CN101789584A - Method for differential protection of sampling value of abrupt change and differential relays - Google Patents

Abstract

The invention discloses a method for differential protection of a sampling value of an abrupt change and differential relays. Because the speed of action of the common steady-state level differential protection relay is low when a serious transformer fault occurs, the invention provides the method for the differential protection of the sampling value of the abrupt change and the differential relays. The differential protection method and the differential relays use the integrated square of difference current of the sampling value of the abrupt change and the product of equivalent both-side current of the sampling value of the abrupt change to form a relay with a high fixed value and a relay with a low fixed value. Test result shows that the differential relays are quite high in safety and quickness.

Description

Suddenly-change sampling value differential protecting method and differential relay

Technical field

The present invention relates to Protection Technology tranformer protection field, particularly a kind of transformer differential protection technology.

Background technology

Along with the capacity of transformer is increasing, the cost of transformer is very expensive, and the capacity of short circuit of system is increasing, serious fault takes place on transformer lead, short circuit current is very big, and pass the transformer body, the insulation of transformer body is produced destroy, the mechanical stress that produces at winding is to the winding of transformer with unshakable in one's determinationly produce very big distortion action simultaneously.Therefore the quick protection of studying transformer becomes the important and urgent problem of transformer main protection research.

The quick protection of transformer mainly is the difference between current fast tripping protection at present; without any locking; for guaranteeing its reliability; definite value is generally 5～12 times transformer rated current; and need to adopt filtering algorithm; therefore this protection has the data window of certain-length could begin computational discrimination; so its common operate time is more than 20ms; and owing to adopt the fixedly mode of definite value; no matter great fault current operate time be identical, when these all are unfavorable for reducing big current failure to the impact of transformer.

If can adopt new algorithm size according to fault current under the prerequisite that does not reduce fail safe to adjust operate time dynamically, excise fault fast according to the order of severity of fault, alleviate impact to the transformer body.

Summary of the invention

For the quick acting that solves transformer takes into account the fail safe of relay simultaneously, the present invention proposes suddenly-change sampling value transformer differential protection method and based on the suddenly-change sampling value differential relay of this differential protecting method.

The present invention is specifically by the following technical solutions:

A kind of suddenly-change sampling value transformer differential protection method is characterized in that, said method comprising the steps of:

(1) gathers the electric current of each side of transformer and the sudden change amount current value of each side by each side current transformer of transformer;

(2) the many sides differential conversion with transformer is that transformer suddenly-change sampling value both sides are differential: an end that the maximum side of the sudden change amount current sampling data absolute value in the many sides of transformer of being gathered is decided to be transformer differential protection; the sudden change amount current sampling data and the equivalent other end that is decided to be transformer differential protection with all the other sides; wherein

Δ i _∑(t)---transformer suddenly-change sampling value differential current;

Δ i _M(t)---the maximum in each pleurapophysis variable current sampling data of transformer;

Δ i _∑-M(t)=Δ i _∑(t)-Δ i _M(t)---other pleurapophysis variable current sampling data sum of transformer;

(3) when satisfying following operation equation, the action of transformer suddenly-change sampling value differential protection:

Operation equation is as follows:

$\mathrm{\Σ}{\mathrm{\Δi}}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ}{\mathrm{\Δi}}_M\left(t\right){\mathrm{\Δi}}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2{\mathrm{\Δi}}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(1\right)$

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄|[Δi _M(t)Δi _∑-M(t)]| _MAX????(2)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10.

I _eBe the transformer rated current;

η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ".

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " other pleurapophysis variable current sampling data sum of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.When transformer generation catastrophe failure, the operate time cheracteristic of described differential protecting method can be along with the size variation of fault current, and when operating current is big more, responsiveness is fast more, has the characteristic of inverse time lag.

The invention also discloses a kind of suddenly-change sampling value transformer differential relay, it is characterized in that based on above-mentioned differential protecting method:

Described relay adopts the poor levelling side integration of sudden change amount current sampling data and the product of sudden change amount current sampling data equivalence both sides electric current to constitute the relay of a high-set setting and the relay of a low definite value, wherein,

The operation equation of described high-set setting relay is as follows:

$\mathrm{\Σ}{\mathrm{\Δi}}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ}{\mathrm{\Δi}}_M\left(t\right){\mathrm{\Δi}}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2{\mathrm{\Δi}}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(1\right)$

The operation equation of described low definite value relay is as follows:

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄|[Δi _M(t)Δi _∑-M(t)]| ^MAX????(2)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10.

I _eBe the transformer rated current;

η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ".

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " other pleurapophysis variable current sampling data sum of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.

η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ";

When described high-set setting actuating of relay equation satisfies, when the dissatisfied and described low definite value actuating of relay equation of perhaps described high-set setting actuating of relay equation satisfies, described suddenly-change sampling value transformer differential relay action.

The value of η is according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ", and is as shown in table 1: table 1

Transformer capacity	The disconnected definite value of adjusting of differential	The value of η
			6300kVA and following	7.0～12.0 times of Ie	??12

Transformer capacity	The disconnected definite value of adjusting of differential	The value of η
			??6300kVA~31500kVA	4.5～7.0 times of Ie	??10
??40000kVA~120000kVA	3.0 ~ 6.0 times of Ie	??8
			More than the 120000kVA	??2.0~5.0	??6

Compared with prior art, the present invention has the following advantages:

The quick protection of transformer mainly is the difference between current fast tripping protection at present; without any locking; for guaranteeing its reliability; definite value is generally 5～12 times transformer rated current; and need to adopt filtering algorithm, so this protection there is the data window of certain-length could begin computational discrimination, so its common operate time is more than 20ms; and owing to adopt the fixedly mode of definite value, regardless of great fault current operate time be identical.

The relay that the present invention proposes is when transformer generation catastrophe failure; its operate time cheracteristic can be along with the size variation of fault current, and when operating current is big more, responsiveness is fast more; characteristic with inverse time lag compared with prior art more meets the basic principle of tranformer protection.This relay has tangible direction character (Δ i simultaneously _M(t) Δ i _∑-M(t)), have that fine anti-CT is saturated, the ability of CT progress of disease error, magnetizing inrush current.Therefore, the suddenly-change sampling value differential relay excision speed that improved catastrophe failure greatly has very high fail safe simultaneously.

Description of drawings

Fig. 1 is the system diagram and the differential protection range specification of typical substation transformer;

Fig. 2 is a conventional transformer typical current quick-break operation curve;

The flow chart that Fig. 3 realizes for function of the present invention.

Embodiment

For above-mentioned purpose of the present invention, feature and advantage can be become apparent more, the specific embodiment of the present invention is described in detail below in conjunction with accompanying drawing.

Referring to Fig. 1, the system diagram and the differential protection range specification of typical substation transformer.

The included scope of curve is the scope of differential protection relay protection among Fig. 1, is called troubles inside the sample space, adopts each side electric current of transformer to constitute.The fault of extra curvature is called external area error.

Referring to Fig. 2, this figure is the typical differential relay operation curve of conventional transformer.Its operation equation is:

$\left|{\stackrel{\·}{I}}_{\mathrm{\Σ}}\right|\≥I_{\mathrm{sd}}---\left(3\right)$

In the formula: Be the transformer differential electric current, by the vector sum calculating of each side electric current;

I _SdFor transformer differential outage stream definite value, adjust by 5～12 times of Ie usually;

Sudden change amount current sampling data transformer differential protection method disclosed in this invention specifically may further comprise the steps in the present embodiment, as shown in Figure 3:

(1) gathers the electric current of each side of transformer and the sudden change amount current value of each side by each side current transformer of transformer;

(2) preferably the high-pressure side is arrived in other side electric current reduction of transformer in the present invention:

With on high-tension side electric current is benchmark, other each side direction high-pressure side reduction.The coefficient of balance that calculates each side is:

Rated current of each side of calculating transformer:

$I_{\mathrm{le}}=\frac{S_e}{\sqrt{3}{U}_{1e}}---\left(4\right)$

In the formula: S _eBe the maximum rated capacity of transformer; U _1eBe each side rated voltage of transformer (should be as the criterion) with the virtual voltage of operation.

Each side secondary rated current of calculating transformer:

$I_{2e}=\frac{I_{1e}}{n_{\mathrm{LH}}}---\left(5\right)$

In the formula: I _1eBe rated current of each side of transformer; n _LHBe each side CT no-load voltage ratio of transformer.

With the high-pressure side is benchmark, in the calculating transformer, the low-pressure side coefficient of balance:

$K_{\mathrm{ph}.M}=\frac{I_{2e.H}}{I_{2e.M}}=\frac{I_{1e.H}/n_{\mathrm{LH}.H}}{I_{1e.M}/n_{\mathrm{LH}.M}}=\frac{S_e/\sqrt{3}{U}_{1e.H}}{S_e/\sqrt{3}{U}_{1e.M}}\·\frac{n_{\mathrm{LH}.M}}{n_{\mathrm{LH}.H}}=\frac{U_{1e.M}}{U_{1e.H}}\·\frac{n_{\mathrm{LH}.M}}{n_{\mathrm{LH}.H}}---\left(6\right)$

$K_{\mathrm{ph},L}=\frac{U_{1e.L}}{U_{1e.H}}\·\frac{n_{\mathrm{LH}.L}}{n_{\mathrm{LH}.H}}---\left(7\right)$

Each phase current of other sides and corresponding coefficient of balance are multiplied each other, promptly get each phase current behind the amplitude compensation.

(3) further preferably each side electric current of transformer is carried out phase compensation:

Each side CT secondary current phase place of transformer is by the software self-correcting, with Δ-＞the Y side carries out phase calibration, Y0/ Δ-11 transformer is an example.Its bearing calibration is as follows:

The Δ side:

$\left\{\begin{array}{c}\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NA}}^{\′}=(\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NA}}-\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NC}})\\ \mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NB}}^{\′}=(\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NB}}-\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NA}})\\ \mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NC}}^{\′}=(\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NC}}-\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{NB}})\end{array}\right.---\left(8\right)$

The Y side:

$\left\{\begin{array}{c}\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MA}}^{\′}=\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MA}}-\mathrm{\Δ}{\stackrel{\·}{I}}_0\\ \mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MB}}^{\′}=\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MB}}-\mathrm{\Δ}{\stackrel{\·}{I}}_0\\ \mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MC}}^{\′}=\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MC}}-\mathrm{\Δ}{\stackrel{\·}{I}}_0\\ \mathrm{\Δ}{\stackrel{\·}{I}}_0=(\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MA}}+\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MB}}\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{MC}})/3\end{array}\right.---\left(9\right)$

In the formula:

Be Y side CT secondary current;

Be each phase current after the correction of Y side. Be Δ side CT secondary current;

Be each phase current after the correction of Δ side; Other mode of connection can be analogized.

The correlation computations of relay all is to carry out on the basis after current phase is proofreaied and correct and be balanced compensated.

(4) the maximum side of the sudden change amount electric current absolute value in the many sides of transformer of being gathered is decided to be an end of transformer differential protection, the other end that the sudden change amount electric current and the equivalence of all the other sides is decided to be transformer differential protection, wherein,

Δ i _∑(t)---transformer suddenly-change sampling value differential current;

Δ i _M(t)---the maximum in each pleurapophysis variable current sampling data of transformer;

Δ i _∑-M(t)=Δ i _∑(t)-Δ i _M(t)---other pleurapophysis variable current sampling data sum of transformer;

The computational methods of suddenly-change sampling value differential current are as follows:

$\mathrm{\Δ}{\stackrel{\·}{I}}_{\mathrm{\Σ}}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\mathrm{\Δ}{\stackrel{\·}{I}}_i---\left(10\right)$

In the formula:

Be the suddenly-change sampling value differential current;

Suddenly-change sampling value sum for all side phase currents.

The integrated square computing formula of suddenly-change sampling value differential current is as follows:

∑Δi _∑ ²(t)(11)

The integral and calculating formula of suddenly-change sampling value product is as follows:

∑Δi _M(t)Δi _∑-M(t)(12)

Ask for square maximum Δ i of suddenly-change sampling value differential current _∑ ²(t) _MAX, the suddenly-change sampling value maximum product | [Δ i _M(t) Δ i _∑-M(t)] | _MAX

(5) when satisfying following arbitrary operation equation, transformer suddenly-change sampling value differential protection moves:

Operation equation is as follows:

$\mathrm{\Σ}{\mathrm{\Δi}}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ}{\mathrm{\Δi}}_M\left(t\right){\mathrm{\Δi}}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2{\mathrm{\Δi}}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(13\right)$

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄|[Δi _M(t)Δi _∑-M(t)]| _MAX????(14)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10.

I _eBe the transformer rated current;

η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ".

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " other pleurapophysis variable current sampling data sum of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.

The following principle of value foundation of η:

Foundation " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ":

Transformer capacity	The disconnected definite value of adjusting of differential	The value of η
			6300kVA and following	7.0～12.0 times of Ie	??12
??6300kVA~31500kVA	4.5～7.0 times of Ie	??10
			??40000kVA~120000kVA	3.0 ~ 6.0 times of Ie	??8
More than the 120000kVA	??2.0~5.0	??6

Satisfy formula (13) or formula (14), then protection action.

According to the operation equation of the transformer differential relay of above-mentioned guard method as shown in the formula:

$\mathrm{\Σ}{\mathrm{\Δi}}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ}{\mathrm{\Δi}}_M\left(t\right){\mathrm{\Δi}}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2{\mathrm{\Δi}}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(15\right)$

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄|[Δi _M(t)Δi _∑-M(t)]| _MAX????(16)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10.

I _eBe the transformer rated current;

η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ".

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " other pleurapophysis variable current sampling data sum of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.The following principle of value foundation of η:

Foundation " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ":

Transformer capacity	The disconnected definite value of adjusting of differential	The value of η
			6300kVA and following	7.0～12.0 times of Ie	??12
??6300kVA~31500kVA	4.5～7.0 times of Ie	??10
			??40000kVA~120000kVA	3.0 ~ 6.0 times of Ie	??8
More than the 120000kVA	??2.0~5.0	??6

Satisfy formula (15) or formula (16), then protection action.

The quick protection of transformer mainly is the difference between current fast tripping protection at present; without any locking; for guaranteeing its reliability; definite value is generally 5～12 times transformer rated current; and need to adopt filtering algorithm, so this protection there is the data window of certain-length could begin computational discrimination, so its common operate time is more than 20ms; and owing to adopt the fixedly mode of definite value, regardless of great fault current operate time be identical.

The relay that the present invention proposes is when transformer generation catastrophe failure; its operate time cheracteristic can be along with the size variation of fault current, and when action current is larger, responsiveness is faster; characteristic with inverse time lag compared with prior art more meets the basic principle of tranformer protection. This relay has obvious direction character (Δ i simultaneously_M(t)Δi _∑-M(t)), have that fine anti-CT is saturated, the ability of CT progress of disease error, excitation surge current. Therefore, the suddenly-change sampling value differential relay excision speed that greatly improved catastrophe failure has very high security simultaneously.

Claims (3)

1. a suddenly-change sampling value transformer differential protection method is characterized in that, said method comprising the steps of:

(1) gathers the electric current of each side of transformer and the sudden change amount current value that calculates each side by each side current transformer of transformer;

(2) the many sides differential conversion with transformer is that transformer suddenly-change sampling value both sides are differential: an end that the maximum side of the sudden change amount current sampling data absolute value in the many sides of transformer of being gathered is decided to be transformer differential protection; the sudden change amount current sampling data and the equivalent other end that is decided to be transformer differential protection with all the other sides; wherein

Δ i _∑(t)---transformer suddenly-change sampling value differential current;

Δ i _M(t)---the maximum in each pleurapophysis variable current sampling data of transformer;

Δ i _∑-M(t)=Δ i _∑(t)-Δ i _M(t)---other pleurapophysis variable current sampling data sum of transformer;

(3) when satisfying following arbitrary operation equation, transformer suddenly-change sampling value differential protection moves:

Operation equation is as follows:

$\mathrm{\Σ\Δ}{i}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ\Δ}{i}_M\left(t\right)\mathrm{\Δ}{i}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2\mathrm{\Δ}{i}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(1\right)$

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄?|[Δi _M(t)Δi _∑-M(t)]| _MAX(2)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10;

I _eBe the transformer rated current;

$\mathrm{\ρ}=\mathrm{\η}-3\cos \frac{\mathrm{\π}}{20\mathrm{ms}}t,$ η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ";

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " all the other pleurapophysis variable current sampling data sums of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.

2. suddenly-change sampling value transformer differential protection method according to claim 1; it is characterized in that: when transformer generation catastrophe failure; the operate time cheracteristic of described differential protecting method can be along with the size variation of fault current; when operating current big more; responsiveness is fast more, has the characteristic of inverse time lag.

3. suddenly-change sampling value transformer differential relay based on claim 1 or 2, it is characterized in that: described relay adopts the poor levelling side integration of sudden change amount current sampling data and the product of sudden change amount current sampling data equivalence both sides electric current to constitute the relay of a high-set setting and the relay of a low definite value, wherein

The operation equation of described high-set setting relay is as follows:

$\mathrm{\Σ\Δ}{i}_{\mathrm{\Σ}}^2\left(t\right)>-C_1\mathrm{\Σ\Δ}{i}_M\left(t\right)\mathrm{\Δ}{i}_{\mathrm{\Σ}-M}\left(t\right)+{(\mathrm{\ρ}\·I_e)}^{2}N+C_2\mathrm{\Δ}{i}_{\mathrm{\Σ}}^2{\left(t\right)}_{\mathrm{MAX}}---\left(1\right)$

The operation equation of described low definite value relay is as follows:

∑Δi _M(t)Δi _∑-M(t)＞C ₃I _e ²N+C ₄|[Δi _M(t)Δi _∑-M(t)]| _MAX(2)

In the formula: N is a cycle sampling number;

C ₁, C ₂, C ₃, C ₄Be constant, determine that according to distinguishing internal fault and external area error span, its span are between 1～10.

I _eBe the transformer rated current;

$\mathrm{\ρ}=\mathrm{\η}-3\cos \frac{\mathrm{\π}}{20\mathrm{ms}}t,$ η carries out value according to " the high-rating generator transformer relay protecting is adjusted and calculated guide rule ";

Δ i _∑ ²(t) _MAXMaximum for transformer suddenly-change sampling value differential current square;

[Δ i _M(t) Δ i _∑-M(t)] | _MAXMaximum product for " maximum in each pleurapophysis variable current sampling data of transformer " and " other pleurapophysis variable current sampling data sum of transformer ";

Δ i _∑ ²(t) _MAXThe order of severity that has reflected fault, [Δ i _M(t) Δ i _∑-M(t)] | _MAXThe character that has reflected fault.When described high-set setting actuating of relay equation satisfies, when the dissatisfied and described low definite value actuating of relay equation of perhaps described high-set setting actuating of relay equation satisfies, described suddenly-change sampling value transformer differential relay action.

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