CN100367605C - Transformer differential protection method with maximum zero-sequence current ratio braking - Google Patents

Abstract

The invention discloses a transformer longitudinal difference protection method with maximum zero-sequence current ratio braking. The maximum value of the braking current representing the through current in the transformer longitudinal difference protection and the zero-sequence current on the grounding side of each neutral point of the transformer is used to perform the maximum value. The weighted sum constitutes the braking current containing zero-sequence current, and the braking current containing zero-sequence current and the differential current of the corresponding phase constitute the braking element of this phase ratio. When the differential current is greater than the braking current containing zero-sequence current When the current is greater than the minimum operating current, the operating signal of the phase ratio braking element is output. The application of 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

Transformer differential protection method with maximum zero-sequence current ratio braking

technical field

The invention relates to a relay protection method of a power system, in particular to a transformer longitudinal differential protection method with maximum zero-sequence current 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 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 and each side adjustment balance, the differential current obtained by adding phases with 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 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 transformer differential protection will malfunction. Obviously, the unbalanced current caused by the zero-sequence fault current on the Y ₀ side is ignored in the ratio braking element of the traditional differential protection, that is, there is no corresponding braking current in the ratio braking element to brake it, thus It may lead to misoperation of transformer longitudinal differential protection.

Contents of the invention

The technical problem to be solved by the present invention is to provide a longitudinal transformer with maximum zero-sequence current ratio braking for the Y ₀ side three-phase current conversion method in the existing transformer longitudinal differential protection technology that cannot completely eliminate the influence of zero-sequence current. Differential protection method, through the weighted summation of the maximum value of the braking current representing the through current in the longitudinal differential protection of the transformer and the zero-sequence current of each neutral point grounding side (or branch) of the transformer to form the braking current containing the zero-sequence current , using the braking current containing zero-sequence current and the differential current of the corresponding phase to form the phase ratio braking element, when the differential current is greater than the braking current containing zero-sequence current and greater than the minimum operating current, the phase ratio is output Action signal of the braking element. The invention has the advantage that it can completely avoid the misoperation of the transformer longitudinal differential protection caused by the ground fault outside the _Y0 side when the errors of the three-phase current transformers are inconsistent.

A transformer longitudinal differential protection method with maximum zero-sequence current ratio braking, characterized in that: through the braking current representing the through current in the transformer longitudinal differential protection and the zero-sequence current of each neutral point grounding side or grounding branch of the transformer The maximum value is weighted and summed to form the braking current containing the maximum zero-sequence current, and the braking current containing the maximum zero-sequence current and the differential current of the corresponding phase are used to form the criterion of this ratio braking. When the differential current When it is greater than the braking current including the maximum zero-sequence current and greater than the minimum operating current, the action signal of the phase rate braking is output. The action criterion of the ratio braking with the maximum zero-sequence current is:

I _d >K _Z ×I _z +K ₀ ×(3I ₁₀ , 3I ₂₀ ,...3I _n0 )max

In the formula, I _d and I _z are respectively the differential current of any one of the three phases of the longitudinal differential protection of the transformer and the brake current representing the crossing current of the phase, 3I ₁₀ , 3I ₂₀ , ... 3I _n0 are each neutral point grounding Zero-sequence current on the side or grounding branch, (3I ₁₀ , 3I ₂₀ ,...3I _n0 )max is the maximum value of the zero-sequence current on the grounding side or grounding branch of each neutral point, K _Z is the ratio braking coefficient, and The value is 0<K _Z <1, and K ₀ is the zero-sequence braking coefficient. When the zero-sequence current, three-phase differential current and three-phase braking current are attributed to the same side, the setting range of K ₀ is 0<K ₀ <1/3, n is the number of transformer neutral grounding sides or grounding branches.

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 braking element of the traditional transformer longitudinal differential protection. Through the weighted summation of the maximum value of the braking current representing the crossing current in the transformer differential protection and the zero-sequence current of each neutral point grounding side (or branch) of the transformer, the braking current containing the zero-sequence current is formed. The braking current of the zero sequence current and the differential current of the corresponding phase constitute the phase ratio braking element. When the differential current is greater than the braking current including the zero sequence current and greater than the minimum operating current, the phase ratio braking element is output. Action signal. The application of this scheme can completely avoid the maloperation of the transformer longitudinal differential protection caused by the ground fault outside the Y ₀ side when the errors of the three-phase current transformers are inconsistent, and can also prevent the differential differential caused by the zero-sequence current in the case of other non-internal faults. The maloperation of transformer longitudinal differential protection caused by balanced current does not affect the correct operation of longitudinal differential protection in the case of faults in the zone.

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

Figure 2 is the schematic wiring diagram of the existing transformer longitudinal differential protection

Fig. 3 is a circuit block diagram of a transformer differential protection element with maximum side zero-sequence ratio braking for realizing the present invention

Fig. 4 is a circuit block diagram of another transformer differential protection element with maximum side zero-sequence ratio braking of the present invention

Detailed ways

Example 1:

A transformer longitudinal differential protection method with maximum zero-sequence current ratio braking, which can be realized through the circuit block diagram of a transformer longitudinal differential protection component with maximum zero-sequence current ratio braking in Fig. 3 . This element is composed of maximum value circuit 01, multipliers A ₁ , B ₁ , C ₁ , 02, adders A ₃ , B ₃ , C ₃ and comparators A ₄ , B ₄ , C ₄ . Among them, the input terminals of the maximum value circuit 01 respectively input the filtered zero-sequence current signals 3I ₁₀ , 3I ₂₀ , and 3I ₃₀ on each neutral point grounding side (or branch) of the transformer, and its output terminal is connected with an input terminal of the multiplier 02 The other input terminal of the multiplier 02 inputs the zero-sequence braking coefficient K ₀ =0.15, and its output terminal is respectively connected to one input terminal of the adder A ₃ , B ₃ , C ₃ ; the multiplier A ₁ , B ₁ , One input terminal of C ₁ respectively inputs the filtered three-phase braking current signals I _za , I _zb , I _zc representing the through current in the transformer differential protection, and the other input terminal inputs the ratio braking coefficient K _Z =0.5; The other input terminals of the adders A ₃ , B ₃ , and C ₃ are respectively connected to the output terminals of the multipliers A ₁ , B ₁ , and C ₁ , and their output terminals are respectively connected to the negative input terminals of the comparators A ₄ , B ₄ , and C ₄ phase connection; the positive input terminals of comparators A ₄ , B ₄ , and C ₄ respectively input the filtered three-phase differential current signals I _da , I _db , and I _dc , and their output terminals output the ratios of A, B, and C phases respectively Differential action signal. n=3 is the number of grounding sides (or branches) of the neutral point of the transformer. When the differential current is greater than the braking current including the maximum side zero-sequence current, the comparator outputs the ratio differential action signal of the corresponding phase. The application of this scheme can completely avoid the misoperation of the transformer differential protection caused by the external ground fault 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 when it is not an internal fault. 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.

Example 2:

A transformer longitudinal differential protection method with maximum zero-sequence current ratio braking, which can be realized through the circuit block diagram of another transformer longitudinal differential protection element with maximum zero-sequence current ratio braking shown in Fig. 4 . The element consists of maximum value circuit 03, subtractor A ₁₁ , B ₁₂ , C ₁₃ , multiplier A ₂₁ , B ₂₂ , C ₂₃ , 04, adder A ₃₁ , B ₃₂ , C ₃₃ , A ₄₁ , B ₄₂ , C ₄₃ and comparators A ₅₁ , B ₅₂ and C ₅₃ constitute. Among them, the positive input terminals of the subtractors A ₁₁ , B ₁₂ , and C ₁₃ respectively input the filtered braking current signals I _za , I zb , and I zc , which represent the through current of the transformer longitudinal differential protection, and the negative input terminals respectively input the transformer longitudinal differential protection signals I za , I _zb , and I _zc . The braking inflection point current value I _reso in the differential protection = 1.1×In _n , where I _n is the rated current of the transformer converted to this side; one input terminal of the multiplier A ₂₁ , B ₂₂ , and C ₂₃ is respectively connected to the subtractor A ₁₁ , The output terminals of B ₁₂ and C ₁₃ and the other input terminal respectively input the slope of the ratio differential polyline S=0.5, and the output terminals are respectively connected to one input terminal of adders A ₃₁ , B ₃₂ , and C ₃₃ ; the adders A ₃₁ , B _32. The other input terminals of C ₃₃ input the minimum operating current value I _op.min = 0.5×I _n respectively, and their output terminals are respectively connected with one input terminal of the adder A ₄₁ , B ₄₂ , and C ₄₃ ; find the maximum value The three input terminals of the circuit 03 respectively input the filtered zero-sequence current signals 3I ₁₀ , 3I ₂₀ , and 3I ₃₀ of each neutral point grounding side (or branch) of the transformer, and its output terminal is connected to an input terminal of the multiplier 04, and the multiplication The other input terminal of the device 04 inputs the zero-sequence braking coefficient K ₀ =0.3, and its output terminals are respectively connected to the other input terminals of the adders A ₄₁ , B ₄₂ , and C ₄₃ ; the comparators A ₅₁ , B ₅₂ , and C ₅₃ The positive input terminals respectively input the filtered three-phase differential current signals I _da , I _db , I _dc , the negative input terminals are respectively connected with the output terminals of the adders A ₄₁ , B ₄₂ , and C ₄₃ , and the output terminals output A , B, C phase ratio differential action signal. When the differential current is greater than the braking current including zero-sequence current, the comparator outputs the ratio differential action signal of the corresponding phase. Applying this scheme, the situation that the ratio differential broken line does not pass the origin can be realized, that is, the ratio braking coefficient Kz=S×(1-I _reso /Iz)+I _op.min /Iz, and the ratio braking coefficient Kz changes with the braking current It can also completely avoid the misoperation of the longitudinal difference protection of the transformer caused by the ground fault outside the Y ₀ side when the errors of the three-phase current transformers are inconsistent. The maloperation of transformer longitudinal differential protection caused by balanced current does not affect the correct operation of longitudinal differential protection in the case of faults in the zone.

Claims (3)

1. transformer longitudinal error protecting method with the maximum zero sequence current ratio brake; it is characterized in that: the maximum in the stalling current by representing through current in the transformer differential protection and the zero-sequence current of each neutral ground side of transformer or ground connection branch is weighted summation and constitutes the stalling current that contains maximum zero sequence current; constitute the criterion that this phase ratio is braked with this stalling current that contains maximum zero sequence current with corresponding differential current mutually; when differential current during greater than the stalling current that contains maximum zero sequence current and greater than minimum working current; export the actuating signal of this phase ratio braking, the operating criterion of band maximum zero sequence current ratio brake is:

I _d＞K _Z×I _z+K ₀×(3I ₁₀、3I ₂₀、……3I _n0)max

I in the formula _d, I _zThe differential current that is respectively any phase in the transformer differential protection three-phase with represent this stalling current of through current mutually, 3I ₁₀, 3I ₂₀... 3I _N0Be the zero-sequence current of each neutral ground side or ground connection branch, (3I ₁₀, 3I ₂₀... 3I _N0) max is the maximum in the zero-sequence current of each neutral ground side or ground connection branch, K _ZBe ratio brake coefficient, K ₀Be the zero-sequence braking coefficient, n is transformer neutral point ground connection side number or ground connection branches.

2. method according to claim 1 is characterized in that: ratio brake coefficient K _ZValue be 0＜K _Z＜1.

3. method according to claim 1 is characterized in that: in zero-sequence current and three-phase differential current, the reduction of three-phase system streaming current under the situation of the same side, the zero-sequence braking COEFFICIENT K ₀Setting range is 0＜K ₀＜1/3.

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