CN100394658C - A Transformer Longitudinal Differential Protection Element with Zero Sequence Ratio Brake - Google Patents

Abstract

The invention discloses a transformer longitudinal differential protection element with zero-sequence ratio braking. The three-phase braking current representing the crossing current in the current transformer differential protection is weighted and summed with the zero-sequence current of the transformer Y ₀ side respectively to form three Phase braking current containing zero-sequence current, using the three-phase braking current containing zero-sequence current to form a corresponding phase ratio differential element with the three-phase differential current in the transformer differential protection, when the differential current is greater than the zero-sequence containing current When the braking current of the current is lower than the braking current, the ratio differential action signal of the corresponding phase is output. Applying this scheme can realize the situation that the ratio differential broken line does not reach the origin, and the ratio braking coefficient changes with the braking current; it can also completely avoid the transformer failure caused by the external grounding fault on the Y ₀ side when the errors of the three-phase current transformers are inconsistent. Malfunction of longitudinal differential protection.

Description

A Transformer Longitudinal Differential Protection Element with Zero Sequence Ratio Brake

technical field

The invention relates to a transformer protection device, in particular to a transformer differential protection element with zero-sequence ratio braking.

Background technique

The current longitudinal differential protection of power transformers consists of components such as differential quick-break, ratio differential, excitation inrush current detection, and over-excitation detection. According to DL/T 684-1999 "Large Generator Transformer Relay Protection Setting Calculation Guidelines", the block diagram of transformer longitudinal differential protection is shown in Figure 1, and the principle wiring example of longitudinal differential protection is shown in Figure 2. Usually, current transformers are used to perform Y/Δ transformation on the three-phase current on the Y ₀ side to eliminate the influence of zero-sequence current. Obviously, after the transformation, each current does not contain the zero-sequence component in the primary current. After these currents are balanced by the intermediate current transformers TAM1~TAM6, the phase currents of the same name are added to obtain the three-phase differential current. Wd is the differential coil. The three-phase braking current is obtained by combining the phase currents of the same name in other ways, and Wres1~Wres3 are the braking coils on each side. It can be seen that neither the differential current nor the braking current obtained from this includes the zero-sequence component in the primary current.

When implementing longitudinal differential protection, there is also the case that the current transformer on the Y ₀ side is all-star connection. At this time, the Y/Δ transformation is often performed on the three-phase secondary current on the Y ₀ side in the protection device, or the Y ₀ side Subtract the zero-sequence current _I0 from the three-phase secondary current on the Δ side and perform Δ/Y transformation on the secondary current on the Δ side, and eliminate the influence of the zero-sequence current through the above transformation. After these transformations, the differential current obtained by adding the phases of the same name and the braking current obtained by other combinations also do not contain the zero-sequence component in the primary current. For example, the phase differential current is obtained by calculating the vector sum of the phase currents of the same name; the braking current of the phase is obtained by calculating the maximum value of the phase current of the same name or by calculating the weighted sum of the phase current amplitudes of the same name, and the braking current can only represent The magnitude of the passing current.

When the transformer has an external ground fault on the Y ₀ side and only this side has power, a large zero-sequence fault current will appear on the Y ₀ side, but no fault current passes through the transformer. At this time, when the errors of the three-phase current transformers on the Y ₀ side are inconsistent, the secondary currents are not equal after the three-phase equal zero-sequence currents on the primary side are transformed by the three-phase current transformers. The above-mentioned traditional three-phase currents on the Y ₀ side The transformation method cannot completely eliminate the influence of zero-sequence current, and will generate unbalanced current in the differential circuit. Since no fault current passes through the transformer at this time, the braking current obtained by the above-mentioned traditional method is very small and will not exceed the braking current before the fault. As long as the differential unbalanced current exceeds the differential threshold, the differential protection of the transformer will malfunction. Obviously, the unbalanced current caused by the zero-sequence fault current on the Y ₀ side is ignored in the ratio differential protection of the traditional longitudinal differential protection, that is, there is no corresponding braking current in the ratio differential element to brake it, so that Make the transformer differential protection malfunction.

Contents of the invention

The technical problem to be solved by the present invention is to provide a transformer longitudinal differential protection element with zero-sequence ratio braking for the transformer differential protection existing in the prior art using the method of Y ₀ side three-phase current conversion, which cannot completely eliminate the zero-sequence The influence of the current on the secondary differential unbalanced current, through the weighted summation of the three-phase braking current representing the through current in the current transformer differential protection and the zero-sequence current of the transformer Y ₀ side to form a three-phase zero-sequence current system The three-phase braking current containing zero-sequence current and the three-phase differential current in the differential protection of the transformer are used to form a corresponding phase ratio differential element. When the differential current is greater than the braking current containing zero-sequence current, Output the ratio differential action signal of the corresponding phase. The invention has the advantage that it can completely avoid the misoperation of the transformer differential protection caused by the grounding fault outside the _Y0 side when the errors of the three-phase current transformers are inconsistent.

A transformer differential protection element with zero-sequence ratio braking, characterized in that the element is composed of first to third subtractors A1, B1, C1, first group of first to third multipliers A2, B2, C2 , the second group of multipliers 01, the first group of first to third adders A3, B3, C3, the second group of first to third adders A4, B4, C4 and the first to third comparators A5, B5 , C5; where the positive input terminals of the first to third subtractors A1, B1, and C1 respectively input the brake current signals I _za , I _zb , and I _zc , which represent the cross-current protection of the transformer after filtering, and their negative The input terminals respectively input the brake inflection point current value Ires0 in the longitudinal differential protection of the transformer, and the output terminals are respectively connected to one input terminal of the first to third multipliers A2, B2 and C2 of the first group; the first to third multipliers of the first group The other input terminals of the multipliers A2, B2, and C2 input the slope S of the ratio differential broken line respectively, and their output terminals are respectively connected to one input terminal of the first to third adders A3, B3, and C3 of the first group; The other input terminals of the first to third adders A3, B3, C3 respectively input the minimum operating current value Iop. One input terminal of the second group of multiplier 01 inputs the filtered zero-sequence current signal 3I ₀ on the transformer Y ₀ side, the other input terminal inputs the zero-sequence braking coefficient K ₀ , and its output terminals are respectively connected to the second group The other input terminals of the first to third adders A4, B4, and C4; the positive input terminals of the first to third comparators A5, B5, and C5 respectively input the filtered three-phase differential current signals I _da and I _db , I _dc , the negative input terminals of which are respectively connected to the output terminals of the first to third adders A4, B4 and C4 of the second group, and the output terminals of the first to third comparators A5, B5 and C5 respectively output phase A , B-phase, C-phase ratio differential action signal. The slope S of the ratio differential broken line has a value of 0<S<0.8. In the case that the zero-sequence current, three-phase differential current and three-phase braking current are attributed to the same side, the zero-sequence braking coefficient K ₀ is 0<K ₀ <1/3. When the differential current is greater than the braking current including zero-sequence current, the ratio differential action signal of the corresponding phase is output.

Compared with the prior art, the beneficial effect of the present invention is that for the first time it is proposed to add zero-sequence braking current to the braking current of the ratio differential element of traditional transformer differential protection. The three-phase braking current through the meter through current is weighted and summed with the zero-sequence current of the transformer Y ₀ side to form the three-phase braking current with zero-sequence current, and the three-phase braking current with zero-sequence current is used to calculate the transformer The three-phase differential current in the differential protection constitutes the corresponding phase ratio differential element. When the differential current is greater than the braking current including the zero-sequence current, the ratio differential action signal of the corresponding phase is output. Applying this scheme can realize the situation that the ratio differential broken line does not pass the origin, and the ratio coefficient changes with the change of the braking current; it can also completely avoid the transformer vertical difference caused by the ground fault outside the Y ₀ side when the errors of the three-phase current transformers are inconsistent. The protection malfunction can also prevent the maloperation of the longitudinal differential protection of the transformer caused by the longitudinal differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions, and does not affect the correct operation of the longitudinal differential protection in the case of internal faults.

Description of drawings

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

Figure 1 is a block diagram of the existing transformer differential protection.

Fig. 2 is a schematic wiring diagram of the existing transformer longitudinal differential protection.

Fig. 3 is a circuit block diagram of a longitudinal differential protection element of a fault component transformer with zero-sequence ratio braking to realize the present invention.

Detailed ways

Example 1:

A transformer longitudinal differential protection element with zero-sequence ratio braking, which can be realized by the circuit of a transformer longitudinal differential protection element with zero-sequence ratio braking in Figure 3. Among them, the slope of the ratio differential broken line is S=0.5. In the case that zero-sequence current, three-phase differential current and three-phase braking current are attributed to the same side, the zero-sequence braking coefficient K ₀ is 0.3. The braking inflection point current I _reso in the transformer longitudinal differential protection = 1.2*In _n , I _n is the transformer rated current converted to this side, the minimum operating current I _op.min = 0.4*I _n , when the differential current is greater than or equal to zero When the braking current of the sequence current, the comparator outputs the ratio differential action signal of the corresponding phase. Applying this scheme can realize the situation that the ratio differential broken line does not reach the origin, and the ratio braking coefficient changes with the braking current; it can also completely avoid the transformer failure caused by the external grounding fault on the Y ₀ side when the errors of the three-phase current transformers are inconsistent. The maloperation of the longitudinal differential protection can also prevent the maloperation of the longitudinal differential protection of the transformer caused by the longitudinal differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions, and does not affect the correct operation of the longitudinal differential protection under the condition of internal faults.

Claims (3)

1. A transformer differential protection element with zero-sequence ratio braking, characterized in that: the element consists of the first to the third subtractor (A1, B1, C1), the first group of the first to the third multiplier ( A2, B2, C2), second set of multipliers (01), first set of first to third adders (A3, B3, C3), second set of first to third adders (A4, B4, C4 ) and the first to third comparators (A5, B5, C5); among them, the positive input terminals of the first to third subtractors (A1, B1, C1) respectively input the representative through-current of the longitudinal differential protection of the transformer after filtering The braking current signals I _za , I _zb , and I _zc of the braking current, their negative input ends are respectively input into the braking inflection point current value I _res0 in the transformer differential protection, and their output ends are respectively connected to the first group of first to third multipliers ( One input terminal of A2, B2, C2); the other input terminal of the first group of first to third multipliers (A2, B2, C2) respectively inputs the slope S of the ratio differential polyline, and its output terminals are respectively connected to the first group One input terminal of the first to third adders (A3, B3, C3); the other input terminal of the first group of first to third adders (A3, B3, C3) respectively input the minimum operating current value I _{op. min} , whose output terminals are respectively connected to one input terminal of the second group of first to third adders (A4, B4, C4); one input terminal of the second group of multipliers (01) is input to the side of transformer Y ₀ after filtering After the zero-sequence current signal 3I ₀ , the other input terminal inputs the zero-sequence braking coefficient K ₀ , and its output terminal is respectively connected to the other input terminal of the second group of first to third adders (A4, B4, C4); The positive input terminals of the first to third comparators (A5, B5, C5) respectively input the filtered three-phase differential current signals I _da , I _db , I _dc , and the negative input terminals of the first to third comparators are respectively connected to the second group of first to The output terminals of the third adder (A4, B4, C4) are connected, and the output terminals of the first to third comparators (A5, B5, C5) respectively output the ratio differential action signals of phase A, phase B, and phase C . 2 . The device according to claim 1 , wherein the slope S of the ratio differential broken line has a value of 0<S<0.8. 3. The component according to claim 1, characterized in that: when the zero-sequence current, three-phase differential current and three-phase braking current are attributed to the same side, the zero-sequence braking coefficient K0 is ₀ <K ₀ <1/3.

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