CN101790689A - Measuring and/or switching device - Google Patents

Abstract

The application discloses methods how to arithmetically calculate a corrected effective value from a real effective value of a secondary current of an iron-cored current transformer when magnetization of the iron core reaches the saturation point during generation of the secondary current from a primary current. The corrected value simulates the case that the saturation point is not reached, thus making it possible to use a smaller than normal iron-cored current transformer in measuring and/or switching devices comprising an iron-cored current transformer, e.g. in a low-voltage circuit breaker.

Description

Measure and/or switchgear

Technical field

The present invention relates to a kind of equipment, it has used the current transformer that has iron core.The current transformer that has iron core converts primary current to secondary current.The device that is used to import primary current correspondingly belongs to this equipment.Secondary current is carried out analysis and evaluation with any one form.In order to satisfy the purpose of this equipment, measured value that is write down or secondary current are used as the benchmark numerical value of switch motion and use.Correspondingly, this equipment is exactly a kind of measurement and/or switchgear.The typical application situation is a low-voltage circuit breaker.

Background technology

By being used to carry out the device of analysis and evaluation, by the secondary current primary current of retrodicting out.All think up to now: the effective value of secondary current and the effective value of primary current are linear substantially.Yet have only when elementary electric current is used for a kind of of iron core with the proportional magnetization of its value, this just may realize.Therefore iron core does not allow the magnetization that reaches capacity.Being in saturated zone does not allow to be reached fully.Owing to this reason, in the equipment of described kind, use a kind of enough large-sized current transformer usually.What probable value must be pursued is: people may use littler current transformer.

Summary of the invention

Therefore, the objective of the invention is to propose measurement a kind of described kind, compact conformation and/or switchgear.

This purpose realizes by following approach, promptly, the device that is used for secondary current is carried out analysis and evaluation is designed for, and considers when analysis and evaluation: when elementary electric current is so high, promptly cause the zone that reaches capacity by the magnetic field that this primary current produced in the magnetization of iron core.This situation just in time is to magnetize no longer the situation that (basically) and primary current are associated linearly.All these situations have caused, and the curve shape of secondary current departs from mutually with the curve shape of primary current.

Thus, promptly be used for the device that secondary current carries out analysis and evaluation is considered the zone that the magnetization at iron core reaches capacity, therefore in the magnetization of iron core, needn't avoid saturated zone again.Therefore current transformer can be designed to littler than normal conditions.

The emphasis problem is the effective value of secondary current for measurement with current transformer and/or switchgear.By using littler current transformer, magnetization at the situation lower core of certain primary current value reaches capacity, and this effective value to compare with the linear feature under the situation of the littler primary current between the effective value of the effective value of secondary current and primary current be too small.Preferably consider this effect by the following method, the device that promptly is used to carry out analysis and evaluation is obtained the effective value of the correction of (especially calculating) secondary current, when in the magnetization curve of iron core seems magnetization at iron core, not reaching capacity, in the secondary current of reality, can obtain the effective value of this correction.Also just simulated following situation by the effective value of proofreading and correct, promptly used the like this large-sized current transformer that has iron core, to such an extent as to secondary current also (basically) be associated with primary current linearly.

As previously mentioned, according to the advantageous applications of principle of the present invention be, equipment according to the present invention is low-voltage circuit breaker, and wherein, the magnetic executive component interrupts primary circuit.Replace to use the basis of actual effective value, now use the effective value of proofreading and correct, that is to say,, the magnetic executive component is activated when the effective value of proofreading and correct has exceeded the setting value (for example at least one ultimate value) of low-voltage circuit breaker as the dropout standard.

The generation of the effective value of proofreading and correct is based on the following fact: iron core, if it is in saturated, then show a kind of characteristic of regulation, to such an extent as to according to the secondary current primary current of in fact can retrodicting out, even secondary current no longer has as the identical curve shape of primary current.Showed already that secondary current can be seen as the secondary current of phase place portion section control: secondary current was also just followed primary current on certain duration, and reduces suddenly under the situation about reaching capacity in the magnetization of iron core.Can stipulate a threshold value in this wise now, thereby just in time equal duration during secondary current is followed primary current linearly basically by the duration that exceeds threshold value that the numerical value of secondary current is obtained.

In one embodiment, compare by analog electronic installation and threshold value, and produce rectangular pulse signal in this wise, promptly the duration of rect.p. equals to exceed the duration of threshold value.This rectangular pulse signal then can come analysis and evaluation by microcontroller after the conversion by analog to digital-converter, its method is to measure the length of rect.p. simply.

Replacedly, whole analysis and evaluation can carry out to digitizing.The contrast of secondary electrical flow valuve and threshold value is equally also carried out after by analog to digital-converter secondary current being changed in microcontroller subsequently.Needn't specially produce the rect.p. curve subsequently.

If by effective secondary current of reality with depend on that the product of the coefficient of the duration of being obtained that exceeds threshold value is used as effective secondary current of correction, so just can handle with computing method the most simply.This correction coefficient K (α) that has the duration α that obtains preferably provides by following formula:

$K\left(\mathrm{\α}\right)=\frac{1}{\sqrt{\frac{1}{\mathrm{\π}}(\mathrm{\α}-\frac{\sin (2\·\mathrm{\α})}{2})}}$

In the sinusoidal primary current, this correction coefficient K (α) becomes 1, if actual secondary current also is similar to sine-shaped words, α is π just in time just also so.In this case, Shi Ji effective secondary current also just needn't be proofreaied and correct a coefficient different with 1.

The duration of obtaining by the numerical value of secondary current that exceeds threshold value is not the unique numerical value that can consider to be used for obtaining the correction coefficient that is used for actual effective secondary current.Therefore also can replacedly stipulate a kind of form factor that is used for secondary current.This form factor is the ratio of the digital average value (being also referred to as rectified mean value) of the effective value of secondary current and secondary current.This measured value form factor can be assigned correction coefficient by means of the combined characteristic curve, utilizes this correction coefficient to be calculated the effective value of the correction of secondary current by the effective value of the reality of secondary current.

Description of drawings

Below with reference to the accompanying drawings preferred implementation of the present invention is illustrated.Shown in the figure:

Fig. 1: according to the electronics trip unit of low-voltage circuit breaker of the present invention;

Fig. 2: when the iron core of current transformer does not enter when saturated the change curve in time of secondary current;

Fig. 3: when the iron core of current transformer enters when saturated the change curve in time of secondary current;

Fig. 4: setting threshold standard on according to the curve of Fig. 3;

Fig. 5: the curve that obtains according to threshold criteria with rect.p.;

Fig. 6: the combined characteristic curve, it has described the relation of the form factor of correction coefficient and measurement;

Fig. 7 is by the effective value of deriving correction according to the change curve in time of the secondary current of an embodiment of the invention.

Embodiment

In low-voltage circuit breaker, from a certain specific effective value of electric current, the circuit that this electric current can be flowed should be interrupted.Low-voltage circuit breaker according to the present invention comprises the electronics trip unit, and it is represented with 10 in Fig. 1 on the whole.The electric current that will not flow in the circuit that will interrupt is now directly used the standard that conduct is used for interrupt circuit, but with it as primary current i _p(t) flow to current transformer 12, this current transformer should have iron core.Current transformer produces secondary current i on primary side _s(t), and this secondary current be used as the standard that makes circuit trip.Secondary current i _s(t) connecting the decline of resistance (load) 14 places and be fed to analog to digital-converter 16.Obtain to be fed to the digital value of microcontroller 18 in this wise, this microcontroller carries out real analysis and evaluation.According to a certain certain criteria, 18 pairs of digitized secondary currents of microcontroller are analyzed, and the latching device by 20 pairs of low-voltage circuit breakers of magnetic executive component sends instruction under certain condition, and mechanically opening flows primary current i _p(t) circuit.

Use such current transformer in traditional low-voltage circuit breaker, in this current transformer, secondary current is of similar shape for desired primary current.For this situation, Fig. 2 shows the secondary current i that is used for sine-shaped primary current _s(t) change curve in time 22.Secondary current equally also is a sinusoidal, and this is because the iron core of current transformer does not reach capacity.

Fig. 3 shows another kind of situation now, at this, be used to produce secondary current curve 22 among current transformer and Fig. 2 and the current transformer used to compare be littler.Under the identical situation of primary current, the magnetization of iron core enters state of saturation.Replace curve 22 subsequently and obtained secondary current curve 24 shown in Figure 3.As seen from Figure 3, in Fig. 3, almost be designed to a counterpart as curve 22 with the part of 26 curves that mark 24, that is to say and passed through a sinusoidal part.From reaching some specific primary currents, the iron core magnetization just enters state of saturation, and curve descends rapidly, sees portion's section 28.Secondary current among Fig. 3 can be seen as the secondary current of phase place portion section control.

Width by curve part section 26 and 28 spikes that limited is a yardstick of the influence degree of magnetization curve, and this is due to the fact that, has promptly reached their nonlinear zone of saturation.Now, determine a threshold value 30 and obtain the width α of spike.The unit of width α is the time.Be phase place yet also it can be regarded as, and α is referred to as conduction angle.Be similar to threshold value 30 also can determine its negative value 30 ', and for the situation that is lower than this negative value, the width α of spike under equally also obtaining.

Now can with curve 24 and threshold value 30 and 30 ' comparative result be aggregated into a curve, it is shown in Figure 5.When exceeding threshold value, curve is in logic high (" comparative result=1 "), and as long as numerically be lower than threshold value 30 or 30 ', the Nagqu line is in logic low (" comparative result=0 ").In Fig. 5, width α is the duration of rect.p. just.The magnetic saturation of iron core is few more, and α is just big more, and curve is continuously more near logic high, and if to reach iron core more and more magnetized saturated, α is just more little so.

Can be by the actual effective value I of secondary current _{Seff, real}Calculate the correction effective value I of secondary current with parameter α _{Seff, korr}, wherein the effective value of Jiao Zhenging be at current transformer bigger and also when encouraging, may not reach zone of saturation in the iron core magnetization time by same primary current the value that may draw.When threshold value 30 or 30 ' enough is low, can derive following formula:

$I_{\mathrm{seff},\mathrm{korr}}=I_{\mathrm{seff},\mathrm{real}}\·K\left(\mathrm{\α}\right)=I_{\mathrm{seff},\mathrm{real}}\·1/\sqrt{\frac{1}{\mathrm{\π}}(\mathrm{\α}-\frac{\sin (2\·\mathrm{\α})}{2})}$

Be designed to: obtain parameter α by microcontroller 18, its method be carry out there digitalized data and threshold value 30 or 30 ' contrast; Also in microcontroller, obtain I _{Seff, real}And obtain I _{Seff, korr}Effective value I when the correction of secondary current intensity _{Seff, korr}When exceeding a predetermined threshold value, just magnetic executive component 20 is threaded off by microcontroller 18.Because it is the effective value of proofreading and correct greater than the actual effective value of secondary current, has therefore been realized dropout than normal conditions quickly, in the cards during by the concerning of a kind of pure linearity between primary current and secondary current as it.

Replace this method, promptly according to threshold value 30 and 30 ' definition come regulation parameter α, obtain it then and be used to calculate corrected value K (α), corrected value K also can obtain with other approach.In this interchangeable solution, use the form factor of secondary current.This form factor is defined as effective value and rectified mean value, that is to say the ratio of digital average value that wherein effective value is:

$I_{\mathrm{seff},\mathrm{real}}=\sqrt{\frac{1}{T}{\∫}_0^T{i}_s^2\left(t\right)\mathrm{dt}},$

Rectified mean value | i _s(t) | for:

$\left|\stackrel{\‾}{i\left(t\right)}\right|=\frac{1}{T}{\∫}_0^T\left|i_s\left(t\right)\right|\mathrm{dt}.$

This form factor can be following approx with conduction angle α opening relationships formula:

$F=\frac{I_{\mathrm{seff},\mathrm{real}}}{\left|\stackrel{\‾}{i\left(t\right)}\right|}=\frac{\sqrt{\frac{1}{\mathrm{\π}}\·(\mathrm{\α}-\frac{\sin (2\·\mathrm{\α})}{2})}}{\frac{\sqrt{2}}{\mathrm{\π}}\·(1-\cos \left(\mathrm{\α}\right))}.$

If use as corrected value K (α) same in above-mentioned replaceable scheme,

$K\left(\mathrm{\α}\right)=\frac{1}{\sqrt{\frac{1}{\mathrm{\π}}(\mathrm{\α}-\frac{\sin (2\·\mathrm{\α})}{2})}},$

So just can obtain the relation between form factor F and correction coefficient K, for example by calculating the above-mentioned formula that is used for different α.Combined characteristic curve family curve in other words be can obtain, correction coefficient K (α) and form factor F=F (α) opening relationships formula made therein.This family curve is shown in Figure 6, and marks with 32 there.If application characteristic curve 32, that is the value of obtaining α fully more just.Family curve 32 especially also can with differently obtain by aforesaid equation, for example according to simulating to the test of current transformer or by means of finite element.

Fig. 7 has summed up the method for application combination family curve 32: by i _s(t) obtain effective value i on the one hand _{Seff, real}And obtain rectified mean value on the other hand | i _s(t) |, there is a kind of relation mutually in they, so that determine form factor F, and derive correction coefficient K by form factor F according to combined characteristic curve 32.The I that obtains before this correction coefficient K then multiply by _{Seff, real}, to obtain I _{Seff, korr}

Identically for two kinds of embodiments be: the effective value that calculates correction according to the actual effective value of secondary current by means of correction coefficient K.Also can consider method in the method according to the invention, as considering to reach the zone of the saturated magnetization of iron core with any one form with other.The consequence of this consideration is: the current transformer that has iron core needn't be excessive.Just no longer need so in the prior art: the current transformer that will have an iron core is designed to so big, thereby secondary current is associated with primary current linearly.

Claims (8)

1. measure and/or switchgear for one kind, have: be used to import primary current (i _p(t)) device; Have the current transformer (12) of iron core, described current transformer converts described primary current to secondary current (i _s(t)); And the device (14,16,18) that is used for described secondary current is carried out analysis and evaluation, it is characterized in that, be used for described secondary current (i _s(t)) the described device (14,16,18) that carries out analysis and evaluation is designed for when analysis and evaluation and considers: as described primary current (i _p(t)) so high, promptly cause the zone that in the magnetization of described iron core, reaches capacity by the magnetic field that described primary current produced.

2. measurement according to claim 1 and/or switchgear is characterized in that, the described device (14,16,18) that is used to carry out analysis and evaluation is obtained the effective value (I of the correction of described secondary current _{Seff, korr}), when in the magnetization curve of described iron core seems magnetization at described iron core, not reaching capacity, in the secondary current of reality, can obtain the effective value of described correction.

3. measure and/or switchgear for one kind, it is characterized in that described measurement and/or switchgear are low-voltage circuit breakers, wherein, as the effective value (I that proofreaies and correct _{Seff, korr}) when exceeding the setup parameter of described low-voltage circuit breaker, magnetic executive component (20) interrupts primary circuit.

4. according to claim 2 or 3 described measurement and/or switchgears, it is characterized in that, define a threshold value (30,30 '), obtain the duration that exceeds described threshold value by the numerical value of time dependent described secondary current, and derive the effective value (I of described correction subsequently by the described duration _{Seff, korr}).

5. measurement according to claim 4 and/or switchgear, it is characterized in that, the circuit that is arranged on the primary side downstream of described current transformer produces the rect.p. curve, in described rect.p. curve, the duration of rect.p. equals to exceed the described duration of described threshold value, wherein described rect.p. curve is offered analog to digital-converter, and write down by microcontroller the duration of described rect.p..

6. measurement according to claim 4 and/or switchgear, it is characterized in that, the primary side of described current transformer (12) is connected with analog to digital-converter (16), and in the microcontroller (18) that is arranged on described analog to digital-converter (16) downstream, realize secondary electrical flow valuve and described threshold value (30,30 ') comparison, thereby described microcontroller is derived the described duration (α) that exceeds described threshold value.

7. according to each described measurement and/or switchgear in the claim 4 to 6, it is characterized in that I _{Seff, korr}=I _{Seff, real}K (α), wherein I _{Seff, real}Be the effective value of described secondary current, and I _{Seff, korr}Be the effective value of the correction of described secondary current, wherein K (α) is the correction coefficient that depends on the described duration α that is obtained, and described correction coefficient is preferably obtained according to following formula:

$K\left(\mathrm{\α}\right)=\frac{1}{\sqrt{\frac{1}{\mathrm{\π}}(\mathrm{\α}-\frac{\sin (2\·\mathrm{\α})}{2})}}.$

8. according to claim 2 or 3 described measurement and/or switchgears, it is characterized in that, obtain and be used for described secondary current (i _s(t)) form factor (F) is as the effective value I of described secondary current _{Seff, real}Digital average value with described secondary current | i _s(t) | ratio, and be that described form factor (F) distributes correction coefficient K according to combined characteristic curve 32, and calculate the effective value I of the correction of described secondary current according to following formula _{Seff, korr}:

I _seff，korr＝I _seff，real·K。

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