CN100367603C - Zero-sequence Braking Method of Maximum Transformation Current to Prevent Maloperation of Transformer Protection - Google Patents

Abstract

The invention discloses a zero-sequence braking method for maximum conversion current to prevent maloperation of transformer protection, using the maximum value of the three-phase current on the _Y0 side of the transformer with zero-sequence components removed and the zero-sequence current on this side to form a ratio braking criterion , when the ratio value is less than the setting value, the brake signal is output to brake the transformer ratio differential protection. Applying this scheme, it is only necessary to collect the three-phase current on the _Y0 side of the power supply, and use the ratio of the maximum value of the three-phase current on the _Y0 side of the transformer that removes the zero-sequence component to the zero-sequence current on this side to brake the component. Completely avoid the maloperation of transformer differential protection caused by the ground fault outside the Y ₀ side when the error of the three-phase current transformer is inconsistent, and also prevent the transformer from being caused by the differential unbalanced current caused by the zero-sequence current under other non-internal fault conditions. Malfunction of differential protection.

Description

Zero-sequence Braking Method of Maximum Transformation Current to Prevent Maloperation of Transformer Protection

technical field

The invention relates to a method for relay protection of an electric power system, in particular to a zero-sequence braking method for maximum conversion current to prevent maloperation of transformer protection.

Background technique

The existing power transformer 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 differential protection misoperation caused by the zero-sequence current of the ground fault outside the Y ₀ side, the method of transforming the three-phase current on the Y ₀ side is widely used 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 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 zero-sequence maximum transformation current that prevents maloperation 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 braking method, the maximum value of the three-phase current on the Y ₀ side of the transformer that removes the zero-sequence component is used to form a ratio braking element with the zero-sequence current on this side. When the ratio value is less than the setting value, the braking signal is output, and the transformer ratio difference Brake for motion protection. The advantage of the present invention is that, relying on the single-side three-phase current, the maximum value of the three-phase current on the _Y0 side of the transformer that removes the zero-sequence component and the zero-sequence current on this side form a ratio brake element, completely avoiding the error of the three-phase current transformer When they are not consistent, the transformer differential protection will malfunction due to the ground fault outside the zone on the Y ₀ side.

A zero-sequence braking method for maximum conversion current to prevent maloperation of transformer protection, which is characterized in that: the maximum value of the three-phase current on the _Y0 side of the transformer that removes the zero-sequence component and the zero-sequence current on this side constitute a ratio braking criterion , when the ratio of the maximum value of the three-phase current on the Y ₀ side of the transformer excluding the zero-sequence component divided by the ratio of the zero-sequence current on this side is less than the set value, a braking signal is output to brake the transformer ratio differential protection;

The basis for the zero-sequence braking of the maximum conversion current is:

${<span\; class="notranslate">\; (</span><span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; -</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; |</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; K</span>}$

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 $3{\stackrel{\&CenterDot;}{I}}_0={\stackrel{\&CenterDot;}{I}}_a+{\stackrel{\&CenterDot;}{I}}_b+{\stackrel{\&CenterDot;}{I}}_c,$

为

的1/3 ${\left(\right|{\stackrel{\&CenterDot;}{I}}_a-{\stackrel{\&CenterDot;}{I}}_0|、|{\stackrel{\&CenterDot;}{I}}_b-{\stackrel{\&CenterDot;}{I}}_0|、|{\stackrel{\&CenterDot;}{I}}_c-{\stackrel{\&CenterDot;}{I}}_0\left|\right)}_{\max }$ 为除去零序分量的变压器Y₀侧的三相电流的最大值，整定值K为0＜K＜1/3。In the formula

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 $3{\stackrel{\&Center\; Dot;}{I}}_0={\stackrel{\&Center\; Dot;}{I}}_a+{\stackrel{\&CenterDot;}{I}}_b+{\stackrel{\&Center\; Dot;}{I}}_c,$

for

1/3 of ${\left(\right|{\stackrel{\&Center\; Dot;}{I}}_a-{\stackrel{\&Center\; Dot;}{I}}_0|,|{\stackrel{\&CenterDot;}{I}}_b-{\stackrel{\&CenterDot;}{I}}_0|,|{\stackrel{\&CenterDot;}{I}}_c-{\stackrel{\&CenterDot;}{I}}_0\left|\right)}_{\max }$ It is the maximum value of the three-phase current on the Y ₀ side of the transformer that removes the zero-sequence component, and the setting value K is 0<K<1/3.

Compared with the prior art, the beneficial effect of the present invention is that it proposes for the first time in the traditional differential protection of transformers, adding a method to remove the zero-sequence component of the transformer Y ₀ side of the maximum value of the three-phase current and the side zero-sequence current The method of forming a ratio brake element, when the ratio value is less than the set value, outputs a brake signal to brake the ratio differential protection of the transformer. Applying this scheme, it is only necessary to collect the three-phase current on the Y ₀ side with the power supply, and use the maximum value of the three-phase current on the Y ₀ side of the transformer that removes the zero-sequence component to form a ratio brake element with the zero-sequence current on this side, which can completely Avoid misoperation of transformer differential protection caused by ground faults outside the Y ₀ side when the errors of three-phase current transformers are inconsistent. Malfunction of manual protection.

Description of drawings

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

Fig. 1 is a circuit block diagram of a zero-sequence brake element for maximum conversion current to prevent maloperation of transformer protection according to the present invention.

Detailed ways

Example 1:

乘法器21、22的一个输入端分别输入变压器Y₀侧的零序电流瞬时值信号

乘法器21的另一个输入端输入1/3，其输出端分别与减法器11～13的负输入端相连接；乘法器22的另一个输入端输入整定值K＝0.2，其输出端接滤波器34的输入端；滤波器31～33的输入端分别与减法器11～13的输出端相接；其输出端分别接求最大值电路4的三个输入端；滤波器34的输出端接比较器4的负输入端；比较器5的正输入端与最大值电路4的输出端相连接，其输出端输出三相制动信号。当比较器的正输入端信号小于负输入端信号，比较器输出0，判有区外接地故障，输出三相制动信号，对变压器比率差动保护进行制动，防止变压器差动保护误动；否则比较器输出1，允许差动保护动作。应用本方案，只需要采集有电源的Y₀侧的三相电流，用三相电流中的最大值与该侧零序电流构成比率制动元件，就可完全避免三相电流互感器误差不一致时，Y₀侧区外接地故障导致的变压器差动保护误动，也可防止其他非内部故障情况下，零序电流造成的差动不平衡电流导致的变压器差动保护误动作。A maximum conversion current zero-sequence braking method for preventing maloperation of transformer differential protection. The method can be realized through the circuit block diagram of a maximum conversion current zero-sequence braking component for preventing transformer protection maloperation in FIG. 1 . The element is composed of subtractors 11-13, multipliers 21, 22, filters 31-34, maximum value seeking circuit 4 and comparator 5; wherein the positive input terminals of the subtractors 11-13 are respectively input to the three voltages of the transformer _Y0 side. Phase current instantaneous value signal

One input terminal of multiplier 21, 22 inputs the zero-sequence current instantaneous value signal of transformer Y ₀ side respectively

Another input terminal of multiplier 21 inputs 1/3, and its output terminal is connected with the negative input terminal of subtractor 11～13 respectively; Another input terminal input setting value K=0.2 of multiplier 22, its output terminal connects filter The input end of device 34; The input end of filter 31～33 is connected with the output end of subtractor 11～13 respectively; Its output end is connected with three input ends of maximum value circuit 4 respectively; The output end of filter 34 is connected The negative input terminal of the comparator 4; the positive input terminal of the comparator 5 is connected with the output terminal of the maximum value circuit 4, and its output terminal outputs a three-phase braking signal. When the signal at the positive input terminal of the comparator is smaller than the signal at the negative input terminal, the comparator outputs 0, and an external ground fault is judged, and a three-phase braking signal is output to brake the transformer ratio differential protection to prevent misoperation of the transformer differential protection ; Otherwise, the output of the comparator is 1, allowing the differential protection to operate. Applying this scheme, it is only necessary to collect the three-phase current of the Y ₀ side with the power supply, and use the maximum value of the three-phase current and the zero-sequence current of this side to form a ratio brake element, which can completely avoid the error of the three-phase current transformer when it is inconsistent , The misoperation of the transformer differential protection caused by the ground fault outside 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 maximum conversion current zero sequence braking method for preventing transformer protection from malfunction is characterized in that: by transformers Y for removing zero-sequence components ₀ The maximum value of the three-phase current on the side and the zero-sequence current on the side form a ratio brake criterion, and when the zero-sequence component of the transformer Y is removed ₀ When the ratio value of the maximum value of the three-phase current on the side divided by the zero-sequence current on the side is smaller than the setting value, a braking signal is output to brake the transformer ratio differential protection; the basis of the maximum transformation current zero sequence braking is as follows:

in the formula

Are respectively a transformer Y ₀ The three-phase fundamental current vector of the side,

is the zero-sequence fundamental current vector of the side,

is composed of

1/3 of the total weight of the composition,

transformer Y for removing zero sequence component ₀ And K is a setting value.

2. The maximum conversion current zero sequence braking method for preventing transformer protection malfunction according to claim 1, characterized in that: the setting value K is more than 0 and less than 1/3.

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