Method for judging the neutral line break of the secondary side of the three-phase current transformer on the high-voltage side of the transformer

Abstract

The present invention discloses a method for distinguishing a neutral line break on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, comprising: collecting the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side; calculating the effective value of the fundamental wave of the zero-sequence current produced by the transformer on the high-voltage side; calculating the effective value of the fundamental wave and each integer harmonic of the zero-sequence current at the neutral point on the high-voltage side; in response to the transformer being initially charged without charging, the effective value of the fundamental wave of the zero-sequence current produced by the transformer on the high-voltage side is lower than a fixed value, and the effective value of the fundamental wave of the zero-sequence current at the neutral point on the high-voltage side is higher than a fixed value, and the ratio of the sum of each integer harmonic of the zero-sequence current at the neutral point on the high-voltage side to the fundamental wave is higher than a fixed value, and it is judged that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken. This technical solution solves the problem that when the three-phase current is almost completely symmetrical and the zero-sequence current is extremely small during normal operation of the transformer, it is difficult to distinguish the neutral line break on the secondary side of the three-phase current transformer on the high-voltage side of the transformer.

Description

Technical Field

[0001] The invention belongs to the field of relay protection of electric power systems, and in particular relates to a method and a device for judging a neutral line break on a secondary side of a three-phase current transformer on a high-voltage side of a transformer. Background Art

[0002] In a power plant, the main transformer transmits the electric energy generated by the generator to the power grid, and increases the output voltage of the power plant to meet the rated high voltage requirements of the transmission power grid. Therefore, the safe and stable operation of the power plant transformer is a prerequisite for the stable power generation and full-load power generation of the generator set, and is the key to the reliable operation of the power plant. At present, there is no method in China to determine whether the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken. This is mainly because when the transformer is operating normally, the three-phase current is balanced, and the zero-sequence current generated by the transformer on the high-voltage side is very small, basically close to zero. Therefore, it is impossible to use the normal working current to reflect whether the neutral line circuit on the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken. If the neutral line circuit of the secondary side of the three-phase current transformer on the high-voltage side is broken due to certain factors (such as: the sampling circuit is missing after maintenance, insulation breakdown caused by line aging, etc.), then when a single-phase grounding fault occurs outside the area of ​​the transformer, the zero-sequence differential protection on the high-voltage side of the transformer may malfunction. At the same time, when the short-circuit current is large, it is very likely to blow up the three-phase current transformer on the high-voltage side, thereby forcing the protected equipment to be shut down for a long time for maintenance, ultimately causing significant economic losses. Summary of the invention

[0003] The purpose of the present invention is to provide a method and device for judging the broken neutral line on the secondary side of the three-phase current transformer on the high-voltage side of the transformer, which solves the problem that the three-phase current is almost completely symmetrical and the zero-sequence current is extremely small during normal operation of the transformer, and the broken neutral line on the secondary side of the three-phase current transformer on the high-voltage side of the transformer is difficult to judge without adding external test equipment and modifying the secondary circuit.

[0004] In order to achieve the above object, the solution of the present invention is:

[0005] A method for determining a broken neutral line on the secondary side of a three-phase current transformer on the high-voltage side of a transformer comprises the following steps:

[0006] Step 1, collecting the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side;

[0007] Step 2, calculating the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and calculating the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side;

[0008] Step 3, when the following conditions are met, determine that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken: the transformer empty charging condition is met, and the self-generated zero-sequence current on the high-voltage side of the transformer is low, and the zero-sequence current of the neutral point on the high-voltage side is high, and the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave.

[0009] In the above step 1, when the high-voltage side of the transformer is a double-mother connection mode, the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing is collected as the three-phase current of the high-voltage side of the transformer; when the high-voltage side of the transformer is a 3 / 2 or 4 / 3 connection mode, the three-phase current of the high-voltage side bushing is collected as the three-phase current of the high-voltage side of the transformer.

[0010] In the above step 3, the transformer empty charging condition is met, including: if the high-voltage side switch of the transformer changes from open to closed, it is determined that the transformer empty charging condition is met; then after a delay of time t, it is determined that the transformer empty charging condition is no longer met.

[0011] In the above step 3, the zero-sequence current generated by the transformer on the high-voltage side is low, including the zero-sequence current fundamental effective value I 3I0_Cal Lower than the zero-sequence current fundamental effective value I generated by the transformer high voltage side 0_set1 , it is determined that the zero-sequence current generated by the transformer on the high-voltage side is low.

[0012] The above transformer high voltage side self-generated zero sequence current fundamental effective value constant I 0_set1 Set to the secondary current value I of the three-phase current transformer on the high-voltage side of the transformer n_HVS K 1 times, k 1 is the reliability coefficient.

[0013] In the above step 3, the high-voltage side neutral point zero-sequence current is high, including the fundamental effective value of the high-voltage side neutral point zero-sequence current I I0_NP Higher than the zero-sequence current fundamental effective value I at the neutral point on the high voltage side 0_set2 , it is determined that the zero-sequence current of the neutral point on the high-voltage side is high.

[0014] The above zero-sequence current fundamental effective value I 0_set2 Set to the secondary current value I of the neutral point zero-sequence current transformer on the high voltage side n_NP K 2 times, k 2 is the reliability coefficient.

[0015] In the above step 3, the sum of the integer harmonics of the zero-sequence current at the neutral point on the high voltage side is higher than the fundamental wave, including, satisfying When the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side;I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, ...; k set It is the constant value of the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave.

[0016] A device for determining a neutral line break on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, comprising:

[0017] A collection module is used to collect the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side;

[0018] A calculation module, used to calculate the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and to calculate the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side; and,

[0019] The judgment module is used to judge that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken when all the following conditions are met: in response to the transformer empty charging condition being met, and the self-produced zero-sequence current on the high-voltage side of the transformer is low, and the zero-sequence current of the neutral point on the high-voltage side is high, and the sum of the integer harmonics of the zero-sequence current of the neutral point on the high-voltage side is higher than the fundamental wave.

[0020] If the high-voltage side of the transformer is a double-mother connection method, the three-phase current on the high-voltage side of the transformer collected by the acquisition module is the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing; if the high-voltage side of the transformer is a 3 / 2 or 4 / 3 connection method, the three-phase current on the high-voltage side of the transformer collected by the acquisition module is the three-phase current of the high-voltage side bushing.

[0021] After adopting the above scheme, the beneficial effect of the present invention is: a new method for distinguishing the broken neutral line on the secondary side of the three-phase current transformer on the high-voltage side of the transformer is realized, and the broken neutral line fault on the secondary side of the three-phase current transformer on the high-voltage side can be quickly identified without adding external test equipment and modifying the secondary circuit, thereby avoiding the possibility of false operation of the zero-sequence differential protection of the main transformer due to out-of-zone faults, and better ensuring the safety of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of current measurement on each side of the power plant transformer in the present invention;

[0023] Among them, CT1 is the three-phase current transformer on the high-voltage side of the transformer, CT2 is the three-phase current transformer on the second high-voltage side of the transformer; CT3 is the neutral point zero-sequence current transformer on the high-voltage side of the transformer, the label 87NN represents the node current association for the disconnection judgment of the neutral point zero-sequence current transformer on the high-voltage side of the transformer, and F is the position of the neutral point zero-sequence current loop on the high-voltage side of the transformer;

[0024] Figure 2 It is a logic block diagram of the determination of the present invention;

[0025] Among them: a is the low self-generated zero-sequence current condition on the high-voltage side of the transformer, b is the high zero-sequence current condition on the neutral point on the high-voltage side, c is the high ratio of the harmonic to the fundamental wave of the zero-sequence current on the neutral point on the high-voltage side, d is the transformer empty charge condition, e is the delayed start / return logic, f and g are the "AND gate" logic, h is the delayed action logic, and i is the action output. DETAILED DESCRIPTION

[0026] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0027] The present invention provides a method for determining a broken neutral line on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, comprising the following steps:

[0028] Step 1, collecting the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side;

[0029] In the step 1, if the high-voltage side of the transformer is a double-mother wiring mode, the three-phase current on the high-voltage side of the transformer is the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing; if the high-voltage side of the transformer is a 3 / 2 or 4 / 3 wiring mode, the three-phase current on the high-voltage side of the transformer is the three-phase current of the high-voltage side bushing;

[0030] Step 2, calculating the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and calculating the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side;

[0031] In step 2, the fast Fourier transform algorithm (FFT algorithm) which has been maturely applied in the field of power system relay protection is used to calculate the effective value I of the zero-sequence current sampled value generated by the transformer high-voltage side. 3I0_Cal , the effective value I is calculated from the zero-sequence current sampling value of the neutral point on the high voltage side I0_NP And Xth harmonic effective value I I0_HmX ,X=2,3,4,…。

[0032] Step 3, in response to the transformer empty charging condition being met, the transformer high-voltage side self-generated zero-sequence current being low, the high-voltage side neutral point zero-sequence current being high, and the sum of each integer harmonic of the high-voltage side neutral point zero-sequence current being high compared to the fundamental wave, it is determined that the secondary side neutral line of the three-phase current transformer on the high-voltage side of the transformer is broken;

[0033] In step 3, if the high-voltage side switch of the transformer changes from open to closed, it is determined that the transformer empty-charge condition is met; then after a delay of time t, the transformer empty-charge condition is no longer met;

[0034] In step 3, the criterion for whether the self-generated zero-sequence current on the high-voltage side of the transformer is low is:

[0035]

[0036] Among them, I3I0_Cal I is the fundamental effective value of zero-sequence current generated by the transformer at the high voltage side; 0_set1 k is the fixed value of the zero-sequence current fundamental effective value generated by the transformer high-voltage side; 1 is the reliability coefficient, ranging from 2.5% to 5%; I n_HVS is the secondary current value of the three-phase current transformer on the high-voltage side of the transformer, which can be 1A or 5A;

[0037] In step 3, the criterion for the high-voltage side neutral point zero-sequence current to be high is:

[0038]

[0039] Among them, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; 0_set2 k is the fixed value of the zero-sequence current fundamental effective value at the neutral point on the high voltage side; 2 is the reliability coefficient, which is 5% to 10%; I n_NP is the secondary current value of the zero-sequence current transformer at the neutral point on the high-voltage side, which can be 1A or 5A;

[0040] In step 3, the criterion for the sum of the integer harmonics of the zero-sequence current at the neutral point on the high voltage side to be higher than the fundamental wave is:

[0041]

[0042] Among them, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, ...; k set It is the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave, and is taken as 0.2 to 0.8.

[0043] Example 1

[0044] refer to Figure 1 The application basis of the present invention is: the three-phase current of the bushing on the high-voltage side of the transformer and the zero-sequence current of the neutral point on the high-voltage side. Figure 1 In the figure, F is the position of the neutral line loop on the secondary side of the transformer high voltage side. Since the three-phase currents are almost completely symmetrical during normal operation of the transformer and the zero-sequence current is extremely small, when a line break occurs at F, the existing transformer protection of the power plant is difficult to identify.

[0045] In order to achieve the purpose of determining the neutral line break on the secondary side of the three-phase current transformer on the high-voltage side of the transformer of the present invention, the present invention sets CT1 as the three-phase current transformer on the bushing on the high-voltage side of the transformer, CT2 is the neutral point zero-sequence current transformer on the high-voltage side of the transformer, and the label 87NN represents the node current association for determining the neutral line break on the three-phase current transformer on the high-voltage side of the transformer.

[0046] The basic parameters of a power plant transformer are as follows:

[0047] Rated capacity S n 1200MVA, the wiring method is YND11, the rated voltage on the high voltage side is U hn 500kV, low voltage side rated voltage U ln The transformer ratio of the high voltage side bushing CT is N CT1 2000A / 1A, the zero-sequence CT ratio of the neutral point on the high-voltage side is N CT2 It is 800A / 1A.

[0048] The embodiment of the present invention provides a method for determining whether a neutral line is broken on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, comprising:

[0049] Obtain the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side;

[0050] Taking the transformer as an example with 3 / 2 connection mode, the three-phase current on the high-voltage side of the transformer is the three-phase current of the high-voltage side bushing;

[0051] Calculate the self-generated zero-sequence current of the bushing on the high-voltage side of the transformer;

[0052] i 3I0_Cal_h (k) = i a_h (k)+i b_h (k)+i c_h (k)

[0053] Among them, i a_h (k), i b_h (k) and i c_h (k) are the three-phase current sampling values ​​of the bushing on the high-voltage side of the transformer; i 3I0_Cal_h (k) is the sampling value of the zero-sequence current produced by the bushing on the high-voltage side of the transformer.

[0054] The mature fast Fourier transform algorithm (FFT algorithm) is used to calculate the effective value I from the zero-sequence current sampling value of the transformer high-voltage side bushing. 3I0_Cal_h , the effective value I is calculated from the zero-sequence current sampling value of the neutral point on the high voltage side I0_NP And Xth harmonic effective value I I0_HmX ,X=2,3,4,…。

[0055] Taking the transformer with 3 / 2 connection as an example, the initial states of the middle switch and the side switch on the high-voltage side are both in the open position. If any switch changes from open to closed, it is determined that the transformer empty-charge condition is met; then after a delay of time t (t is 60s), the transformer empty-charge condition is no longer met.

[0056] Taking the transformer with 3 / 2 connection as an example, the judgment condition for the low self-generated zero-sequence current on the high-voltage side of the transformer is: the effective value of the zero-sequence current fundamental wave produced by the bushing on the high-voltage side of the transformer is lower than the fixed value I 0_set1 ;

[0057] The specific protection criteria are:

[0058]

[0059] Among them, I 3I0_Cal_h k is the effective value of the zero-sequence current fundamental wave generated by the bushing on the high-voltage side of the transformer; 1 is the reliability coefficient, taking 2.5%; I n_HVS The secondary current value of the three-phase current transformer of the bushing on the high-voltage side of the transformer is 1A.

[0060] The judgment condition for the high-voltage side neutral point zero-sequence current is high is: the zero-sequence current fundamental effective value of the high-voltage side neutral point is higher than the fixed value I 0_set2 ;

[0061] The specific protection criteria are:

[0062]

[0063] Among them, I I0_NP k is the fundamental effective value of zero-sequence current at the neutral point on the high voltage side; 2 is the reliability coefficient, taking 5%; I n_NP is the secondary current value of the zero-sequence current transformer at the neutral point on the high-voltage side, which is 1A.

[0064] The judgment condition for the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point of the high-voltage side to the fundamental wave is: the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point of the high-voltage side to the fundamental wave is higher than the fixed value k set .

[0065] The specific protection criteria are:

[0066]

[0067] Among them, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, 5 (the cut-off frequency of the acquisition device is 325 Hz, and the maximum measurable harmonic is the fifth harmonic); k set The constant value is the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave, which is taken as 0.5.

[0068] Based on the above, the disconnection judgment logic block diagram is as follows Figure 2 As shown, a method for determining the disconnection of the neutral line on the secondary side of the three-phase current transformer on the high-voltage side of the transformer is as follows:

[0069]

[0070] When the transformer is empty and the above action equation is satisfied, a delay of T (T is 60ms) will be given to indicate that the zero-sequence current transformer at the neutral point on the high-voltage side is disconnected.

[0071] After adopting the method of the present invention, without adding external test equipment and modifying the secondary circuit, the problem that the three-phase current is almost completely symmetrical during normal operation of the transformer, the zero-sequence current is extremely small, and the neutral line on the secondary side of the three-phase current transformer on the high-voltage side of the transformer is difficult to judge.

[0072] The present invention also provides a device for determining a neutral line break on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, comprising:

[0073] A collection module is used to collect the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side;

[0074] Among them, if the high-voltage side of the transformer is a double-mother wiring method, the three-phase current on the high-voltage side of the transformer collected by the collection module is the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing; if the high-voltage side of the transformer is a 3 / 2 or 4 / 3 wiring method, the three-phase current on the high-voltage side of the transformer collected by the collection module is the three-phase current of the high-voltage side bushing;

[0075] A calculation module, used to calculate the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and to calculate the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side; and,

[0076] A judgment module is used to judge that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken when all the following conditions are met: in response to the transformer empty charging condition being met, and the self-generated zero-sequence current on the high-voltage side of the transformer is low, and the zero-sequence current at the neutral point on the high-voltage side is high, and the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave;

[0077] If the high-voltage side switch of the transformer changes from open to closed, the judgment module determines that the transformer empty-charge condition is met; then after a delay of time t, the judgment module determines that the transformer empty-charge condition is no longer met;

[0078] Among them, the judgment module determines that the self-generated zero-sequence current on the high-voltage side of the transformer is low based on:

[0079]

[0080] Among them, I 3I0_Cal I is the fundamental effective value of zero-sequence current generated by the transformer at the high voltage side; 0_set1 k is the fixed value of the zero-sequence current fundamental effective value generated by the transformer high-voltage side; 1is the reliability coefficient, ranging from 2.5% to 5%; I n_HVS is the secondary current value of the three-phase current transformer on the high-voltage side of the transformer, which can be 1A or 5A;

[0081] Among them, the criterion for the judgment module to determine that the zero-sequence current of the neutral point on the high-voltage side is high is:

[0082]

[0083] Among them, I I0_NP is the fundamental effective value of zero-sequence current at the neutral point on the high voltage side; I 0_set2 k is the fixed value of the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; 2 is the reliability coefficient, which is 5% to 10%; I n_NP is the secondary current value of the zero-sequence current transformer at the neutral point on the high-voltage side, which can be 1A or 5A;

[0084] Among them, the judgment module determines that the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave as follows:

[0085]

[0086] Among them, I I0_NP is the fundamental effective value of zero-sequence current at the neutral point on the high voltage side; I I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, ...; k set It is the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave, and is taken as 0.2 to 0.8.

[0087] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for determining a broken neutral line on the secondary side of a three-phase current transformer on the high-voltage side of a transformer, characterized in that The steps include: Step 1, collecting the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side; Step 2, calculating the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and calculating the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side; Step 3, when the following conditions are met, determine that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken: the transformer empty charging condition is met, and the self-generated zero-sequence current on the high-voltage side of the transformer is low, and the high-voltage side neutral point zero-sequence current is high, and the sum of the integer harmonics of the high-voltage side neutral point zero-sequence current is higher than the fundamental wave; In step 3, the sum of the integer harmonics of the zero-sequence current at the neutral point of the high-voltage side is higher than the fundamental wave, including satisfying When the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, ...; k set It is the constant value of the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave.

2. The method according to claim 1, characterized in that: In the step 1, when the high-voltage side of the transformer is in a double-mother connection mode, the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing is collected as the three-phase current of the high-voltage side of the transformer; when the high-voltage side of the transformer is in a 3 / 2 or 4 / 3 connection mode, the three-phase current of the high-voltage side bushing is collected as the three-phase current of the high-voltage side of the transformer.

3. The method according to claim 1, characterized in that: In the step 3, the transformer empty-charge condition is met, including: if the high-voltage side switch of the transformer changes from open to closed, it is determined that the transformer empty-charge condition is met; and then after a delay of time t, it is determined that the transformer empty-charge condition is no longer met.

4. The method according to claim 1, characterized in that: In the step 3, the self-generated zero-sequence current on the high-voltage side of the transformer is low, including the zero-sequence current fundamental effective value I 3I0_Cal Lower than the zero-sequence current fundamental effective value I generated by the transformer high voltage side 0_set1 , it is determined that the zero-sequence current generated by the transformer on the high-voltage side is low.

5. The method according to claim 4, characterized in that: The zero-sequence current fundamental effective value constant I 0_set1 Set to the secondary current value I of the three-phase current transformer on the high-voltage side of the transformer n_HVS k1 times, where k1 is the reliability coefficient.

6. The method according to claim 1, characterized in that: In step 3, the high-voltage side neutral point zero-sequence current is high, including the high-voltage side neutral point zero-sequence current fundamental effective value I I0_NP Higher than the zero-sequence current fundamental effective value I at the neutral point on the high voltage side 0_set2 , it is determined that the zero-sequence current of the neutral point on the high-voltage side is high.

7. The method according to claim 6, characterized in that: The zero-sequence current fundamental effective value constant I 0_set2 Set to the secondary current value I of the neutral point zero-sequence current transformer on the high voltage side n_NP k2 times, where k2 is the reliability coefficient.

8. A device for determining the neutral line break of the secondary side of a three-phase current transformer on the high-voltage side of a transformer, characterized in that: include, A collection module is used to collect the three-phase current on the high-voltage side of the transformer and the zero-sequence current at the neutral point on the high-voltage side; A calculation module, used to calculate the effective value of the zero-sequence current fundamental wave generated by the transformer at the high-voltage side, and to calculate the effective value of the zero-sequence current fundamental wave and each integer harmonic at the neutral point at the high-voltage side; and, A judgment module is used to judge that the neutral line of the secondary side of the three-phase current transformer on the high-voltage side of the transformer is broken when all the following conditions are met: in response to the transformer empty charging condition being met, and the self-generated zero-sequence current on the high-voltage side of the transformer is low, and the zero-sequence current at the neutral point on the high-voltage side is high, and the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave; The sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave, including, satisfying When the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side is higher than the fundamental wave, I I0_NP I is the fundamental effective value of the zero-sequence current at the neutral point on the high voltage side; I0_HmX is the effective value of the Xth harmonic of the neutral point zero-sequence current on the high-voltage side, X = 2, 3, 4, ...; k set It is the constant value of the ratio of the sum of the integer harmonics of the zero-sequence current at the neutral point on the high-voltage side to the effective value of the fundamental wave.

9. The device according to claim 8, characterized in that: If the high-voltage side of the transformer is a double-mother connection method, the three-phase current on the high-voltage side of the transformer collected by the acquisition module is the three-phase current of the high-voltage side switch or the three-phase current of the high-voltage side bushing; if the high-voltage side of the transformer is a 3 / 2 or 4 / 3 connection method, the three-phase current on the high-voltage side of the transformer collected by the acquisition module is the three-phase current of the high-voltage side bushing.

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