CN100367609C - Transformer longitudinal differential protection element with multi-side zero-sequence current ratio braking - Google Patents

Abstract

The invention discloses a transformer longitudinal differential protection element with multi-side zero-sequence current ratio braking. The three-phase braking current representing the through current in the current differential protection of the transformer is respectively connected to the grounding side (or branch) of each neutral point. The weighted summation value of the zero-sequence current is weighted and summed to form the three-phase braking current containing zero-sequence current, and the three-phase braking current containing zero-sequence current is used to form the three-phase differential current in the transformer differential protection. The corresponding phase ratio braking element, when the differential current is greater than the braking current including the zero-sequence current, 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.

Description

Transformer longitudinal differential protection element with multi-side zero-sequence current ratio braking

technical field

The invention relates to a power system relay protection element, in particular to a transformer differential protection element 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 object of the present invention is to provide a transformer longitudinal differential protection element with multi-side zero-sequence current ratio braking, using the current three-phase braking current representing the through current in the differential protection of transformers to connect with each neutral point grounding side (or The weighted summation value of the zero-sequence current of the branch) is weighted and summed to form a three-phase braking current containing zero-sequence current, which is used to separate the three-phase differential protection in the transformer differential protection with the braking current containing zero-sequence current. The current constitutes the braking element of the corresponding phase ratio. 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. 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 longitudinal differential protection element with multi-side zero-sequence current ratio braking, characterized in that the element is composed of A-phase multiplier A1, B-phase multiplier B1, C-phase multiplier C1, and the first multiplier M1, A-phase adder A3, B-phase adder B3, C-phase adder C3, first adder M0, A-phase comparator A4, B-phase comparator B4, C-phase comparator C4 and the nth Two multipliers 01, 02, ... 0n are formed; among them, one input terminal of the A-phase multiplier A1, the B-phase multiplier B1 and the C-phase multiplier C1 is respectively input into the differential protection of the transformer to represent the passing current. The other input terminals of the filtered A-phase braking current signal I _za , B-phase braking current signal I _zb and C-phase braking current signal I _zc are input with ratio braking coefficient K _z ; n second One input terminal of the multipliers 01, 02, ... 0n respectively inputs the filtered zero-sequence current signals 3I ₁₀ , 3I ₂₀ , ... 3I _n0 of each neutral point grounding side or grounding branch of the transformer, and the other The input terminals respectively input preset weights k ₁₀ , k ₂₀ , ...k _n0 , and their respective output terminals are respectively connected to the input terminals of the first adder M0; the output terminals of the first adder M0 are connected with the first multiplier One input terminal of the first multiplier M1 is connected; the other input terminal of the first multiplier M1 inputs the zero-sequence braking coefficient K ₀ , and its output terminals are respectively connected to the A-phase adder A3, B-phase adder B3 and C to add One input end of the multiplier C3; the other input end of the A-phase adder A3, the B-phase adder B3 and the C-phase adder C3 are respectively connected to the A-phase multiplier A1 and the B-phase multiplier B1 and the respective output terminals of the C phase multiplier C1, the respective output terminals of the A phase adder A3, the B phase adder B3 and the C phase adder C3 are respectively connected to the A phase comparator A4, the B phase comparator B4, It is connected with the respective negative input terminals of the C-phase comparator C4; the respective positive input terminals of the A-phase comparator A4, the B-phase comparator B4 and the C-phase comparator C4 respectively input the filtered A-phase differential current signal I _da , The output terminals of the B-phase differential current signal I _db and the C-phase differential current signal I _dc respectively output the ratio differential action signals of the A-phase, B-phase and C-phase. The value of the ratio braking coefficient K _z is 0<K _z <1; the value of the zero-sequence braking coefficient K ₀ is 0<K ₀ <1/3; the preset weights k ₁₀ , k ₂₀ ,... k _n0 is 0<k _i0 ≤1, where i=1, 2, ... n; n is the number of transformer neutral grounding sides or grounding branches. 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.

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 current to the braking current of the ratio differential element of the traditional transformer differential protection. The three-phase brake current passing through the meter and the weighted sum of the zero-sequence current of each neutral point grounding side (or branch) are weighted and summed to form a three-phase brake current with zero-sequence current. The braking current containing zero-sequence current and the three-phase differential current in the transformer differential protection respectively constitute the corresponding ratio braking element. 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. The application of this scheme can completely avoid the misoperation of the transformer differential protection caused by the external grounding fault on the Y ₀ side with the only power supply when the errors of the three-phase current transformers are inconsistent, and can also prevent other non-internal faults from being caused by zero-sequence current. The transformer differential protection misoperation caused by the differential unbalanced current does not affect the correct operation of the differential protection under the fault condition 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 element with multi-side zero-sequence current ratio braking for realizing the present invention

Detailed ways

Example 1:

A transformer longitudinal differential protection element with multi-side zero-sequence current ratio braking can be realized through the circuit block diagram in Figure 3. The element is composed of multipliers A1, B1, C1, M1, 01, 02, 03, adders A3, B3, C3, M0 and comparators A4, B4, C4. Among them, the ratio braking coefficient K _z in the existing ratio differential protection is 0.7; the preset weights k ₁₀ , k ₂₀ , k ₃₀ are 0.5, and n=3 is the number of transformer neutral point grounding sides ( Or the number of branches), the zero-sequence braking coefficient K ₀ is 0.3. 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.

Claims (4)

1. transformer longitudinal error protecting element with multiple side zero sequence current ratio braking is characterized in that: this element by individual second multiplier of A phase multiplier (A1), B phase multiplier (B1), C phase multiplier (C1), first multiplier (M1), A addition musical instruments used in a Buddhist or Taoist mass (A3), B addition musical instruments used in a Buddhist or Taoist mass (B3), C addition musical instruments used in a Buddhist or Taoist mass (C3), first adder (M0), A phase comparator (A4), B phase comparator (B4), C phase comparator (C4) and n (01,02 ... 0n) constitute; Wherein A phase multiplier (A1), B phase multiplier (B1) and C mutually multiplier (C1) input separately represent in the input transformer differential protection respectively through current through filtered A phase stalling current signal I _Za, B phase stalling current signal I _ZbWith C stalling current signal I mutually _Zc, its another input is separately all imported ratio brake coefficient K _zIndividual second multiplier of n (01,02 ... 0n) input separately respectively each neutral ground side of input transformer or ground connection branch through filtered zero sequence current signal 3I ₁₀, 3I ₂₀... 3I _N0, its another input is separately imported predefined weights k respectively ₁₀, k ₂₀... k _N0, its output separately connects each input of first adder (M0) respectively; The output of first adder (M0) is connected with an input of first multiplier (M1); Another input input zero-sequence braking COEFFICIENT K of first multiplier (M1) ₀, its output connects A addition musical instruments used in a Buddhist or Taoist mass (A3), B addition musical instruments used in a Buddhist or Taoist mass (B3) and C addition musical instruments used in a Buddhist or Taoist mass (C3) input separately respectively; A addition musical instruments used in a Buddhist or Taoist mass (A3), B addition musical instruments used in a Buddhist or Taoist mass (B3) and C addition musical instruments used in a Buddhist or Taoist mass (C3) another input separately connect A multiplier (A1), B phase multiplier (B1) and C multiplier (C1) output separately mutually mutually respectively, and A addition musical instruments used in a Buddhist or Taoist mass (A3), B addition musical instruments used in a Buddhist or Taoist mass (B3) and C addition musical instruments used in a Buddhist or Taoist mass (C3) output separately are connected with A phase comparator (A4), B phase comparator (B4) and C phase comparator (C4) negative input end separately respectively; A phase comparator (A4), B phase comparator (B4) and C phase comparator (C4) positive input terminal are separately imported the differential current signal I mutually through filtered A respectively _Da, B phase differential current signal I _DbWith C differential current signal I mutually _Dc, its output is separately exported A phase, B phase and C percentage differential actuating signal mutually respectively, and wherein n is transformer neutral point ground connection side number or ground connection branches.

2. element according to claim 1 is characterized in that: ratio brake coefficient K _zValue be 0＜K _z＜1.

3. element according to claim 1 is characterized in that: predefined weights k ₁₀, k ₂₀... k _N0Be 0＜k _I0≤ 1, wherein, i=1,2 ... n.

4. element 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 ₀Be 0＜K ₀＜1/3.

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