CN100407534C - Three-phase braking device to prevent maloperation of transformer differential protection - Google Patents

Abstract

A three-phase braking device to prevent maloperation of transformer differential protection, by using the three-phase differential current in the transformer differential protection and the zero-sequence current on the Y ₀ side to form a ratio braking element, when the differential current and zero-sequence When the current ratio value is less than the setting value K, it is judged that the corresponding phase differential current is the error current caused by an external fault, the comparator outputs 0, the signal is output through OR gate 4, and when the OR gate 4 outputs 0, the three-phase differential protection outlet is blocked; otherwise OR gate 4 outputs 1, allowing three-phase differential protection to operate. The advantage of this scheme is that it can completely avoid the maloperation of the transformer differential protection caused by the ground fault outside the zone on the Y ₀ side when the errors of the three-phase current transformers are inconsistent, and it will not affect the correct operation of the differential protection under the fault condition in the zone.

Description

Three-phase braking device to prevent maloperation of transformer differential protection

technical field

The invention relates to a transformer protection device, in particular to a three-phase brake device for preventing maloperation of 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 the power transformer with Y ₀ /Δ connection, in order to prevent the differential protection misoperation caused by the zero-sequence current of the ground fault outside the Y ₀ side, the method of transforming the three-phase current on the Y ₀ side is widely used to eliminate the influence of the zero-sequence current . However, when the errors of the three-phase current transformers on the Y ₀ side are inconsistent, and the transformer only has power supply on the Y ₀ side where an external fault occurs, the traditional method cannot eliminate the influence of the zero-sequence current caused by the external ground fault on the Y ₀ side. There is a large differential unbalanced current, and the ratio braking element and inrush braking element cannot perform reliable braking, especially when the load current on the other side of the transformer 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 three-phase braking device for preventing maloperation of transformer differential protection. By using the three-phase differential current in the transformer differential protection and the zero-sequence current on the Y ₀ side to form a ratio braking element, when When the ratio of differential current to zero-sequence current is less than the setting value K, the corresponding phase differential current is judged to be an error current caused by an external fault, and the three-phase differential protection outlet is blocked after the signal is output through the OR gate. The invention has the advantages that it can completely avoid the misoperation of the transformer differential protection caused by the grounding fault outside the zone on the _Y0 side when the errors of the three-phase current transformers are inconsistent, and does not affect the correct operation of the differential protection under the fault condition in the zone.

A three-phase brake device for preventing maloperation of transformer differential protection, the circuit structure of the device is shown in Figure 1, and the feature is that the device is composed of first filters 11-13, second filters 14, multiplier 2 , comparators 31-33, and OR gate 4, in which the input terminals of the first filters 11-13 respectively input the A, B, C three-phase differential current instantaneous value signals i _da , i _db , i formed by the transformer differential protection _dc , the input terminal of the second filter 14 inputs the zero-sequence current instantaneous value signal 3i _o of the transformer Y ₀ side, its output terminal is connected to one input terminal of the multiplier 2, and the other input terminal of the multiplier 2 inputs the setting value K for comparison The negative input terminals of the comparators 31-33 are connected with the output terminals of the multiplier 2, the positive input terminals thereof are respectively connected with the output terminals of the first filters 11-13, and the output terminals of the comparators 31-33 are connected with the three of the OR gate 4 respectively. The input terminals are connected, and the output terminal of OR gate 4 outputs a three-phase braking signal. When the positive input signal of the comparators 31-33 is smaller than the negative input signal, the comparator outputs 0, and it is judged that the corresponding phase differential current is the error current caused by an external fault, and the signal is output through the OR gate 4, and the OR gate 4 outputs 0. , to block the three-phase ratio differential protection outlet, otherwise OR gate 4 outputs 1, allowing the three-phase differential protection to operate. 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.

Compared with the prior art, the present invention has the advantage of proposing for the first time that in the traditional transformer differential protection, the three-phase differential current in the transformer differential protection is added to the braking element with the ratio of the zero-sequence current on the Y ₀ side, when the ratio When the value is less than the setting value K, it is judged that the corresponding phase differential current is the error current caused by an external fault, the signal is output through the OR gate, and the outlet of the three-phase ratio differential protection is blocked. Applying this scheme can completely avoid the misoperation of the transformer differential protection caused by the ground fault outside the zone on the Y ₀ side when the errors of the three-phase current transformers are inconsistent, and can also prevent the differential protection caused by the zero-sequence current under other non-internal fault conditions. The maloperation of transformer differential protection caused by balanced 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 three-phase braking device to prevent maloperation of transformer differential protection.

Detailed ways

Example 1:

A three-phase braking device for preventing maloperation of transformer differential protection. Its circuit structure is shown in Figure 1. When the positive input signal of the comparator 31-33 is smaller than the negative input signal, the comparator outputs 0, and the corresponding phase difference is judged. The dynamic current is the error current caused by the fault outside the area. The signal is output through the OR gate 4. When the OR gate 4 outputs 0, the main outlet of the three-phase ratio differential protection is blocked; otherwise, the OR gate 4 outputs 1 to allow the differential protection to operate. When the differential current and zero-sequence current are all attributed to the same side and the same transformation ratio, the setting value K is _0.1 ; Transformer differential protection misoperation caused by ground fault, and does not affect the correct operation of differential protection in the case of internal faults.

Claims (2)

1. A three-phase brake device for preventing maloperation of transformer differential protection, characterized in that: the device consists of a first filter (11～13) and a second filter (14), a multiplier (2), a comparison devices (31-33) and OR gates (4), wherein the input terminals of the first filters (11-13) respectively input the instantaneous value signals (i _da , i _db , i _dc ), the input terminal of the second filter (14) inputs the zero-sequence current instantaneous value signal (3i _o ) of the transformer Y ₀ side, and its output terminal is connected to an input terminal of the multiplier (2), and the multiplier The other input terminal of (2) inputs the setting value K, the negative input terminal of the comparator (31～33) is connected with the output terminal of the multiplier (2), and its positive input terminal is respectively connected with the first filter (11～13 ), the output terminals of the comparator (31～33) are respectively connected with the three input terminals of the OR gate (4), and the output terminals of the OR gate (4) output the three-phase braking signal; when the comparator (31 The signal at the positive input terminal in ~33) is smaller than the signal at the negative input terminal, the comparator outputs 0, and it is judged that the differential current of the corresponding phase is the error current caused by an external fault, the signal is output through the OR gate (4), and the OR gate (4) outputs 0 When , the outlet of the three-phase ratio differential protection is blocked. 2 . The device according to claim 1 , wherein the setting value K is 0<K<1/3 when both the differential current and the zero-sequence current are attributed to the same side and the same transformation ratio.

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