CN106771812A - A kind of recognition methods of transformer current transformer disconnection and device - Google Patents

Abstract

The invention relates to a disconnection identification method and device of a transformer current transformer, wherein the disconnection identification method includes: judging whether the start-up condition for the disconnection discrimination of the current transformer is satisfied; if the start-up condition is met, judging whether the disconnection judgment condition is met; If all disconnection judgment conditions are met, it is determined that the current transformer on the local side of the transformer is disconnected. By combining the current criterion and the voltage criterion, the invention can accurately determine whether the current transformer on a certain side of the transformer is disconnected, and provides a basis for whether the differential protection of the transformer operates.

Description

A method and device for identifying disconnection of a transformer current transformer

technical field

The invention relates to a transformer current transformer disconnection identification method and device, belonging to the technical field of electric power system relay protection.

Background technique

"Electrical Industry Safety Work Regulations" stipulates that it is strictly forbidden to open the circuit when the secondary circuit of the live current transformer is working. The current transformers used in large units and ultra-high voltage equipment have a large number of secondary winding turns and a high open circuit voltage. The higher secondary voltage may not only damage the insulation of the secondary winding and secondary equipment, but also burn the iron core due to overheating, and even threaten personal safety.

In addition, for transformer differential protection, when the transformer current transformer is disconnected, a large unbalanced differential current will appear in the circuit, causing differential protection to malfunction. Therefore, accurately identifying whether the transformer current transformer is disconnected can provide a basis for whether the transformer differential protection operates.

Contents of the invention

The object of the present invention is to provide a transformer current transformer disconnection identification method and device for solving the problem of accurately judging whether the transformer current transformer is disconnected.

In order to solve the above technical problems, the present invention provides a transformer current transformer disconnection identification method, including the following solutions:

Method 1: including the following steps

Step 1, judging whether the starting condition for the disconnection judgment of the current transformer is satisfied;

Step 2, if the start condition is met, judge the following disconnection judgment condition, the disconnection judgment condition is:

(1) The three-phase phase currents on the transformer’s own side are not zero before the disconnection discrimination starts, and the three-phase phase currents on the transformer’s own side do not increase after the disconnection discrimination starts;

(2) There is no change in the three-phase phase currents on the other side of the transformer when the disconnection is judged and started, including phase current mutations, zero-sequence currents, and negative-sequence currents;

(3) There is no change in the three-phase phase voltage on the transformer's own side and other sides when the disconnection is judged and started, including phase voltage mutation, zero-sequence voltage and zero-sequence voltage mutation;

Step 3, if all the above disconnection judging conditions are satisfied, it is determined that the current transformer on the transformer side is disconnected.

Method scheme 2: On the basis of method scheme 1, the starting conditions for the disconnection judgment of the current transformer described in step 1 are:

I _Φ1 (t-nT)-I _Φ1 (t)＞I _SET1

Among them, n is a positive integer, indicating the number of cycles before the current cycle of the three-phase phase current on the transformer’s own side, I _Φ1 (t) is the three-phase phase current amplitude on the transformer’s own side when the disconnection discrimination starts, I _Φ1 (t-nT) is the three-phase phase current amplitude before n cycles on the transformer's own side when the disconnection discrimination starts, I _SET1 is the current threshold value of the transformer's own side, and the value range is _0.06IN ~ _0.08IN , I _N It is the secondary rated current of the current transformer on the transformer side.

Method scheme 3 and 4: on the basis of method scheme 1 or 2 respectively, the discriminant formula for the discontinuous line discrimination condition (1) in step 2 is:

Among them, K ₁ is a constant, the value range is 1.2 ~ 1.4, I _Φ1.min (t-nT) is the minimum phase current amplitude among the three-phase currents before n cycles on the transformer's own side when the disconnection discrimination starts;

The discriminant formula of the disconnection condition (2) is:

Among them, I _Φ2 (t) is the three-phase phase current amplitude on the other side of the transformer when the disconnection discrimination starts, and I _Φ2 (t-nT) is the three-phase phase current amplitude on the other side of the transformer n cycles before the disconnection discrimination startup value, |I _Φ2 (t)-I _Φ2 (t-nT)| is the three-phase phase current amplitude on the other side of the transformer at the start of the disconnection discrimination and the three-phase phase current at the other side of the transformer n cycles before the start of the disconnection discrimination The absolute value of the difference of the current amplitude, I ₂ (t) and 3I ₀ (t) are the negative sequence current amplitude and zero sequence current amplitude of the other side of the transformer when the disconnection discrimination starts, respectively, and I _SET2 is the other side of the transformer The current threshold value ranges from _0.08IN to _0.2IN ;

The discriminant formula of disconnection condition (3) is:

Among them, U _Φ (t) is the three-phase phase voltage amplitude on the transformer's own side or other sides when the disconnection discrimination starts, and U _Φ (t-nT) is the n cycles of the transformer's own side or other sides when the disconnection discrimination starts The previous three-phase phase voltage amplitude, |U _Φ (t)-U _Φ (t-nT)| is the three-phase phase voltage amplitude of the transformer itself or other sides when the disconnection discrimination starts, and the voltage amplitude of the transformer when the disconnection discrimination starts The absolute value of the difference of the three-phase phase voltage amplitudes before n cycles on this side or other sides, 3U ₀ (t) is the zero-sequence voltage amplitude of the transformer on this side or other sides when the disconnection discrimination starts, 3U ₀ (t-nT) is the zero-sequence voltage amplitude of n cycles before the transformer's own side or other sides when the disconnection discrimination starts, |3U ₀ (t)-3U ₀ (t-nT)| is the disconnection discrimination startup The absolute value of the difference between the zero-sequence voltage amplitude of this side or other sides of the transformer and the zero-sequence voltage amplitude of n cycles before the start of the disconnection discrimination of the transformer, U _SET1 is the three-phase phase voltage of the transformer The threshold value ranges from 0.1U _N to 0.2U _N , U _SET2 is the transformer zero-sequence voltage threshold value ranges from 0.02U _N to 0.1U _N , and U _N is the secondary rated phase voltage of the transformer PT.

Method scheme five and six: on the basis of method scheme three or four respectively, n is equal to 2.

The present invention also provides a transformer current transformer disconnection identification device, including the following solutions:

Installation scheme one: including

A unit for judging whether the start-up condition for the disconnection judgment of the current transformer is met;

A unit for judging the following disconnection judging conditions if the starting conditions are met, and the disconnection judging conditions are:

(1) The three-phase phase currents on the transformer’s own side are not zero before the disconnection discrimination starts, and the three-phase phase currents on the transformer’s own side do not increase after the disconnection discrimination starts;

(2) There is no change in the three-phase phase currents on the other side of the transformer when the disconnection is judged and started, including phase current mutations, zero-sequence currents, and negative-sequence currents;

(3) There is no change in the three-phase phase voltage on the transformer's own side and other sides when the disconnection is judged and started, including phase voltage mutation, zero-sequence voltage and zero-sequence voltage mutation;

The unit used to determine the disconnection of the current transformer on the transformer’s own side if all the above-mentioned disconnection judgment conditions are met.

Device scheme two: on the basis of device scheme one, the starting conditions for the disconnection judgment of the current transformer are:

I _Φ1 (t-nT)-I _Φ1 (t)＞I _SET1

Among them, n is a positive integer, indicating the number of cycles before the current cycle of the three-phase phase current on the transformer’s own side, I _Φ1 (t) is the three-phase phase current amplitude on the transformer’s own side when the disconnection discrimination starts, I _Φ1 (t-nT) is the three-phase phase current amplitude before n cycles on the transformer's own side when the disconnection discrimination starts, I _SET1 is the current threshold value of the transformer's own side, and the value range is _0.06IN ~ _0.08IN , I _N It is the secondary rated current of the current transformer on the transformer side.

Device scheme 3 and 4: on the basis of device scheme 1 or 2 respectively, the discriminant formula for the disconnection criterion (1) is:

Among them, K ₁ is a constant, the value range is 1.2 ~ 1.4, I _Φ1.min (t-nT) is the minimum phase current amplitude among the three-phase currents before n cycles on the transformer's own side when the disconnection discrimination starts;

The discriminant formula of the disconnection condition (2) is:

Among them, I _Φ2 (t) is the three-phase phase current amplitude on the other side of the transformer when the disconnection discrimination starts, and I _Φ2 (t-nT) is the three-phase phase current amplitude on the other side of the transformer n cycles before the disconnection discrimination startup value, |I _Φ2 (t)-I _Φ2 (t-nT)| is the three-phase phase current amplitude on the other side of the transformer at the start of the disconnection discrimination and the three-phase phase current at the other side of the transformer n cycles before the start of the disconnection discrimination The absolute value of the difference of the current amplitude, I ₂ (t) and 3I ₀ (t) are the negative sequence current amplitude and zero sequence current amplitude of the other side of the transformer when the disconnection discrimination starts, respectively, and I _SET2 is the other side of the transformer The current threshold value ranges from _0.08IN to _0.2IN ;

The discriminant formula of disconnection condition (3) is:

Among them, U _Φ (t) is the three-phase phase voltage amplitude on the transformer's own side or other sides when the disconnection discrimination starts, and U _Φ (t-nT) is the n cycles of the transformer's own side or other sides when the disconnection discrimination starts The previous three-phase phase voltage amplitude, |U _Φ (t)-U _Φ (t-nT)| is the three-phase phase voltage amplitude of the transformer itself or other sides when the disconnection discrimination starts, and the voltage amplitude of the transformer when the disconnection discrimination starts The absolute value of the difference of the three-phase phase voltage amplitudes before n cycles on this side or other sides, 3U ₀ (t) is the zero-sequence voltage amplitude of the transformer on this side or other sides when the disconnection discrimination starts, 3U ₀ (t-nT) is the zero-sequence voltage amplitude of n cycles before the transformer's own side or other sides when the disconnection discrimination starts, |3U ₀ (t)-3U ₀ (t-nT)| is the disconnection discrimination startup The absolute value of the difference between the zero-sequence voltage amplitude of this side or other sides of the transformer and the zero-sequence voltage amplitude of n cycles before the start of the disconnection discrimination of the transformer, U _SET1 is the three-phase phase voltage of the transformer The threshold value ranges from 0.1U _N to 0.2U _N , U _SET2 is the transformer zero-sequence voltage threshold value ranges from 0.02U _N to 0.1U _N , and U _N is the secondary rated phase voltage of the transformer PT.

Device scheme five and six: on the basis of device scheme three or four respectively, n is equal to 2.

The beneficial effects of the present invention are:

By judging the changes of the three-phase phase current and the three-phase phase voltage on the transformer's own side and other sides, it can be accurately judged whether the current transformer on the transformer's own side is disconnected, providing a basis for whether the transformer differential protection operates.

Description of drawings

Figure 1 is a schematic diagram of the main wiring of a 220kV transformer;

Fig. 2 is a flow chart of a method for identifying disconnection of a transformer current transformer.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Taking the 220kV transformer as an example, the main wiring diagram is shown in Figure 1. During normal operation, the circuit breakers on the high-voltage side, medium-voltage side and low-voltage side of the transformer are closed. The side current transformer and voltage transformer are TA3 and TV3 respectively. During normal operation, if TA1 is disconnected and the differential current is greater than the starting current setting value of the differential protection, it will cause the main transformer differential protection to trip.

Taking the high-voltage side of the transformer as an example, the flow chart of the transformer current transformer disconnection identification method is shown in Figure 2, which specifically includes the following steps:

Step 1. Determine whether the high-voltage side of the transformer meets the start-up conditions for the disconnection of the current transformer. The start-up conditions are:

I _Φ1 (t-nT)-I _Φ1 (t)＞I _SET1

Among them, n is a positive integer, indicating the number of cycles before the current cycle of the three-phase phase current on the high-voltage side of the transformer, I _Φ1 (t) is the amplitude of the three-phase phase current on the high-voltage side of the transformer when the disconnection discrimination starts, I _Φ1 (t-nT) is the three-phase phase current amplitude before n cycles on the high-voltage side of the transformer when the disconnection discrimination starts, I _SET1 is the current threshold value of the high-voltage side of the transformer, and the value range is _0.06IN ～ _0.08IN , I _N is the secondary rated current of the current transformer on the high voltage side of the transformer.

If the high-voltage side of the transformer does not meet the starting conditions for the disconnection judgment of the current transformer, it is determined that the current transformer on the high-voltage side of the transformer is not disconnected.

Step 2. Determine whether the following disconnection criteria are met:

(1) The three-phase phase currents on the high voltage side of the transformer are not zero before the disconnection discrimination starts, and the three-phase phase currents on the high voltage side of the transformer do not increase after the disconnection discrimination starts;

(2) There is no change in the three-phase phase current on the other side of the transformer when the disconnection is judged and started, including the sudden change of phase current, zero-sequence current and negative-sequence current;

(3) There is no change in the three-phase phase voltage on the high-voltage side and other sides of the transformer when the disconnection is detected, including phase voltage mutations, zero-sequence voltages, and zero-sequence voltage mutations.

The discriminant formula for the disconnection condition (1) is:

Among them, K ₁ is a constant with a value range of 1.2 to 1.4, and I _Φ1.min (t-nT) is the minimum phase current amplitude among the three-phase currents before n cycles on the high voltage side of the transformer when the disconnection discrimination starts.

The discriminant formula of the disconnection condition (2) is:

Among them, I _Φ2 (t) is the three-phase phase current amplitude on the other side of the transformer (medium voltage side or low voltage side) when the disconnection discrimination starts, and I _Φ2 (t-nT) is the other side of the transformer (medium voltage side) when the disconnection discrimination starts. voltage side or low voltage side) three-phase phase current amplitude before n cycles, |I _Φ2 (t)-I _Φ2 (t-nT)| is the difference between the three-phase phase current amplitude and The absolute value of the difference of the three-phase phase current amplitudes before n cycles on the other side of the transformer at the start of the disconnection discrimination, I ₂ (t) and 3I ₀ (t) respectively, the negative sequence current at the other sides of the transformer at the start of the disconnection discrimination Amplitude and zero-sequence current amplitude, I _SET2 is the threshold value of the current on the other side of the transformer, and the value range is _0.08IN ~ _0.2IN .

If the current at any one of the medium-voltage side and the low-voltage side does not satisfy the judgment formula of the disconnection judgment condition (2), it is determined that the disconnection judgment condition (2) is not satisfied.

The discriminant formula of disconnection condition (3) is:

Among them, U _Φ (t) is the three-phase phase voltage amplitude on the high-voltage side or other sides of the transformer when the disconnection discrimination starts, and U _Φ (t-nT) is n cycles of the high-voltage side or other sides of the transformer when the disconnection discrimination starts The previous three-phase phase voltage amplitude, |U _Φ (t)-U _Φ (t-nT)| is the three-phase phase voltage amplitude of the high voltage side or other side of the transformer at the start of the disconnection discrimination and the transformer at the start of the disconnection discrimination The absolute value of the difference between the three-phase phase voltage amplitudes before n cycles on the high voltage side or other sides, 3U ₀ (t) is the zero sequence voltage amplitude of the high voltage side or other sides of the transformer when the disconnection discrimination starts, 3U ₀ (t-nT) is the zero-sequence voltage amplitude of n cycles before the high-voltage side of the transformer or other sides when the disconnection discrimination starts, |3U ₀ (t)-3U ₀ (t-nT)| is the disconnection discrimination startup The absolute value of the difference between the zero-sequence voltage amplitude on the high-voltage side or other sides of the transformer and the zero-sequence voltage amplitude before n cycles on the high-voltage side or other sides of the transformer at the start of disconnection discrimination, U _SET1 is the three-phase phase voltage of the transformer The threshold value ranges from 0.1U _N to 0.2U _N , U _SET2 is the transformer zero-sequence voltage threshold value ranges from 0.02U _N to 0.1U _N , and U _N is the secondary rated phase voltage of the transformer PT.

That is, it is judged whether the voltages on the high, medium and low sides of the transformer all satisfy the discriminant formula of the above-mentioned disconnection discrimination condition (3), if the voltage on any side does not satisfy the discriminant formula of the disconnection discrimination condition (3), then it is judged Disconnection discrimination condition (3) is not satisfied.

Step 3, if all the above disconnection judging conditions are satisfied, it is determined that the current transformer on the high voltage side of the transformer is disconnected.

If it is determined that the current transformer on the high-voltage side of the transformer is disconnected, a disconnection alarm command will be issued, which can be sent to the differential protection device to provide a reliable basis for whether the differential protection operates; at the same time, the disconnection alarm command will be sent Give an alarm to the alarm equipment and prompt the maintenance personnel to repair it in time. If the high-voltage side of the transformer does not meet any of the disconnection judgment conditions, it is determined that the current transformer on the high-voltage side of the transformer is not disconnected.

In this embodiment, the positive integer n is all taken as 2, and it can also be taken as an appropriate value as required, such as 1, 3, 4, etc., without affecting the accuracy of CT disconnection discrimination.

The transformer current transformer disconnection identification method in the present invention combines the current criterion and the voltage criterion, can accurately determine whether the current transformer on a certain side of the transformer is disconnected, and effectively solves the possible error of differential protection after the current transformer is disconnected. moving problem.

The present invention also provides a transformer current transformer disconnection identification device, comprising:

A unit for judging whether the start-up condition for the disconnection judgment of the current transformer is met;

A unit for judging the following disconnection judging conditions if the starting conditions are met, and the disconnection judging conditions are:

(1) The three-phase phase currents on the transformer’s own side are not zero before the disconnection discrimination starts, and the three-phase phase currents on the transformer’s own side do not increase after the disconnection discrimination starts;

(2) There is no change in the three-phase phase currents on the other side of the transformer when the disconnection is judged and started, including phase current mutations, zero-sequence currents, and negative-sequence currents;

(3) There is no change in the three-phase phase voltage on the transformer's own side and other sides when the disconnection is judged and started, including phase voltage mutation, zero-sequence voltage and zero-sequence voltage mutation;

The unit used to determine the disconnection of the current transformer on the transformer’s own side if all the above-mentioned disconnection judgment conditions are met.

The above transformer current transformer disconnection identification device is actually a computer solution based on the transformer current transformer disconnection identification method, that is, a software framework, and the software can run in the protection equipment. Since the above-mentioned transformer current transformer disconnection identification method has been sufficiently clearly and completely introduced, each unit in the disconnection identification device will not be described in detail.

Claims (8)

1. A transformer current transformer disconnection identification method, is characterized in that, comprises the following steps: Step 1, judging whether the starting condition for the disconnection judgment of the current transformer is satisfied; Step 2, if the start condition is met, judge the following disconnection judgment condition, the disconnection judgment condition is: (1) The three-phase phase currents on the transformer’s own side are not zero before the disconnection discrimination starts, and the three-phase phase currents on the transformer’s own side do not increase after the disconnection discrimination starts; (2) There is no change in the three-phase phase currents on the other side of the transformer when the disconnection is judged and started, including phase current mutations, zero-sequence currents, and negative-sequence currents; (3) There is no change in the three-phase phase voltage on the transformer's own side and other sides when the disconnection is judged and started, including phase voltage mutation, zero-sequence voltage and zero-sequence voltage mutation; Step 3, if all the above disconnection judging conditions are satisfied, it is determined that the current transformer on the transformer side is disconnected. 2. transformer current transformer disconnection identification method according to claim 1, is characterized in that, the starting condition of current transformer disconnection discrimination described in step 1 is: I _Φ1 (t-nT)-I _Φ1 (t)＞I _SET1 Among them, n is a positive integer, indicating the number of cycles before the current cycle of the three-phase phase current on the transformer’s own side, I _Φ1 (t) is the three-phase phase current amplitude on the transformer’s own side when the disconnection discrimination starts, I _Φ1 (t-nT) is the three-phase phase current amplitude before n cycles on the transformer's own side when the disconnection discrimination starts, I _SET1 is the current threshold value of the transformer's own side, and the value range is _0.06IN ~ _0.08IN , I _N It is the secondary rated current of the current transformer on the transformer side. 3. transformer current transformer disconnection identification method according to claim 1 or 2, is characterized in that, the discriminant formula of step 2 disconnection discrimination condition (1) is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1.</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right.$ Among them, K ₁ is a constant, the value range is 1.2 ~ 1.4, I _Φ1.min (t-nT) is the minimum phase current amplitude among the three-phase currents before n cycles on the transformer's own side when the disconnection discrimination starts; The discriminant formula for the disconnection condition (2) is: $\left\{\begin{array}{c}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right.$ Among them, I _Φ2 (t) is the three-phase phase current amplitude on the other side of the transformer when the disconnection discrimination starts, and I _Φ2 (t-nT) is the three-phase phase current amplitude on the other side of the transformer n cycles before the disconnection discrimination startup value, |I _Φ2 (t)-I _Φ2 (t-nT)| is the three-phase phase current amplitude on the other side of the transformer at the start of the disconnection discrimination and the three-phase phase current at the other side of the transformer n cycles before the start of the disconnection discrimination The absolute value of the difference of the current amplitude, I ₂ (t) and 3I ₀ (t) are the negative sequence current amplitude and zero sequence current amplitude of the other side of the transformer when the disconnection discrimination starts, respectively, and I _SET2 is the other side of the transformer The current threshold value ranges from _0.08IN to _0.2IN ; The discriminant formula of disconnection condition (3) is: $\left\{\begin{array}{c}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ <span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right.$ Among them, U _Φ (t) is the three-phase phase voltage amplitude on the transformer's own side or other sides when the disconnection discrimination starts, and U _Φ (t-nT) is the n cycles of the transformer's own side or other sides when the disconnection discrimination starts The previous three-phase phase voltage amplitude, |U _Φ (t)-U _Φ (t-nT)| is the three-phase phase voltage amplitude of the transformer itself or other sides when the disconnection discrimination starts, and the voltage amplitude of the transformer when the disconnection discrimination starts The absolute value of the difference of the three-phase phase voltage amplitudes before n cycles on this side or other sides, 3U ₀ (t) is the zero-sequence voltage amplitude of the transformer on this side or other sides when the disconnection discrimination starts, 3U ₀ (t-nT) is the zero-sequence voltage amplitude of n cycles before the transformer's own side or other sides when the disconnection discrimination starts, |3U ₀ (t)-3U ₀ (t-nT)| is the disconnection discrimination startup The absolute value of the difference between the zero-sequence voltage amplitude of this side or other sides of the transformer and the zero-sequence voltage amplitude of n cycles before the start of the disconnection discrimination of the transformer, U _SET1 is the three-phase phase voltage of the transformer The threshold value ranges from 0.1U _N to 0.2U _N , U _SET2 is the transformer zero-sequence voltage threshold value ranges from 0.02U _N to 0.1U _N , and U _N is the secondary rated phase voltage of the transformer PT. 4. The transformer current transformer disconnection identification method according to claim 3, characterized in that n is equal to 2. 5. A transformer current transformer disconnection identification device, characterized in that it comprises: A unit for judging whether the start-up condition for the disconnection judgment of the current transformer is met; A unit for judging the following disconnection judging conditions if the starting conditions are met, and the disconnection judging conditions are: (1) The three-phase phase currents on the transformer’s own side are not zero before the disconnection discrimination starts, and the three-phase phase currents on the transformer’s own side do not increase after the disconnection discrimination starts; (2) There is no change in the three-phase phase currents on the other side of the transformer when the disconnection is judged and started, including phase current mutations, zero-sequence currents, and negative-sequence currents; (3) There is no change in the three-phase phase voltage on the transformer's own side and other sides when the disconnection is judged and started, including phase voltage mutation, zero-sequence voltage and zero-sequence voltage mutation; The unit used to determine the disconnection of the current transformer on the transformer’s own side if all the above-mentioned disconnection judgment conditions are met. 6. The transformer current transformer disconnection identification device according to claim 5, characterized in that, the starting condition for the disconnection discrimination of the current transformer is: I _Φ1 (t-nT)-I _Φ1 (t)＞I _SET1 Among them, n is a positive integer, indicating the number of cycles before the current cycle of the three-phase phase current on the transformer’s own side, I _Φ1 (t) is the three-phase phase current amplitude on the transformer’s own side when the disconnection discrimination starts, I _Φ1 (t-nT) is the three-phase phase current amplitude before n cycles on the transformer's own side when the disconnection discrimination starts, I _SET1 is the current threshold value of the transformer's own side, and the value range is _0.06IN ~ _0.08IN , I _N It is the secondary rated current of the current transformer on the transformer side. 7. transformer current transformer disconnection recognition device according to claim 5 or 6, is characterized in that, the discrimination formula of disconnection discrimination condition (1) is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 1.</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right.$ Among them, K ₁ is a constant, the value range is 1.2 ~ 1.4, I _Φ1.min (t-nT) is the minimum phase current amplitude among the three-phase currents before n cycles on the transformer's own side when the disconnection discrimination starts; The discriminant formula of the disconnection condition (2) is: $\left\{\begin{array}{c}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right.$ Among them, I _Φ2 (t) is the three-phase phase current amplitude on the other side of the transformer when the disconnection discrimination starts, and I _Φ2 (t-nT) is the three-phase phase current amplitude on the other side of the transformer n cycles before the disconnection discrimination startup value, |I _Φ2 (t)-I _Φ2 (t-nT)| is the three-phase phase current amplitude on the other side of the transformer at the start of the disconnection discrimination and the three-phase phase current at the other side of the transformer n cycles before the start of the disconnection discrimination The absolute value of the difference of the current amplitude, I ₂ (t) and 3I ₀ (t) are the negative sequence current amplitude and zero sequence current amplitude of the other side of the transformer when the disconnection discrimination starts, respectively, and I _SET2 is the other side of the transformer The current threshold value ranges from _0.08IN to _0.2IN ; The discriminant formula of disconnection condition (3) is: $\left\{\begin{array}{c}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ <span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right.$ Among them, U _Φ (t) is the three-phase phase voltage amplitude on the transformer's own side or other sides when the disconnection discrimination starts, and U _Φ (t-nT) is the n cycles of the transformer's own side or other sides when the disconnection discrimination starts The previous three-phase phase voltage amplitude, |U _Φ (t)-U _Φ (t-nT)| is the three-phase phase voltage amplitude of the transformer itself or other sides when the disconnection discrimination starts, and the voltage amplitude of the transformer when the disconnection discrimination starts The absolute value of the difference of the three-phase phase voltage amplitudes before n cycles on this side or other sides, 3U ₀ (t) is the zero-sequence voltage amplitude of the transformer on this side or other sides when the disconnection discrimination starts, 3U ₀ (t-nT) is the zero-sequence voltage amplitude of n cycles before the transformer's own side or other sides when the disconnection discrimination starts, |3U ₀ (t)-3U ₀ (t-nT)| is the disconnection discrimination startup The absolute value of the difference between the zero-sequence voltage amplitude of this side or other sides of the transformer and the zero-sequence voltage amplitude of n cycles before the start of the disconnection discrimination of the transformer, U _SET1 is the three-phase phase voltage of the transformer The threshold value ranges from 0.1U _N to 0.2U _N , U _SET2 is the transformer zero-sequence voltage threshold value ranges from 0.02U _N to 0.1U _N , and U _N is the secondary rated phase voltage of the transformer PT. 8 . The transformer current transformer disconnection identification device according to claim 7 , wherein n is equal to 2. 9 .