CN104201658A

CN104201658A - Power line differential protection method based on virtual brake current

Info

Publication number: CN104201658A
Application number: CN201410476013.6A
Authority: CN
Inventors: 柳焕章; 王兴国; 周泽昕; 姜宪国
Original assignee: State Grid Corp of China SGCC; China Electric Power Research Institute Co Ltd CEPRI
Current assignee: State Grid Corp of China SGCC; State Grid Zhejiang Electric Power Co Ltd; China Electric Power Research Institute Co Ltd CEPRI
Priority date: 2014-09-17
Filing date: 2014-09-17
Publication date: 2014-12-10
Anticipated expiration: 2034-09-17
Also published as: CN104201658B

Abstract

The invention provides a power line differential protection method based on virtual brake current. The method includes the steps of I, acquiring bilateral current values of a power line and subjecting the bilateral current values to low pass filtering; II, performing Fourier transform to obtain phasors m and n; III, subjecting the phasors m and n to capacitance-current compensation; and IV, constructing virtual current, determining a differential protection basis criterion according to the virtual current, and judging whether differential protection acts or not. The method has the advantages that the differential protection criterion is well adaptive, highly sensitive to internal faults, insusceptible to load current and high in transition resistance; in case of external faults, protection is reliable and idle.

Description

The differential guard method of a kind of transmission line based on virtual stalling current

Technical field

The present invention relates to a kind of method of field of relay protection in power, specifically relate to the differential guard method of a kind of transmission line based on virtual stalling current.

Background technology

Current differential protection, as the main protection of circuit, is used widely in 220kV and above circuit.The phasor of the general access line of the braking amount both sides electric current of transmission line differential current protection is poor, but it is larger affected by load current, and in heavy load situation in generating region when high resistive fault, the sensitivity of current differential protection, exists the risk of tripping.

In prior art, current differential protection adopts ratio brake, for braking amount; when restraint coefficient is chosen time less than normal; may cause external area error time, protect malfunction, reliability decrease, and in the time that restraint coefficient is excessive, affect the sensitivity of differential protection in the time of internal fault.The braking amount of choosing current differential protection is significant for improving protective value, the sensitivity of protecting can improve troubles inside the sample space time, and while ensureing external area error, current differential protection is failure to actuate simultaneously.

Therefore, need to provide a kind of current differential protection braking amount selection scheme with adaptation function.

Summary of the invention

For overcoming above-mentioned the deficiencies in the prior art, the invention provides the differential guard method of a kind of transmission line based on virtual stalling current.

Realizing the solution that above-mentioned purpose adopts is:

The differential guard method of transmission line based on virtual stalling current, its improvements are: said method comprising the steps of:

I, obtain the current value of described transmission line both sides and it is carried out to low-pass filtering;

II, carry out Fourier transform, obtain phasor

III, to described phasor carry out condenser current compensation;

IV, constructing virtual electric current, determine differential protection criterion according to described virtual current, judges whether differential protection moves.

Further, described step IV comprises the following steps:

S401, determine the actuating quantity of described differential protection, determine the braking amount of described differential protection according to described virtual current;

S402, determine described differential protection criterion, judge according to described differential protection criterion whether differential protection moves, when meeting described differential protection criterion, differential protection action, otherwise differential protection is failure to actuate.

Further, in described step S401, described actuating quantity is wherein, be respectively described transmission line both sides electric current phasor value.

Further, in described step S401, determine that described braking amount comprises the following steps:

Step 1, according to described phasor build virtual current

Step 2, determine described braking amount according to described virtual current

In formula, be respectively described transmission line both sides electric current phasor value; for braking amount; K is restraint coefficient; for getting with the greater between the two, for getting with smaller between the two, for corresponding electric current phasor, for corresponding electric current phasor, for corresponding electric current phasor.

Further, in described step S402, determine described differential protection criterion as shown in the formula:

| {\overset{\cdot}{I}}_{m} + {\overset{\cdot}{I}}_{n} | >

K | \frac{\min (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)}{\max (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)} {\overset{\cdot}{I}}_{\max} - {\overset{\cdot}{I}}_{\min} |,

Wherein, for actuating quantity, for described braking amount;

Judge whether described differential protection criterion meets, if meet differential protection action, otherwise described differential protection is failure to actuate.

Further, if circuit in the time of normal condition or external area error, differential protection is failure to actuate;

If circuit is in the time of troubles inside the sample space, if described actuating quantity is greater than described braking amount, differential protection action; If described actuating quantity is less than described braking amount, differential protection is failure to actuate.

Compared with prior art, the present invention has following beneficial effect:

1, current differential protection criterion provided by the invention has good adaptability, and troubles inside the sample space is highly sensitive, not affected by load current, and resistance to transition resistance ability is strong; When external area error, protection is reliably failure to actuate.

2, the full current differential protection criterion total with prior art compare, when troubles inside the sample space, the criterion actuating quantity that existing criterion and the present invention propose identical, and the criterion braking amount that the present invention proposes existing criterion when restraint coefficient identical (K=k), braking amount of the present invention so the criterion that the present invention proposes is highly sensitive in existing criterion.

3, the full current differential protection criterion total with prior art when external area error, work as K=k, the criterion that the present invention proposes has identical reliability with existing criterion; In the time of K > k, the criterion reliability that the present invention proposes is better than existing criterion, can not reduce the sensitivity of the criterion of the present invention's proposition simultaneously.

4, transmission line current differential protection provided by the invention builds braking amount based on virtual current; troubles inside the sample space is highly sensitive in existing differential protection criterion; can quick acting in the time of high resistance ground, when external area error, reliability is better than existing current differential protection criterion.

5, transmission line current differential protection criterion provided by the invention is adjusted without carrying out outside, automatically realizes by device internal processes, and self adaptation regulates the braking amount of protection, reaches quick acting in the time of troubles inside the sample space, when external area error, is reliably failure to actuate.

Brief description of the drawings

Fig. 1 is the differential protection flow chart of the transmission line based on virtual stalling current of the present invention;

Fig. 2 is faulty line schematic diagram in the present embodiment;

Fig. 3 is the differential protection action phasor diagram of troubles inside the sample space in the present invention;

Fig. 4 is the differential protection action phasor diagram of external area error in the present invention;

Relatively schematic diagram of differential protection braking amount of the present invention and existing differential protection braking amount when Fig. 5 is troubles inside the sample space.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

As shown in Figure 1; Fig. 1 is the differential protection flow chart of the transmission line based on virtual stalling current of the present invention; the invention provides the differential guard method of a kind of transmission line; by the electric current of alternative route both sides; constructing virtual electric current; this electric current has retained the amplitude information of phase information and the small electric stream side of larger electric current side simultaneously, utilizes virtual current and small electric stream to form braking amount.The differential protection of transmission line of the present invention can self adaptation adjustment the performance of protection, there is good adaptivity, under the identical condition of external area error reliability, when troubles inside the sample space, criterion sensitivity and resistance to transition resistance ability are better than existing criterion.Specifically comprise the following steps:

The current value of step 1, collection transmission line both sides also carries out low-pass filtering to it, and low-pass filtering obtains I _mand I (k) _n(k);

Step 2, to I _mand I (k) _n(k) carry out Fourier transform, obtain electric current phasor

Step 3, to described phasor carry out condenser current compensation;

Step 4, judge according to differential protection criterion whether differential protection moves.

In step 2, to I _mand I (k) _n(k) carry out Fourier transform, Fourier transform formula is as follows:

\{\begin{matrix} a_{m} = \frac{1}{N} [2 Σ_{k = 1}^{N - 1} I_{m} (k) \sin (k \frac{2 π}{N})] \\ b_{m} = \frac{1}{N} [I_{m} (0) + 2 Σ_{k = 1}^{N - 1} I_{m} (k) \cos (k \frac{2 π}{N}) + I_{m} (N)] \end{matrix}

\{\begin{matrix} a_{n} = \frac{1}{N} [2 Σ_{k = 1}^{N - 1} I_{n} (k) \sin (k \frac{2 π}{N})] \\ b_{n} = \frac{1}{N} [I_{n} (0) + 2 Σ_{k = 1}^{N - 1} I_{n} (k) \cos (k \frac{2 π}{N}) + I_{n} (N)] \end{matrix}

In formula, N is sampled point, gets 24; I _m(k), I _n(k) be respectively the current sampling data after low-pass filtering;

Press following formula and obtain electric current phasor amplitude and phase place:

\{\begin{matrix} I_{m} = \frac{\sqrt{a_{m}^{2} + b_{m}^{2}}}{\sqrt{2}} \\ α_{m} = \arctan \frac{b_{m}}{a_{m}} \end{matrix}, \{\begin{matrix} I_{m} = \frac{\sqrt{a_{n}^{2} + b_{n}^{2}}}{\sqrt{2}} \\ α_{n} = \arctan \frac{b_{n}}{a_{n}} \end{matrix}

In step 3, to phasor carry out condenser current compensation, condenser current compensation formula is:

{\overset{\cdot}{I}}_{m}^{'} = {\overset{\cdot}{I}}_{m} - {\overset{\cdot}{I}}_{c . m}, {\overset{\cdot}{I}}_{n}^{'} = {\overset{\cdot}{I}}_{n} - {\overset{\cdot}{I}}_{c . n}

Wherein,

{\overset{\cdot}{I}}_{c . m} = \frac{({\overset{\cdot}{U}}_{m} - {\overset{\cdot}{U}}_{0})}{- j 2 X_{c 1}} + \frac{{\overset{\cdot}{U}}_{0}}{- j 2 X_{c 0}}, {\overset{\cdot}{I}}_{c . n} = \frac{({\overset{\cdot}{U}}_{n} - {\overset{\cdot}{U}}_{0})}{- j 2 X_{c 1}} + \frac{{\overset{\cdot}{U}}_{0}}{- j 2 X_{c 0}},

be respectively transmission line both sides voltage phasor value; for protection installation place residual voltage; x _c1, X _c0for positive sequence capacitive reactance, zero sequence capacitive reactance.

Step 4, judge according to differential protection criterion whether differential protection moves.Specifically comprise the following steps:

S401, the actuating quantity of determining described differential protection and braking amount;

S402, determine described differential protection criterion, judge according to described differential protection criterion whether differential protection moves;

If when electric current is normal condition or external area error, differential protection is failure to actuate;

If when electric current is troubles inside the sample space, comparison amount and described braking amount, if described actuating quantity is greater than described braking amount, differential protection action; If described actuating quantity is less than described braking amount, differential protection is failure to actuate.

When troubles inside the sample space, described braking amount approaches 0, and described actuating quantity is greater than described braking amount, and differential protection action, excises fault fast; When external area error, described actuating quantity approaches 0, and described braking amount is greater than described actuating quantity, and described differential protection criterion is reliable, and differential protection is failure to actuate.

In step S401, calculate determine for actuating quantity, be respectively described transmission line both sides electric current phasor value.

In step S401, determine described braking amount by following formula:

In formula, be respectively described transmission line both sides electric current phasor value; for braking amount; K is restraint coefficient, generally gets 0<K<1; for getting with the greater between the two, for getting with smaller between the two, for corresponding electric current phasor, for corresponding electric current phasor, for corresponding electric current phasor.

In the present embodiment, setting K is 0.4, relatively with

When

| {\overset{\cdot}{I}}_{m} + {\overset{\cdot}{I}}_{n} | > 0.4 | \frac{\min (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)}{\max (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)} {\times \overset{\cdot}{I}}_{\max} - {\overset{\cdot}{I}}_{\min} |

Time, current differential protection action;

When

| {\overset{\cdot}{I}}_{m} + {\overset{\cdot}{I}}_{n} | < 0.4 | \frac{\min (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)}{\max (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)} {\times \overset{\cdot}{I}}_{\max} - {\overset{\cdot}{I}}_{\min} |

Time, current differential protection is failure to actuate.

Fig. 2 is faulty line schematic diagram in the present embodiment, E _m, E _nfor the equivalent power supply in circuit both sides, protection is arranged on 1 and 2 places, and the electric current that flows through protection 1 and 2 is respectively f1 is troubles inside the sample space point, and F2 is external area error point.

Fig. 3 is the differential protection action phasor diagram of troubles inside the sample space, when troubles inside the sample space, with between angle be less than 90 °, can find out, be greater than protection action.

Fig. 4 is the differential protection action phasor diagram of external area error, when external area error, with between angle be greater than 90 °, can find out, be less than protection is failure to actuate.

When Fig. 5 is troubles inside the sample space, relatively schematic diagram of differential protection braking amount of the present invention and existing differential protection braking amount, can find, when troubles inside the sample space, and the differential protection braking amount that the present invention proposes be significantly less than existing differential protection braking amount criterion is highly sensitive in existing criterion.

Finally should be noted that: above embodiment is only for illustrating the application's technical scheme but not restriction to its protection range; although the application is had been described in detail with reference to above-described embodiment; those of ordinary skill in the field are to be understood that: those skilled in the art still can carry out all changes, revise or be equal to replacement to the embodiment of application after reading the application; but these change, revise or be equal to replacement, within the claim protection range all awaiting the reply in application.

Claims

1. the differential guard method of the transmission line based on virtual stalling current, is characterized in that: said method comprising the steps of:

II, carry out Fourier transform, obtain phasor

III, to described phasor carry out condenser current compensation;

2. the method for claim 1, is characterized in that: described step IV comprises the following steps:

3. method as claimed in claim 2, is characterized in that: in described step S401, described actuating quantity is wherein, be respectively described transmission line both sides electric current phasor value.

4. method as claimed in claim 2, is characterized in that: in described step S401, determine that described braking amount comprises the following steps:

Step 1, according to described phasor build virtual current

5. method as claimed in claim 2, is characterized in that: in described step S402, determine described differential protection criterion as shown in the formula:

| {\overset{\cdot}{I}}_{m} + {\overset{\cdot}{I}}_{n} | > K | \frac{\min (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)}{\max (| {\overset{\cdot}{I}}_{m} |, | {\overset{\cdot}{I}}_{n} |)} {\overset{\cdot}{I}}_{\max} - {\overset{\cdot}{I}}_{\min} |,

Wherein, for actuating quantity, for described braking amount;

6. method as claimed in claim 2, is characterized in that: if circuit in the time of normal condition or external area error, differential protection is failure to actuate;