CN103633630A - Protection method for identifying fault braches based on zero-sequence active ratio - Google Patents

Abstract

The invention relates to a protection method for identifying fault braches based on the zero-sequence active ratio. The method includes: collecting bus voltage U1 and branch current I1 of a branch 1, collecting bus voltage U2 and branch current I2 of a branch 2, and collecting neutral point current I0 of a low-voltage side; calculating zero-sequence voltage U10 and zero-sequence current I10 of the branch 1; calculating zero-sequence voltage U20 and zero-sequence current I20 of the branch 2; calculating zero-sequence active power P1 of the branch 1, and calculating zero-sequence active power P2 of the branch 2; if P1>3P2, determining that earth fault happens to the branch 1, sending a tripping command to a circuit breaker QF1, if P2>3P1, considering that earth fault happens to the branch 2, and sending a tripping command to a circuit breaker QF2; otherwise, considering that fault happens to both the branch 1 and the branch 2, and simultaneously sending tripping commands to the circuit breakers QF1 and QF2. By the method, the problem that the two branches on the low-voltage side of a low-resistance earthing transformer trip non-selectively is solved, and reliability of mains supply is improved.

Description

A kind of guard method that has work ratio identification fault branch based on zero sequence

Technical field

The present invention relates to relay protection of power system and automatic field, be specifically related to a kind of zero-sequence protection method.

Background technology

Domestic big city power distribution network adopts cable line more, for protection cable machinery, when certain root cable generation damage in insulation, dwindle fault incidence, adopt main transformer low-pressure side Neutral Point Through Low Resistance, while there is metallicity single phase ground fault in system, the electric current that current protection scheme provides with this circuit zero sequence CT for the protection of every line segregation is as this line-to-ground fault criterion, the zero-sequence current that main transformer standby zero-sequence current protection employing main transformer low-pressure side neutral point CT provides is simultaneously as failure criterion, the standby of line-to-ground fault and the protection of busbar grounding fault are done in the zero-sequenceprotection of main transformer low-pressure side, differential cooperation of employing time between two-stage protection.Along with distribution development is larger, every line load is more and more heavier, also higher to power supply reliability requirement, is the capacity-load ratio that reduces transformer, the outlet number of same main transformer power supply can not be too much, therefore occurs that main transformer low-pressure side has two branch switches to divide the situation for two sections of buses.

On main transformer low-pressure side zero-sequenceprotection setting principle, adopt main transformer branch 1 the low standby zero sequence overcurrent protection T1 time limit to excise low-side switch 1, low-side switch 2 is excised in the low standby zero sequence overcurrent protection T2 time limit by main transformer branch 2.If earth fault is in branch 2, the result Shi Xiantiao branch 1 of protection action, if fault is not eliminated, continues to jump branch 2, has so just caused the excision of two sections of bus non-selectivities, has expanded power failure range.

Summary of the invention

For solving the above-mentioned problems in the prior art, the invention discloses a kind of guard method that has work ratio identification fault branch based on zero sequence.

The present invention specifically by the following technical solutions.

Based on zero sequence, have a guard method for work ratio identification fault branch, be applicable to the Fault Identification of low resistance grounding step down side two branches, it is characterized in that, described guard method is according to the size identification earth fault branch of two branch's zero sequence active power.

Said method comprising the steps of:

(1) gather busbar voltage U1 and the branch current I1 of described grounding transformer low-pressure side branch 1, gather busbar voltage U2 and the branch current I2 of branch 2, gather low-pressure side neutral point current I0;

(2) calculate residual voltage phasor U10 and the zero-sequence current phasor I10 of described branch 1;

$U10=\frac{U1a+U1b+U1c}{3}$

$I10=\frac{I1a+I1b+I1c}{3}$

Wherein: U1a represents branch's 1 bus a phase voltage phasor, U1b represents branch's 1 bus b phase voltage phasor, and U1c represents branch's 1 bus c phase voltage phasor; I1a represents branch's 1 bus a phase current phasor, and I1b represents branch's 1 bus b phase current phasor, and I1c represents branch's 1 bus c phase current phasor;

(3) the residual voltage phasor U20 of Branch Computed 2 and zero-sequence current phasor I20;

$U20=\frac{U2a+U2b+U2c}{3}$

$I20=\frac{I2a+I2b+I2c}{3}$

Wherein: U2a represents branch's 2 bus a phase voltage phasors, U2b represents branch's 2 bus b phase voltage phasors, and U2c represents branch's 2 bus c phase voltage phasors; I2a represents branch's 2 bus a phase current phasors, and I2b represents branch's 2 bus b phase current phasors, and I2c represents branch's 2 bus c phase current phasors.

(4) the zero sequence active power P1 of Branch Computed 1, the zero sequence active power P2 of Branch Computed 2;

Wherein: U10 represents branch's 1 residual voltage phasor,

the conjugation that represents branch's 1 zero-sequence current phasor; U20 represents branch's 2 residual voltage phasors, the conjugation that represents branch's 2 zero-sequence current phasors; Re represents to get the real part of phasor;

(5) when low-pressure side neutral point current I0 is greater than the zero-sequence current definite value of setting and time delay when setting time limit T, according to homopolar power size identification fault branch, if P1>3P2, regard as branch 1 earth fault occurs, send out trip signal to the bus circuit breaker Q F1 of branch 1, if P2>3P1 thinks that the bus circuit breaker Q F2 of 2 generation earth fault ，Gei branches 2 of branch sends out trip signal; Otherwise think that branch road 1 and branch road 2 all break down, send trip signal to bus circuit breaker Q F1 and QF2 simultaneously.

The present invention can correctly identify earth fault branch by the size of zero sequence active power, has solved the problem of low resistance grounding step down side two branches non-selectivity tripping operations, has improved the reliability of mains supply.

Accompanying drawing explanation

Fig. 1 is low resistance grounding step down side mode of connection schematic diagram;

Fig. 2 the present invention is based on the guard method flow chart that zero sequence has work ratio identification fault branch.

Embodiment

Below in conjunction with accompanying drawing and example, the present invention is described in further detail.

Be illustrated in figure 1 low resistance grounding main transformer low-pressure side mode of connection schematic diagram, step down side Neutral Point Through Low Resistance, current transformer I0 measures neutral point current.Step down side is received branch's 1 bus through circuit breaker Q F1, through circuit breaker Q F2, receives branch's 2 buses.Voltage transformer U1 measurement branches 1 busbar voltage, voltage transformer U2 measurement branches 2 busbar voltages, current transformer I1 measurement branches 1 electric current, current transformer I2 measurement branches 2 electric currents.

Be the guard method flow chart that has work ratio identification fault branch based on zero sequence disclosed by the invention as shown in Figure 2, described guard method comprises the following steps:

Step 1: the busbar voltage U1 that gathers branch 1 with voltage transformer, Current Transformer gathers branch current I1, with voltage transformer, gather the busbar voltage U2 of branch 2, Current Transformer gathers branch current I2, and Current Transformer gathers low-pressure side neutral point current I0(monophase current);

The secondary winding of current transformer, voltage transformer is linked in microcomputer protecting device, by AD, gathers and obtain the sampled value sequence that is sampled electric signal, by Fourier algorithm, calculate the phasor value of above-mentioned voltage and current sample value sequence.

Step 2: the residual voltage phasor U10 of Branch Computed 1 and zero-sequence current phasor I10:

$U10=\frac{U1a+U1b+U1c}{3}$

$I10=\frac{I1a+I1b+I1c}{3}$

Wherein: U1a represents branch's 1 bus a phase voltage phasor, U1b represents branch's 1 bus b phase voltage phasor,

U1c represents branch's 1 bus c phase voltage phasor; I1a represents branch's 1 bus a phase current phasor, and I1b represents minute

Prop up 1 bus b phase current phasor, I1c represents branch's 1 bus c phase current phasor.

Step 3: the residual voltage phasor U20 of Branch Computed 2 and zero-sequence current phasor I20;

$U20=\frac{U2a+U2b+U2c}{3}$

$I20=\frac{I2a+I2b+I2c}{3}$

Wherein: U2a represents branch's 2 bus a phase voltage phasors, U2b represents branch's 2 bus b phase voltage phasors,

U2c represents branch's 2 bus c phase voltage phasors; I2a represents branch's 2 bus a phase current phasors, and I2b represents minute

Prop up 2 bus b phase current phasors, I2c represents branch's 2 bus c phase current phasors.

Step 4: the zero sequence active power P1 of Branch Computed 1, the zero sequence active power P2 of Branch Computed 2;

Wherein: U10 represents branch's 1 residual voltage phasor, and I10 represents the conjugation of branch's 1 zero-sequence current phasor; U20

Represent branch's 2 residual voltage phasors, I20 represents the conjugation of branch's 2 zero-sequence current phasors; Re represents to get phasor

Real part.

Step 5: the zero-sequence current definite value (being generally 120A to 200A) and the time delay that are greater than setting when neutral point electric current I 0 are generally 0.5S to 1.0 second to setting time limit T() time, according to homopolar power size identification fault branch tripping branch circuit breaker, if P1>3P2, regard as branch 1 earth fault occurs, send out trip signal to circuit breaker Q F1, if P2>3P1 thinks that earth fault occurs in branch 2, send out trip signal to circuit breaker Q F2, otherwise think that branch road 1 and branch road 2 all break down, send trip signal to circuit breaker Q F1 and QF2 simultaneously.

Claims (3)

1. based on zero sequence, have a guard method for work ratio identification fault branch, be applicable to the Fault Identification of low resistance grounding step down side two branches, it is characterized in that, described guard method is according to the size identification earth fault branch of two branch's zero sequence active power.

2. guard method according to claim 1, is characterized in that, described guard method comprises the following steps:

(1) gather busbar voltage U1 and the branch current I1 of described grounding transformer low-pressure side branch 1, gather busbar voltage U2 and the branch current I2 of branch 2, gather low-pressure side neutral point current I0;

(2) calculate residual voltage phasor U10 and the zero-sequence current phasor I10 of described branch 1;

$U10=\frac{U1a+U1b+U1c}{3}$

$I10=\frac{I1a+I1b+I1c}{3}$

Wherein: U1a represents branch's 1 bus a phase voltage phasor, U1b represents branch's 1 bus b phase voltage phasor, and U1c represents branch's 1 bus c phase voltage phasor; I1a represents branch's 1 bus a phase current phasor, and I1b represents branch's 1 bus b phase current phasor, and I1c represents branch's 1 bus c phase current phasor;

(3) the residual voltage phasor U20 of Branch Computed 2 and zero-sequence current phasor I20;

$U20=\frac{U2a+U2b+U2c}{3}$

$I20=\frac{I2a+I2b+I2c}{3}$

Wherein: U2a represents branch's 2 bus a phase voltage phasors, U2b represents branch's 2 bus b phase voltage phasors, and U2c represents branch's 2 bus c phase voltage phasors; I2a represents branch's 2 bus a phase current phasors, and I2b represents branch's 2 bus b phase current phasors, and I2c represents branch's 2 bus c phase current phasors.

(4) the zero sequence active power P1 of Branch Computed 1, the zero sequence active power P2 of Branch Computed 2;

Wherein: U10 represents branch's 1 residual voltage phasor,

the conjugation that represents branch's 1 zero-sequence current phasor; U20 represents branch's 2 residual voltage phasors,

the conjugation that represents branch's 2 zero-sequence current phasors; Re represents to get the real part of phasor;

(5) when low-pressure side neutral point current I0 is greater than the zero-sequence current definite value of setting and time delay when setting time limit T, according to homopolar power size identification fault branch, if P1>3P2, regard as branch 1 earth fault occurs, send out trip signal to the bus circuit breaker Q F1 of branch 1, if P2>3P1 thinks that the bus circuit breaker Q F2 of 2 generation earth fault ，Gei branches 2 of branch sends out trip signal; Otherwise think that branch road 1 and branch road 2 all break down, send trip signal to bus circuit breaker Q F1 and QF2 simultaneously.

3. guard method according to claim 2, is characterized in that:

In step (5), described zero-sequence current definite value is 120A to 200A, and described setting time limit T is 0.5S to 1.0 second.

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