CN102798753B - Short-circuit detection method and device - Google Patents

Abstract

The invention discloses a short-circuit detection method and a short-circuit detection device. The short-circuit detection method comprises the following steps of: sampling n transient current values of a circuit, wherein n is an integer more than or equal to 3; acquiring n current integral values corresponding to sampling moments of the n transient current values; determining an estimation value of a current peak value of the circuit by using the n transient current values and the n current integral values according to an ohm law equation of the circuit; and if the estimation value of the current peak value is greater than a preset threshold value, determining that short circuit occurs. The embodiment of the invention also provides the short circuit detection device. According to the short-circuit detection method and the short-circuit detection device which are provided by the embodiment of the invention, short circuit can be timely detected before short circuit current reaches the peak value.

Description

A kind of method for detecting short circuit and device

Technical field

The present invention relates to circuit engineering field, be specifically related to a kind of method for detecting short circuit and device.

Background technology

In distribution network, isolating switch is usually utilized to carry out short-circuit protection to circuit.Namely, detect be short-circuited time, make isolating switch disconnect supply line.But the larger short-circuit current that occurs during short circuit (usually tens to hundreds of KA) can make isolating switch impaired, as made mechanical contact of isolating switch etc. impaired.Therefore, always wished before short-circuit current reaches peak value, the generation of short circuit detected early, to be still not enough to make circuit breaker trip in time when damaging isolating switch in the size of short-circuit current, thus protective breaker extend serviceable life of isolating switch.

In addition, for the isolating switch with ZSI (Zone-Selection Interlocking) function, detect that the generation of short circuit is even more important early.In the circuit employing the isolating switch with ZSI function; the protection zone of the corresponding different stage of isolating switch, when breaking down in subordinate protection zone, to should the isolating switch of subordinate protection zone trip rapidly; locking higher level protection zone, optionally coordinates to realize inter-stage simultaneously.But, if the generation of short circuit can not be detected early, then cannot realize current limliting in advance, probably occur the situation that two different stage protection zones are protected simultaneously, affect the realization of ZSI function.

Summary of the invention

Embodiments provide a kind of method for detecting short circuit and device, before short-circuit current reaches peak value, the generation of short circuit can be detected in time.

The embodiment of the present invention provides following technical scheme.

The method for detecting short circuit that the embodiment of the present invention provides comprises: n instantaneous current value of a circuit of sampling, n be more than or equal to 3 integer; Obtain n the current integration values corresponding with the sampling instant of a described n instantaneous current value; Utilize a described n instantaneous current value and a described n current integration values, based on the Ohm law equation of described circuit, determine the estimated value of the current peak of described circuit; When the estimated value of described current peak is greater than predetermined threshold, be defined as being short-circuited.In this detection method, owing to make use of the integrated value of electric current to estimate current peak, thus weakening current fluctuation to a certain extent may estimate on current peak the impact that causes.Thus, this detection method is adopted can to estimate the size of current peak in time and comparatively with being as the criterion.

In one embodiment of the invention, determine that the step of the estimated value of current peak comprises further: by the Ohm law both members of described circuit the first computing formula of obtaining of integration simultaneously, by respectively a described n instantaneous current value and described n current integration values being substituted into described first computing formula, calculate the estimated value of described current peak.

In one embodiment of the invention, the first computing formula has following form:

[R(t)]＝[-γ，P，Q]·[A(t)，B(t)，C(t)] ^T，

Wherein, R (t) is the function of the variable quantity of current integration values described in sampling time t;

A (t) is the function of the variable quantity of instantaneous current value in sampling time t;

B (t) and C (t) is respectively the function of the frequency of sampling time t and power supply:

P, Q, γ are respectively the combination of function comprising described current peak to be determined.

In this embodiment, the combination of the known quantity in the first computing formula and the combination of unknown quantity are distinguished.Thus, as long as obtain the value of the combination of unknown quantity in computation process according to the value of the combination of known quantity, then unknown quantity to be determined is calculated according to the size of the combination of unknown quantity, i.e. current peak.This approach simplifies computation process, accelerate computing velocity.

In one embodiment of the invention, in the first computing formula,

The instantaneous current value that R (t)=I (t)-I (0), wherein I (t)=∫ i (t) dt, i (t) is sampling time t;

$A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},$ $B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},$ $C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w};$ W represents the angular frequency of power supply;

Current peak $I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.$

In one embodiment of the invention, for power-factor angle, and the method also comprises: the instantaneous current value and corresponding current integration values that sample according to described n, determines the power factor of described circuit.Thus, adopt and not only can estimate current peak in this way, some eigenwerts of circuit can also be determined, such as power factor.

In one embodiment of the invention, determine that the estimated value of current peak also comprises: when n is greater than 3, utilize the least square regression estimation technique, determine the estimated value of described current peak.

The short-circuit detecting device that the embodiment of the present invention provides comprises: current sample module, for n instantaneous current value of a circuit of sampling, wherein n be more than or equal to 3 integer; Current integration module, for obtaining n the current integration values corresponding with the sampling instant of a described n instantaneous current value; Current peak estimation module, for utilizing a described n instantaneous current value and a described n current integration values, based on the Ohm law of described circuit, determines the estimated value of the current peak of described circuit; Short circuit determination module, for when the estimated value of described current peak is greater than predetermined threshold, is defined as being short-circuited.

In one embodiment of the invention, described current peak estimation module is used for by respectively a described n instantaneous current value and described n current integration values being substituted into described first computing formula, calculate the estimated value of described current peak, wherein said first computing formula be by the Ohm law both members of described circuit simultaneously integration obtain.

In one embodiment of the invention, the first computing formula has following form:

[R(t)]＝[-γ，P，Q]·[A(t)，B(t)，C(t)] ^T，

Wherein, R (t) is the function of the variable quantity of current integration values described in sampling time t;

A (t) is the function of the variable quantity of instantaneous current value in sampling time t;

B (t) and C (t) is respectively the function of the frequency of sampling time t and power supply:

P, Q, γ are respectively the combination of function comprising described current peak to be determined.

In one embodiment of the invention, in the first computing formula,

The instantaneous current value that R (t)=I (t)-I (0), wherein I (t)=∫ i (t) dt, i (t) is sampling time t;

$A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},$ $B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},$ $C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w};$ W represents the angular frequency of power supply;

Current peak $I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.$

In one embodiment of the invention, for power-factor angle, described device also comprises:

Power factor calculates module, for the instantaneous current value that to sample according to described n and corresponding current integration values, determines the power factor of described circuit.

In one embodiment of the invention, described current peak estimation module also comprises: least square submodule, for utilizing the least square regression estimation technique, determines the estimated value of described current peak.

When the method for detecting short circuit adopting the embodiment of the present invention to provide and device can be short-circuited in circuit, before short-circuit current reaches peak value, the generation of short circuit detected in time, avoid the appearance of circuit short circuit currents peak value, reduce the short-circuit current value of actual appearance, thus reduce the infringement of short-circuit current to isolating switch, achieve low-yield loss simultaneously.

And; when realizing ZSI protection; owing to detecting the generation of short circuit in time; reduce the short-circuit current value of actual appearance; can more early protect corresponding protection zone; thus realize current limliting in advance, avoid the situation occurring protecting the protection zone of two different stages, realize full selection function.

In addition, the method for detecting short circuit provided according to the embodiment of the present invention and device, while estimation current peak, the parameter of other circuit can also be estimated, as power factor etc., thus know the distribution situation of circuit middle impedance, be convenient to carry out line diagnosis and line optimization to circuit.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of the equivalent circuit of electric network in the embodiment of the present invention.

Fig. 2 is the process flow diagram of method for detecting short circuit in the embodiment of the present invention.

Fig. 3 is the schematic diagram of the current value of actual measurement and the estimated value of current peak in the embodiment of the present invention.

Fig. 4 is the schematic diagram of the structure of short-circuit detecting device in the embodiment of the present invention.

Embodiment

In order to make the object of the embodiment of the present invention, technical scheme and advantage clearly, below illustrating is described in further detail the embodiment of the present invention.

Generally, an Alternating Current Power Supply network equivalence can become the circuit structure shown in Fig. 1.In some cases, Alternating Current Power Supply network also can be equivalent to other form.Here only for the equivalent electrical circuit shown in Fig. 1, the present invention is described.As shown in Figure 1, the circuit structure of this equivalence comprises alternate voltage source V (t) and at least one a resistive load R and inductive load L.Wherein, resistive load R and inductive load L can change with actual conditions.Such as, when be short-circuited fault time, supply network still can be equivalent to structure as shown in Figure 1, but difference is that resistive load R diminishes when a short circuit occurs, thus makes the ER effect flowing through resistive load R and inductive load L large.

Especially, when being short-circuited, the electric current in the equivalent electrical circuit shown in Fig. 1 non-momentary reaches maximal value.On the contrary, hold back stream effect due to inductive load L in equivalent electrical circuit, short-circuit current progressively will reach maximal value within a period of time.This variation tendency of short-circuit current makes generation short circuit likely early being detected.That is, theoretically, just can estimate current maxima on the horizon by some current values in sampling equivalent electrical circuit as shown in Figure 1 and whether exceed predetermined threshold (as the threshold value that isolating switch can bear), if exceeded, show to have occurred short circuit, circuit breaker trip should be made immediately, cut off supply line.This thinking is called short circuit Forecasting Methodology.

Below, the theoretical foundation of above-mentioned short circuit Forecasting Methodology is first analyzed.

According to Ohm law, equivalent electrical circuit as shown in Figure 1 can meet following formula:

$V_m\cos (\mathrm{wt}+\mathrm{\θ})=R\·i\left(t\right)+L\·\frac{\mathrm{di}\left(t\right)}{\mathrm{dt}}---\left(1\right)$

Wherein, V _mrepresent the peak value of alternate voltage source V (t),

And here I _peakrepresent the maximum current flow through in the equivalent electrical circuit shown in Fig. 1, i.e. current peak;

W represents the angular frequency of voltage source V (t), for general municipal administration power supply, and such as w=2 π × 50Hz;

θ represents the initial phase angle of voltage source V (t),

T represents the time.

In formula (1), w, t and i (t) are the amounts that can directly measure, and in equivalent electrical circuit R, L, V (t) initial phase angle and expect to predict the current peak I that obtains _peakit is all the unknown quantity that cannot directly measure.Such as, because load is complicated, be generally difficult to the size determining R and L, and R can change because of short trouble, so such as cannot predict invariable R or L when short circuit occurs.

Consider above-mentioned factor, inventor proposes, by formula (1) both sides integration simultaneously, to obtain following formula (2) in the present invention:

${\∫}_0^t{V}_m\cos (\mathrm{wt}+\mathrm{\θ})\mathrm{dt}=R\·{\∫}_0^{t}i\left(t\right)\mathrm{dt}+L\·(i\left(t\right)-i\left(0\right))---\left(2\right)$

Then formula (2) is converted, to carry out the element in representation formula (2) by measurable amount as far as possible, and seek the relation between measurable amount and the unknown quantity that cannot measure.

Such as, in one embodiment of the invention, make I (t)=∫ i (t) dt, and use power-factor angle concept, namely ( also the amount for not directly measuring), then have

In formula (3), w, t and i (t) they are still the amounts that can directly measure, and in equivalent electrical circuit the initial phase angle θ of V (t) and maximum current value I _peakit is all the unknown quantity that cannot directly measure.

Again the combination of measurable amount and the combination of unmeasurable quantity are distinguished.

Wherein, for the combination of measurable amount:

Make R (t)=I (t)-I (0), $A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},$ $B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},$ $C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w},$

Then formula (3) is transformed to

For the combination of unknown quantity, order

Then formula (3) is transformed to further

[R(t)]＝[-γ，P，Q]·[A(t)，B(t)，C(t)] ^T(5)

Formula (5) comprises the combination P of three unknown quantitys, Q, γ.So utilize momentary current i (t) obtained at least three time-sampling points just can calculate P, the value of Q, γ with corresponding i (t) integrated value I (t)=∫ i (t) dt.And then according to the relation between P, Q, γ, namely following formula (6), just can obtain current peak:

$I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.---\left(6\right)$

Above, be deduced theoretically for the exemplary formula of of estimating current peak.But, it should be appreciated by those skilled in the art that based on above-mentioned derivation thinking, the computing formula of other forms of expression can also be obtained according to the integration of Ohm law equation.Such as, when distinguishing measurable amount and immeasurablel unknown quantity, can be out of shape A (t), B (t) and C (t).Such as can make R (t)=w (I (t)-I (0)), A ' (t)=i (t)-i (0), B ' (t)=sin (wt), C ' (t)=cos (wt)-1.For another example, can not also introduce and directly use R and L.Thus, can obtain based on formula (2) multiple for calculating I _peakformula, and be not limited to formula (5) and (6).

Below with reference to the equivalent electrical circuit shown in Fig. 1, in conjunction with the above-mentioned formula (5) that provides and (6), the method for detecting short circuit that the embodiment of the present invention provides is described in detail.

Fig. 2 is the process flow diagram of method for detecting short circuit in the embodiment of the present invention.As shown in Figure 2, the method comprises the steps.

Step 21, carries out n continuous sampling to the electric current in circuit, obtains n instantaneous current value, namely determines the value of i (t).Wherein n be more than or equal to 3 integer.

Step 22, obtains n the current integration values corresponding with the sampling instant of this n instantaneous current value, and then determines the value of R (t).

In actual applications, for the ease of operation, the instantaneous current value in resistive load can be measured, and calculate the integration of this instantaneous current value.It will be appreciated by those skilled in the art that, in this step, other modes also can be adopted to obtain n current integration values, such as, can the current value on inductive load be measured, calculate the current integration values of n sampling instant, or integrating circuit can be used to obtain the integrated value of electric current.

Step 23, according to this n instantaneous current value and a corresponding n current integration values, determines the estimated value of current peak according to formula (5) and (6).

In this step, A (t) can be determined, B (t), C (t) according to n instantaneous current value.Afterwards, according to the R (t) that current integration values obtains in integrating step 22, according to formula (6), determine P, the value of Q, γ.

Particularly, in order to determine P, Q, the value of these three variablees of γ, the minimum value of n is 3, namely, will respectively at time point t=1, instantaneous current value i (t) that t=2 and t=3 place samples and corresponding current integration values, for people's formula (5), can obtain:

$[R\left(1\right),R\left(2\right),R\left(3\right)]=[-\mathrm{\γ},P,Q]\·\left[\begin{array}{c}A\left(1\right),A\left(2\right),A\left(3\right)\\ B\left(1\right),B\left(2\right),B\left(3\right)\\ C\left(1\right),C\left(2\right),C\left(3\right)\end{array}\right]---\left(7\right)$

Above-mentioned formula (7) is utilized can P to be obtained, the value of Q, γ.

In actual applications, in order to avoid the impact of noise, can 3 be greater than to the continuous sampling frequency n of electric current, such as n=4, i.e. R (t), A (t), B (t), the value of C (t) has four groups, now, can the least square regression estimation technique be passed through, determine P, the value of Q, γ.So, by the estimation adopting the least square regression estimation technique to carry out current peak, can noise-decreasing on the impact of the estimated result of current peak, improve the accuracy of estimated result.

Determine P, after the value of Q, γ, calculate the estimated value I of current peak according to formula (6) _peak.

Step 24, by the estimated value I of peak value of short _peakcompare with predetermined threshold, if I _peakwhen being greater than predetermined threshold, be defined as there occurs short circuit.

From foregoing description, whether the method provided by the embodiment of the present invention, by momentary current sampled value and corresponding current integration values, can be estimated current peak, thus before electric current reaches peak value, detect in time and have short circuit to occur.

In actual applications, the method also comprises when determining to be short-circuited, and generates short-circuit detection signal.This short-circuit detection signal can be used for triggering the trip operation of isolating switch, thus makes isolating switch carry out short-circuit protection in time.

In addition, in another embodiment, the method also comprises according to this n instantaneous current value and this current integration values, determines other parameters of this circuit, as power factor.According to and the value of the γ determined in step 23, the power-factor angle of this circuit can be determined thus know the distribution situation of circuit middle impedance, be convenient to carry out line diagnosis and line optimization to circuit.

Fig. 3 is the schematic diagram of the current value of actual measurement and the estimated value of current peak in the embodiment of the present invention.In the present embodiment, after there occurs short circuit in circuit, utilize the method that the embodiment of the present invention provides, this short circuit is detected.As shown in Figure 3, the curve being positioned at below is the current value of actual measurement, and the curve being positioned at top is the estimated value of the current peak determined according to embodiment of the present invention supplying method, and the sampling period of electric current is 20 μ s.

As can be seen from Figure 3, after there occurs short circuit in circuit, due to the existence of inductive load, the change of the current value of actual measurement is also not obvious.But according to the method that the embodiment of the present invention provides, after initial sampling several times terminates soon, just there is larger change in the estimated value of current peak.Particularly, in figure 3, the short-circuit current preset is 153KA, and its current peak can predictedly in 100 μ s arrive, thus determines to there occurs short circuit in circuit.Visible, after the short circuit of reality occurs, this short circuit can be detected rapidly, exactly before electric current to peaking.

Can find out, in the method for detecting short circuit that the embodiment of the present invention provides, n instantaneous current value of sampling, wherein n be more than or equal to 3 integer; Obtain n the current integration values that this n instantaneous current value is corresponding; Utilize this n instantaneous current value and n current integration values, based on the Ohm law equation of circuit, determine the estimated value of the current peak of this circuit, when the estimated value of this current peak is greater than predetermined threshold, determine to be short-circuited.So, when being short-circuited in circuit, before short-circuit current reaches peak value, short circuit can be detected in time, avoid the appearance of circuit short circuit currents peak value, reduce the short-circuit current value of actual appearance, thus reduce the infringement of short-circuit current to isolating switch, achieve low-yield loss simultaneously.

And; when realizing ZSI protection; owing to detecting the generation of short circuit in time; reduce the short-circuit current value of actual appearance; can more early protect corresponding protection zone; thus realize current limliting in advance, avoid the situation occurring protecting the protection zone of two different stages, realize full selection function.

In addition, according to the method for detecting short circuit that the embodiment of the present invention provides, while estimation current peak, the parameter of other circuit can also be estimated, as power factor etc., thus know the distribution situation of circuit middle impedance, be convenient to carry out line diagnosis and line optimization to circuit.

Fig. 4 is the structural drawing of short-circuit detecting device in the embodiment of the present invention.As shown in Figure 4, this device comprises current sample module 41, current integration module 42, current peak estimation module 43 and short circuit determination module 44.

Wherein, current sample module 41 is for n instantaneous current value of a circuit of sampling, such as this circuit at least comprises a voltage source (V), a resistive load (R) and an inductive load (L), wherein, n be more than or equal to 3 integer; Current integration module 42 is for obtaining the n corresponding with the sampling instant of this n instantaneous current value current integration values; Current peak estimation module 43, for according to this n instantaneous current value and n current integration values, based on the Ohm law equation of this circuit, determines the estimated value of the current peak of this circuit; Short circuit determination module 44, for when the estimated value of this current peak is greater than predetermined threshold, is defined as being short-circuited.

Further, described current peak estimation module 43 is for by substituting into the first computing formula by a described n instantaneous current value and a described n current integration values respectively, calculate the estimated value of described current peak, wherein said first computing formula be by the Ohm law both members of described circuit simultaneously integration obtain.This first computing formula such as has following form:

[R(t)]＝[-γ，P，Q]·[A(t)，B(t)，C(t)] ^T，

Wherein, R (t) is the function of the variable quantity of current integration values described in sampling time t;

A (t) is the function of the variable quantity of instantaneous current value in sampling time t;

B (t) and C (t) is respectively the function of the frequency of sampling time t and power supply:

P, Q, γ are respectively the combination of function comprising described current peak to be determined.

Such as, in embodiments of the present invention,

The instantaneous current value that R (t)=I (t)-I (0), wherein I (t)=∫ i (t) dt, i (t) is sampling time t;

$A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},$ $B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},$ $C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w},$ W represents the angular frequency of power supply;

Current peak $I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.$

In above-mentioned formula, for power-factor angle, the device in the embodiment of the present invention also comprises: power factor calculates module 45, for the instantaneous current value that to sample according to this n and corresponding current integration values, determines the power factor of circuit.The distribution situation of circuit middle impedance can be known thus, be convenient to carry out line diagnosis and line optimization to circuit.

In addition, this current peak estimation module also comprises least square submodule 46, for utilizing the least square regression estimation technique, determines the estimated value of this current peak.By the estimation adopting least square regression estimation technique module to carry out current peak value, can noise-decreasing on the impact of estimated result, improve the accuracy of estimated result.

Can find out, the short-circuit detecting device that the embodiment of the present invention provides, when being short-circuited in circuit, before short-circuit current reaches peak value, short circuit can be detected in time, avoid the appearance of circuit short circuit currents peak value, reduce the short-circuit current value of actual appearance, thus reduce the infringement of short-circuit current to isolating switch, achieve low-yield loss simultaneously.

And; when realizing ZSI protection; owing to detecting the generation of short circuit in time; reduce the short-circuit current value of actual appearance; can more early protect corresponding protection zone; thus realize current limliting in advance, avoid the situation occurring protecting the protection zone of two different stages, realize full selection function.

In addition, according to the short-circuit detecting device that the embodiment of the present invention provides, while estimation current peak, the parameter of other circuit can also be estimated, as power factor etc., thus know the distribution situation of circuit middle impedance, be convenient to carry out line diagnosis and line optimization to circuit.

The invention discloses a kind of method for detecting short circuit and device.In method for detecting short circuit, n instantaneous current value of a circuit of sampling, n be more than or equal to 3 integer; Obtain n the current integration values corresponding with the sampling instant of this n instantaneous current value; Utilize this n instantaneous current value and n current integration values, based on the Ohm law equation of circuit, determine the estimated value of the current peak of this circuit; When the estimated value of this current peak is greater than predetermined threshold, be defined as being short-circuited.The embodiment of the present invention additionally provides a kind of short-circuit detecting device.The method for detecting short circuit provided according to the embodiment of the present invention and device, before short-circuit current reaches peak value, can detect the generation of short circuit in time.

The above, be only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Can to being improved appropriately according to a preferred embodiment of the invention in concrete implementation process, to adapt to the concrete needs of concrete condition.Therefore be appreciated that the specific embodiment of the present invention as herein described just plays an exemplary role, not in order to limit the scope of the invention.

Claims (8)

1. a method for detecting short circuit, comprising:

Sampling (21) one circuit n instantaneous current value, n be more than or equal to 3 integer;

Obtain n the current integration values that (22) are corresponding with the sampling instant of a described n instantaneous current value;

Utilize a described n instantaneous current value and a described n current integration values, based on the first following computing formula, determine the estimated value of the current peak of (23) described circuit, wherein said first computing formula is obtained by the anomalous integral equation conversion simultaneously of the Ohm law both members for described circuit

[R(t)]＝[-γ,P,Q]·[A(t),B(t),C(t)] ^T，

Wherein, R (t) is the function of the variable quantity of current integration values described in sampling time t;

A (t) is the function of the variable quantity of instantaneous current value in sampling time t;

B (t) and C (t) is respectively the function of the frequency of sampling time t and power supply:

P, Q, γ are respectively the function comprising described current peak to be determined.

When the estimated value of described current peak is greater than predetermined threshold, determine that (24) are for being short-circuited.

2. method according to claim 1, wherein, in described first computing formula,

The instantaneous current value that R (t)=I (t)-I (0), wherein I (t)=∫ i (t) dt, i (t) is sampling time t;

$A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w};$ Wherein w represents the angular frequency of power supply

Current peak $I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.$

3. method according to claim 2, wherein, for power-factor angle, and described method also comprises the instantaneous current value and corresponding current integration values that sample according to described n, determines the power-factor angle of described circuit.

4. method according to claim 1, wherein, when n is greater than 3, determines that the estimated value of current peak also comprises: utilize the least square regression estimation technique, determines the estimated value of described current peak.

5. a short-circuit detecting device, comprising:

Current sample module (41), for n instantaneous current value of a circuit of sampling, wherein n be more than or equal to 3 integer;

Current integration module (42), for obtaining n the current integration values corresponding with the sampling instant of a described n instantaneous current value;

Current peak estimation module (43), for utilizing a described n instantaneous current value and a described n current integration values, based on the first following computing formula, determine the estimated value of the current peak of described circuit, wherein said first computing formula is obtained by the anomalous integral equation conversion simultaneously of the Ohm law both members for described circuit

[R(t)]＝[-γ,P,Q]·[A(t),B(t),C(t)] ^T，

Wherein, R (t) is the function of the variable quantity of current integration values described in sampling time t;

A (t) is the function of the variable quantity of instantaneous current value in sampling time t;

B (t) and C (t) is respectively the function of the frequency of sampling time t and power supply:

P, Q, γ are respectively the function comprising described current peak to be determined;

Short circuit determination module (44), for when the estimated value of described current peak is greater than predetermined threshold, is defined as being short-circuited.

6. device according to claim 5, wherein, in described first computing formula,

The instantaneous current value that R (t)=I (t)-I (0), wherein I (t)=∫ i (t) dt, i (t) is sampling time t;

$A\left(t\right)=\frac{i\left(t\right)-i\left(0\right)}{w},B\left(t\right)=\frac{\sin \left(\mathrm{wt}\right)}{w},C\left(t\right)=\frac{\cos \left(\mathrm{wt}\right)-1}{w};$ W represents the angular frequency of power supply

Current peak $I_{\mathrm{peak}}=\sqrt{\frac{P^2+Q^2}{1+{\mathrm{\γ}}^2}}.$

7. device according to claim 6, wherein, for power-factor angle, described device also comprises:

Power factor calculates module (45), for the instantaneous current value that to sample according to described n and corresponding current integration values, determines the power-factor angle of described circuit.

8. device according to claim 11, wherein, described current peak estimation module also comprises:

Least square submodule (46), for utilizing the least square regression estimation technique, determines the estimated value of described current peak.