Transformer protection method, system and equipment based on aperiodic component change characteristics and medium

Abstract

The invention discloses a transformer protection method, system and device based on aperiodic component change characteristics and a medium, and relates to the technical field of transformer protection. The method comprises the following steps: when a differential protection element of a transformer is started, calculating a second harmonic proportion and a non-periodic component change rate, and if a second harmonic braking criterion and a non-periodic component criterion are met, increasing an action threshold value; when the second harmonic braking criterion is not met, calculating the change rate of a CT transmission side aperiodic component, and judging whether the aperiodic component criterion is met or not, if yes, increasing an action threshold value, and if not, executing a differential protection action; when the non-periodic component criterion is met, it is judged that the CT is in a saturated state, sympathetic inrush current exists, the protection action threshold value is increased till the set condition is met, and the differential protection threshold returns to the original value. The working mode of differential protection can be optimized, and maloperation caused by sympathetic inrush current is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer protection, and in particular to a transformer protection method, system, equipment and medium based on non-periodic component variation characteristics. Background Art

[0002] Differential protection is an important method of transformer protection. Its basic principle is to determine whether there is an internal fault in the transformer by comparing the difference between the current at the input (primary side) and output (secondary side) of the transformer.

[0003] When the transformer is operating normally, the current at the input and output should be equal, and the output signal of the differential protection device is zero. When a fault occurs inside the transformer, the current at the input and output will no longer be equal, and the differential protection device will detect this difference. When the difference exceeds the set threshold, the protection action will be activated to cut off the power supply to the transformer to avoid further damage.

[0004] In order to improve the reliability of differential protection, some auxiliary protection functions are usually set in the differential protection device, such as zero-sequence current protection, overcurrent protection, etc. At the same time, some technical means are also used to reduce the impact of unbalanced current, such as the use of second harmonic braking and other methods.

[0005] However, in the scenario of parallel operation of transformers, after the air-dropped transformer is closed under no-load condition, the parallel operation transformer will generate harmonic surge current due to the harmonic effect. The harmonic surge current causes local transient saturation of the current transformer due to its long-lasting non-periodic component, making the secondary harmonic braking in the differential protection invalid. The slow attenuation of the harmonic surge current causes the protection to operate for a long time, seriously affecting the operation of the power system. Summary of the invention

[0006] The object of the present invention is to provide a transformer protection method, system, device and medium based on the variation characteristics of non-periodic components, which can optimize the working mode of differential protection and avoid false operation due to inrush current.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A transformer protection method based on non-periodic component variation characteristics, comprising:

[0009] When the differential protection element of the transformer is started, the second harmonic proportion and the non-periodic component change rate are calculated. If the second harmonic braking criterion and the non-periodic component criterion are met, the action threshold value is increased; the non-periodic component criterion is used to determine whether the CT is in a saturated state;

[0010] When the second harmonic braking criterion is not met, the change rate of the non-periodic component on the CT transmission side is calculated, and it is determined whether the non-periodic component criterion is met. If it is met, the action threshold value is increased; if it is not met, the differential protection action is performed;

[0011] When the non-periodic component criterion is met, it is determined that the CT is in a saturated state and there is a surge current. The protection action threshold is increased until the set condition is met, and the threshold of the differential protection returns to the original value.

[0012] Optionally, the non-periodic component criterion is specifically:

[0013] The non-periodic component k in the differential flow is set, the difference dk of the non-periodic component k is used to characterize the change rate of the non-periodic component in the differential flow, and a criterion based on the non-periodic component k is constructed;

[0014] When the data within the sampling time continuously satisfies dk>k th1 And dk <k th2 When , it is identified as a response flow; where k th1 and k th2 To set the threshold.

[0015] Optionally, the non-periodic component change rate:

[0016]

[0017] Wherein, N is the number of sampling points in each cycle; k(i) is the non-periodic component value calculated in the i-th cycle, and T is the power frequency period.

[0018] Optionally, the setting conditions specifically include:

[0019] The first judgment condition: the differential current of the operating transformer always remains smaller than the action threshold value of the original differential protection;

[0020] The second judgment condition: the differential current of the running transformer first enters the action area and then exits.

[0021] The present invention also provides a transformer protection system based on non-periodic component variation characteristics, comprising:

[0022] A calculation module, used for calculating the proportion of the second harmonic and the rate of change of the non-periodic component when the differential protection element of the transformer is started, and raising the action threshold value if the second harmonic braking criterion and the non-periodic component criterion are met; the non-periodic component criterion is used to determine whether the CT is in a saturated state;

[0023] The first judgment module is used for calculating the change rate of the non-periodic component on the CT transmission side when the second harmonic braking criterion is not met, and judging whether the non-periodic component criterion is met, and if so, increasing the action threshold value, and if not, executing the differential protection action;

[0024] The second judgment module is used to determine that the CT is in a saturated state and there is a surge current when the non-periodic component criterion is met, and to increase the protection action threshold until the set condition is met, and the threshold of the differential protection returns to the original value.

[0025] The present invention also provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the transformer protection method based on the above-mentioned non-periodic component change characteristics.

[0026] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the transformer protection method based on the non-periodic component variation characteristics as described above.

[0027] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0028] The present invention discloses a transformer protection method, system, device and medium based on the non-periodic component change characteristics. The method includes: when the differential protection element of the transformer is started, the second harmonic proportion and the non-periodic component change rate are calculated. If the second harmonic braking criterion and the non-periodic component criterion are met, the action threshold value is increased; when the second harmonic braking criterion is not met, the change rate of the non-periodic component on the CT transmission side is calculated, and it is judged whether the non-periodic component criterion is met. If it is met, the action threshold value is increased, and if it is not met, the differential protection action is performed; when the non-periodic component criterion is met, it is judged that the CT is in a saturated state and there is a response inrush current, and the action threshold value of the protection is increased until the set condition is met, and the threshold of the differential protection returns to the original value. The present invention can optimize the working mode of the differential protection to avoid its false operation due to the response inrush current. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 It is a flow chart of a transformer protection method based on non-periodic component variation characteristics of the present invention;

[0031] Figure 2 Schematic diagram of a single-phase transformer in this embodiment;

[0032] Figure 3 This is the wiring diagram of the Yd11 transformer in this embodiment;

[0033] Figure 4 : is a trend diagram of the attenuation of the non-periodic component of the inrush current in this embodiment; wherein, part (a) is a trend diagram of the Yy connection transformer; part (b) is a trend diagram of the Yd11 connection transformer;

[0034] Figure 5 It is a schematic diagram of the stages of increasing the differential protection action threshold in this embodiment. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The object of the present invention is to provide a transformer protection method, system, device and medium based on the variation characteristics of non-periodic components, which can optimize the working mode of differential protection and avoid false operation due to inrush current.

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] As a first aspect, the present invention provides Figure 1 A transformer protection method based on non-periodic component variation characteristics is shown, comprising:

[0039] Step 100: When the differential protection element of the transformer is started, the second harmonic proportion and the non-periodic component change rate are calculated. If the second harmonic braking criterion and the non-periodic component criterion are met, the action threshold value is increased; the non-periodic component criterion is used to determine whether the CT is in a saturation state.

[0040] Step 200: When the second harmonic braking criterion is not met, the rate of change of the non-periodic component on the CT transmission side is calculated, and it is determined whether the non-periodic component criterion is met. If it is met, the action threshold value is increased; if it is not met, the differential protection action is performed.

[0041] Step 300: When the non-periodic component criterion is met, it is determined that the CT is in a saturated state and there is a surge current, and the protection action threshold is increased until the set condition is met, and the threshold of the differential protection returns to the original value.

[0042] As a specific implementation, the non-periodic component criterion is specifically:

[0043] Set the non-periodic component k in the differential flow, use the difference dk of the non-periodic component k to characterize the change rate of the non-periodic component in the differential flow, and construct a criterion based on the non-periodic component k; when the data within the sampling time continuously satisfies dk>k th1 And dk <k th2 When , it is identified as a response flow; where k th1 and k th2 To set the threshold.

[0044] Among them, the non-periodic component change rate is:

[0045]

[0046] Wherein, N is the number of sampling points in each cycle; k(i) is the non-periodic component value calculated in the i-th cycle, and T is the power frequency period.

[0047] As a specific implementation, the setting conditions specifically include:

[0048] The first judgment condition: the differential current of the operating transformer always remains smaller than the action threshold value of the original differential protection; the second judgment condition: the differential current of the operating transformer first enters the action area and then exits.

[0049] Based on the above technical solution, the following embodiments are provided.

[0050] In this embodiment, in order to simplify the analysis process and explore its basic principles, a single-phase transformer will be taken as an example for in-depth analysis. The equivalent circuit diagram of a single-phase transformer when an inrush current occurs is as follows: Figure 2 As shown in the figure, R σ1 , L σ1 is the resistance and leakage inductance of the primary side of the transformer, R σ2 , L σ2 is the resistance and leakage inductance of the secondary side of the transformer, L μ is the transformer excitation inductance, and the excitation resistance is ignored.

[0051] When a transformer has a turn-to-turn short circuit, it can be regarded as a three-winding transformer with a short circuit in the third winding. Therefore, the turn-to-turn short circuit is equivalent to connecting the short-circuited turn leakage inductance L in parallel on the excitation branch. k The attenuation constants τ and τ′ equations can be listed respectively when the transformer experiences inrush current and turns short circuit.

[0052]

[0053] After the inrush current occurs, the core will continuously switch between saturation and unsaturation states. μ The instantaneous value of is also changing. When a turn-to-turn short circuit occurs, the leakage inductance L k The value of is basically unchanged, so the equivalent excitation inductance will be smaller when a short circuit occurs. When a surge current occurs, the decay time constant of the loop is larger, and the non-periodic component in the current decays more slowly and decreases slowly. When a transformer short circuit occurs, the decay time constant is smaller, and the non-periodic component in the current decays faster. Therefore, the change rate of the non-periodic component can be used to distinguish the two working conditions.

[0054] Taking a single-phase transformer as an example, the difference between the trend of the non-periodic component of the current when the transformer is inrush current and short-circuited between turns is analyzed in principle. For a three-phase transformer, in addition to the three-phase symmetry of the excitation branch, it can be extended to a three-phase transformer. When a short-circuit occurs between turns, the non-periodic component decays faster. However, the three-phase excitation branch of a three-phase transformer is asymmetrical, and the law of the attenuation of the non-periodic component at this time needs further discussion.

[0055] Analysis Figure 3 Take the transformer wiring diagram as an example. The three-phase transformer is composed of three single-phase transformers.

[0056] Write the equation and solve it. Since the excitation branch current is the sum of the circulating current and the line current, the Δ side circulating current and the primary side current can be obtained as:

[0057]

[0058] Where i Δ is the Δ side circulation, i A ,i B ,i C , respectively, the three-phase current, L σ , L σΔ is the leakage inductance of the primary and secondary sides. Therefore, for the transformer with Yy connection, there is almost no electrical or magnetic interaction between the phases, so the excitation current of each phase decays only according to the parameters of their respective circuits. That is, the decay rate of the excitation current is positively correlated with the magnitude of the current. For the transformer with Yd11 connection, since there is a circulating current on the Δ side, the excitation current of a certain phase not only flows through the circuit of the phase, but also passes through the circuits of the other two phases, and is decayed by the parameters of the other two phases. From the above analysis, it can be seen that the Yd11 transformer is affected by the circulating current on the Δ side when the magnetic flux is saturated, and the decay rates of the currents of each phase affect each other, resulting in the current that originally decays faster decaying slower, and the current that decays slower decaying faster, thereby reducing the difference in the decay speed of the currents of each phase.

[0059] Since the current on the Δ side cannot be accurately obtained, the phase differential compensation method is adopted when calculating the differential current of the Yd11 transformer in practice, so the differential current of each phase is:

[0060]

[0061] From the above formula, we can know that the differential current per phase is the difference between the two-phase currents, so the attenuation of the differential current per phase is related to the impedance parameters of the two phases. Figure 4 As shown in the figure, due to the phase difference compensation, the speed of the originally fast change is reduced, and the speed of the slow change is accelerated, thereby reducing the difference in the change rate of each phase current change.

[0062] In summary, the Yd11 transformer has little difference in attenuation rate between differential currents due to the Δ-side circulating current and phase difference compensation, but when an internal fault occurs, the attenuation constant decreases due to the change in the parameters of the fault phase. Therefore, by comparing the attenuation rate of the non-periodic component in the differential current, it is ensured that the inrush current does not malfunction.

[0063] like Figure 5 As shown, for the current transformer saturation detection method based on non-periodic components:

[0064] According to the above differential protection misoperation analysis, it can be found that this abnormal misoperation is caused by CT saturation caused by the long-term non-periodic component in the response surge current. In this case, the differential current is mainly composed of the error current caused by CT saturation, and the harmonic component is relatively low. Since the traditional second harmonic criterion cannot effectively prevent such misoperation, this embodiment proposes a new CT saturation detection algorithm based on the analysis of the CT saturation mechanism during such misoperation. The CT saturation process is divided into two stages: 1) After the response surge current is generated, the non-periodic component flows into the current transformer. In this stage, the current transformer is not saturated yet, the differential current is small, and the non-periodic component of the current generates an increasingly large bias flux in the CT core. At this time, since the CT is not saturated yet, the excitation current in the CT is still small. 2) As the bias flux accumulates, the magnetic flux of the CT core approaches saturation, while the transmission side remains unsaturated. The low amplitude of the periodic component causes the magnetic flux to be confined to the local hysteresis loop near the saturation point, so that the inductance maintains a relatively low value. This causes the differential current to contain periodic components and significant non-periodic components, affecting harmonic identification and forming local transient saturation. When the CT core is saturated, the excitation inductance decreases rapidly, causing the non-periodic components to pass through the excitation branch, thereby significantly reducing the non-periodic components in the transmission current. The above analysis reveals that CT saturation causes the non-periodic components of the transmission current to decrease, and proposes the corresponding saturation detection principle. This embodiment only analyzes the single-phase CT saturation to generalize to three-phase.

[0065] Define the non-periodic component of the current transformer transmission current:

[0066]

[0067] Where N is the sampling point per cycle, and the subscript m is the CT current on the primary and secondary sides of the transformer. Define the mutation amount of the non-periodic component of the CT transformer current.

[0068] S m (n) = {[I dc,m (n)-I dc,m (ni)]-[I dc,m (ni)-I dc,m (n-2i]}m=1,2

[0069] Wherein, i is an integer, which is set to N / 10 in this embodiment. Under normal circumstances, the CT saturation detection is in a normal state. When the current on the CT transmission side of both sides of the transformer shows an increased non-periodic component, it is judged that the CT may enter a saturation state.

[0070]

[0071] In the formula, K set1 In this embodiment, it is set to 0.2, I dset is the setting value of the action. After the differential protection enters the braking zone, the non-periodic component on the CT transmission side drops rapidly. This differential current is likely to be caused by CT saturation. Therefore, the next step will be judged.

[0072] (S1>S set >S2)&(|I dc,1 |<K set2 |I dc,1 |)&(I d <I dset )

[0073] In the formula, K set2 In this embodiment, it is set to 0.8, S set is the threshold of the mutation amount. The above formula shows that the non-periodic component of the transformer secondary side CT begins to decay less than the primary side.

[0074] (|I dc,2 |<K set1 |I dc,1 |)&(S1<S set )&(I d >I dset )

[0075] The above equation indicates that the non-periodic component of the transformer secondary CT decays to almost 0. During this period, the differential protection enters the action area, resulting in false operation due to the saturation of the transformer secondary CT. At this time, it is judged that the transformer secondary CT is saturated. The above process is also applicable to the CT on the primary side of the transformer. Generally, the CT enters the saturation state after two cycles. In the CT saturation state, the protection false operation is avoided by increasing the protection action threshold and reducing the protection action area.

[0076] As a second aspect, the present invention further provides a transformer protection system based on non-periodic component variation characteristics, comprising:

[0077] A calculation module, used for calculating the proportion of the second harmonic and the rate of change of the non-periodic component when the differential protection element of the transformer is started, and raising the action threshold value if the second harmonic braking criterion and the non-periodic component criterion are met; the non-periodic component criterion is used to determine whether the CT is in a saturated state;

[0078] The first judgment module is used for calculating the change rate of the non-periodic component on the CT transmission side when the second harmonic braking criterion is not met, and judging whether the non-periodic component criterion is met, and if so, increasing the action threshold value, and if not, executing the differential protection action;

[0079] The second judgment module is used to determine that the CT is in a saturated state and there is a surge current when the non-periodic component criterion is met, and to increase the protection action threshold until the set condition is met, and the threshold of the differential protection returns to the original value.

[0080] As a third aspect, the present invention further provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the above-mentioned transformer protection method based on the non-periodic component change characteristics.

[0081] As a fourth aspect, the present invention further provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the transformer protection method based on the non-periodic component variation characteristics as described above.

[0082] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0083] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A transformer protection method based on non-periodic component variation characteristics, characterized in that: include: When the differential protection element of the transformer is started, the second harmonic proportion and the rate of change of the non-periodic component are calculated. If the second harmonic restraint criterion and the non-periodic component criterion are met, the action threshold is increased; The non-periodic component criterion is used to determine whether the CT is in a saturation state; When the second harmonic braking criterion is not met, the change rate of the non-periodic component on the CT transmission side is calculated, and it is determined whether the non-periodic component criterion is met. If it is met, the action threshold value is increased; if it is not met, the differential protection action is performed; When the non-periodic component criterion is met, it is determined that the CT is in a saturated state and there is a surge current. The protection action threshold is increased until the set condition is met, and the threshold of the differential protection returns to the original value.

2. The transformer protection method based on the non-periodic component variation characteristics according to claim 1 is characterized in that: The non-periodic component criterion is specifically: The non-periodic component k in the differential flow is set, the difference dk of the non-periodic component k is used to characterize the change rate of the non-periodic component in the differential flow, and a criterion based on the non-periodic component k is constructed; When the data within the sampling time continuously satisfies dk>k th1 And dk <k th2 When , it is identified as a response flow; where k th1 and k th2 To set the threshold.

3. The transformer protection method based on non-periodic component variation characteristics according to claim 2 is characterized in that: The non-periodic component change rate: Wherein, N is the number of sampling points in each cycle; k(i) is the non-periodic component value calculated in the i-th cycle, and T is the power frequency period.

4. The transformer protection method based on non-periodic component variation characteristics according to claim 1, characterized in that: The setting conditions specifically include: The first judgment condition: the differential current of the operating transformer always remains smaller than the action threshold value of the original differential protection; The second judgment condition: the differential current of the running transformer first enters the action area and then exits.

5. A transformer protection system based on non-periodic component variation characteristics, characterized in that: include: A calculation module, used for calculating the proportion of the second harmonic and the rate of change of the non-periodic component when the differential protection element of the transformer is started, and increasing the action threshold value if the second harmonic braking criterion and the non-periodic component criterion are met; The non-periodic component criterion is used to determine whether the CT is in a saturation state; The first judgment module is used for calculating the change rate of the non-periodic component on the CT transmission side when the second harmonic braking criterion is not met, and judging whether the non-periodic component criterion is met, and if so, increasing the action threshold value, and if not, executing the differential protection action; The second judgment module is used to determine that the CT is in a saturated state and there is a surge current when the non-periodic component criterion is met, and to increase the protection action threshold until the set condition is met, and the threshold of the differential protection returns to the original value.

6. An electronic device, characterized in that: The electronic device comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the transformer protection method based on non-periodic component variation characteristics according to any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that: A computer program is stored therein, and when the computer program is executed by a processor, a transformer protection method based on non-periodic component variation characteristics as described in any one of claims 1 to 4 is implemented.

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