-phase current and speed measured in real time. Calculate the fault characteristic quantity.

8. The method for diagnosing inter-turn short-circuit fault of stator winding of phase modulator based on electromagnetic torque according to claim 1, characterized in that: The step S4 includes: the more serious the stator winding inter-turn short circuit fault is, the greater the fault characteristic value T FI The larger the value, the fault threshold δ is set according to the structural performance of the phase regulator and the actual diagnosis requirements.

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