CN105743073A - Improved inverse time limit over-current protection method - Google Patents

Abstract

The invention discloses an improved inverse time limit over-current protection method. A measured impedance is calculated by voltage and current magnitudes collected at a protective installation position; the ratio of the measured impedance to a line impedance is utilized as an acceleration factor of protection time-delay action time; the action speed in an internal fault is accelerated; and the acceleration factor is subjected to a segmental value taking method so that the action speed in an external fault is ensured. According to the improved inverse time limit over-current protection method, the action speed of traditional inverse time over-current protection is improved and the cooperative relationship between upper protection and lower protection is ensured.

Description

A kind of inverse time over-current protection method of improvement

Technical field

The invention belongs to system for distribution network of power relay protection field, be specifically related to a kind of inverse time over-current protection method of improvement.

Background technology

Along with distributed power source (distributedgeneration; referred to as DG) increasingly it is widely applied in power distribution network, its feature being better than using the three-step charging of fixing action current can be demonstrated according to the inverse time current protection of short circuit current adaptive change.But, the synchronizing calculation method of tradition inverse time over-current protection, poor in order to ensure the operation time limit that the superior and the subordinate protect so that longer near the operating time of protection of mains side, therefore need to take corrective measure, reduce the action delay of protection.

At present, the domestic scholar of having proposes the action delay adopting low-voltage accelerated factor to reduce protection, for troubles inside the sample space, is greatly accelerated the speed of action of protection, has good effect.But, for external area error, low-voltage accelerated factor can reduce the action delay of protection equally, and the operation time limit reducing the superior and the subordinate's protection is poor, have impact on matching relationship, it is possible to cause back-up protection misoperation in extreme circumstances.The present invention adopts Low ESR accelerated factor, and for troubles inside the sample space, low-voltage accelerated factor can reduce the action delay of protection；And for external area error, the matching relationship of the superior and the subordinate's protection will not be destroyed.

Summary of the invention

When present invention aims to distributed power source access power distribution network; the operation time limit of conventional electrical distribution net inverse time over-current protection is affected; there is provided a kind of inverse time over-current protection method of improvement, it is ensured that the power distribution network containing distributed power source occurs to excise fault to fast and reliable during short trouble under various running statuses.

The technical scheme is that a kind of inverse time over-current protection method of improvement; use voltage, the magnitude of current of protecting installation place to collect; calculate measurement impedance; use the ratio measuring impedance with line impedance; as the accelerated factor of protection time-delay action, the computing formula namely protecting time-delay action is:

T=0.14Z^*T_d/[(I/I_OP)^α-β]

In formula, Z^*For Low ESR accelerated factor, T_dFor time setting coefficient, I_OPFor starting current, I is fault current, and α is the curve shape coefficient of inverse time lag, and β is translation coefficient.

As preferably, Low ESR accelerated factor Z^*According to the method that equation below adopts segmentation value,

$Z*=\left\{\begin{array}{cc}{Z}_m/Z_{Line}& Z_m/Z_{Line}<1\\ 1& Z_m/Z_{Line}\&GreaterEqual;1\end{array}\right.$

Wherein, Z_mFor measuring impedance, Z_LineFor line impedance.

As preferably, for the circuit of electrical network end distance power supply farthest, starting current I_OPWith time setting coefficient T_dSynchronizing calculation method be: according to time delay over-current protection calculate its starting current I₁, at this electric current I₁Under effect, its operation time limit t₁It is taken as the maximum actuation time limit；When circuit head end breaks down, at electric current I₂Under, take operation time limit t₂For the intrinsic movement time of protective relaying device, by I₁、t₁, and I₂、t₂These two groups of data bring formula t=0.14T into_d/[(I/I_OP)^α-β] in calculate determine starting current I_OPWith time setting coefficient T_d。

As preferably, for other circuit except the circuit except electrical network end distance power supply farthest, starting current I_OPWith time setting coefficient T_dSynchronizing calculation method be: when circuit head end breaks down, fault current I₃Corresponding operation time limit t₃Intrinsic movement time for protective relaying device；When line end breaks down, fault current I₄Corresponding operation time limit t₄Intrinsic movement time for next stage protective relaying device adds a ladder time, by I₃、t₃, and I₄、t₄These two groups of data bring formula t=0.14T into_d/[(I/I_OP)^α-β] in calculate determine starting current I_OPWith time setting coefficient T_d。

Compared with prior art, the inventive method uses measures the impedance ratio with line impedance as the accelerated factor of protection time-delay action, accelerates the speed of action of troubles inside the sample space；And to the method that accelerated factor adopts segmentation value, it is ensured that speed of action during external area error.The present invention is effectively increased the speed of action of tradition inverse time over-current protection, and ensure that the matching relationship between the superior and the subordinate's protection.

Accompanying drawing explanation

Fig. 1 is distribution network system structure chart.

Fig. 2 is the graph of relation of operation time limit that distinct methods is corresponding and abort situation, wherein the operation time limit figure of the guard method of (a), (b), (c) is tradition inverse time over-current protection respectively, low-voltage is accelerated inverse time over-current protection and the present invention.

Detailed description of the invention

Below with reference to the drawings and specific embodiments, technical scheme is described in detail.

The present embodiment illustrates for the radial pattern power distribution network shown in Fig. 1; this power distribution network contains three series circuits AB, BC, CD; it is respectively configured protection 1,2,3; all adopt the inverse time over-current protection of improvement; namely use voltage, the magnitude of current that protection 1,2,3 place collects, calculate the measurement impedance of correspondence, use the ratio measuring impedance and line impedance; as the accelerated factor of protection time-delay action, the computing formula of its protection time-delay action is:

T=0.14Z^*T_d/[(I/I_OP)^α-β]

In formula, the value of each parameter is as follows:

(1) translation coefficient β generally takes 1, and the curve shape factor alpha of conventional inverse time lag generally takes 0.02.

(2)Z^*For Low ESR accelerated factor, Z^*Value is Z_m/Z_Line, namely measure the ratio of impedance and line impedance, the method adopting segmentation value, it is shown below,

$Z*=\left\{\begin{array}{cc}{Z}_m/Z_{Line}& Z_m/Z_{Line}<1\\ 1& Z_m/Z_{Line}\&GreaterEqual;1\end{array}\right.$

Z_LineLine impedance for protected circuit.

(3) starting current I_OPWith time setting coefficient T_dSynchronizing calculation method as follows:

The protection 3 that first computed range power supply is farthest, calculates its starting current according to time delay over-current protection, is designated as I₃₁, under this function of current, its operation time limit t=0.14T_d/[(I/I_OP)^α-β] it is taken as the maximum actuation time limit (e.g., 3.5s), it is designated as t₃₁；When circuit CD head end breaks down, the fault current that protection installation place records is designated as I₃₂, take t=0.14T_d/[(I/I_OP)^α-β] for intrinsic movement time (generally taking 40ms) of protective relaying device, it is designated as t₃₂.Thereby determine that starting current I_OP3With time setting coefficient T_d3。

Then calculating protection 2, when circuit BC head end breaks down, electric current is designated as I₂₁, take t=0.14T_d/[(I/I_OP)^α-β] for intrinsic movement time (i.e. 40ms) of protective relaying device, it is designated as t₂₁；When circuit BC end breaks down, electric current is designated as I₂₂, take t=0.14T_d/[(I/I_OP)^α-β] for intrinsic movement time of next stage protective relaying device plus a ladder time (i.e. 0.54s), be designated as t₂₂.Thereby determine that starting current I_OP2With time setting coefficient T_d2。

The computational methods of protection 1 are identical with protection 2, obtain starting current I_OP1With time setting coefficient T_d1

Fig. 2 (a), (b), (c) are tradition inverse time over-current protection respectively, low-voltage is accelerated inverse time over-current protection and the operation time limit figure of guard method of the present invention.As seen from the figure; when troubles inside the sample space; the inverse time over-current protection that the low-voltage of figure (b) is accelerated; traditional inverse time over-current protection of ratio figure (a); quick action, but during external area error, poor with the action delay of subordinate circuit diminish; the matching relationship between the superior and the subordinate's protection cannot be ensure that, it is possible to cause back-up protection misoperation.Scheme the guard method of the present invention shown in (c) when troubles inside the sample space, quick action；During external area error, still poor with the action delay of subordinate's circuit one ladder time of maintenance, it is ensured that the matching relationship between the superior and the subordinate's protection.

Above example is only the technological thought that the present invention is described, it is impossible to limits protection scope of the present invention, every technological thought proposed according to the present invention, any change done on technical scheme basis with this, each falls within scope.

Claims (4)

1. the inverse time over-current protection method improved; it is characterized in that; use voltage, the magnitude of current of protecting installation place to collect; calculate measurement impedance; use the ratio measuring impedance with line impedance; as the accelerated factor of protection time-delay action, the computing formula namely protecting time-delay action is:

T=0.14Z^*T_d/[(I/I_OP)^α-β]

In formula, Z^*For Low ESR accelerated factor, T_dFor time setting coefficient, I_OPFor starting current, I is fault current, and α is the curve shape coefficient of inverse time lag, and β is translation coefficient.

2. inverse time over-current protection method according to claim 1, it is characterised in that Low ESR accelerated factor Z^*According to the method that equation below adopts segmentation value,

$Z^{*}=\left\{\begin{array}{cc}{Z}_m/Z_{Line}& Z_m/Z_{Line}<1\\ 1& Z_m/Z_{Line}\&GreaterEqual;1\end{array}\right.$

Wherein, Z_mFor measuring impedance, Z_LineFor line impedance.

3. inverse time over-current protection method according to claim 1, it is characterised in that for the circuit of electrical network end distance power supply farthest, starting current I_OPWith time setting coefficient T_dSynchronizing calculation method be: according to time delay over-current protection calculate its starting current I₁, at this electric current I₁Under effect, its operation time limit t₁It is taken as the maximum actuation time limit；When circuit head end breaks down, at electric current I₂Under, take operation time limit t₂For the intrinsic movement time of protective relaying device, by I₁、t₁, and I₂、t₂These two groups of data bring formula t=0.14T into_d/[(I/I_OP)^α-β] in calculate determine starting current I_OPWith time setting coefficient T_d。

4. inverse time over-current protection method according to claim 1, it is characterised in that for other circuit except the circuit except electrical network end distance power supply farthest, starting current I_OPWith time setting coefficient T_dSynchronizing calculation method be: when circuit head end breaks down, fault current I₃Corresponding operation time limit t₃Intrinsic movement time for protective relaying device；When line end breaks down, fault current I₄Corresponding operation time limit t₄Intrinsic movement time for next stage protective relaying device adds a ladder time, by I₃、t₃, and I₄、t₄These two groups of data bring formula t=0.14T into_d/[(I/I_OP)^α-β] in calculate determine starting current I_OPWith time setting coefficient T_d。