CN106771812A - A kind of recognition methods of transformer current transformer disconnection and device - Google Patents

Abstract

The present invention relates to a kind of recognition methods of transformer current transformer disconnection and device, broken string recognition methods therein includes：Judge whether to meet the entry condition that current transformer circuit supervision fail differentiates；If meeting entry condition, judge whether to meet broken string criterion；If meeting all broken string criterions, transformer this side current transformer circuit supervision fail is judged.The present invention is combined by by electric current criterion and voltage criterion, can accurately judge whether transformer side current transformer breaks, and is whether transformer differential protection acts offer foundation.

Description

A kind of recognition methods of transformer current transformer disconnection and device

Technical field

The present invention relates to a kind of recognition methods of transformer current transformer disconnection and device, belong to relay protection of power system Technical field.

Background technology

《Electrical safe working order》Regulation, powered secondary loop of mutual inductor forbids open circuit when working.Large-sized unit And the current transformer that extra-high tension unit is used, the Secondary Winding number of turn is more, and open-circuit voltage is very high.Secondary voltage higher not only may be used Can be damaged the insulation of Secondary Winding and secondary device, and iron core can be made to be burnt because of overheat, or even threaten person peace Entirely.

In addition, for transformer differential protection, when there is transformer current transformer disconnection, occurring in loop larger Material unaccounted for stream, cause differential protection malfunction.Therefore, identify whether transformer current transformer breaks exactly, can be with For whether transformer differential protection acts offer foundation.

The content of the invention

It is accurate for solving it is an object of the invention to provide a kind of recognition methods of transformer current transformer disconnection and device Judge the problem whether transformer current transformer breaks.

In order to solve the above technical problems, the invention provides a kind of transformer current transformer disconnection recognition methods, including Following scheme：

Method scheme one：Comprise the following steps

Step 1, judges whether to meet the entry condition of current transformer circuit supervision fail differentiation；

Step 2, if meeting the entry condition, judges following broken string criterion, and the broken string differentiates bar Part is：

(1) this side three-phase phase current of transformer is not zero before broken string differentiation starts, and broken string differentiates transformer sheet after startup Side three-phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero Sequence electric current and negative-sequence current；

(3) this side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage is prominent Variable, residual voltage and residual voltage Sudden Changing Rate；

Step 3, if meeting above-mentioned all broken string criterions, judges transformer this side current transformer circuit supervision fail.

Method scheme two：On the basis of method scheme one, the trip bar that current transformer circuit supervision fail described in step 1 differentiates Part is：

I_Φ1(t-nT)-I_Φ1(t) ＞ I_SET1

Wherein, n is a positive integer, several cycles before indication transformer this side current cycle of three-phase phase current Number, I_Φ1T () is the three-phase phase current magnitude of this side of transformer when broken string differentiates startup, I_Φ1(t-nT) start for broken string differentiates When transformer this side n Zhou Boqian three-phase phase current magnitude, I_SET1It is this side electric current threshold value of transformer, span is 0.06I_N~0.08I_N, I_NIt is the secondary rated current of this side current transformer of transformer.

Method scheme three, four：Respectively on the basis of method scheme one or two, step 2 interrupt line criterion (1) is sentenced Other formula is：

Wherein, K₁It is constant, span is 1.2~1.4, I_Φ1.min(t-nT) it is transformer sheet when broken string differentiates to be started Minimum phase current magnitude in the three-phase current of the Zhou Boqian of side n；

Broken string criterion (2) discrimination formula be：

Wherein, I_Φ2T () is the three-phase phase current magnitude of other sides of transformer when broken string differentiates startup, I_Φ2(t-nT) it is disconnected The three-phase phase current magnitude of transformer other sides n Zhou Boqian when line differentiates startup, | I_Φ2(t)-I_Φ2(t-nT) | for broken string differentiates The three-phase of transformer other sides n Zhou Boqian when the three-phase phase current magnitude of other sides of transformer differentiates startup with broken string during startup The absolute value of the difference of phase current magnitude, I₂(t) and 3I₀T () is respectively the negative phase-sequence electricity of other sides of transformer when broken string differentiates startup Stream amplitude and zero-sequence current amplitude, I_SET2It is other side electric current threshold values of transformer, span is 0.08I_N~0.2I_N；

Broken string criterion (3) discrimination formula be：

Wherein, U_ΦT () is the three-phase phase voltage amplitude of this side of transformer or other sides when broken string differentiates startup, U_Φ(t-nT) It is the three-phase phase voltage amplitude of n Zhou Boqian of this side of transformer or other sides when broken string differentiates to be started, | U_Φ(t)-U_Φ(t-nT) | it is this side of transformer when the three-phase phase voltage amplitude and broken string of this side of transformer when broken string differentiates to be started or other sides differentiate to be started Or the absolute value of the difference of the three-phase phase voltage amplitude of n Zhou Boqian of other sides, 3U₀Transformation when () starts for broken string differentiates t This side of device or the residual voltage amplitude of other sides, 3U₀(t-nT) it is n that broken string differentiates this side of transformer or other sides when starting The residual voltage amplitude of Zhou Boqian, | 3U₀(t)-3U₀(t-nT) | for broken string differentiate start when this side of transformer or other sides zero The difference of the residual voltage amplitude of n Zhou Boqian of this side of transformer or other sides when sequence voltage amplitude differentiates startup with broken string Absolute value, U_SET1It is Three-Phase Transformer phase voltage threshold value, span is 0.1U_N~0.2U_N, U_SET2It is transformer zero sequence electricity Pressure gate threshold value, span is 0.02U_N~0.1U_N, U_NIt is bis- specified phase voltages of transformer PT.

Method scheme five, six：Respectively on the basis of method scheme three or four, n is equal to 2.

Present invention also offers a kind of transformer current transformer disconnection identifying device, including following scheme：

Device scheme one：Including

The unit of the entry condition for judging whether to meet current transformer circuit supervision fail differentiation；

If for meeting the entry condition, the unit judged following broken string criterion, the broken string is sentenced Other condition is：

(1) this side three-phase phase current of transformer is not zero before broken string differentiation starts, and broken string differentiates transformer sheet after startup Side three-phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero Sequence electric current and negative-sequence current；

(3) this side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage is prominent Variable, residual voltage and residual voltage Sudden Changing Rate；

If for meeting above-mentioned all broken string criterions, judging the unit of this side current transformer circuit supervision fail of transformer.

Device scheme two：On the basis of device scheme one, the entry condition that the current transformer circuit supervision fail differentiates is：

I_Φ1(t-nT)-I_Φ1(t) ＞ I_SET1

Wherein, n is a positive integer, several cycles before indication transformer this side current cycle of three-phase phase current Number, I_Φ1T () is the three-phase phase current magnitude of this side of transformer when broken string differentiates startup, I_Φ1(t-nT) start for broken string differentiates When transformer this side n Zhou Boqian three-phase phase current magnitude, I_SET1It is this side electric current threshold value of transformer, span is 0.06I_N~0.08I_N, I_NIt is the secondary rated current of this side current transformer of transformer.

Device scheme three, four：Respectively on the basis of device scheme one or two, the discrimination formula of broken string criterion (1) For：

Wherein, K₁It is constant, span is 1.2~1.4, I_Φ1.min(t-nT) it is transformer sheet when broken string differentiates to be started Minimum phase current magnitude in the three-phase current of the Zhou Boqian of side n；

Broken string criterion (2) discrimination formula be：

Wherein, I_Φ2T () is the three-phase phase current magnitude of other sides of transformer when broken string differentiates startup, I_Φ2(t-nT) it is disconnected The three-phase phase current magnitude of transformer other sides n Zhou Boqian when line differentiates startup, | I_Φ2(t)-I_Φ2(t-nT) | for broken string differentiates The three-phase of transformer other sides n Zhou Boqian when the three-phase phase current magnitude of other sides of transformer differentiates startup with broken string during startup The absolute value of the difference of phase current magnitude, I₂(t) and 3I₀T () is respectively the negative phase-sequence electricity of other sides of transformer when broken string differentiates startup Stream amplitude and zero-sequence current amplitude, I_SET2It is other side electric current threshold values of transformer, span is 0.08I_N~0.2I_N；

Broken string criterion (3) discrimination formula be：

Wherein, U_ΦT () is the three-phase phase voltage amplitude of this side of transformer or other sides when broken string differentiates startup, U_Φ(t-nT) It is the three-phase phase voltage amplitude of n Zhou Boqian of this side of transformer or other sides when broken string differentiates to be started, | U_Φ(t)-U_Φ(t-nT) | it is this side of transformer when the three-phase phase voltage amplitude and broken string of this side of transformer when broken string differentiates to be started or other sides differentiate to be started Or the absolute value of the difference of the three-phase phase voltage amplitude of n Zhou Boqian of other sides, 3U₀Transformation when () starts for broken string differentiates t This side of device or the residual voltage amplitude of other sides, 3U₀(t-nT) it is n that broken string differentiates this side of transformer or other sides when starting The residual voltage amplitude of Zhou Boqian, | 3U₀(t)-3U₀(t-nT) | for broken string differentiate start when this side of transformer or other sides zero The difference of the residual voltage amplitude of n Zhou Boqian of this side of transformer or other sides when sequence voltage amplitude differentiates startup with broken string Absolute value, U_SET1It is Three-Phase Transformer phase voltage threshold value, span is 0.1U_N~0.2U_N, U_SET2It is transformer zero sequence electricity Pressure gate threshold value, span is 0.02U_N~0.1U_N, U_NIt is bis- specified phase voltages of transformer PT.

Device scheme five, six：Respectively on the basis of device scheme three or four, n is equal to 2.

The beneficial effects of the invention are as follows：

By differentiating the situation of change of this side of transformer and other side three-phase phase currents and three-phase phase voltage, can accurately sentence Break and transformer this side current transformer and whether break, be whether transformer differential protection acts offer foundation.

Brief description of the drawings

Fig. 1 is 220kV transformer main electrical scheme schematic diagrames；

Fig. 2 is the flow chart of transformer current transformer disconnection recognition methods.

Specific embodiment

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

By taking 220kV transformers as an example, main electrical scheme schematic diagram is as shown in Figure 1.High voltage side of transformer, medium voltage side during normal operation With low-pressure side breaker closing, high voltage side current transformer and voltage transformer are respectively TA1 and TV1, medium voltage side Current Mutual Inductance Device and voltage transformer are respectively TA2 and TV2, and low-pressure side current transformer and voltage transformer are respectively TA3 and TV3.Normally During operation, if broken string TA1 occurs and difference stream is more than differential protection starting current definite value, transform er differential protection jump is will result in Lock.

By taking high voltage side of transformer as an example, the flow chart of transformer current transformer disconnection recognition methods is as shown in Fig. 2 specific Comprise the following steps：

Step 1, judges whether high voltage side of transformer meets the entry condition of current transformer circuit supervision fail differentiation, entry condition For：

I_Φ1(t-nT)-I_Φ1(t) ＞ I_SET1

Wherein, n is a positive integer, several cycles before the current cycle of three-phase phase current of indication transformer high-pressure side Number, I_Φ1The on high-tension side three-phase phase current magnitude of transformer, I when () starts for broken string differentiates t_Φ1(t-nT) for broken string differentiates The three-phase phase current magnitude of n Zhou Boqian of high voltage side of transformer, I during startup_SET1It is high voltage side of transformer electric current threshold value, value Scope is 0.06I_N~0.08I_N, I_NIt is the secondary rated current of high voltage side of transformer current transformer.

If high voltage side of transformer is unsatisfactory for the entry condition of current transformer circuit supervision fail differentiation, high voltage side of transformer electricity is judged Current transformer does not break.

Step 2, judges whether to meet following broken string criterion：

(1) high voltage side of transformer three-phase phase current is not zero before broken string differentiation starts, and broken string differentiates transformer after startup High-pressure side three-phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero Sequence electric current and negative-sequence current；

(3) high voltage side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage Sudden Changing Rate, residual voltage and residual voltage Sudden Changing Rate.

Broken string criterion (1) discrimination formula be：

Wherein, K₁It is constant, span is 1.2~1.4, I_Φ1.min(t-nT) transformer is high when differentiating startup for broken string Press the minimum phase current magnitude in the three-phase current of the Zhou Boqian of side n.

Broken string criterion (2) discrimination formula be：

Wherein, I_Φ2The three-phase phase current width of other sides (medium voltage side or low-pressure side) of transformer when () starts for broken string differentiates t Value, I_Φ2(t-nT) it is the three-phase phase current of n Zhou Boqian of other side (medium voltage side or low-pressure sides) of transformer when broken string differentiates to be started Amplitude, | I_Φ2(t)-I_Φ2(t-nT) | for the three-phase phase current magnitude of other sides of transformer differentiates with broken string when broken string differentiates to be started The absolute value of the difference of the three-phase phase current magnitude of transformer other sides n Zhou Boqian, I during startup₂(t) and 3I₀T () is broken respectively The negative-sequence current amplitude and zero-sequence current amplitude of other sides of transformer, I when line differentiates startup_SET2It is other side electric current doors of transformer Threshold value, span is 0.08I_N~0.2I_N。

If the electric current of any side is unsatisfactory for the discrimination formula of above-mentioned broken string criterion (2) in medium voltage side and low-pressure side When, then judge to be unsatisfactory for broken string criterion (2).

Broken string criterion (3) discrimination formula be：

Wherein, U_ΦT () is the three-phase phase voltage amplitude of high voltage side of transformer or other sides when broken string differentiates startup, U_Φ(t- NT) be broken string differentiate start when high voltage side of transformer or other sides n Zhou Boqian three-phase phase voltage amplitude, | U_Φ(t)-U_Φ (t-nT) | start time-varying for the three-phase phase voltage amplitude of high voltage side of transformer or other sides when broken string differentiates to be started differentiates with broken string The absolute value of the difference of the three-phase phase voltage amplitude of n Zhou Boqian of depressor high-pressure side or other sides, 3U₀T () differentiates for broken string The residual voltage amplitude of high voltage side of transformer or other sides, 3U during startup₀(t-nT) it is transformer high-voltage when broken string differentiates to be started The residual voltage amplitude of n Zhou Boqian of side or other sides, | 3U₀(t)-3U₀(t-nT) | for transformer is high when broken string differentiates to be started The zero of n Zhou Boqian of high voltage side of transformer or other sides when the residual voltage amplitude of pressure side or other sides differentiates startup with broken string The absolute value of the difference of sequence voltage amplitude, U_SET1It is Three-Phase Transformer phase voltage threshold value, span is 0.1U_N~0.2U_N, U_SET2It is transformer residual voltage threshold value, span is 0.02U_N~0.1U_N, U_NIt is bis- specified phase voltages of transformer PT.

It is, judging whether the voltage of high, medium and low three side of transformer is satisfied by sentencing for above-mentioned broken string criterion (3) Other formula, if the voltage of any side is unsatisfactory for the discrimination formula of broken string criterion (3), judgement is unsatisfactory for broken string and differentiates bar Part (3).

Step 3, if meeting above-mentioned all broken string criterions, judges high voltage side of transformer current transformer circuit supervision fail.

If it is determined that high voltage side of transformer current transformer circuit supervision fail, then send break alarm instruction, can be by the break alarm Instruction is sent to differential protection device, is whether differential protection acts offer reliable basis；The break alarm is instructed simultaneously is sent out Give warning device to be alarmed, point out maintenance personal's on-call maintenance.If thering is high voltage side of transformer to be unsatisfactory for any one to break During criterion, then judge that high voltage side of transformer current transformer does not break.

In the present embodiment, positive integer n is taken as 2, in the case where CT broken string discriminant accuracy is not influenceed, also dependent on Need to carry out appropriate value, such as 1,3,4 is equivalent.

Be combined for electric current criterion and voltage criterion by the transformer current transformer disconnection recognition methods in the present invention, can be accurate Really judge whether transformer side current transformer breaks, differential protection may malfunction after efficiently solving current transformer circuit supervision fail Problem.

Present invention also offers a kind of transformer current transformer disconnection identifying device, including：

The unit of the entry condition for judging whether to meet current transformer circuit supervision fail differentiation；

If for meeting the entry condition, the unit judged following broken string criterion, the broken string is sentenced Other condition is：

(1) this side three-phase phase current of transformer is not zero before broken string differentiation starts, and broken string differentiates transformer sheet after startup Side three-phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero Sequence electric current and negative-sequence current；

(3) this side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage is prominent Variable, residual voltage and residual voltage Sudden Changing Rate；

If for meeting above-mentioned all broken string criterions, judging the unit of this side current transformer circuit supervision fail of transformer.

Above-mentioned transformer current transformer disconnection identifying device, is actually built upon the knowledge of transformer current transformer disconnection A kind of computer solution in other method, i.e., a kind of software architecture, software can be run in protection equipment.Due to The introduction of enough complete displays is carried out to above-mentioned transformer current transformer disconnection recognition methods, therefore the broken string has been recognized and is filled Each unit is no longer described in detail in putting.

Claims (8)

1. a kind of transformer current transformer disconnection recognition methods, it is characterised in that comprise the following steps：

Step 1, judges whether to meet the entry condition of current transformer circuit supervision fail differentiation；

Step 2, if meeting the entry condition, judges following broken string criterion, and the broken string criterion is：

(1) this side three-phase phase current of transformer is not zero before broken string differentiation starts, and broken string differentiates this side three of transformer after startup Phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero sequence electricity Stream and negative-sequence current；

(3) this side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage Sudden Changing Rate, Residual voltage and residual voltage Sudden Changing Rate；

Step 3, if meeting above-mentioned all broken string criterions, judges transformer this side current transformer circuit supervision fail.

2. transformer current transformer disconnection recognition methods according to claim 1, it is characterised in that described in step 1 Current transformer circuit supervision fail differentiate entry condition be：

I_Φ1(t-nT)-I_Φ1(t) ＞ I_SET1

Wherein, n is a positive integer, the number of several cycles before indication transformer this side current cycle of three-phase phase current Mesh, I_Φ1T () is the three-phase phase current magnitude of this side of transformer when broken string differentiates startup, I_Φ1(t-nT) for when broken string differentiates to be started The three-phase phase current magnitude of transformer this side n Zhou Boqian, I_SET1It is this side electric current threshold value of transformer, span is 0.06I_N~0.08I_N, I_NIt is the secondary rated current of this side current transformer of transformer.

3. transformer current transformer disconnection recognition methods according to claim 1 and 2, it is characterised in that step 2 is interrupted The discrimination formula of line criterion (1) is：

$\left\{\begin{array}{c}{I}_{\mathrm{\&Phi;}1}\left(t\right)<K_1{I}_{\mathrm{\&Phi;}1}(t-nT)\\ I_{\mathrm{\&Phi;}1.\min }(t-nT)>I_{SET1}\end{array}\right.$

Wherein, K₁It is constant, span is 1.2~1.4, I_Φ1.min(t-nT) for this side of transformer n when broken string differentiates to be started Minimum phase current magnitude in the three-phase current of Zhou Boqian；

Broken string criterion (2) discrimination formula be：

$\left\{\begin{array}{c}|I_{\mathrm{\&Phi;}2}\left(t\right)-I_{\mathrm{\&Phi;}2}(t-nT)|<I_{SET1}\\ I_2\left(t\right)<I_{SET2}\\ 3I_0\left(t\right)<I_{SET2}\end{array}\right.$

Wherein, I_Φ2T () is the three-phase phase current magnitude of other sides of transformer when broken string differentiates startup, I_Φ2(t-nT) for broken string is sentenced Not Qi Dong when transformer other sides n Zhou Boqian three-phase phase current magnitude, | I_Φ2(t)-I_Φ2(t-nT) | start for broken string differentiates When other sides of transformer three-phase phase current magnitude differentiate that the three-phase of transformer other sides n Zhou Boqian when starting is mutually electric with broken string Flow the absolute value of the difference of amplitude, I₂(t) and 3I₀T () is respectively the negative-sequence current width of other sides of transformer when broken string differentiates startup Value and zero-sequence current amplitude, I_SET2It is other side electric current threshold values of transformer, span is 0.08I_N~0.2I_N；

Broken string criterion (3) discrimination formula be：

$\left\{\begin{array}{c}|U_{\mathrm{\&Phi;}}\left(t\right)-U_{\mathrm{\&Phi;}}(t-nT)|<U_{SET1}\\ |3U_0\left(t\right)-3U_0(t-nT)|<U_{SET2}\\ 3U_0\left(t\right)<U_{SET1}\end{array}\right.$

Wherein, U_ΦT () is the three-phase phase voltage amplitude of this side of transformer or other sides when broken string differentiates startup, U_Φ(t-nT) it is disconnected The three-phase phase voltage amplitude of n Zhou Boqian of this side of transformer or other sides when line differentiates startup, | U_Φ(t)-U_Φ(t-nT) | be Broken string differentiate start when this side of transformer or other sides three-phase phase voltage amplitude with broken string differentiate start when this side of transformer or The absolute value of the difference of the three-phase phase voltage amplitude of n Zhou Boqian of other sides, 3U₀Transformer when () starts for broken string differentiates t This side or the residual voltage amplitude of other sides, 3U₀(t-nT) be broken string differentiate when starting this side of transformer or n of other sides it is all The residual voltage amplitude of wavefront, | 3U₀(t)-3U₀(t-nT) | it is the zero sequence of this side of transformer or other sides when broken string differentiates to be started The difference of the residual voltage amplitude of n Zhou Boqian of this side of transformer or other sides is exhausted when voltage magnitude differentiates startup with broken string To value, U_SET1It is Three-Phase Transformer phase voltage threshold value, span is 0.1U_N~0.2U_N, U_SET2It is transformer residual voltage Threshold value, span is 0.02U_N~0.1U_N, U_NIt is bis- specified phase voltages of transformer PT.

4. transformer current transformer disconnection recognition methods according to claim 3, it is characterised in that n is equal to 2.

5. a kind of transformer current transformer disconnection identifying device, it is characterised in that including：

The unit of the entry condition for judging whether to meet current transformer circuit supervision fail differentiation；

If for meeting the entry condition, the unit judged following broken string criterion, the broken string differentiates bar Part is：

(1) this side three-phase phase current of transformer is not zero before broken string differentiation starts, and broken string differentiates this side three of transformer after startup Phase phase current does not increase；

(2) other side three-phase phase currents of transformer are not changed in when broken string differentiates startup, including difference of phase currents, zero sequence electricity Stream and negative-sequence current；

(3) this side of transformer and other side three-phase phase voltages are not changed in when broken string differentiates startup, including phase voltage Sudden Changing Rate, Residual voltage and residual voltage Sudden Changing Rate；

If for meeting above-mentioned all broken string criterions, judging the unit of this side current transformer circuit supervision fail of transformer.

6. transformer current transformer disconnection identifying device according to claim 5, it is characterised in that the Current Mutual Inductance Device broken string differentiate entry condition be：

I_Φ1(t-nT)-I_Φ1(t) ＞ I_SET1

Wherein, n is a positive integer, the number of several cycles before indication transformer this side current cycle of three-phase phase current Mesh, I_Φ1T () is the three-phase phase current magnitude of this side of transformer when broken string differentiates startup, I_Φ1(t-nT) for when broken string differentiates to be started The three-phase phase current magnitude of transformer this side n Zhou Boqian, I_SET1It is this side electric current threshold value of transformer, span is 0.06I_N~0.08I_N, I_NIt is the secondary rated current of this side current transformer of transformer.

7. the transformer current transformer disconnection identifying device according to claim 5 or 6, it is characterised in that broken string differentiates The discrimination formula of condition (1) is：

$\left\{\begin{array}{c}{I}_{\mathrm{\&Phi;}1}\left(t\right)<K_1{I}_{\mathrm{\&Phi;}1}(t-nT)\\ I_{\mathrm{\&Phi;}1.\min }(t-nT)>I_{SET1}\end{array}\right.$

Wherein, K₁It is constant, span is 1.2~1.4, I_Φ1.min(t-nT) for this side of transformer n when broken string differentiates to be started Minimum phase current magnitude in the three-phase current of Zhou Boqian；

Broken string criterion (2) discrimination formula be：

$\left\{\begin{array}{c}|I_{\mathrm{\&Phi;}2}\left(t\right)-I_{\mathrm{\&Phi;}2}(t-nT)|<I_{SET1}\\ I_2\left(t\right)<I_{SET2}\\ 3I_0\left(t\right)<I_{SET2}\end{array}\right.$

Wherein, I_Φ2T () is the three-phase phase current magnitude of other sides of transformer when broken string differentiates startup, I_Φ2(t-nT) for broken string is sentenced Not Qi Dong when transformer other sides n Zhou Boqian three-phase phase current magnitude, | I_Φ2(t)-I_Φ2(t-nT) | start for broken string differentiates When other sides of transformer three-phase phase current magnitude differentiate that the three-phase of transformer other sides n Zhou Boqian when starting is mutually electric with broken string Flow the absolute value of the difference of amplitude, I₂(t) and 3I₀T () is respectively the negative-sequence current width of other sides of transformer when broken string differentiates startup Value and zero-sequence current amplitude, I_SET2It is other side electric current threshold values of transformer, span is 0.08I_N~0.2I_N；

Broken string criterion (3) discrimination formula be：

$\left\{\begin{array}{c}|U_{\mathrm{\&Phi;}}\left(t\right)-U_{\mathrm{\&Phi;}}(t-nT)|<U_{SET1}\\ |3U_0\left(t\right)-3U_0(t-nT)|<U_{SET2}\\ 3U_0\left(t\right)<U_{SET1}\end{array}\right.$

Wherein, U_ΦT () is the three-phase phase voltage amplitude of this side of transformer or other sides when broken string differentiates startup, U_Φ(t-nT) it is disconnected The three-phase phase voltage amplitude of n Zhou Boqian of this side of transformer or other sides when line differentiates startup, | U_Φ(t)-U_Φ(t-nT) | be Broken string differentiate start when this side of transformer or other sides three-phase phase voltage amplitude with broken string differentiate start when this side of transformer or The absolute value of the difference of the three-phase phase voltage amplitude of n Zhou Boqian of other sides, 3U₀Transformer when () starts for broken string differentiates t This side or the residual voltage amplitude of other sides, 3U₀(t-nT) be broken string differentiate when starting this side of transformer or n of other sides it is all The residual voltage amplitude of wavefront, | 3U₀(t)-3U₀(t-nT) | it is the zero sequence of this side of transformer or other sides when broken string differentiates to be started The difference of the residual voltage amplitude of n Zhou Boqian of this side of transformer or other sides is exhausted when voltage magnitude differentiates startup with broken string To value, U_SET1It is Three-Phase Transformer phase voltage threshold value, span is 0.1U_N~0.2U_N, U_SET2It is transformer residual voltage Threshold value, span is 0.02U_N~0.1U_N, U_NIt is bis- specified phase voltages of transformer PT.

8. transformer current transformer disconnection identifying device according to claim 7, it is characterised in that n is equal to 2.