阅读说明：本技术 三相三绕组变压器感应电压带局部放电试验参数估算方法 (Three-phase three-winding transformer induction voltage band partial discharge test parameter estimation method ) 是由 赵军 邢超 高骏 孟令明 段昕 王卓然 相晨萌 于 2019-09-16 设计创作，主要内容包括：本发明涉及一种三相三绕组变压器感应电压带局部放电试验参数估算方法,其包括步骤1、联立方程组,求解分布电容值；步骤2、根据分布电容值,折算到三相绕组端部集中电容；步骤3、利用得到的集中电容计算得到高压侧试验容性无功功率；步骤4、考虑纵向电容分量,计算得到总无功功率；步骤5、根据总无功功率,计算得到三相三绕组变压器在试验时等效入口电容值；步骤6、根据并联谐振原理,利用得到的等效入口电容值求得需要匹配的电抗值；在步骤1-步骤6运行的同时,计算得到三相同时加压时三相绕组的有功功率<Image he="19" wi="12" file="DEST_PATH_IMAGE002.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>及有功电流<Image he="18" wi="13" file="DEST_PATH_IMAGE003.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>。本发明简单明了,可依据低电压等级绝缘试验及相关部件出厂试验数据即可进行变压器局部放电试验参数估算,具备普遍适应性。(The invention relates to a method for estimating local discharge test parameters of an induction voltage belt of a three-phase three-winding transformer, which comprises the following steps of 1, solving a distributed capacitance value by using a simultaneous equation set; step 2, converting to a concentrated capacitor at the end part of the three-phase winding according to the distributed capacitance value; step 3, calculating by using the obtained centralized capacitor to obtain high-voltage side test capacitive reactive power; step 4, considering the longitudinal capacitance component, and calculating to obtain total reactive power; step 5, calculating to obtain an equivalent inlet capacitance value of the three-phase three-winding transformer during testing according to the total reactive power; step 6, according to the parallel resonance principle, obtaining a reactance value to be matched by using the obtained equivalent inlet capacitance value; operating from step 1 to step 6Meanwhile, the active power of the three-phase winding is calculated when the three phases are simultaneously pressurized And active current . The method is simple and clear, can estimate the parameters of the partial discharge test of the transformer according to the low-voltage-level insulation test and the factory test data of related parts, and has general adaptability.)

1. A method for estimating local discharge test parameters of an induction voltage of a three-phase three-winding transformer is characterized by comprising the following steps:

step 1, solving a distribution capacitance value by using a simultaneous equation set;

Step 2, converting the distributed capacitance value solved in the step 1 into a concentrated capacitance at the end part of the three-phase winding;

Step 3, according to the test requirements of the new national standard, calculating by using the concentrated capacitor obtained in the step 2 to obtain the capacitive reactive power of the high-voltage side test;

step 4, considering the longitudinal capacitance component, correcting the calculation formula of the capacitive reactive power in the step 3, and calculating to obtain the total reactive power;

Step 5, calculating to obtain an equivalent inlet capacitance value of the three-phase three-winding transformer during testing according to the total reactive power obtained in the step 4;

Step 6, according to the parallel resonance principle, obtaining a reactance value needing to be matched by using the equivalent inlet capacitance value obtained in the step 5;

And (4) calculating to obtain the active power P and the active current I of the three-phase winding when the three phases are simultaneously pressurized according to the new national standard test requirements while the steps 1 to 6 are operated.

2. The method for estimating parameters of the partial discharge test of the induced voltage band of the three-phase three-winding transformer according to claim 1, wherein the simultaneous equations in the step 1 are represented by the following formula (1):

Wherein, C₁₃Representing the capacitance of the high voltage winding to the low voltage winding; c₁₂Representing the capacitance of the high voltage winding to the medium voltage winding; c₂₃Representing the capacitance of the medium voltage winding to the low voltage winding; c_hThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_lThe capacitance of the low-voltage winding to the rest windings and the ground is represented; c_hmlRepresenting the capacitance of the high-voltage winding, the medium-voltage winding and the low-voltage winding to the ground; c_hmRepresenting the capacitance of the high voltage winding, the medium voltage winding to the low voltage winding and the ground; c_mlThe capacitance of the medium-voltage winding, the low-voltage winding to the high-voltage winding and the ground is represented; c_hlthe capacitance of the high-voltage winding and the low-voltage winding to the medium-voltage winding and the ground is represented;

Setting the capacitance C of the high-voltage winding to the low-voltage winding of the three-phase three-winding transformer₁₃Solving to obtain the capacitance C of the high-voltage winding to the ground₁Capacitance C of the medium voltage winding to the ground₂and a capacitance C of the low voltage winding to ground₃。

3. the method for estimating the parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer as claimed in claim 2, wherein the algorithm for converting to the concentrated capacitance of the three-phase winding end in the step 2 is as follows: the capacitance C of the high-voltage winding to the ground calculated in the step 1 is calculated₁Capacitance C of the medium voltage winding to the ground₂And low pressureWinding to ground capacitance C₃Are respectively divided by 3 to obtain C₁/3、C₂/3、C₃/3。

4. The method for estimating parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer as claimed in claim 2, wherein the formula (2) for calculating the high-voltage side test capacitive reactive power in the step 3 is as follows:

wherein Q is_∑' denotes high side test capacitive reactive power; u represents a test voltage; omega represents angular momentum, equal to 2 pi f, f is the test frequency; k₁representing the transformation ratio of the high-voltage winding to the medium-voltage winding; k₂Indicating the transformation ratio of the high voltage winding to the low voltage winding.

5. the method for estimating parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer as claimed in claim 2, wherein the formula (3) for calculating the total reactive power in the step 4 is as follows:

Wherein Q is_∑represents the total reactive power; c_hThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; alpha represents the square root of the ratio of the sum of the capacitance to ground of a unit length of the winding and the capacitance to the adjacent winding to the longitudinal capacitance of the unit length; iota represents the winding length; u represents a test voltage; omega represents angular momentum, which is equal to 2 pi f, and f is test frequency in the partial discharge test; k₁Representing the transformation ratio of the high-voltage winding to the medium-voltage winding; k₂indicating the transformation ratio of the high voltage winding to the low voltage winding.

6. The method for estimating parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer as claimed in claim 5, wherein the formula (4) for calculating the equivalent inlet capacitance value of the three-phase three-winding transformer in the step 5 during the test is as follows:

Namely, it is

Wherein, C_∑The equivalent inlet capacitance value of the three-phase three-winding transformer during the test is shown.

7. The method for estimating parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer as claimed in claim 6, wherein the equation (5) for obtaining the reactance value to be matched according to the parallel resonance principle in step 6 is as follows:

8. The method for estimating parameters of the partial discharge test in the induction voltage band of the three-phase three-winding transformer according to claim 1, wherein the calculation formula (6) of the active power of the three-phase windings when the three phases are simultaneously pressurized is as follows:

Wherein, P represents the active power of the three-phase winding when the three phases are pressurized simultaneously; f represents the test frequency in the partial discharge test; f. of_nRepresents the rated frequency of the transformer; b is_mRepresents the magnetic flux density under rated conditions; b'_mRepresents the magnetic flux density at the time of the test; p₀Represents the no-load loss under rated conditions; k represents a multiple of the test voltage; m and n are both coefficients, and the values thereof are different according to the cold rolling or hot rolling of the adopted silicon steel sheet.

9. The method for estimating parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer according to claim 1 or 8, wherein the calculation formula (7) of the active current when the three phases are pressurized simultaneously is as follows:

Wherein, I represents active current when three phases are pressurized simultaneously; k₂Representing the transformation ratio of the high-voltage winding to the low-voltage winding; u represents a test voltage; p represents the active power of the three-phase winding when the three phases are simultaneously pressurized.

10. The method for estimating the parameters of the partial discharge test of the induction voltage band of the three-phase three-winding transformer according to claim 1, wherein the new national standard is GB/T1094.3-2017 part 3 of power transformer: insulation level, insulation test and external insulating air.

Technical Field

The invention belongs to the technical field of intelligent operation and inspection, and particularly relates to a method for estimating local discharge test parameters of an induction voltage band of a three-phase three-winding transformer.

Background

With the continuous expansion of the power grid scale, the high-speed increase of the equipment loading amount and frequent equipment quality problems, higher requirements are put on field tests, wherein the partial discharge test of the transformer induction voltage belt is widely developed in field handover tests and diagnostic tests as a sensitive acceptance test. Because the test of partial discharge of the induction voltage band of the transformer generally adopts a low-voltage excitation and symmetrical or unilateral pressurization wiring mode, large-scale test equipment such as a variable frequency power supply, an intermediate excitation transformer, a compensation reactor and the like is required. Due to the influences of different capacities, different transformation ratios and other factors, the transformer is subjected to field test blindly without parameter estimation, so that the situation that test equipment cannot meet test requirements easily occurs, and even the situation that the field configuration test equipment far exceeds the test requirements causes waste of manpower and time.

For this reason, in the case of adjusting the capacitive current of the transformer under test using the compensation reactor during the test, it is necessary to estimate the active power and the reactive power, especially the reactive power, of the transformer under test during the test so as to prepare an appropriate amount of the compensation reactor. But at present, due to the new national standard 1094.3-2017 part 3 of the power transformer: insulation level, insulation test and external insulation air gap provide requirements for three-phase transformer induced voltage band partial discharge test for simultaneously pressurizing and checking phase-to-phase insulation of three phases, and the condition that the three phases are all test phases is considered in an estimation algorithm.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for estimating local discharge test parameters of an induction voltage band of a three-phase three-winding transformer.

In order to solve the technical problems, the invention adopts the following technical scheme:

A method for estimating local discharge test parameters of an induction voltage of a three-phase three-winding transformer comprises the following steps:

step 1, solving a distributed capacitance value by using a simultaneous equation set as shown in the following formula (1): setting the capacitance C of the high-voltage winding to the low-voltage winding of the three-phase three-winding transformer₁₃Solving to obtain the capacitance C of the high-voltage winding to the ground₁Capacitance C of the medium voltage winding to the ground₂And a capacitance C of the low voltage winding to ground₃；

Wherein, C₁₃Representing the capacitance of the high voltage winding to the low voltage winding; c₁₂representing the capacitance of the high voltage winding to the medium voltage winding; c₂₃Representing the capacitance of the medium voltage winding to the low voltage winding; c_hThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_lThe capacitance of the low-voltage winding to the rest windings and the ground is represented; c_hmlRepresenting the capacitance of the high-voltage winding, the medium-voltage winding and the low-voltage winding to the ground; c_hmRepresenting the capacitance of the high voltage winding, the medium voltage winding to the low voltage winding and the ground; c_mlthe capacitance of the medium-voltage winding, the low-voltage winding to the high-voltage winding and the ground is represented; c_hlThe capacitance of the high-voltage winding and the low-voltage winding to the medium-voltage winding and the ground is represented;

Step 2, converting to that the concentrated capacitance at the end part of the three-phase winding is respectively C₁/3、C₂/3、C₃/3；

Step 3, calculating to obtain the high-voltage side test capacitive reactive power Q according to the new national standard test requirements and the formula (2)_∑’：

wherein U represents a test voltage; omega represents angular momentum, equal to 2 pi f, f is the test frequency; k₁Representing the transformation ratio of the high-voltage winding to the medium-voltage winding; k₂representing the transformation ratio of the high-voltage winding to the low-voltage winding;

step 4, considering the longitudinal capacitance component, correcting the formula (2) to obtain a formula (3), and calculating according to the formula (3) to obtain the total reactive power Q_∑；

wherein, C_hthe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; alpha represents the square root of the ratio of the sum of the capacitance to ground of a unit length of the winding and the capacitance to the adjacent winding to the longitudinal capacitance of the unit length; iota represents the winding length;

step 5, according to the total reactive power Q_∑Calculating to obtain equivalent inlet capacitance C of the three-phase three-winding transformer in the test_∑the calculation formula (4) is as follows:

Namely, it is

Step 6, obtaining a reactance value L to be matched according to a parallel resonance principle, wherein a calculation formula (5) is as follows:

According to the working frequency range of the frequency conversion cabinet of the transformer induction voltage band partial discharge test equipment being 30Hz-300Hz, the frequency conversion cabinet works in the best state when the frequency of the transformer induction voltage band partial discharge test equipment is selected to be within the range of 100Hz-200Hz, the test frequency f is selected to be 150Hz, and the parameter L of the compensation reactor is calculated.

further, when the steps 1 to 6 are performed, according to the new national standard test requirements, the active power P and the active current I of the three-phase winding when the three phases are simultaneously pressurized are respectively calculated according to the formula (6) and the formula (7):

Wherein f represents the test frequency in the partial discharge test; f. of_nRepresents the rated frequency of the transformer; b is_mrepresents the magnetic flux density under rated conditions; b'_mRepresents the magnetic flux density at the time of the test; p₀Represents the no-load loss under rated conditions; k represents a multiple of the test voltage; m and n are both coefficients, and the values thereof are different according to the cold rolling or hot rolling of the adopted silicon steel sheet;

Further, B_mThe magnetic flux density under rated conditions is shown, and the magnetic flux density of silicon steel sheets adopted in the market at present is 1.2-1.7 Tesla. Preferably, B_mIt was 1.7T.

Furthermore, m and n are both coefficients, and the values are 1.3 and 1.8 when hot rolled silicon steel sheets are adopted and 1.6 and 1.9 when cold rolled silicon steel sheets are adopted, and the existing transformer basically adopts the cold rolled silicon steel sheets. Preferably, m and n are 1.6 and 1.9.

Further, the capacitance C between the high-voltage winding and the low-voltage winding of the three-phase three-winding transformer set in the step 1₁₃The value of (a) is 600pF-900 pF. Preferably, C₁₃Is 800 pF.

Further, because no value of the internal shielding continuous winding is provided at present, and most of the transformers adopt the internal shielding continuous winding at present, the value range of the alpha iota for the internal shielding continuous winding in the step 4 is given by referring to the value range of the intertwined winding, and is 1.3-3.5.

Preferably, the value of alpha iota for the inner shielding continuous winding is 2.5;

Further, the new national standard is 1094.3-2017 part 3 of power transformer: the requirements of insulation level, insulation test and external insulation air gap on the induced voltage test of the three-phase three-winding transformer are that three phases are simultaneously pressurized for testing, and the reactive power is the sum of the reactive power of the three-phase windings during the transformer test.

The invention has the following beneficial effects:

the method for estimating the test parameters of the three-phase three-winding transformer during the induction voltage partial discharge measurement test is simple and clear, can estimate the parameters of the transformer partial discharge test according to the low-voltage-level insulation test and relevant part delivery test data, has general adaptability, and is suitable for estimating the parameters of the partial discharge test of the transformers of various voltage levels. The method improves the test efficiency, reduces the manpower waste and time loss caused by blind configuration of test equipment, and can compare the test parameters with the real-time test parameters in the test to master the test condition by accurately estimating the test parameters.

Because the transformer induction voltage band partial discharge test generally needs to use large-scale test equipment such as a variable frequency power supply, an intermediate excitation transformer, a compensation reactor and the like, the mass is large, and the operation is difficult. And because factors such as voltage class, rated capacity, structural style influence are tried on the transformer, the entry capacitance value has some differences, if do not carry out the parameter estimation and test blindly, the condition that test equipment can't satisfy experimental requirement easily appears, carry out equipment replacement again, often can influence test time, cause equipment can not accomplish the experiment in the maintenance time of regulation, can't throw the fortune on time, cause the electric wire netting to be forced to adjust the operation mode, and then influence electric wire netting safe and stable operation, thereby the condition that thereby the field configuration test equipment far surpassed experimental demand and cause manpower and time waste appears even.

The method can effectively utilize the transformer delivery test or handover test parameters to estimate the partial discharge test parameters of the induction voltage band of the transformer, namely the inlet capacitance value, the reactive power, the compensation reactor parameter, the active power and the active current.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail and fully with reference to the following embodiments.

According to new national standard 1094.3-2017 part 3 of power transformer: the related requirements in insulation level, insulation test and external insulation air gap, large and medium power transformers with 110kV and above voltage levels are mostly graded insulation transformers, and induction voltage belt partial discharge tests of windings and sleeves are used as test items before commissioning of the transformers, so that main insulation and longitudinal insulation of the graded insulation transformers can be checked, and internal defects of the transformers caused by improper design, poor process or external factors and the like can be found through partial discharge measurement.

the embodiment relates to a method for estimating local discharge test parameters of an induction voltage belt of a three-phase three-winding transformer, aiming at improving the test efficiency, reducing the labor waste and the time loss caused by blind configuration of test equipment, and simultaneously accurately estimating the test parameters, comparing the test parameters with the real-time test parameters in the test and mastering the test condition. Which comprises the following steps:

Step 1, solving a distributed capacitance value by using a simultaneous equation set as shown in the following formula (1): setting the capacitance C of the high-voltage winding to the low-voltage winding of the three-phase three-winding transformer₁₃Solving to obtain the capacitance C of the high-voltage winding to the ground₁capacitance of medium voltage winding to groundquantity C₂And a capacitance C of the low voltage winding to ground₃；

wherein, C₁₃Representing the capacitance of the high voltage winding to the low voltage winding; c₁₂representing the capacitance of the high voltage winding to the medium voltage winding; c₂₃Representing the capacitance of the medium voltage winding to the low voltage winding; c_hThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_lThe capacitance of the low-voltage winding to the rest windings and the ground is represented; c_hmlRepresenting the capacitance of the high-voltage winding, the medium-voltage winding and the low-voltage winding to the ground; c_hmRepresenting the capacitance of the high voltage winding, the medium voltage winding to the low voltage winding and the ground; c_mlThe capacitance of the medium-voltage winding, the low-voltage winding to the high-voltage winding and the ground is represented; c_hlThe capacitance of the high-voltage winding and the low-voltage winding to the medium-voltage winding and the ground is represented;

step 2, converting to that the concentrated capacitance at the end part of the three-phase winding is respectively C₁/3、C₂/3、C₃/3；

Step 3, calculating to obtain the high-voltage side test capacitive reactive power Q according to the new national standard test requirements and the formula (2)_∑’：

Wherein U represents a test voltage; omega represents angular momentum, equal to 2 pi f, f is the test frequency; k₁Representing the transformation ratio of the high-voltage winding to the medium-voltage winding; k₂Representing the transformation ratio of the high-voltage winding to the low-voltage winding;

Step 4, considering the longitudinal capacitance component, correcting the formula (2) to obtain a formula (3), and calculating according to the formula (3) to obtain the total reactive power Q_∑；

Wherein, C_hthe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; alpha represents the square root of the ratio of the sum of the capacitance to ground of a unit length of the winding and the capacitance to the adjacent winding to the longitudinal capacitance of the unit length; iota represents the winding length;

Step 5, according to the total reactive power Q_∑Calculating to obtain equivalent inlet capacitance C of the three-phase three-winding transformer in the test_∑The calculation formula (4) is as follows:

Namely, it is

Step 6, obtaining a reactance value L to be matched according to a parallel resonance principle, wherein a calculation formula (5) is as follows:

According to the working frequency range of the frequency conversion cabinet of the transformer induction voltage band partial discharge test equipment being 30Hz-300Hz, the frequency conversion cabinet works in the best state when the frequency of the transformer induction voltage band partial discharge test equipment is selected to be within the range of 100Hz-200Hz, the test frequency f is selected to be 150Hz, and the parameter L of the compensation reactor is calculated.

Further, when the steps 1 to 6 are performed, according to the new national standard test requirements, the active power P and the active current I of the three-phase winding when the three phases are simultaneously pressurized are respectively calculated according to the formula (6) and the formula (7):

wherein f represents the test frequency in the partial discharge test; f. of_nRepresents the rated frequency of the transformer; b is_mRepresents the magnetic flux density under rated conditions; b is'_mRepresents the magnetic flux density at the time of the test; p₀Represents the no-load loss under rated conditions; k represents a multiple of the test voltage; m and n are both coefficients, and the values thereof are different according to the cold rolling or hot rolling of the adopted silicon steel sheet;

Further, B_mThe magnetic flux density under rated conditions is shown, and the magnetic flux density of silicon steel sheets adopted in the market at present is 1.2-1.7 Tesla. Preferably, B_mIt was 1.7T.

Furthermore, m and n are both coefficients, and the values are 1.3 and 1.8 when hot rolled silicon steel sheets are adopted and 1.6 and 1.9 when cold rolled silicon steel sheets are adopted, and the existing transformer basically adopts the cold rolled silicon steel sheets. Preferably, m and n are 1.6 and 1.9.

Further, the capacitance C between the high-voltage winding and the low-voltage winding of the three-phase three-winding transformer set in the step 1₁₃the value of (a) is 600pF-900 pF. Preferably, C₁₃Is 800 pF.

further, because no value of the internal shielding continuous winding is provided at present, and most of the transformers adopt the internal shielding continuous winding at present, the value range of the alpha iota for the internal shielding continuous winding in the step 4 is given by referring to the value range of the intertwined winding, and is 1.3-3.5.

Preferably, the value of alpha iota for the inner shielding continuous winding is 2.5;

Further, the new national standard is 1094.3-2017 part 3 of power transformer: the requirements of insulation level, insulation test and external insulation air gap on the induced voltage test of the three-phase three-winding transformer are that three phases are simultaneously pressurized for testing, and the reactive power is the sum of the reactive power of the three-phase windings during the transformer test.

The main technical concept of the invention is as follows:

The method mainly considers the estimation method of test parameters such as reactive power and active power parameters, test resonant frequency, inductance of a compensation reactor and the like in the partial discharge test of the induction voltage band of the three-phase three-winding transformer, the current flowing through the winding of the transformer is mainly represented as capacitance current during the test, and a field test loop can enable the test loop to be close to a parallel resonance state by adjusting the frequency of a test system.

And estimating partial parameters of capacitive reactive power and inductive reactive power in the test by using related parameters such as capacitance test values in a transformer factory test or a handover test.

the capacitance test of the transformer winding is a routine test project of the transformer, and usually, when the dielectric loss of the winding is measured, the lumped parameter capacitance between the winding and the rest windings and between the winding and the ground is obtained. The value is a parallel value of the capacitance between several windings and the capacitance of the windings to the ground, and in order to enable the measured data to reflect the real situation of the windings more accurately, the measured data needs to be combined into an equation set to solve the distributed capacitance. Taking a three-winding transformer as an example, according to different wiring modes, 7 different equations can be listed, and 6 of the equations can be taken for solving.

The simultaneous equations are as follows:

Wherein, C₁₃Representing the capacitance of the high voltage winding to the low voltage winding; c₁₂Representing the capacitance of the high voltage winding to the medium voltage winding; c₂₃Representing the capacitance of the medium voltage winding to the low voltage winding; c_hThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_mThe capacitance of the high-voltage winding to the rest windings and the ground is represented; c_lThe capacitance of the low-voltage winding to the rest windings and the ground is represented; c_hmlRepresenting the capacitance of the high-voltage winding, the medium-voltage winding and the low-voltage winding to the ground; c_hmRepresenting the capacitance of the high voltage winding, the medium voltage winding to the low voltage winding and the ground; c_mlThe capacitance of the medium-voltage winding, the low-voltage winding to the high-voltage winding and the ground is represented; c_hlthe capacitance of the high-voltage winding and the low-voltage winding to the medium-voltage winding and the ground is represented;

Considering the accurate calculation of the inlet capacitance, the capacitance between the high-voltage winding and the low-voltage winding of the three-phase transformer in the patent can be taken as 800 pF.

From which C can be derived₁、C₂、C₃I.e. the sum of the capacitances distributed to ground by the whole winding, then converted into C for the concentrated capacitance at the end of the winding_nAnd/3, n is 1, 2 and 3.

the high side test phase reactive power can be calculated. Here according to new national standard 1094.3-2017 power transformer part 3: insulation level, insulation test and external insulation air gap provide requirements for three-phase transformer induced voltage band partial discharge test for simultaneously pressurizing and checking phase-to-phase insulation of three phases, and the condition that the three phases are all test phases is considered in an estimation algorithm.

The capacitive reactive power is:

At present, a three-phase three-winding transformer winding with a voltage level of more than 110kV is generally in an internal shielding continuous winding structure form, and the effect of longitudinal capacitance components cannot be ignored.

In the case of considering the effect of the longitudinal capacitance component, α is the square root of the ratio of the sum of the capacitance to ground per unit length of the winding and the capacitance to adjacent windings to the longitudinal capacitance per unit length, and ι is the winding length. Alpha iota is a suggested value of 2.5 for the inner shield continuous winding.

Because the winding form of the low-voltage winding is generally a spiral structure and is different from the winding forms of the high-voltage winding and the medium-voltage winding, the influence of longitudinal capacitance components is not considered, and the calculation formula of the total reactive power of the three-phase three-winding transformer during the induction voltage band partial discharge test is as follows:

The calculation formula of the equivalent inlet capacitance of the three-phase three-winding transformer in the test is as follows:

namely, it isAnd (3) setting the inductance of the compensation reactor as L, and estimating the resonant frequency in a parallel resonance state during the test according to the following formula:

The parameters of the existing compensation reactor can be matched according to the estimated equivalent inlet capacitance of the transformer, so that the situation that the test parameters of the field equipment cannot meet the test requirements is avoided.

Meanwhile, according to new national standard 1094.3-2017 part 3 of power transformer: the requirements of insulation level, insulation test and external insulation air gap on the induced voltage test of the three-phase three-winding transformer are that three phases are simultaneously pressurized for testing, and the active power of the transformer during the test is the sum of the active power of the three-phase windings.

Meanwhile, according to the test requirements of the new national standard, the active power P and the active current I of the three-phase winding are respectively estimated according to the formula (6) and the formula (7) when the three phases are simultaneously pressurized under the parallel resonance state:

wherein f represents the test frequency in the partial discharge test; f. of_nRepresents the rated frequency of the transformer; b is_mRepresents the magnetic flux density under rated conditions; b'_mRepresents the magnetic flux density at the time of the test; p₀represents the no-load loss under rated conditions; k represents a multiple of the test voltage; m and n are both coefficients, and the values thereof are different according to the cold rolling or hot rolling of the adopted silicon steel sheet; according to the condition that most of the transformer cores adopt cold-rolled silicon steel sheets at present, m and n are generally 1.6 and 1.9.

The active current of the low-voltage side of the transformer during the test can be the test current flowing through the high-voltage side of the excitation transformer, so that the transformation ratio of the excitation transformer can be selected according to the active current, and the current flowing through the frequency conversion cabinet and the power supply cable in the whole test system can be estimated.

the method is suitable for the estimation of the parameters of the induction withstand voltage and the partial discharge test in the stages of transformer manufacturing, handover, routine and the like, and has the characteristic of simple and accurate estimation of the parameters of the partial discharge test of the transformer.

According to the requirements of the transformer induction voltage band partial discharge test in the new national standard 1094.3-2017, the tested transformer presents a capacitive load during the test. Therefore, the capacitance parameters of the windings on each side of the transformer distributed to the ground are combined with the voltage grade, the transformation ratio, the magnetic flux density, the no-load loss and other related parameters of the transformer, the inlet capacitance of the transformer in the induction voltage withstand voltage belt partial discharge test is estimated, and the key test parameters such as the equipment configuration parameters of the compensation reactor and the frequency of the parallel resonance test in the induction voltage withstand are further determined.