CN100350704C - Alternating and Zero Sequence braking method for preventing transformer protection from malfunction - Google Patents

Abstract

The invention discloses a phase-to-phase and zero-sequence braking method for preventing misoperation of transformer protection. The phase-to-phase current obtained after transformation on the _Y0 side of the transformer is used to form a ratio braking criterion with the zero-sequence current on this side. When the ratio value is less than the set When the value is , the brake signal of the corresponding phase is output to brake the transformer ratio differential protection. Applying this scheme, it is only necessary to collect the three-phase current of the Y ₀ side with power supply and the zero-sequence current of this side, and rely on the interphase current obtained after the unilateral current transformation and the zero-sequence current to form a ratio braking element, which can completely avoid the three-phase current When the transformer errors are inconsistent, the transformer differential protection maloperation caused by the ground fault outside the zone on the Y ₀ side.

Description

A Phase-to-Phase and Zero-Sequence Braking Method to Prevent Maloperation of Transformer Protection

technical field

The invention relates to a method for relay protection of a power system, in particular to a method for interphase and zero-sequence braking to prevent maloperation of transformer protection

Background technique

The existing power transformer longitudinal differential protection device uses a ratio braking element, that is, through the ratio of differential current and through current, to identify external faults and internal faults; at the same time, through inrush current and overexcitation braking elements, that is, through Analyze the waveform or harmonic content of the differential current to identify the 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 zero-sequence current of the ground fault outside the Y ₀ side from causing the vertical differential protection to malfunction, the method of transforming the three-phase current on the Y ₀ side is widely used at present 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, inrush current and over-excitation braking element cannot perform reliable braking, especially when the transformer load current is small or even zero, the ratio braking element, The inrush brake component cannot brake this, as long as the error current exceeds the threshold, the transformer longitudinal differential protection will malfunction. In Patent Application No. 200410016305.8 "Phase-Separated Differential Current Method for Preventing Misoperation of Transformer Differential Protection", the method of judging the ground fault outside the Y ₀ side by the ratio of the differential current to the zero-sequence current can overcome the above defects, but Differential current acquisition is complex.

Contents of the invention

The technical problem to be solved by the present invention is to provide a phase-to-phase and zero-sequence system that prevents misoperation of transformer protection 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 dynamic method, the phase-to-phase current of the transformer Y ₀ side and the zero-sequence current of this side constitute the ratio braking criterion. When the ratio value is less than the setting value, the phase-to-phase braking signal is output to control the ratio differential protection of the corresponding phase transformer. move. The advantage of the present invention is that the differential protection of the transformer caused by the external grounding fault on the Y ₀ side when the error of the three-phase current transformer is inconsistent is completely avoided by relying on the proportional braking of the phase-to-phase current obtained after the unilateral current conversion and the zero-sequence current on this side Malfunction.

A phase-to-phase and zero-sequence braking method for preventing misoperation of transformer protection, which is characterized in that: the phase-to-phase current on the _Y0 side of the transformer and the zero-sequence current on this side form a ratio braking criterion, when the phase-to-phase current on the _Y0 side is divided by When the ratio value of the zero-sequence current on this side is less than the setting value K, the phase-to-phase braking signal is output to brake the ratio differential protection of the corresponding phase transformer; the basis for phase-to-phase and zero-sequence braking is:

$<span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; K</span>}$

中任意一相间基波电流向量， 分别为变压器Y₀侧的三相基波电流向量，

为该侧零序基波电流向量，即 $3{\stackrel{\&CenterDot;}{I}}_0={\stackrel{\&CenterDot;}{I}}_a+{\stackrel{\&CenterDot;}{I}}_b+{\stackrel{\&CenterDot;}{I}}_c$ K为整定值，其值为0＜K＜1/3。In the formula is the three-phase phase-to-phase current on the Y ₀ side of the transformer

In any one of the phase-to-phase fundamental current vectors, are the three-phase fundamental current vectors on the side of transformer Y ₀ ,

is the zero-sequence fundamental current vector on this side, that is $3{\stackrel{\&CenterDot;}{I}}_0={\stackrel{\&Center\; Dot;}{I}}_a+{\stackrel{\&Center\; Dot;}{I}}_b+{\stackrel{\&Center\; Dot;}{I}}_c$ K is the setting value, its value is 0<K<1/3.

Compared with the prior art, the beneficial effect of the present invention is that in the traditional transformer differential protection, it is proposed for the first time to add a brake criterion of ratio between the phase-to-phase current on the _Y0 side of the transformer and the zero-sequence current on this side, when the ratio When the value is less than the setting value, the brake signal between the phases is output to brake the corresponding phase transformer ratio differential protection. Applying this scheme, it is only necessary to collect the three-phase current of the _Y0 side with power supply and the zero-sequence current of this side, and rely on the interphase current obtained after the unilateral current conversion and the zero-sequence current of this side to form a braking element, which can completely avoid the three-phase current When the errors of the phase current transformers are inconsistent, the misoperation of the transformer differential protection caused by the ground fault outside the Y ₀ side can also prevent the differential protection of the transformer caused by the differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions Misoperation.

Description of drawings

The specific implementation manner of the present invention will be further described in detail below in conjunction with the attached circle.

Fig. 1 is a circuit block diagram of a phase-to-phase and zero-sequence braking element for preventing misoperation of transformer protection according to the present invention.

Detailed ways

Example 1:

A phase-to-phase and sequence braking method for preventing maloperation of transformer differential protection, which can be realized by a circuit of phase-to-phase and zero-sequence braking components for preventing transformer protection malfunction as shown in FIG. 1 . The element is composed of subtractors 11-13, filters 21-24, multipliers 3, and comparators 41-43, wherein the positive input terminals of the subtractors 11-13 input the three-phase current instantaneous value signal i of the transformer _Y0 side respectively _a , i _b , i _c , the negative input terminals respectively input the commutation three-phase current instantaneous value signals i _b , i _c , i _a on the side of transformer Y ₀ , and their output terminals are respectively connected to the input terminals of filters 21-23; The input terminal of the multiplier 24 inputs the zero-sequence current instantaneous value signal 3i _o of this side, and its output terminal is connected with one input terminal of the multiplier 3; the other input terminal of the multiplier 3 inputs the setting value K=0.1, and its output terminals are respectively Connected to the negative input terminals of the comparators 41-43; the output terminals of the comparators 41-43 respectively output the braking signals of A, B and C phases. When the positive input signal in the comparator is smaller than the negative input signal, the comparator outputs 0, and the corresponding phase is judged to have an external ground fault, and the corresponding phase brake signal is output to brake the transformer ratio differential protection to prevent transformer differential Protection malfunction; otherwise, the comparator outputs 1, allowing the corresponding phase differential protection to operate. Applying this scheme, it is only necessary to collect the three-phase current of the Y ₀ side with power supply and the zero-sequence current of this side, and rely on the interphase current obtained after the current conversion and the zero-sequence current to form a ratio brake element, which can completely avoid the error of the three-phase current transformer When inconsistent, the misoperation of the transformer differential protection caused by the external ground fault on the Y ₀ side can also prevent the misoperation of the transformer differential protection caused by the differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions.

Claims (2)

1. A phase-to-phase and zero-sequence braking method for preventing misoperation of transformer protection, characterized in that: the phase-to-phase current on the _Y0 side of the transformer and the zero-sequence current on this side form a ratio braking criterion, when the phase-to-phase current on the _Y0 side When the ratio value divided by the zero-sequence current of this side is less than the setting value, the brake signal between the phases is output to brake the ratio differential protection of the corresponding phase transformer; the basis for phase-to-phase and zero-sequence braking is: $<span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; K</span>}$ In the formula

is the three-phase phase-to-phase current on the Y ₀ side of the transformer

In any one of the phase-to-phase fundamental current vectors,

are the three-phase fundamental current vectors on the side of transformer Y ₀ ,

is the zero-sequence fundamental current vector on this side, that is $3{\stackrel{\&Center\; Dot;}{I}}_0={\stackrel{\&Center\; Dot;}{I}}_a+{\stackrel{\&Center\; Dot;}{I}}_b+{\stackrel{\&Center\; Dot;}{I}}_c,$ K is the setting value. 2. The method according to claim 1, characterized in that: the setting value K is 0<K<1/3.

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