CN100433488C - A Phase Sequence Combination Braking Method to Prevent Misoperation of Multi-branch Transformer Differential Protection - Google Patents

Abstract

A phase-sequence synthesis braking method for preventing maloperation of multi-branch transformer differential protection, through the fundamental positive-sequence current or fundamental negative-sequence current of the three-phase differential current in the differential protection of the transformer and the grounding side of each neutral point ( or branch) of the maximum value of the zero-sequence current constitutes the ratio braking criterion, when the ratio value is less than the setting value K, it is judged as an external ground fault on the neutral point grounding side, and a three-phase braking signal is output, and the three-phase ratio difference Braking for motion protection. The invention has the advantage that it can completely avoid the misoperation of the transformer differential protection caused by the grounding fault outside the grounding side of the neutral point grounding side when the errors of the three-phase current transformers are inconsistent.

Description

A Phase Sequence Combination Braking Method to Prevent Misoperation of Multi-branch Transformer Differential Protection

technical field

The invention relates to a transformer protection method, in particular to a phase sequence synthesis braking method for preventing maloperation of multi-branch transformer differential protection.

Background technique

The existing power transformer differential protection device uses the ratio braking criterion, that is, the ratio of the differential current to the through current, to identify the external fault and the internal fault; at the same time, it uses the inrush current and over-excitation braking criterion, namely By analyzing the waveform or harmonic content of the differential current, the excitation inrush current and over-excitation current can be identified to achieve the purpose of identifying internal faults. For power transformers with neutral points directly grounded on two or more sides, when an external ground fault occurs on one neutral point grounding side, a large ground fault zero-sequence current may occur on multiple grounding sides. In order to prevent the zero-sequence current from causing differential protection misoperation, the method of transforming the three-phase current on the grounding side of the neutral point is widely used at present to eliminate the influence of the zero-sequence current. However, when the errors of the three-phase current transformers on the grounding side are inconsistent, and the transformer only has power supply on the grounding side where an external fault occurs, the traditional method cannot eliminate the influence of the zero-sequence current caused by the external grounding fault on the grounding side, and there will be a large The differential unbalanced current, the ratio braking criterion and the inrush braking criterion cannot perform reliable braking, especially when the transformer load current is small or even zero, the ratio braking criterion, the inrush braking criterion Criterion can not brake this, as long as the error current exceeds the threshold, the transformer differential protection will malfunction.

Contents of the invention

The purpose of the present invention is to provide a phase-sequence synthesis braking method to prevent misoperation of multi-branch transformer differential protection, through the fundamental wave positive sequence current or fundamental wave negative sequence current of the three-phase differential current in the transformer differential protection and each The maximum value of the zero-sequence current on the neutral point grounding side (or branch) constitutes the ratio braking criterion. When the ratio value is less than the set value, it is judged as an external ground fault on the neutral point grounding side, and a three-phase braking signal is output. Brake the three-phase ratio differential protection. The invention has the advantage that it can completely avoid the misoperation of the transformer differential protection caused by the grounding fault outside the grounding side of the neutral point grounding side when the errors of the three-phase current transformers are inconsistent.

A phase-sequence synthesis braking method for preventing maloperation of multi-branch transformer differential protection, characterized in that: using the fundamental positive sequence current or fundamental negative sequence current of the three-phase differential current in the differential protection of transformers and each neutral The maximum value of the zero-sequence current 3I ₁₀ , 3I ₂₀ , ... 3I _no on the grounding side or branch constitutes the ratio brake criterion, when the fundamental positive sequence current or fundamental negative sequence current of the three-phase differential current is divided by each When the ratio of the maximum value of the zero-sequence current on the grounding side of the neutral point or the branch is less than the setting value K, it is judged as an external grounding fault, and a three-phase braking signal is output to brake the three-phase ratio differential protection to prevent the transformer from Misoperation of differential protection;

Discrimination basis for phase-sequence synthetic braking of multi-branch transformer ground fault outside the area:

f(i _da , i _db , i _dc )/(3I ₁₀ , 3I ₂₀ ,...3I _no )max<K

where f(i _da , i _db , i _dc ) is the fundamental positive sequence current or fundamental negative sequence current of the three-phase differential current in the transformer differential protection, 3I ₁₀ , 3I ₂₀ , ... 3I _no are the The zero-sequence current obtained by filtering the zero-sequence current instantaneous value (3i ₁₀ , 3i ₂₀ , ... _{3i no} ) of the neutral point grounding side or branch, (3I ₁₀ , 3I ₂₀ , ... 3I _no )max is the neutral The maximum value of the zero-sequence current on the grounding side or branch, K is the setting value, when the zero-sequence current and the three-phase differential current are attributed to the same side and the same transformation ratio, the setting value K is 0<K<1 , n is the number of transformer neutral grounding sides or branches.

Compared with the prior art, the present invention has the advantage of proposing for the first time that the fundamental wave positive-sequence current or fundamental negative-sequence current of the three-phase differential current in the differential protection of transformers is formed by the maximum value of the zero-sequence current on the grounding side of each neutral point. Ratio braking criterion, when the ratio value is less than the setting value, it is judged as an external ground fault on the neutral point grounding side, and a three-phase braking signal is output to perform braking on the three-phase ratio differential protection. Applying this scheme can completely avoid the maloperation of transformer differential protection caused by the external ground fault on the neutral point grounding side when the errors of the three-phase current transformers are inconsistent, and can also prevent the differential protection caused by zero-sequence current under other non-internal fault conditions. The maloperation of transformer differential protection caused by dynamic unbalanced current does not affect the correct operation of differential protection in the case of internal faults.

Description of drawings

Fig. 1 is a circuit block diagram of a positive sequence synthesizing brake device for preventing misoperation of multi-branch transformer differential protection according to the present invention.

Detailed ways

Example 1

A phase-sequence synthesis braking method for preventing misoperation of multi-branch transformer differential protection, which can be realized by the circuit of a positive-sequence synthesis braking device for preventing multi-branch transformer differential protection misoperation in Figure 1. The device is composed of filters 01, 02, 03, fundamental positive sequence filter 1, filter 2, maximum value circuit 3, multiplier 4, and comparator 5, where the input terminals of filters 01, 02, and 03 are respectively 3i ₁₀ , 3i 20 , 3i ₃₀ , 3i 10 , 3i ₂₀ , 3i ₃₀ are obtained by filtering the zero-sequence current instantaneous value signals 3i 10 , 3i ₂₀ , 3i 30 of each neutral point grounding side or branch of the input transformer, and the filter is 3I ₁₀ , _{3I 20 ,} 3I ₃₀ The output terminals of 01, 02, and 03 are respectively connected to the input terminals of the maximum value seeking circuit 3, one input terminal of the multiplier 4 is connected to the output terminal of the maximum value seeking circuit 3, and the other input terminal inputs the setting value K, and the comparator The negative input terminal of 5 is connected to the output terminal of the multiplier 4, and the three input terminals of the fundamental positive sequence filter 1 respectively input the three-phase differential current instantaneous value signals i _da , i _db , i obtained from the transformer differential protection _dc , the output terminal of which is connected to the input terminal of filter 2, the output terminal of filter 2 is connected to the positive input terminal of comparator 5, and comparator 5 outputs a three-phase braking signal. When the differential current and zero-sequence current are attributed to the same side and the same transformation ratio, the setting value K is 0.1. When the signal at the positive input terminal of comparator 5 is smaller than the signal at the negative input terminal, comparator 5 outputs 0, and it is judged as an external ground fault, and the outlet of the three-phase ratio differential protection is blocked; otherwise, comparator 5 outputs 1, allowing the three-phase differential protection to operate . The advantage of applying this method is that it can completely avoid the misoperation of the transformer differential protection caused by the ground fault outside the neutral point grounding side, and does not affect the correct operation of the differential protection under the fault condition in the zone.

Claims (1)

1. A phase-sequence synthesis braking method for preventing misoperation of multi-branch transformer differential protection, characterized in that: utilize the fundamental positive-sequence current or fundamental negative-sequence current of the three-phase differential current in the transformer differential protection and each The maximum value of the zero-sequence current (3I ₁₀ , 3I ₂₀ , ... 3I _no ) on the grounding side of the neutral point or branch constitutes the ratio braking criterion, when the fundamental positive sequence current or the fundamental negative sequence current of the three-phase differential current When the ratio of the current divided by the maximum value of the zero-sequence current on the grounding side of each neutral point or branch is less than the setting value K, it is judged as an external grounding fault, and a three-phase braking signal is output, and the three-phase ratio differential protection is carried out. Braking to prevent maloperation of transformer differential protection; Discrimination basis for phase-sequence synthetic braking of multi-branch transformer ground fault outside the area: f(i _da , i _db , i _dc )/(3I ₁₀ , 3I ₂₀ ,...3I _no )max<K In the formula, f(i _da , i _db , , i _dc ) is the fundamental positive sequence current or fundamental negative sequence current of the three-phase differential current in the transformer differential protection, 3I ₁₀ , 3I ₂₀ , ... 3I _no are each The zero-sequence current obtained by filtering the zero-sequence current instantaneous value (3i ₁₀ , 3i ₂₀ , ... _{3i no} ) of the neutral point grounding side or branch, (3I ₁₀ , 3I ₂₀ , ... 3I _no )max is the The maximum value of the zero-sequence current on the grounding side of the neutral point or the branch, and K is the setting value. When the zero-sequence current and the three-phase differential current are attributed to the same side and the same transformation ratio, the setting value K is 0<K< 1, n is the number of transformer neutral grounding sides or branches.

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