CN203117407U - Residual magnetism measuring system of current transformer - Google Patents

Abstract

The utility model discloses a residual magnetism measuring system of a current transformer. An upper computer is connected with a measurement process operating unit through a data collecting unit, the measurement process operating unit is connected with a secondary side of the current transformer, and the secondary side of the current transformer is further connected with the upper computer through the data collecting unit. The upper computer receives data signals, sent by the data collecting unit, of the current transformer, a closed state of a relay is controlled, under the condition of the open circuit of a primary side of the current transformer, forward direction charging enabling the current transformer to be in a saturation condition, electro-discharging and reverse direction charging enabling the current transformer to be in a saturation condition are carried out on the secondary side in sequence, magnetic flux variable quantity of a forward direction charging process, magnetic flux variable quantity of an electro-discharging process and magnetic flux variable quantity of a reverse direction charging process are obtained by operation, the three kinds of magnetic flux variable quantity are operated, accurate residual magnetism factors can be obtained, residual magnetism factor measuring errors caused by the fact that initial iron core magnetic flux of the current transformer is not zero are eliminated, accuracy of the current transformer for measuring the residual magnetism factors is improved, fairness of the current transformer used in electric energy measuring and trade settlement is ensured, and the residual magnetism measuring system of the current transformer has good application prospect.

Description

The remanence of current transformer measuring system

Technical field

The utility model relates to a kind of remanence of current transformer measuring system, belongs to the electrical energy parameter field of measuring technique.

Background technology

Direct current remanent magnetism in the current transformer can influence transformer error; thereby influence metering and protective value; manufacturing plant is merely able to guarantee do not have remanent magnetism before current transformer dispatches from the factory; the error effect amount that causes thus is limited in the acceptable ranges; if the error when current signal is taken from and is subjected to direct current remanent magnetism to influence serious current transformer will to cause actual motion increases; current transformer influences significantly meter characteristic after producing remanent magnetism; double above than error under the normal condition; and even it is seriously overproof; cause electric energy metrical and trade settlement injustice; electromagnetic current transducer accounts for the overwhelming majority in the electrical network, exists direct current remanent magnetism to influence problem in various degree.In order to keep instrument not to be subjected to the damage of fault current; the metering winding is easier to be saturated; the easier remanent magnetism that makes remains on higher level; in order to guarantee that measuring apparatus accuracy and protective relaying device obtain the correctness of current signal; must research and analyse the direct current magnetic after effect; take the effective precautionary measures; therefore the remanent magnetism coefficient then is that an important parameter of researching DC magnetic after effect presses for and selects reasonable method that the remanent magnetism coefficient is accurately measured G216847-1997 " technical requirement of protective current transformer, transient characterisitics " regulation to adopt AC method; first DC-method; second DC-method and capacity discharge method measure the remanent magnetism coefficient, below are the particular content to these four kinds of methods; the explanation of the deficiency that exists and the part that requires further improvement:

(1) AC method

Particular content is: the secondary terminal at current transformer applies sine wave AC voltage, the primary side open circuit, measure corresponding exciting current and induced voltage, and need measure the value of secondary terminal direct current resistance in addition, carry out related operation and obtain the dynamic hystersis loop of current transformer iron core, when current transformer is saturated, corresponding magnetic flux s is the saturation flux amount, regulate exciting current then, the magnetic flux r of correspondence is remanent magnetism when exciting current is zero, and the remanent magnetism coefficient of trying to achieve current transformer is Kr=φ r/ φ s;

Exist not enough: AC method is not considered the non-vanishing this situation of the initial magnetic flux of current transformer; Can not directly obtain the value of Secondary Winding direct current resistance in the test process, test process is loaded down with trivial details; If the inductance value of Secondary Winding coil is very big, the field voltage that reaching capacity needs can be very high, to measuring difficulty and safe operation aspect certain influence arranged.

(2) first DC-method

Particular content is: with the primary side open circuit of current transformer, applying a suitable DC voltage at the secondary terminal charges, electric current reaches steady state value in the loop, cut off direct supply then, secondary inductance begins discharge, reduce to zero up to loop current, measure corresponding exciting current and induced voltage, carry out related operation and obtain the exciting characteristic curve of current transformer, when current transformer is saturated, corresponding magnetic flux s is the saturation flux amount, and the magnetic flux r of correspondence is remanent magnetism when exciting current is zero, and the remanent magnetism coefficient of trying to achieve current transformer is Kr=φ r/ φ s;

Exist not enough: first DC-method is not considered the non-vanishing this situation of the initial magnetic flux of mutual inductor; If the inductance value of Secondary Winding coil is very little, then charging process is very short, is unfavorable for the accurate collection of electric current, voltage data.

(3) second DC-method

Particular content is: with the primary side open circuit of current transformer, the electric charge that adopts capacitor from the secondary terminal to the current transformer iron core excitation, applying a suitable DC voltage at the secondary terminal charges, electric current reaches steady state value Im in the loop, in measuring process, measure time constant T, T is carried out related operation obtain magnetizing inductance Lm, according to the formula φ=Lm*Im that calculates magnetic flux, calculate saturation flux amount φ s respectively, remanent magnetism φ r, the remanent magnetism coefficient of finally trying to achieve current transformer are Kr=φ r/ φ s;

Exist not enough: the non-vanishing situation of initial magnetic flux of not considering current transformer; Measuring process is loaded down with trivial details, complicated operation.

(4) capacity discharge method

Particular content is: with the primary side open circuit of current transformer, the electric charge that adopts capacitor from the secondary terminal to the current transformer iron core excitation, saturated up to iron core, measure corresponding exciting current and induced voltage, carry out related operation and obtain the exciting characteristic curve of current transformer, when current transformer was saturated, corresponding magnetic flux s was the saturation flux amount, the magnetic flux r of correspondence is remanent magnetism when exciting current is zero, and the remanent magnetism coefficient of trying to achieve current transformer is Kr=φ r/ φ s;

Exist not enough: capacity discharge method is not considered the non-vanishing situation of the initial magnetic flux of mutual inductor; Measuring process is loaded down with trivial details, complicated operation.

Need improvements: can be known by the described classic method test curve of Fig. 1, when the initial magnetic flux of current transformer is non-vanishing, φ s survey=φ s ﹣ φ (0), φ r survey=φ r ﹣ φ (0) in like manner, when calculating the remanent magnetism coefficient, Kr=φ r survey/φ s survey=(φ r ﹣ φ (0))/(φ s ﹣ φ (0)), therefore φ (0) is more big, the error of remanent magnetism COEFFICIENT K r is just more big, above-mentioned four kinds of methods, owing to ignore the non-vanishing volume situation of initial magnetic flux of current transformer, measure the remanent magnetism coefficient and have error, so in new measuring method, need to consider the non-vanishing situation of the initial magnetic flux of current transformer.

The utility model content

In order to overcome the deficiency that measures the method existence of remanent magnetism coefficient in the prior art at four kinds of above-mentioned current transformers, a kind of remanence of current transformer measuring system that provides, can avoid because ignoring the measuring error that the initial magnetic flux of mutual inductor brings when non-vanishing, improved the accuracy that current transformer measures the remanent magnetism coefficient, guarantee that current transformer in the justice of electric energy metrical and trade settlement use, has a good application prospect.

In order to achieve the above object, the technical scheme that adopts of the utility model is:

A kind of remanence of current transformer measuring system is characterized in that: comprise

The measuring process operating unit is used for current transformer charging operations, discharge operation and reverse charging operation;

Data acquisition unit, the secondary side data of be used for gathering current transformer, and send the data-signal of gathering to host computer;

Host computer is used for receiving the data-signal that data acquisition unit is gathered, and carries out data and handles, and calculates and demonstrates the remanent magnetism coefficient, judges the circuit running status of measuring process operating unit automatically, the mode of operation of control survey process operation unit;

Described host computer is connected with the measuring process operating unit by data acquisition unit, and described measuring process operating unit is connected with the secondary side of current transformer, and the secondary side of described current transformer also is connected with host computer by data acquisition unit.

Aforesaid remanence of current transformer measuring system, it is characterized in that: described measuring process operating unit comprises DC source, first relay, second relay, the 3rd relay and discharge resistance, described first relay control DC source forward inserts the secondary side of current transformer, second relay control DC source oppositely inserts the secondary side of current transformer, and the 3rd relay control discharge resistance inserts the secondary side of current transformer.

Aforesaid remanence of current transformer measuring system is characterized in that: described data acquisition unit comprises

Current sensor is for the exciting current signal that measures current transformer;

Voltage sensor is for the terminal voltage of the secondary side terminal that measures current transformer;

Data collecting card be used for to be gathered current signal and the voltage signal of current sensor, voltage sensor output, sends host computer to, and receive host computer send control signal, the folding of control survey process operation unit repeat circuit.

The beneficial effects of the utility model are: the data-signal of the current transformer that the utility model host computer receiving data units transmits, carrying out related data handles, calculate the remanent magnetism coefficient, and judge the running status of measuring process operating unit automatically, the closure state of pilot relay, under the primary side open-circuit condition of current transformer, terminal in secondary side carries out positive charge successively to the current transformer state of saturation, discharge, reverse charging is to the current transformer state of saturation, measure secondary terminals voltage and exciting current in these three processes, obtain the positive charge process through computing, discharge process, the flux change amount of reverse charging process, again to this three flux change amounts computing, can obtain remanent magnetism coefficient accurately, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanent magnetism coefficient measuring error of the non-vanishing generation of the initial magnetic flux unshakable in one's determination of current transformer, improved the accuracy that current transformer measures the remanent magnetism coefficient, guarantee that current transformer in the justice of electric energy metrical and trade settlement use, has a good application prospect.

Description of drawings

Fig. 1 is the test curve of traditional remanence of current transformer measuring method.

Fig. 2 is the system chart of remanence of current transformer measuring system of the present utility model.

Fig. 3 is the structure principle chart of remanence of current transformer measuring system of the present utility model.

The structure principle chart of Fig. 4 remanence of current transformer measuring system of the present utility model.

Fig. 5 is the test curve of remanence of current transformer measuring method of the present utility model.

Embodiment

Below in conjunction with Figure of description, the utility model is further described.

As shown in Figures 2 and 3, remanence of current transformer measuring system of the present utility model comprises

The measuring process operating unit is used for current transformer 29 charging operations, discharge operation and reverse charging operation;

Data acquisition unit, the secondary side data of be used for gathering current transformer 29, and send the data-signal of gathering to host computer 14;

Host computer 14 is used for receiving the data-signal that data acquisition unit is gathered, and carries out data and handles, and calculates and demonstrates the remanent magnetism coefficient, judges the circuit running status of measuring process operating unit automatically, the mode of operation of control survey process operation unit;

Host computer 14 is connected with the measuring process operating unit by data acquisition unit, and the measuring process operating unit is connected with the secondary side of current transformer 29, and the secondary side of current transformer 29 also is connected with host computer 14 by data acquisition unit.

Described measuring process operating unit comprises DC source 1, first relay 2, second relay 5, the 3rd relay 8 and discharge resistance 10, first relay 2 is provided with normally opened contact 3,4, second relay 5 is provided with normally opened contact 6,7, the 3rd relay 8 is provided with normally opened contact 9, first relay, 2 control DC source, 1 forward inserts the secondary side of current transformer, second relay, 5 control DC source 1 oppositely insert the secondary side of current transformer 29, and the 3rd relay 8 control discharge resistances 10 insert the secondary side of current transformer 29;

Described data acquisition unit comprises current sensor 11, is used for measuring the exciting current signal of current transformer 29; Voltage sensor 12 is for the terminal voltage of the secondary side terminal that measures current transformer 29; Data collecting card 13 be used for to be gathered current signal and the voltage signal of current sensor 11, voltage sensor 12 outputs, sends host computer 14 to, and receive host computer 14 send control signal, the folding of each relay in the control survey process operation unit.

Need before the test first link 15 of current sensor 11 is connected with the secondary side end 16 of the same name of current transformer 29, second link 17 of current sensor 11 is connected with secondary side different name end 18, with the first input end 19 of measuring process operating unit, second input end 20, the 3rd input end 21 respectively with data collecting card 13 output terminal 22,23,24 be connected, first output terminal 25 with the measuring process operating unit, two output terminals 26 of current sensor 11 respectively with the A/D input end 27 of data collecting card 13, A/D input end 28 is connected.

The data-signal of the current transformer 29 that host computer 14 receiving data units of the present utility model transmit, carrying out related data handles, calculate the remanent magnetism coefficient, and judge the running status of measuring process operating unit automatically, control the closure state of each relay, under the primary side open-circuit condition of current transformer 29, terminal to secondary side carries out positive charge successively to current transformer 29 state of saturation, discharge, reverse charging is to current transformer 29 state of saturation, measure secondary terminals voltage and exciting current in these three processes, obtain the positive charge process through computing, discharge process, the flux change amount of reverse charging process, again to this three flux change amounts computing, can obtain remanent magnetism coefficient accurately, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanent magnetism coefficient measuring error of the non-vanishing generation of the initial magnetic flux unshakable in one's determination of current transformer, improved the accuracy that current transformer measures the remanent magnetism coefficient, concrete measuring method, as shown in Figure 4, may further comprise the steps

First relay, 2 closures in step (1) the host computer 14 control survey process operation unit to the operation of current transformer 29 positive charge, are calculated Secondary Winding direct current resistance resistance R _CT

Step (2) judges whether current transformer 29 has arrived the positive charge state of saturation, if arrived the positive charge state of saturation, 2 disconnections of first relay, the 3rd relay 8 closures in the host computer 14 control survey process operation unit, current transformer 29 is carried out discharge operation, calculate the flux change amount φ in the positive charge operating process ₁

Step (3) is judged whether current transformer 29 discharges and is finished, if discharge is finished, second relay, 5 closures, the 3rd relay 8 disconnect in the host computer 14 control survey process operation unit, to current transformer 29 reverse chargings operation, calculate the flux change amount φ in the discharge process ₂

Step (4) judges whether current transformer 29 has arrived the reverse charging state of saturation, if arrived the reverse charging state of saturation, 5 disconnections of second relay, the 3rd relay 8 closures in the host computer 14 control survey process operation unit, current transformer 29 is carried out discharge operation, calculate the flux change amount φ in the reverse charging operating process ₃

Step (5) judges whether current transformer 29 discharges and finishes that if discharge is finished, the 3rd relay 8 disconnects in the host computer 14 control survey process operation unit;

Step (6) is according to the flux change amount φ in the discharge process ₂With the flux change amount φ in the reverse charging operating process ₃, the remanent magnetism coefficient of calculating current transformer 29;

The remanent magnetism coefficient of the current transformer 29 of 14 pairs of calculating of step (7) host computer is preserved and is shown.

Calculate Secondary Winding direct current resistance resistance R in the step (1) _CT, obtain according to formula (1)

$R_{\mathrm{CT}}=\frac{U_1}{I_1}---\left(1\right)$

Wherein, I ₁Be exciting current I in the operating process of current transformer positive charge _mStablize the Current Transformer Secondary side current value when constant, U ₁Be exciting current I in the operating process of current transformer positive charge _mStablize the current transformer secondary side magnitude of voltage when constant;

Calculate the flux change amount φ in the positive charge operating process in the step (2) ₁Method as follows,

1) according to formula (2), obtains positive charge to exciting current I _mStablize the flux change amount Φ when constant ₀,

${\mathrm{\Φ}}_0={\∫}_{t_0}^{t_1}(U-R*I_m)\mathrm{dt}---\left(2\right)$

Wherein, R is 1, I for the direct current resistance preset value _mBe exciting current, U is the voltage at Current Transformer Secondary terminal two ends, t ₀Be the initial time of positive charge, t ₁For working as exciting current I _mStablize the moment when constant;

2) according to formula (3), obtain the flux change amount φ in the positive charge operating process ₁It is as follows,

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002913647400021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}$

（3）

Wherein, t2 is the moment of positive charge state of saturation.

The derivation of formula (3) is as follows, and the flux change amount φ 1 in the positive charge operating process is,

${\mathrm{\&Phi;}}_1{\&Integral;}_{t_0}^{t_2}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002913647400021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-{\&Integral;}_{t_0}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(11\right)$

In the following formula ${\&Integral;}_{t_0}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}={\&Integral;}_{t_0}^{t_1}(R_{\mathrm{CT}}*I_m)\mathrm{dt}+{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(12\right)$

Can be got by formula (11), (12),

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_1}\mathrm{Udt}-{\&Integral;}_{t_0}^{t_1}(R_{\mathrm{CT}}*I_m)\mathrm{dt}-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(13\right)$

By formula (2) Shi Kede,,

${\&Integral;}_{t_0}^{t_1}(R*I_m)\mathrm{dt}={\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt}---\left(14\right)$

Obtain formula (3) by formula (13), (14),

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002913647400021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(3\right)$

Flux change amount φ in the described calculating discharge process of step (3) ₂, obtaining according to formula (4), formula (4) is as follows,

${\mathrm{\&Phi;}}_2={\&Integral;}_{t_2}^{t_3}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(4\right)$

Wherein, t ₃For discharge in the step (3) finish the moment.

Flux change amount φ in the described calculating reverse charging of step (4) operating process ₃, obtaining according to formula (5), formula (5) is as follows,

${\mathrm{\&Phi;}}_3={\&Integral;}_{t_3}^{t_4}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(5\right)$

Wherein, t ₄Be the moment of reverse charging state of saturation.

The method of the remanent magnetism coefficient of the described calculating current transformer of step (6) is as follows,

1) according to formula (6), the flux value φ when the calculating positive charge is saturated _s,

φ _s=φ _r﹣φ ₂ （6）

Wherein, φ _rBe remanence of current transformer;

2) according to formula (7), calculate reverse saturation flux value-φ _s,

-φ _s=-φ _r﹣φ ₃ （7）

3) according to formula (6) and formula (7), obtain

φs=﹣(φ2+φ3)/2 （8）

φr=(φ2﹣φ3)/2 （9）

4) according to the remanent magnetism COEFFICIENT K _rComputing formula (10) obtains the remanent magnetism COEFFICIENT K _rFor,

K _r=φ _r/φ _s （10）

With formula (4), formula (5), formula (8) and formula (9) substitution formula (10), obtain the remanent magnetism COEFFICIENT K _rFor,

$K_r=\frac{{\&Integral;}_{t_2}^{t_4}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}}{{\&Integral;}_{t_3}^{t_4}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}-{\&Integral;}_{t_2}^{t_3}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}}.$

As shown in Figure 5, adopt the test curve of the utility model thermometrically method, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanent magnetism coefficient measuring error of the non-vanishing generation of the initial magnetic flux unshakable in one's determination of current transformer, improved the accuracy that current transformer measures the remanent magnetism coefficient greatly.

More than show and described ultimate principle of the present utility model, principal character and advantage.The technician of the industry should understand; the utility model is not restricted to the described embodiments; that describes in above-described embodiment and the instructions just illustrates principle of the present utility model; under the prerequisite that does not break away from the utility model spirit and scope; the utility model also has various changes and modifications, and these changes and improvements all fall in claimed the utility model scope.The claimed scope of the utility model is defined by appending claims and equivalent thereof.

Claims (3)

1. a remanence of current transformer measuring system is characterized in that: comprise

The measuring process operating unit is used for current transformer charging operations, discharge operation and reverse charging operation;

Data acquisition unit, the secondary side data of be used for gathering current transformer, and send the data-signal of gathering to host computer;

Host computer is used for receiving the data-signal that data acquisition unit is gathered, and carries out data and handles, and calculates and demonstrates the remanent magnetism coefficient, judges the circuit running status of measuring process operating unit automatically, the mode of operation of control survey process operation unit;

Described host computer is connected with the measuring process operating unit by data acquisition unit, and described measuring process operating unit is connected with the secondary side of current transformer, and the secondary side of described current transformer also is connected with host computer by data acquisition unit.

2. remanence of current transformer measuring system according to claim 1, it is characterized in that: described measuring process operating unit comprises DC source, first relay, second relay, the 3rd relay and discharge resistance, described first relay control DC source forward inserts the secondary side of current transformer, second relay control DC source oppositely inserts the secondary side of current transformer, and the 3rd relay control discharge resistance inserts the secondary side of current transformer.

3. remanence of current transformer measuring system according to claim 1, it is characterized in that: described data acquisition unit comprises

Current sensor is for the exciting current signal that measures current transformer;

Voltage sensor is for the terminal voltage of the secondary side terminal that measures current transformer;

Data collecting card be used for to be gathered current signal and the voltage signal of current sensor, voltage sensor output, sends host computer to, and receive host computer send control signal, the folding of control survey process operation unit repeat circuit.

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