Method for analyzing current change rate of on-load tap changer of converter transformer

Abstract

The application discloses a method for analyzing breaking current change rate of a converter transformer vacuum on-load tap changer, which comprises the following steps: 1) establishing a converter transformer load current analytical expression; 2) obtaining a breaking current stress expression; 3) establishing a vacuum on-load tap changer breaking current stress analytical expression; 4) according to the vacuum on-load tap changer breaking current stress analytical expression, establishing a vacuum on-load tap changer breaking current change rate analytical expression; 5) analyzing the vacuum on-load tap changer breaking current change rate analytical expression to determine the breaking current change rate influencing factors; and 6) according to the breaking current change rate influencing factors, performing sensitivity analysis on the vacuum on-load tap changer breaking current change rate to obtain the influence degree of each breaking current change rate influencing factor on the breaking current change rate. The application can accurately calculate the breaking current change rate of the converter transformer vacuum on-load tap changer and quantitatively analyze the influencing factors.

Description

Technical Field

[0001] This invention relates to the field of transient characteristic analysis of tap changers, specifically a method for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer. Background Technology

[0002] On-load tap changers are crucial components in converter transformers, compensating for voltage fluctuations and optimizing the transformer's control angle. Unlike AC power transformers, the load current flowing through a converter transformer is not a sine wave but rather resembles a square wave due to harmonics generated by the nonlinearity of the power electronic devices within the converter.

[0003] The load current flowing through the grid-side tap changer has a higher rate of change of current (di / dt) than that of the power transformer, resulting in a higher rate of change of breaking current (di / dt) on the vacuum tube during the switching process, which increases the difficulty of switching.

[0004] Therefore, it is necessary to analyze the rate of change of the breaking current on each vacuum tube when the tap changer is switched in the converter transformer, and to analyze the factors affecting the rate of change of the breaking current, so as to provide theoretical support for the design and selection of vacuum tubes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer, comprising the following steps:

[0006] 1) Monitor the DC side current of the converter transformer and establish an analytical formula for the load current of the converter transformer based on the DC side current;

[0007] Furthermore, the method for establishing the analytical expression of the converter transformer load current based on the DC side current is based on the Fourier decomposition method.

[0008] Furthermore, the converter transformer includes a Y / Y type converter transformer and a Y / Δ type converter transformer, with a 30° phase difference between their valve-side windings;

[0009] The Y / Y type converter transformer includes two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are star-connected.

[0010] The Y / Δ converter transformer includes two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are delta-connected.

[0011] Furthermore, when the converter transformer is a Y / Y type converter transformer, the analytical expression for the load current of the converter transformer is as follows:

[0012]

[0013] In the formula, ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Y converter transformer; k2 is the turns ratio of the Y / Y converter transformer; O n t is the harmonic current factor; t is time.

[0014] Among them, the nth harmonic component X n Harmonic current factor O n They are shown below:

[0015]

[0016]

[0017] In the formula, α and μ represent the firing angle and commutation angle, respectively; S1 and S2 represent intermediate parameters; and the initial phase φ of the nth harmonic is... n =nφ1; fundamental wave initial phase angle

[0018] Furthermore, when the converter transformer is a Y / Δ type converter transformer, the analytical expression for the load current of the converter transformer is as follows:

[0019]

[0020] In the formula, I A2 φ is the load current of the Y / Δ converter transformer; ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Δ converter transformer; k2 is the turns ratio of the Y / Δ converter transformer; O n Harmonic current factor;

[0021] Among them, the nth harmonic component X n As shown below:

[0022]

[0023] In the formula, O n This is the harmonic current factor.

[0024] 2) Perform circuit analysis on the physical circuit of each vacuum tube of the vacuum on-load tap changer during the breaking process to obtain the stress expression for the breaking current;

[0025] Furthermore, the vacuum tubes of the vacuum on-load tap changer include vacuum tube V3, which performs the task of switching the main on / off contacts, and vacuum tube V1, which performs the task of switching the transition contacts.

[0026] The expression for the breaking current stress of vacuum tube V3 is I. V3 =I A ;I V3 I is the switching current of vacuum tube V3; A This refers to the AC side load current.

[0027] The expression for the breaking current stress of vacuum tube V1 is: U st I is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer; R is the resistance; V1 This is the switching current of vacuum tube V1.

[0028] 3) Substitute the load current analytical expression into the breaking current stress expression to establish the breaking current stress analytical expression for a vacuum on-load tap changer.

[0029] Furthermore, the analytical formula for the breaking current stress of the vacuum on-load tap changer includes the analytical formula (6) for the breaking current stress of vacuum tube V3 and the analytical formula (7) for the breaking current stress of vacuum tube V1, namely:

[0030]

[0031]

[0032] In the formula, x% is the percentage of electrode voltage; E m is the phase voltage amplitude. k is the converter transformer turns ratio.

[0033] 4) Based on the analytical formula of the breaking current stress of the vacuum on-load tap changer, establish the analytical formula of the breaking current change rate of the vacuum on-load tap changer.

[0034] Furthermore, the analytical formula for the rate of change of the breaking current of the vacuum on-load tap changer includes the analytical formula (8) for the rate of change of the breaking current of vacuum tube V3 and the analytical formula (9) for the rate of change of the breaking current of vacuum tube V1, namely:

[0035]

[0036]

[0037] In the formula, These represent the rate of change of the breaking current of vacuum tube V3 and vacuum tube V1, respectively.

[0038] 5) Analyze the analytical expression of the rate of change of breaking current of vacuum on-load tap changer and determine the factors affecting the rate of change of breaking current.

[0039] Furthermore, the factors affecting the rate of change of breaking current include the factors affecting the rate of change of breaking current of vacuum tube V3 and the factors affecting the rate of change of breaking current of vacuum tube V1.

[0040] Factors affecting the rate of change of the breaking current of vacuum tube V3 include the DC side current I. d , firing angle α, commutation angle μ;

[0041] Factors affecting the rate of change of the breaking current of vacuum tube V1 include the DC side current I. d , firing angle α, commutation angle μ, power factor angle φ1, stage voltage and transition resistance R.

[0042] 6) Based on the factors affecting the rate of change of breaking current, a sensitivity analysis was conducted on the rate of change of breaking current of the vacuum on-load tap changer to obtain the degree of influence of each factor on the rate of change of breaking current.

[0043] Furthermore, the calculation of the influence of various factors on the rate of change of breaking current includes the rate of change of breaking current of vacuum tube V3 with respect to the DC side current I. d The sensitivity of the switching current of vacuum tube V3 with respect to the firing angle α, the sensitivity of the switching current of vacuum tube V3 with respect to the commutation angle μ, and the sensitivity of the switching current of vacuum tube V1 with respect to the DC side current I. d The sensitivity of the vacuum tube V1 switching current change rate with respect to the firing angle α, the sensitivity of the vacuum tube V1 switching current change rate with respect to the commutation angle μ, the sensitivity of the vacuum tube V1 switching current change rate with respect to the power factor angle φ1, the sensitivity of the vacuum tube V1 switching current change rate with respect to the stage voltage, and the sensitivity of the vacuum tube V1 switching current change rate with respect to the transition resistance R.

[0044] Among them, the rate of change of the switching current of vacuum tube V3 is related to the DC side current I. d Sensitivity As shown below:

[0045]

[0046] Among them, the sensitivity of the rate of change of the switching current of vacuum tube V3 with respect to the firing angle α. As shown below:

[0047]

[0048] Wherein, parameter Z n Parameter Y, sensitivity They are shown below:

[0049] Z n =O n cos(nt+φ n(12)

[0050]

[0051]

[0052] Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to commutation angle μ As shown below:

[0053]

[0054] Among them, sensitivity As shown below:

[0055]

[0056] The rate of change of the breaking current of vacuum tube V3 with respect to the DC side current I d Sensitivity As shown below:

[0057]

[0058] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to firing angle α As shown below:

[0059]

[0060] Among them, sensitivity As shown below:

[0061]

[0062] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to commutation angle μ As shown below:

[0063]

[0064] Among them, sensitivity As shown below:

[0065]

[0066] Sensitivity of the rate of change of the switching current of vacuum tube V1 with respect to the power factor angle φ1 As shown below:

[0067]

[0068] Among them, Z n Sensitivity regarding the power factor angle φ1 As shown below:

[0069]

[0070] The rate of change of the breaking current of vacuum tube V1 with respect to the stage voltage The sensitivity is as follows:

[0071]

[0072] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to transition resistance R As shown below:

[0073]

[0074] In the formula, U st This is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer.

[0075] The technical effects of this invention are undeniable. This invention can accurately calculate the rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer and quantitatively analyze its influencing factors.

[0076] It is worth noting that this invention fully considers the influence of multiple factors when analyzing the rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer. The rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer is affected by factors such as current level, transition resistance, firing angle, commutation angle, and power factor. Among them, the commutation angle and firing angle not only affect the harmonic content of the load current, but also affect the system power factor, thereby affecting the rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer.

[0077] Therefore, this invention fully considers the coupling effect of commutation angle, firing angle, and power factor, and accurately characterizes the effects of various factors affecting the rate of change of the breaking current of the vacuum on-load tap changer in the converter transformer. Based on this, by solving the sensitivity of the rate of change of the breaking current of the vacuum on-load tap changer with respect to each influencing factor, a quantitative analysis of the degree of influence of each factor on the rate of change of the breaking current can be performed.

[0078] This patent discloses a method for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer. The basic idea of ​​this invention is that traditional analytical methods for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer are based solely on the ideal load current (square wave) of the converter transformer. This results in a large error in the analytical expression for the rate of change of breaking current. This invention fully considers the influence of the commutation angle and firing angle on the load current. The analytical expression for the converter transformer load current is obtained through Fourier decomposition, taking into account the quantitative influence of the commutation angle and firing angle, thus improving the accuracy of the analytical calculation. Circuit analysis of the physical circuit of the on-load tap changer breaking process yields the expression for the breaking current. Substituting the analytical expression for the load current into the expression for the breaking current, the analytical expression for the breaking current of the vacuum on-load tap changer is obtained, and consequently, the analytical expression for the rate of change of breaking current of the vacuum on-load tap changer is derived. Finally, sensitivity analysis of various factors is performed on the rate of change of breaking current of the vacuum on-load tap changer to quantitatively determine the degree of influence of each factor on the rate of change of breaking current. Attached Figure Description

[0079] Figure 1 This is a flowchart of the method.

[0080] Figure 2 This refers to the switching process of a vacuum on-load tap changer. Detailed Implementation

[0081] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0082] Example 1:

[0083] See Figures 1 to 2 The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer includes the following steps:

[0084] 1) Monitor the DC side current of the converter transformer and establish an analytical formula for the load current of the converter transformer based on the DC side current;

[0085] The method of establishing the analytical expression of the converter transformer load current based on the DC side current is based on the Fourier decomposition method.

[0086] The converter transformer includes a Y / Y type converter transformer and a Y / Δ type converter transformer;

[0087] The Y / Y type converter transformer includes two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are star-connected.

[0088] The Y / Δ type converter transformer consists of two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are delta-connected.

[0089] When the converter transformer is a Y / Y type converter transformer, the analytical expression for the load current of the converter transformer is as follows:

[0090]

[0091] In the formula, ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Y converter transformer; k2 is the turns ratio of the Y / Y converter transformer; O n Harmonic current factor;

[0092] Among them, the nth harmonic component X n Harmonic current factor O n They are shown below:

[0093]

[0094]

[0095] In the formula, α and μ represent the firing angle and commutation angle, respectively; S1 and S2 represent intermediate parameters; and the initial phase φ of the nth harmonic is... n =nφ1; fundamental wave initial phase angle

[0096] When the converter transformer is a Y / Δ type converter transformer, the analytical expression for the load current of the converter transformer is as follows:

[0097]

[0098] In the formula, I A2 φ is the load current of the Y / Δ converter transformer; ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Δ converter transformer; k2 is the turns ratio of the Y / Δ converter transformer; O n Harmonic current factor;

[0099] Among them, the nth harmonic component X n As shown below:

[0100]

[0101] In the formula, O n This is the harmonic current factor.

[0102] 2) Perform circuit analysis on the physical circuit of each vacuum tube of the vacuum on-load tap changer during the breaking process to obtain the stress expression for the breaking current;

[0103] The vacuum tubes of the vacuum on-load tap changer include vacuum tube V3, which is responsible for switching the main on / off contacts, and vacuum tube V1, which is responsible for switching the transition contacts.

[0104] The expression for the breaking current stress of vacuum tube V3 is I. V3 =I A ;I V3 I is the switching current of vacuum tube V3; A This refers to the AC side load current.

[0105] The expression for the breaking current stress of vacuum tube V1 is: U st I is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer; R is the resistance; V1 This is the switching current of vacuum tube V1.

[0106] 3) Substitute the load current analytical expression into the breaking current stress expression to establish the breaking current stress analytical expression for a vacuum on-load tap changer.

[0107] The analytical formula for the breaking current stress of the vacuum on-load tap changer includes the analytical formula (6) for the breaking current stress of vacuum tube V3 and the analytical formula (7) for the breaking current stress of vacuum tube V1, namely:

[0108]

[0109]

[0110] In the formula, x% is the percentage of electrode voltage; E m This represents the phase voltage amplitude.

[0111] 4) Based on the analytical formula of the breaking current stress of the vacuum on-load tap changer, establish the analytical formula of the breaking current change rate of the vacuum on-load tap changer.

[0112] The analytical formula for the rate of change of breaking current of the vacuum on-load tap changer includes the analytical formula (8) for the rate of change of breaking current of vacuum tube V3 and the analytical formula (9) for the rate of change of breaking current of vacuum tube V1, that is:

[0113]

[0114]

[0115] In the formula, These represent the rate of change of the breaking current of vacuum tube V3 and vacuum tube V1, respectively.

[0116] 5) Analyze the analytical expression of the rate of change of breaking current of vacuum on-load tap changer and determine the factors affecting the rate of change of breaking current.

[0117] The factors affecting the rate of change of breaking current include the factors affecting the rate of change of breaking current of vacuum tube V3 and the factors affecting the rate of change of breaking current of vacuum tube V1.

[0118] Factors affecting the rate of change of the breaking current of vacuum tube V3 include the DC side current I. d , firing angle α, commutation angle μ;

[0119] Factors affecting the rate of change of the breaking current of vacuum tube V1 include the DC side current I. d , firing angle α, commutation angle μ, power factor angle φ1, stage voltage and transition resistance R.

[0120] 6) Based on the factors affecting the rate of change of breaking current, a sensitivity analysis was conducted on the rate of change of breaking current of the vacuum on-load tap changer to obtain the degree of influence of each factor on the rate of change of breaking current.

[0121] The calculation of the influence of various factors on the rate of change of breaking current includes the rate of change of breaking current of vacuum tube V3 with respect to the DC side current I. d The sensitivity of the switching current of vacuum tube V3 with respect to the firing angle α, the sensitivity of the switching current of vacuum tube V3 with respect to the commutation angle μ, and the sensitivity of the switching current of vacuum tube V1 with respect to the DC side current I. d The sensitivity of the vacuum tube V1 switching current change rate with respect to the firing angle α, the sensitivity of the vacuum tube V1 switching current change rate with respect to the commutation angle μ, the sensitivity of the vacuum tube V1 switching current change rate with respect to the power factor angle φ1, the sensitivity of the vacuum tube V1 switching current change rate with respect to the stage voltage, and the sensitivity of the vacuum tube V1 switching current change rate with respect to the transition resistance R.

[0122] Among them, the rate of change of the switching current of vacuum tube V3 is related to the DC side current I. d Sensitivity As shown below:

[0123]

[0124] Among them, the sensitivity of the rate of change of the switching current of vacuum tube V3 with respect to the firing angle α. As shown below:

[0125]

[0126] Wherein, parameter Z n Parameter Y, sensitivity They are shown below:

[0127] Z n =O n cos(nt+φ n (12)

[0128]

[0129]

[0130] Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to commutation angle μ As shown below:

[0131]

[0132] Among them, sensitivity As shown below:

[0133]

[0134] The rate of change of the breaking current of vacuum tube V3 with respect to the DC side current I d Sensitivity As shown below:

[0135]

[0136] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to firing angle α As shown below:

[0137]

[0138] Among them, sensitivity As shown below:

[0139]

[0140] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to commutation angle μ As shown below:

[0141]

[0142] Among them, sensitivity As shown below:

[0143]

[0144] Sensitivity of the rate of change of the switching current of vacuum tube V1 with respect to the power factor angle φ1 As shown below:

[0145]

[0146] Among them, Z n Sensitivity regarding the power factor angle φ1 As shown below:

[0147]

[0148] The rate of change of the breaking current of vacuum tube V1 with respect to the stage voltage The sensitivity is as follows:

[0149]

[0150] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to transition resistance R As shown below:

[0151]

[0152] In the formula, U st This is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer.

[0153] Example 2:

[0154] See Figures 1 to 2 The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer includes the following steps:

[0155] 1) The analytical expression of the converter transformer load current is obtained through Fourier decomposition.

[0156] The analytical formula for the load current of the converter transformer takes into account the effects of the firing angle and the commutation angle.

[0157] The analytical formula for the load current of the converter transformer takes into account the coupling effect of the firing angle, commutation angle and power factor.

[0158] Conventional high-voltage direct current (HVDC) transmission typically uses a 12-pulse converter as the converter transformer, consisting of two 6-pulse converters connected in series on the DC side, and the AC side connected in parallel through the grid-side windings of the converter transformer. Both converter transformers have a star connection on the grid side with the same phase, while the valve-side windings are connected differently—one star and the other delta—with a 30° phase difference. d For DC side current, I A1 and I A2 The values ​​represent the load currents (grid-side currents) of the star-star (Y / Y) converter transformer and the star-delta (Y / Δ) converter transformer, respectively. k1 and k2 represent the turns ratios of the Y / Y and Y / Δ converter transformers, respectively. A This is the AC side load current.

[0159] Fourier decomposition of the load current of a Y / Y converter transformer yields the following analytical expression:

[0160]

[0161] Where ω is the angular frequency, n represents the harmonic order, n = 6k ± 1 (k = 1, 2, 3...), φ n X represents the initial phase of the nth harmonic. n For the nth harmonic component:

[0162]

[0163] Because the firing angle α and the commutation angle μ will affect I A1 The content of middle harmonics has an impact, so the harmonic component X n Harmonic current factor O needs to be taken into account n ,

[0164]

[0165] The initial phase angle of the fundamental wave can be obtained by assuming that the AC power and DC power in the DC transmission system are equal (ignoring losses).

[0166]

[0167] Where α is the firing angle, μ is the commutation angle, and φ is the firing angle. n =nφ1.

[0168] Similarly, the Fourier decomposition of the load current of a Y / Δ converter transformer yields the following analytical expression:

[0169]

[0170] at this time,

[0171]

[0172] 2) Obtain the stress expression for the vacuum tube breaking current of the vacuum on-load tap changer.

[0173] Circuit analysis was performed on the physical circuit of the vacuum tubes of the vacuum on-load tap changer during the breaking process, and the stress expression of the breaking current of each vacuum tube was obtained.

[0174] 3) Obtain the analytical expression for the breaking current stress of the vacuum on-load tap changer.

[0175] Substituting the load current analytical expression into the stress expression of the breaking current of each vacuum tube, we obtain the analytical expression of the breaking current stress of the vacuum on-load tap changer.

[0176] 4) Obtain the analytical expression for the rate of change of the breaking current of the vacuum on-load tap changer.

[0177] By differentiating the analytical expression for the breaking current stress of the vacuum on-load tap changer, we obtain the analytical expression for the rate of change of the breaking current of the vacuum on-load tap changer.

[0178] 5) Obtain the factors affecting the rate of change of breaking current.

[0179] By analyzing the analytical expression of the rate of change of breaking current of a vacuum on-load tap changer, the factors affecting the rate of change of breaking current are obtained.

[0180] 6) Analysis method for factors affecting the rate of change of breaking current of vacuum on-load tap changer of converter transformer.

[0181] The method for analyzing the rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer obtains the degree of influence of each factor on the rate of change of the breaking current by solving the sensitivity of the rate of change of the breaking current of the vacuum on-load tap changer with respect to each influencing factor.

[0182] The sensitivity calculation method for the rate of change of breaking current dI of a vacuum on-load tap changer with respect to the influencing factor x is as follows:

[0183]

[0184] Example 3:

[0185] See Figures 1 to 2 The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer includes the following steps:

[0186] 1) The analytical expression of the converter transformer load current is obtained through Fourier decomposition.

[0187] The analytical formula for the load current of the converter transformer takes into account the effects of the firing angle and the commutation angle.

[0188] The analytical formula for the load current of the converter transformer takes into account the coupling effect of the firing angle, commutation angle and power factor.

[0189] Fourier decomposition of the load current of the Y / Δ converter transformer yields the following analytical expression:

[0190]

[0191] Among them I d For DC side current, I A φ represents the load current (grid-side current) of the Y / Δ converter transformer, k is the transformation ratio of the Y / Δ converter transformer, ω is the angular frequency, n represents the harmonic order, n=6k±1 (k=1,2,3...), φ n X represents the initial phase of the nth harmonic. n For the nth harmonic component:

[0192]

[0193] Because the firing angle α and the commutation angle μ will affect I A1 The content of middle harmonics has an impact, so the harmonic component X n Harmonic current factor O needs to be taken into account n ,

[0194]

[0195] The initial phase angle of the fundamental wave can be obtained by assuming that the AC power and DC power in the DC transmission system are equal (ignoring losses).

[0196]

[0197] Where α is the firing angle, μ is the commutation angle, and φ is the firing angle. n =nφ1.

[0198] 2) Obtain the stress expression for the vacuum tube breaking current of the vacuum on-load tap changer.

[0199] Figure 1 This describes the switching process of a vacuum on-load tap changer from the Nth position to the N+1th position. During this switching process, vacuum tube V3 performs the switching task of the main on / off contact, and vacuum tube V1 performs the switching task of the transition contact. Analysis shows that vacuum tube V1 is switched off in steps (g)-(h), and vacuum tube V3 is switched off in steps (c)-(d). Circuit analysis of the physical circuits for the switching steps of vacuum tubes V1 and V3 yields the stress expressions for the switching current of each vacuum tube.

[0200] The switching process of the vacuum OLTC from the Nth gear to the N+1th gear mainly consists of 13 steps ((a)-(m)). Figure 1 The solid red line in the middle represents the path through which the load current flows in the converter transformer. st This refers to the inter-electrode voltage between the two gear positions.

[0201] U st =x%E=x%E m sinωt=U stm sinωt (5)

[0202] Where x% is the polarity percentage (tap switch adjustment step size), E is the AC phase voltage, E m U is the phase voltage amplitude. stm This represents the interstage voltage amplitude.

[0203] In step (c) Figure 1 (c) The load current completes the process of transferring from the main branch to the main switching branch. The load current flowing through V3 is...

[0204] I V3 =I A (6)

[0205] Therefore, the expression for the breaking current when vacuum tube V3 is switched off in steps (c)-(d) is I. V3 =I A .

[0206] In step (g) ( Figure 1 (g) When both gears are in a short-circuit state with both on simultaneously, the load current flows through both transition branches at the same time. Due to the presence of inter-electrode voltage, a circulating current I is generated between the two gears. C During this stage, the current flowing through V1 is:

[0207]

[0208] Among them, circulation I C for:

[0209]

[0210] Therefore, the expression for the breaking current when vacuum tube V1 is switched off in steps (g)-(h) is:

[0211] 3) Obtain the analytical expression for the breaking current stress of the vacuum on-load tap changer.

[0212] Substituting the load current analytical expression into the stress expression of the breaking current of each vacuum tube, we obtain the analytical expression of the breaking current stress of the vacuum on-load tap changer.

[0213] Therefore, the analytical expression for the breaking current of V3 is:

[0214]

[0215] Substituting equations (1) and (5) into equation (7), we obtain the analytical expression for the V3 breaking current:

[0216]

[0217] 4) Obtain the analytical expression for the rate of change of the breaking current of the vacuum on-load tap changer.

[0218] By differentiating the analytical expression for the breaking current stress of the vacuum tube, we obtain the analytical expression for the rate of change of the breaking current of the vacuum on-load tap changer.

[0219] Differentiating equation (9), we obtain the analytical expression for the rate of change of the breaking current of V3:

[0220]

[0221] Differentiating equation (10), we obtain the analytical expression for the rate of change of the breaking current of V1:

[0222]

[0223] 5) Obtain the factors affecting the rate of change of breaking current.

[0224] By analyzing the analytical expression of the rate of change of breaking current of a vacuum on-load tap changer, the factors affecting the rate of change of breaking current are obtained.

[0225] Analysis of equation (11) shows that the factors affecting the rate of change of the switching current of vacuum tube V3 are: DC side current I d , firing angle α, commutation angle μ.

[0226] Analysis of equation (12) shows that the factors affecting the rate of change of the switching current of vacuum tube V1 are: DC side current I d , firing angle α, commutation angle μ, power factor angle φ1, stage voltage and transition resistance R.

[0227] 6) Analysis method for factors affecting the rate of change of breaking current of vacuum on-load tap changer of converter transformer.

[0228] The method for analyzing the rate of change of the breaking current of the vacuum on-load tap changer of the converter transformer obtains the degree of influence of each factor on the rate of change of the breaking current by solving the sensitivity of the rate of change of the breaking current of the vacuum on-load tap changer with respect to each influencing factor.

[0229] By solving the sensitivity of the rate of change of the breaking current of the vacuum on-load tap changer to the firing angle α, commutation angle μ, power factor angle φ1, and transition resistance R, the influence of each factor on the rate of change of the breaking current can be obtained.

[0230] 6.1) Rate of change of switching current of vacuum tube V3 with respect to DC side current I d Sensitivity

[0231]

[0232] 6.2) Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to firing angle α

[0233] First, solve O n Regarding the sensitivity of the firing angle α, O n As shown in equation (3). For ease of calculation, let...

[0234]

[0235] K2=cosα-cos(α+μ) (15)

[0236] but,

[0237]

[0238] set up

[0239] Z n=O n cos(nt+φ n (17)

[0240]

[0241] at this time

[0242]

[0243] The sensitivity of the rate of change of the V3 breaking current to the firing angle α is:

[0244]

[0245] 6.3) Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to commutation angle μ

[0246] Solve for O n Regarding the sensitivity of the commutation angle μ,

[0247]

[0248] at this time

[0249]

[0250] The sensitivity of the rate of change of the V3 interrupting current to the commutation angle μ is:

[0251]

[0252] 6.4) Rate of change of switching current of vacuum tube V1 with respect to DC side current I d Sensitivity

[0253]

[0254] 6.5) Sensitivity of the rate of change of the switching current of vacuum tube V1 with respect to the firing angle α

[0255] The rate of change of the breaking current of vacuum tube V1 is shown in equation (12). Since the rate of change of the breaking current is affected by the coupling effect of the firing angle α, the commutation angle μ, and the power factor angle φ1, Z n The sensitivity is different from that of vacuum tube V3.

[0256] at this time,

[0257]

[0258] The sensitivity of the rate of change of V1 switching current with respect to the firing angle α is:

[0259]

[0260] 6.6) Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to commutation angle μ

[0261] Solve for Z n Regarding the sensitivity of the commutation angle μ,

[0262]

[0263] The sensitivity of the rate of change of V1 interrupting current to the commutation angle μ is:

[0264]

[0265] 6.7) Sensitivity of the rate of change of the switching current of vacuum tube V1 with respect to the power factor angle φ1

[0266] Solve for Z n Sensitivity regarding the power factor angle φ1

[0267]

[0268] The sensitivity of the rate of change of the breaking current of V1 to the power factor angle φ1 is:

[0269]

[0270] 6.6) Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to stage voltage

[0271]

[0272] 6.6) Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to transition resistance R

[0273] Solve for the sensitivity of the rate of change of the switching current of V1 with respect to the transition resistance R.

[0274]

[0275] Example 4:

[0276] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer in converter transformer includes the following steps:

[0277] 1) Monitor the DC side current of the converter transformer and establish the analytical expression of the load current of the converter transformer based on the DC side current.

[0278] 2) Perform circuit analysis on the physical circuit of each vacuum tube of the vacuum on-load tap changer during the breaking process to obtain the expression for the breaking current stress.

[0279] 3) Substitute the load current analytical expression into the breaking current stress expression to establish the breaking current stress analytical expression for a vacuum on-load tap changer.

[0280] 4) Based on the analytical formula of the breaking current stress of the vacuum on-load tap changer, establish the analytical formula of the breaking current change rate of the vacuum on-load tap changer.

[0281] 5) Analyze the analytical expression of the rate of change of breaking current of vacuum on-load tap changer and determine the factors affecting the rate of change of breaking current.

[0282] 6) Based on the factors affecting the rate of change of breaking current, a sensitivity analysis was conducted on the rate of change of breaking current of the vacuum on-load tap changer to obtain the degree of influence of each factor on the rate of change of breaking current.

[0283] Example 5:

[0284] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. The method for establishing the analytical expression of load current of converter transformer based on DC side current is based on Fourier decomposition.

[0285] Example 6:

[0286] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. The converter transformer includes Y / Y type converter transformer and Y / Δ type converter transformer, and the phase difference between the valve side windings of the two types of transformers is 30°.

[0287] The Y / Y type converter transformer includes two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are star-connected.

[0288] The Y / Δ type converter transformer consists of two converter transformers; the grid-side windings of the two converter transformers are star-connected and have the same phase; the valve-side windings of the two converter transformers are delta-connected.

[0289] Example 7:

[0290] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. When the converter transformer is a Y / Y type, the analytical expression for the load current of the converter transformer is as follows:

[0291]

[0292] In the formula, ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Y converter transformer; k2 is the turns ratio of the Y / Y converter transformer; O nt is the harmonic current factor; t is time.

[0293] Among them, the nth harmonic component X n Harmonic current factor O n They are shown below:

[0294]

[0295]

[0296] In the formula, α and μ represent the firing angle and commutation angle, respectively; S1 and S2 represent intermediate parameters; and the initial phase φ of the nth harmonic is... n =nφ1; fundamental wave initial phase angle

[0297] Example 8:

[0298] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. When the converter transformer is a Y / Δ type, the analytical expression for the load current of the converter transformer is as follows:

[0299]

[0300] In the formula, I A2 φ is the load current of the Y / Δ converter transformer; ω is the angular frequency; n represents the harmonic order; n = 6k ± 1; k is a positive integer; φ n X is the initial phase of the nth harmonic; n For the nth harmonic component; I d I is the DC side current. A1 k1 is the load current of the Y / Δ converter transformer; k2 is the turns ratio of the Y / Δ converter transformer; O n Harmonic current factor;

[0301] Among them, the nth harmonic component X n As shown below:

[0302]

[0303] In the formula, O n This is the harmonic current factor.

[0304] Example 9:

[0305] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. The vacuum tubes of the vacuum on-load tap changer include vacuum tube V3, which is responsible for switching the main on and off contacts, and vacuum tube V1, which is responsible for switching the transition contacts.

[0306] The expression for the breaking current stress of vacuum tube V3 is I. V3=I A ;I V3 I is the switching current of vacuum tube V3; A This refers to the AC side load current.

[0307] The expression for the breaking current stress of vacuum tube V1 is: U st I is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer; R is the resistance; V1 This is the switching current of vacuum tube V1.

[0308] Example 10:

[0309] The method for analyzing the rate of change of breaking current of the vacuum on-load tap changer in a converter transformer is described in Example 4. The analytical formula for the breaking current stress of the vacuum on-load tap changer includes the analytical formula (6) for the breaking current stress of vacuum tube V3 and the analytical formula (7) for the breaking current stress of vacuum tube V1, namely:

[0310]

[0311]

[0312] In the formula, x% is the percentage of electrode voltage; E m is the phase voltage amplitude; k is the converter transformer turns ratio.

[0313] Example 11:

[0314] The method for analyzing the rate of change of breaking current of the vacuum on-load tap changer in a converter transformer is described in Example 4. The analytical formula for the rate of change of breaking current of the vacuum on-load tap changer includes the analytical formula (8) for the rate of change of breaking current of vacuum tube V3 and the analytical formula (9) for the rate of change of breaking current of vacuum tube V1, namely:

[0315]

[0316]

[0317] In the formula, These represent the rate of change of the breaking current of vacuum tube V3 and vacuum tube V1, respectively.

[0318] Example 12:

[0319] The method for analyzing the rate of change of breaking current of vacuum on-load tap changer of converter transformer is described in Example 4. The factors affecting the rate of change of breaking current include the factors affecting the rate of change of breaking current of vacuum tube V3 and the factors affecting the rate of change of breaking current of vacuum tube V1.

[0320] Factors affecting the rate of change of the breaking current of vacuum tube V3 include the DC side current I. d, firing angle α, commutation angle μ;

[0321] Factors affecting the rate of change of the breaking current of vacuum tube V1 include the DC side current I. d , firing angle α, commutation angle μ, power factor angle φ1, stage voltage and transition resistance R.

[0322] Example 13:

[0323] The method for analyzing the rate of change of breaking current of the vacuum on-load tap changer in a converter transformer is described in Example 4. The calculation of the influence of various factors on the rate of change of breaking current includes the rate of change of breaking current of vacuum tube V3 with respect to the DC side current I. d The sensitivity of the switching current of vacuum tube V3 with respect to the firing angle α, the sensitivity of the switching current of vacuum tube V3 with respect to the commutation angle μ, and the sensitivity of the switching current of vacuum tube V1 with respect to the DC side current I. d The sensitivity of the vacuum tube V1 switching current change rate with respect to the firing angle α, the sensitivity of the vacuum tube V1 switching current change rate with respect to the commutation angle μ, the sensitivity of the vacuum tube V1 switching current change rate with respect to the power factor angle φ1, the sensitivity of the vacuum tube V1 switching current change rate with respect to the stage voltage, and the sensitivity of the vacuum tube V1 switching current change rate with respect to the transition resistance R.

[0324] Among them, the rate of change of the switching current of vacuum tube V3 is related to the DC side current I. d Sensitivity As shown below:

[0325]

[0326] Among them, the sensitivity of the rate of change of the switching current of vacuum tube V3 with respect to the firing angle α. As shown below:

[0327]

[0328] Wherein, parameter Z n Parameter Y, sensitivity They are shown below:

[0329] Z n =O n cos(nt+φ n (12)

[0330]

[0331]

[0332] Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to commutation angle μ As shown below:

[0333]

[0334] Among them, sensitivity As shown below:

[0335]

[0336] The rate of change of the breaking current of vacuum tube V3 with respect to the DC side current I d Sensitivity As shown below:

[0337]

[0338] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to firing angle α As shown below:

[0339]

[0340] Among them, sensitivity As shown below:

[0341]

[0342] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to commutation angle μ As shown below:

[0343]

[0344] Among them, sensitivity As shown below:

[0345]

[0346] Sensitivity of the rate of change of the switching current of vacuum tube V1 with respect to the power factor angle φ1 As shown below:

[0347]

[0348] Among them, Z n Sensitivity regarding the power factor angle φ1 As shown below:

[0349]

[0350] The rate of change of the breaking current of vacuum tube V1 with respect to the stage voltage The sensitivity is as follows:

[0351]

[0352] Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to transition resistance R As shown below:

[0353]

[0354] In the formula, U st This is the inter-electrode voltage between the Nth and N+1th positions of the vacuum on-load tap changer.

Claims

1. A method for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer, characterized in that, Includes the following steps: Step 1) Monitor the DC side current of the converter transformer and establish an analytical expression for the load current of the converter transformer based on the DC side current; Step 2) Perform circuit analysis on the physical circuit of the vacuum tubes of the vacuum on-load tap changer during the breaking process to obtain the stress expression for the breaking current; Step 3) Substitute the load current analytical expression into the breaking current stress expression to establish the breaking current stress analytical expression for the vacuum on-load tap changer. Step 4) Based on the analytical formula of the breaking current stress of the vacuum on-load tap changer, establish the analytical formula of the breaking current change rate of the vacuum on-load tap changer. Step 5) Analyze the analytical expression of the breaking current change rate of the vacuum on-load tap changer and determine the influencing factors of the breaking current change rate. Step 6) Based on the factors affecting the rate of change of breaking current, perform sensitivity analysis on the rate of change of breaking current of vacuum on-load tap changer to obtain the degree of influence of each factor affecting the rate of change of breaking current on the rate of change of breaking current. The vacuum tubes of the vacuum on-load tap changer include vacuum tube V3, which is responsible for switching the main on / off contacts, and vacuum tube V1, which is responsible for switching the transition contacts. The expression for the breaking current stress of vacuum tube V3 is as follows: ; This is the switching current of vacuum tube V3; This refers to the AC side load current. The expression for the breaking current stress of vacuum tube V1 is: ; This refers to the interstage voltage between the Nth and N+1th stages of a vacuum on-load tap changer. For transition resistance; This is the switching current of vacuum tube V1; The analytical formula for the breaking current stress of the vacuum on-load tap changer includes the analytical formula (6) for the breaking current stress of vacuum tube V3 and the analytical formula (7) for the breaking current stress of vacuum tube V1, namely: （6） （7） In the formula, x% is the stage voltage percentage; E m The phase voltage amplitude is represented by k; the transformer turns ratio is represented by t; and time is represented by t. ω is the angular frequency; n represents the harmonic order; k is a positive integer; X is the initial phase of the nth harmonic; n For the nth harmonic component; I d This is the DC side current; O n Harmonic current factor; The power factor angle; Among them, the nth harmonic component X n As shown below: （5） The analytical formula for the rate of change of breaking current of the vacuum on-load tap changer includes the analytical formula (8) for the rate of change of breaking current of vacuum tube V3 and the analytical formula (9) for the rate of change of breaking current of vacuum tube V1, that is: （8） （9） In the formula, , These represent the rate of change of the breaking current of vacuum tube V3 and vacuum tube V1, respectively. The factors affecting the rate of change of breaking current include the factors affecting the rate of change of breaking current of vacuum tube V3 and the factors affecting the rate of change of breaking current of vacuum tube V1. Factors affecting the rate of change of the breaking current of vacuum tube V3 include the DC side current I. d , firing angle α, commutation angle μ; Factors affecting the rate of change of the breaking current of vacuum tube V1 include the DC side current I. d , firing angle α, commutation angle μ, power factor angle Level voltage and transition resistance R; The calculation of the influence of various factors on the rate of change of breaking current includes the rate of change of breaking current of vacuum tube V3 with respect to the DC side current I. d The sensitivity of the switching current of vacuum tube V3 with respect to the firing angle α, the sensitivity of the switching current of vacuum tube V3 with respect to the commutation angle μ, and the sensitivity of the switching current of vacuum tube V1 with respect to the DC side current I. d The sensitivity of the switching current of vacuum tube V1 with respect to the firing angle α, the sensitivity of the switching current of vacuum tube V1 with respect to the commutation angle μ, and the sensitivity of the switching current of vacuum tube V1 with respect to the power factor angle. The sensitivity of the vacuum tube V1 switching current change rate with respect to the stage voltage, and the sensitivity of the vacuum tube V1 switching current change rate with respect to the transition resistance R. Among them, the rate of change of the switching current of vacuum tube V3 is related to the DC side current I. d Sensitivity As shown below: （10） Among them, the sensitivity of the rate of change of the switching current of vacuum tube V3 with respect to the firing angle α. As shown below: （11） Among them, parameters ,parameter Sensitivity They are shown below: （12） （13） （14） Sensitivity of the rate of change of switching current of vacuum tube V3 with respect to commutation angle μ As shown below: （15） Among them, sensitivity As shown below: （16） The rate of change of the switching current of vacuum tube V1 with respect to the DC side current I d Sensitivity As shown below: （17） Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to firing angle α As shown below: （18） Among them, sensitivity As shown below: （19） Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to commutation angle μ As shown below: （20） Among them, sensitivity As shown below: （21） The rate of change of the breaking current of vacuum tube V1 with respect to the power factor angle Sensitivity As shown below: （22） Among them, Z n Regarding the power factor angle Sensitivity As shown below: （23） The rate of change of the breaking current of vacuum tube V1 with respect to the stage voltage The sensitivity is as follows: （24） Sensitivity of the rate of change of switching current of vacuum tube V1 with respect to transition resistance R As shown below: （25）。 2. The method for analyzing the rate of change of breaking current of a vacuum on-load tap changer in a converter transformer according to claim 1, characterized in that, The method of establishing the analytical expression of the converter transformer load current based on the DC side current is based on the Fourier decomposition method.

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