CN100367606C - Transformer longitudinal difference protection method with multi-side zero-sequence current ratio brake - Google Patents

Abstract

The invention discloses a transformer longitudinal difference protection method with multi-side zero-sequence current ratio braking, through the braking current representing the through current in the transformer longitudinal difference protection and the zero-sequence current of each neutral point grounding side or branch of the transformer The weighted summation value is weighted and summed to form the braking current containing zero-sequence current, and the braking current containing 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 is greater than When the braking current includes zero-sequence current and is greater than the minimum operating current, it will output the operating signal of the phase ratio braking. The application of this scheme can completely avoid the maloperation of the transformer longitudinal 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.

Description

Transformer longitudinal difference protection method with multi-side zero-sequence current ratio brake

technical field

The invention relates to a relay protection method of a power system, in particular to a transformer differential protection method with multi-side 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 transformer with multi-side zero-sequence current ratio braking in view of the fact that the three-phase current conversion method on the Y ₀ side in the existing transformer differential protection technology cannot completely eliminate the influence of zero-sequence current In the longitudinal difference protection method, the weighted summation of the brake current representing the through current in the longitudinal difference protection of the transformer and the zero-sequence current of each neutral point grounding side (or branch) of the transformer is weighted and summed to form a zero-sequence current control system. Dynamic current, use 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, output the The action signal of the ratio brake 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 difference protection method with multi-side zero-sequence current ratio braking, characterized in that: through the braking current representing the through current in the transformer longitudinal difference protection and the zero-sequence current of each neutral point grounding side or grounding branch of the transformer The weighted summation value of the weighted summation 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 criterion of this ratio braking. When the differential current When it is greater than the braking current including 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 multi-side zero-sequence current is:

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

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 The zero-sequence current of the side or the grounding branch, k ₁₀ , k ₂₀ , ...k _n0 are the set weights, 3I ₁₀ ×k ₁₀ +3I ₂₀ ×k ₂₀ +...+3I _n0 ×k _n0 are the neutral The weighted summation value of the zero-sequence current of the point grounding side or the grounding branch, K _Z is the ratio braking coefficient, its value is 0<K _Z <1, K ₀ is the zero-sequence braking coefficient, when the zero-sequence current and the three-phase difference When the moving current and three-phase braking current are attributed to the same side and the weights are greater than 0 and less than or equal to 1, the zero-sequence braking coefficient K ₀ can be adjusted in the range of 0<K ₀ <1/3; n It 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. The weighted summation of the brake current representing the through current in the transformer differential protection and the zero-sequence current of each neutral point grounding side (or branch) of the transformer is weighted and summed to form the brake current containing zero-sequence current. The braking current with 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 containing 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 embodiments 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 ratio braking element with multi-side zero-sequence current ratio braking for realizing the present invention

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

Detailed ways

Example 1:

A transformer longitudinal differential protection method with multi-side zero-sequence current ratio braking, which can be realized through the circuit block diagram of a transformer longitudinal differential protection ratio braking component with multi-side zero-sequence current ratio braking in Figure 3 . This element is composed of multipliers A ₁ , B ₁ , C ₁ , M ₁ , 01, 02, 03, adders A ₃ , B ₃ , C ₃ , M ₀ , and comparators A ₄ , B ₄ , C ₄ . Among them, one input terminal of the multiplier A ₁ , B ₁ , and C ₁ is respectively input into the filtered three-phase braking current signals I _za , I _zb , I _zc representing the cross-current in the differential protection of the transformer, and the other input terminal is Input ratio braking coefficient K _Z = 0.4; one input terminal of multiplier 01, 02, 03 respectively inputs zero-sequence current signal 3I ₁₀ , 3I ₂₀ , 3I ₃₀ of each neutral point grounding side (or branch) of the transformer after filtering , and the other input end respectively inputs preset weights k ₁₀ , k ₂₀ , k ₃₀ , the value is 0.4, and its output end is respectively connected to the three input ends of the adder M ₀ ; the output end of the adder M ₀ is connected to the multiplication One input terminal of the multiplier M ₁ is connected; the other input terminal of the multiplier M ₁ inputs the setting value K ₀ =0.2, and its output terminals are respectively connected to one input terminal of the adder A ₃ , B ₃ , and C ₃ ; the adder A _3. The other input terminals of B ₃ and C ₃ are respectively connected to the output terminals of multipliers A ₁ , B ₁ , and C ₁ , and their output terminals are respectively connected to the negative input terminals of comparators A ₄ , B ₄ , and C ₄ ; The positive input terminals of the 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 ratio differential actions of phases A, B, and C respectively. 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 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 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.

Example 2:

A transformer longitudinal differential protection method with multi-side zero-sequence current ratio braking, which can be obtained through the circuit block diagram of another transformer longitudinal differential protection ratio braking component with multi-side zero-sequence current ratio braking in Figure 4 accomplish. The element consists of subtractors A ₁₁ , B ₁₂ , C ₁₃ , multipliers A ₂₁ , B ₂₂ , C ₂₃ , 011, 021, 031, M ₄ , adders A ₃₁ , B ₃₂ , C ₃₃ , A ₄₁ , B ₄₂ , C ₄₃ , M ₃ and comparators A ₅₁ , B ₅₂ , C ₅₃ . 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 = 1.2×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 terminal of C ₃₃ inputs the minimum operating current value I _op.min = 0.4×I _n respectively, and its output terminal is respectively connected with one input terminal of adder A ₄₁ , B ₄₂ , C ₄₃ ; the multiplier 011 One input terminal of , 021, 031 respectively inputs the filtered zero-sequence current signal 3I ₁₀ , 3I ₂₀ , 3I ₃₀ of each neutral point grounding side (or branch) of the transformer, and the other input terminal respectively inputs preset weights k ₁₀ , k ₂₀ , k ₃₀ , the value is 0.3, the output terminals of which are connected to the three input terminals of the adder _M3 ; the output terminal of the adder _M3 is connected to one input terminal of the multiplier _M4 , and the other input terminal of the multiplier _M4 One input input zero-sequence braking coefficient K ₀ is 0.3. The output terminals of the multiplier _M4 are respectively connected to the other input terminals of the adders _A41 , _B42 and _C43 ; the positive input terminals of the comparators _A51 , _B52 and _C53 respectively input the filtered three-phase differential The negative input ends of the current signals I _da , I _db , and I _dc are respectively connected to the output ends of the adders A ₄₁ , B ₄₂ , and C ₄₃ , and their output ends output ratio differential action signals of phases A, B, and C, respectively. 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 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 multiple side zero sequence current ratio braking; it is characterized in that: the weighted sum value of 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 zero-sequence current; constitute the criterion that this phase ratio is braked with this stalling current that contains zero-sequence current with corresponding differential current mutually; when differential current during greater than the stalling current that contains zero-sequence current and greater than minimum working current; export the actuating signal of this phase ratio braking, the operating criterion of band multiple side zero sequence current ratio braking is:

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

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, k ₁₀, k ₂₀... k _N0Be the weights of setting, 3I ₁₀* k ₁₀+ 3I ₂₀* k ₂₀+ ... + 3I _N0* k _N0Be the weighted sum value of 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 to the same side and described each weights greater than 0 and be less than or equal under 1 the situation zero-sequence braking COEFFICIENT K ₀Setting range is 0＜K ₀＜1/3.

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