CN100394657C - Phase Split Braking Device to Prevent Misoperation of Multi-Branch Transformer Differential Protection - Google Patents

Abstract

A phase-splitting braking device for preventing misoperation of multi-branch transformer differential protection, which is composed of the maximum value of the three-phase differential current obtained from the transformer differential protection and the zero-sequence current of each neutral point grounding side or branch of the transformer Ratio braking element, using the ratio value to judge the ground fault outside the zone, when the ratio value is less than the setting value K, the comparator outputs 0, judges that the corresponding phase differential current is the error current caused by the fault outside the zone, and outputs the corresponding phase braking signal , brake the differential protection of the corresponding phase ratio to prevent misoperation of the transformer differential protection; otherwise, the comparator outputs 1 to allow the corresponding phase differential protection to operate. The advantage of this scheme 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 in the case of a fault in the zone.

Description

Phase Split Braking Device to Prevent Misoperation of Multi-Branch Transformer Differential Protection

technical field

The invention relates to a transformer protection device, in particular to a phase-splitting brake device for preventing maloperation of multi-branch transformer differential protection.

Background technique

The existing power transformer differential protection device uses a ratio brake element, that is, the ratio of the differential current to the through current, to identify the fault outside the zone and the fault in the zone; The waveform or harmonic content of the differential current is used to identify the excitation inrush current and over-excitation current to achieve the purpose of identifying internal faults. For a power transformer with neutral points directly grounded on two or more sides, when an external ground fault occurs on one grounding side, a large ground fault zero-sequence current may occur on multiple 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 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 on the neutral point grounding side where an external fault occurs, the traditional method cannot eliminate the zero-sequence current caused by the external grounding fault on the neutral point grounding side. Influenced, there will be a large differential unbalanced current, and the ratio braking element and inrush braking element cannot perform reliable braking, especially when the transformer load current is small or even zero. The inrush brake component cannot 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-splitting brake device for preventing misoperation of multi-branch transformer differential protection, through the three-phase differential current obtained from the transformer differential protection and the zero-sequence current of each neutral point grounding side or branch The maximum value in constitutes a ratio braking element. When the ratio value is less than the setting value K, the corresponding phase differential current is judged to be the error current caused by an external fault, and the corresponding phase braking signal is output to brake the corresponding phase ratio differential protection. , to prevent maloperation of transformer differential protection; the advantage of the invention is that it can completely avoid misoperation of transformer differential protection caused by grounding fault outside the neutral point grounding side when the errors of three-phase current transformers are inconsistent.

A phase-splitting brake device for preventing misoperation of differential protection of multi-branch transformers, the circuit structure of the device is shown in Figure 1, and the feature is that the device is composed of second filters 11-13, maximum value circuit 2, multiplication 3, comparators 41-43, and n first filters 01, 02, ... 0n, where the input ends of the n first filters 01, 02, ... 0n are respectively input to the neutral point grounding side of the transformer or branched zero-sequence current instantaneous value signals 3i ₁₀ , 3i ₂₀ , ... 3i _n0 , whose output terminals are respectively connected to the input terminals of the maximum value seeking circuit 2, and one input terminal of the multiplier 3 is connected to the maximum value seeking circuit 2 output terminal, the other input terminal of which inputs the setting value K, the negative input terminals of the comparators 41-43 are connected to the output terminal of the multiplier 3, and the input terminals of the second filters 11-13 respectively input the voltage obtained from the transformer differential protection The output terminals of the three-phase differential current instantaneous value signals i _da , i _db , and i _dc are respectively connected to the positive input terminals of comparators 41-43, and the comparators 41-43 respectively output phase A, phase B, and phase C braking Signal. When the positive input signal in the comparators 41-43 is smaller than the negative input signal, the comparator outputs 0, and judges that the corresponding phase differential current is the error current caused by an external fault, and outputs the corresponding phase braking signal, and the corresponding phase differential current The protection performs braking to prevent the transformer differential protection from malfunctioning; otherwise, the comparator outputs 1, allowing the corresponding phase differential protection to operate. 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<K<1/3, and n is the number of neutral grounding sides or branches of the transformer.

Compared with the prior art, the advantage of the present invention is that the maximum value of the three-phase differential current obtained from the transformer differential protection and the zero-sequence current of each neutral point grounding side or branch constitutes a ratio braking element, when the ratio value When it is less than the setting value K, it is judged that the corresponding phase differential current is an error current caused by an external fault, and the corresponding phase ratio differential protection outlet is blocked. 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 faults in the zone.

Description of drawings

Figure 1 is a circuit block diagram of a phase-splitting braking device to prevent misoperation of multi-branch transformer differential protection.

Detailed ways

Example 1

A phase-splitting brake device for preventing misoperation of differential protection of multi-branch transformers. The circuit structure of the device is shown in Figure 1, and the number of transformer neutral point grounding sides is n=3. When the positive input signal in the comparators 41-43 is smaller than the negative input signal, the comparator outputs 0, judges that the corresponding phase differential current is the error current caused by an external fault, outputs the corresponding phase braking signal, and controls the corresponding phase ratio difference Braking by the dynamic protection to prevent misoperation of the transformer differential protection; otherwise, the comparator outputs 1 to allow the corresponding phase differential protection to operate. In the case that the differential current and the zero-sequence current are attributed to the same side and the same transformation ratio, K is 0.1. The advantage of this device 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 (2)

1. A phase-splitting brake device for preventing misoperation of multi-branch transformer differential protection, characterized in that: the device consists of a second filter (11～13), a maximum value circuit (2), a multiplier (3) , comparators (41~43), and n first filters (01, 02, ... 0n), wherein the input terminals of the n first filters (01, 02, ... 0n) are respectively input into each of the transformers The zero-sequence current instantaneous value signal (3i ₁₀ , 3i ₂₀ ... 3i _n0 ) on the grounding side or branch of the neutral point, the output terminals of which are respectively connected to the input terminals of the maximum value circuit (2), and the maximum value circuit (2) The output terminal of the multiplier (3) is connected to an input terminal of the multiplier (3), and the other input terminal of the multiplier (3) inputs the setting value K, and its output terminal is connected to the negative input terminal of the comparator (41-43), and the second filter ( The input terminals of 11~13) respectively input the three-phase differential current instantaneous value signals (i _da , i _db , i _dc ) obtained from the transformer differential protection, and the output terminals are respectively connected with the positive input of the comparators (41~43) The terminals are connected with each other, and the comparators (41-43) output braking signals of phase A, phase B and phase C respectively, and n is the number of neutral point grounding sides or branches of the transformer. 2. The brake device according to claim 1, characterized in that, when the differential current and the zero-sequence current are attributed to the same side and the same transformation ratio, the setting value K is 0<K<1/3.

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