CN103176147B - Current transformer remanence measurement system and method - Google Patents

Abstract

The invention discloses current transformer remanence measurement system and method. An upper computer receives current transformer data signals transmitted by a data unit. Related data processing is performed to calculate remanence coefficient. Operation states of an operating unit are automatically judged during measurement, and on and off of a relay are controlled. When the primary side of a current transformer is open, the secondary side is sequentially subjected to positive charging, discharging and revere charging until the current transformer is saturated. Flux variations in positive charging process, discharging process and revere charging process are obtained by calculation. The three flux variations are then calculated to obtain accurate remanence coefficient. Therefore, errors in remanence coefficient measurement caused when initial core flux of the current transformer is not zero are eliminated, accuracy in remanence coefficient measurement for the current transformer is increased, and fairness in electric energy measurement and trade settlement for the current transformer is guaranteed. The current transformer remanence measurement system and method have promising application prospect.

Description

Remanence of current transformer measuring system and measuring method

Technical field

The present invention relates to a kind of remanence of current transformer measuring system and measuring method, belong to electrical energy parameter field of measuring technique.

Background technology

Direct current remanent magnetism in current transformer can affect transformer error, thereby impact metering and protective value, manufacturing plant is merely able to guarantee there is no remanent magnetism before current transformer dispatches from the factory, the error effect amount causing is thus limited in a qualified scope, if current signal is taken from and is subject to direct current remanent magnetism to affect the error of serious current transformer when causing actual motion to increase, current transformer affects significantly meter characteristic after producing remanent magnetism, than error under normal condition, double above, and even seriously overproof, cause electric energy metrical and trade settlement unjust, in electrical network, electromagnetic current transducer accounts for the overwhelming majority, exist in various degree direct current remanent magnetism to affect problem.In order to keep instrument not to be subject to the damage of fault current, measure winding is more easily saturated, more easily make remanent magnetism remain 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 direct current magnetic after effect, take the effective precautionary measures, remanence coefficient is that therefore an important parameter of researching DC magnetic after effect adopts AC method in the urgent need to selecting rational method accurately to measure G216847-1997 < < protective current transformer, transient characterisitics technical requirement > > regulation to remanence coefficient, the first DC-method, the second DC-method and capacity discharge method measure remanence coefficient, it is below the particular content to these four kinds of methods, the explanation of the deficiency existing and the part requiring further improvement:

(1) AC method

Particular content is: on the secondary terminals of current transformer, apply sine wave AC voltage, primary side open circuit, measure corresponding exciting current and induced voltage, and need measure in addition the value of secondary terminals direct current resistance, 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 saturation flux amount, then regulate exciting current, when exciting current is zero, corresponding magnetic flux r is remanent magnetism, and the remanence coefficient of trying to achieve current transformer is Kr=φ r/ φ s;

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

(2) first DC-method

Particular content is: by the primary side open circuit of current transformer, at secondary terminals, applying a suitable DC voltage charges, until electric current reaches steady state value in loop, then cut off direct supply, secondary inductance starts electric discharge, until loop current reduces to zero, 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 saturation flux amount, when exciting current is zero, corresponding magnetic flux r is remanent magnetism, the remanence coefficient of trying to achieve current transformer is Kr=φ r/ φ s,

Shortcomings: the 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, charging process is very short, is unfavorable for the accurate collection of electric current, voltage data.

(3) second DC-method

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

Shortcomings: 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: by the primary side open circuit of current transformer, the electric charge that adopts capacitor from secondary terminals to current transformer iron core excitation, until unshakable in one's determination saturated, 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 saturation flux amount, when exciting current is zero, corresponding magnetic flux r is remanent magnetism, and the remanence coefficient of trying to achieve current transformer is Kr=φ r/ φ s;

Shortcomings: 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: by the classic method test curve described in Fig. 1, can be known, 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, while calculating remanence coefficient, Kr=φ r survey/φ s survey=(φ r-φ (0))/(φ s-φ (0)), therefore φ (0) is larger, the error of remanence coefficient Kr is just larger, above-mentioned four kinds of methods, owing to ignoring the non-vanishing volume situation of initial magnetic flux of current transformer, measure remanence coefficient and have error, so need to consider the non-vanishing situation of the initial magnetic flux of current transformer in new measuring method.

Summary of the invention

In order to overcome the deficiency that measures the method existence of remanence coefficient in prior art for four kinds of above-mentioned current transformers, a kind of remanence of current transformer measuring system and the measuring method that provide, can avoid the measuring error of bringing when non-vanishing because ignoring the initial magnetic flux of mutual inductor, improved the accuracy that current transformer measures remanence 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 solution adopted in the present invention is:

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

Measuring process operating unit, for operating current transformer charging operations, discharge operation and reverse charging;

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

Host computer, the data-signal gathering for receiving data acquisition unit, carries out data processing, calculates and demonstrates remanence coefficient, the circuit running status of automatic decision measuring process operating unit, the mode of operation of control survey process operation unit;

Described host computer is connected with 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 is also 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, the first relay, the second relay, the 3rd relay and discharge resistance, the secondary side of described the first Control DC source forward access current transformer, the second Control DC source oppositely accesses the secondary side of current transformer, the secondary side of the 3rd Control discharge resistance access current transformer.

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

Current sensor, for measuring the exciting current signal of current transformer;

Voltage sensor, for measuring the terminal voltage of the secondary side terminal of current transformer;

Data collecting card, for gathering current signal and the voltage signal of current sensor, voltage sensor output, sends host computer to, and receives the control signal of sending of host computer, the folding of control survey process operation unit repeat circuit.

The measuring method of the remanence of current transformer measuring system based on above-mentioned, is characterized in that: comprises the following steps,

The first relay closes in step (1) PC control measuring process operating unit, to the operation of current transformer positive charge, calculates Secondary Winding direct current resistance resistance R _cT;

Step (2) judges whether current transformer has arrived positive charge state of saturation, if arrived positive charge state of saturation, the first relay disconnection, the 3rd relay closes in PC control measuring process operating unit, current transformer is carried out to discharge operation, calculate the flux change amount φ in positive charge operating process ₁;

Step (3) judges whether current transformer has discharged, if discharged, in PC control measuring process operating unit, the second relay closes, the 3rd relay disconnect, and to current transformer reverse charging operation, calculate the flux change amount φ in discharge process ₂;

Step (4) judges whether current transformer has arrived reverse charging state of saturation, if arrived reverse charging state of saturation, the second relay disconnection, the 3rd relay closes in PC control measuring process operating unit, current transformer is carried out to discharge operation, calculate the flux change amount φ in reverse charging operating process ₃;

Step (5) judges whether current transformer has discharged, if discharged, in PC control measuring process operating unit, the 3rd relay disconnects;

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

Step (7) host computer is preserved the remanence coefficient of the current transformer calculating and is shown.

The measuring method of aforesaid remanence of current transformer measuring system, is characterized in that: step (1) is calculated Secondary Winding direct current resistance resistance R _cT, according to formula (1), obtain

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

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

The measuring method of aforesaid remanence of current transformer measuring system, is characterized in that: step (2) is calculated the flux change amount φ in positive charge operating process ₁method as follows:

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

${\mathrm{\&Phi;}}_0={\&Integral;}_{t_0}^{t_1}(U-R*I_m)\mathrm{dt}---\left(2\right)$

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

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

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}$

（3）

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

The measuring method of aforesaid remanence of current transformer measuring system, is characterized in that: the flux change amount φ in the described calculating discharge process of step (3) ₂, according to formula (4), obtaining, 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 discharged in step (3) the moment.

The measuring method of aforesaid remanence of current transformer measuring system, is characterized in that: the flux change amount φ in the described calculating reverse charging of step (4) operating process ₃, according to formula (5), obtaining, 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 ₄for the moment of reverse charging state of saturation.

The measuring method of aforesaid remanence of current transformer measuring system, is characterized in that: the method for the remanence coefficient of the described calculating current transformer of step (6) is as follows,

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

φ _s=φ _r-φ ₂ （6）

Wherein, φ _rfor 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 remanence coefficient K _rcomputing formula (10), obtains remanence coefficient K _rfor,

K _r=φ _r/φ _s （10）

By formula (4), formula (5), formula (8) and formula (9) substitution formula (10), obtain remanence coefficient K _rfor,

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

The invention has the beneficial effects as follows: the data-signal of the current transformer that host computer receiving data units of the present invention transmits, carry out Correlation method for data processing, calculate remanence coefficient, and the running status of automatic decision measuring process operating unit, 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 current transformer state of saturation, electric discharge, reverse charging is to current transformer state of saturation, measure secondary terminals voltage and exciting current in these three processes, through computing, obtain positive charge process, discharge process, the flux change amount of reverse charging process, again to this three flux change amounts computing, can obtain remanence coefficient accurately, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanence 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 remanence coefficient, guarantee that current transformer is in the justice of electric energy metrical and trade settlement use, have a good application prospect.

Accompanying drawing explanation

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 invention.

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

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

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

Embodiment

Below in conjunction with Figure of description, the present invention is further illustrated.

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

Measuring process operating unit, for operating current transformer 29 charging operations, discharge operation and reverse charging;

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

Host computer 14, the data-signal gathering for receiving data acquisition unit, carries out data processing, calculates and demonstrates remanence coefficient, the circuit running status of automatic decision measuring process operating unit, the mode of operation of control survey process operation unit;

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

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

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

Before test, need the first link 15 of current sensor 11 to be connected with the secondary side Same Name of Ends 16 of current transformer 29, the second link 17 of current sensor 11 is connected with secondary side different name end 18, by the first input end of measuring process operating unit 19, the second input end 20, the 3rd input end 21 respectively with data collecting card 13 output terminal 22,23,24 be connected, by the first output terminal 25 of 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 invention transmit, carry out Correlation method for data processing, calculate remanence coefficient, and the running status of automatic decision measuring process operating unit, control the closure state of each relay, under the primary side open-circuit condition of current transformer 29, the terminal of secondary side is carried out to positive charge successively to current transformer 29 state of saturation, electric discharge, reverse charging is to current transformer 29 state of saturation, measure secondary terminals voltage and exciting current in these three processes, through computing, obtain positive charge process, discharge process, the flux change amount of reverse charging process, again to this three flux change amounts computing, can obtain remanence coefficient accurately, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanence 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 remanence coefficient, concrete measuring method, as shown in Figure 4, comprise the following steps,

The first relay 2 closures in step (1) host computer 14 control survey process operation unit, to current transformer 29 positive charge operations, calculate Secondary Winding direct current resistance resistance R _cT;

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

Step (3) judges whether current transformer 29 has discharged, if discharged, in host computer 14 control survey process operation unit, the second relay 5 closures, the 3rd relay 8 disconnect, and to current transformer 29 reverse charging operations, calculate the flux change amount φ in discharge process ₂;

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

Step (5) judges whether current transformer 29 has discharged, if discharged, in host computer 14 control survey process operation unit, the 3rd relay 8 disconnects;

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

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

In step (1), calculate Secondary Winding direct current resistance resistance R _cT, according to formula (1), obtain

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

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

In step (2), calculate the flux change amount φ in positive charge operating process ₁method as follows,

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

${\mathrm{\&Phi;}}_0={\&Integral;}_{t_0}^{t_1}(U-R*I_m)\mathrm{dt}---\left(2\right)$

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

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

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}$

（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 positive charge operating process is,

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}={\&Integral;}_{t_0}^{t_2}\mathrm{Udt}-{\&Integral;}_{t_0}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(11\right)$

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

By formula (11), (12), can be obtained,

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

By formula (2) Shi Ke get,,

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

By formula (13), (14), obtain formula (3),

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(3\right)$

Flux change amount φ in the described calculating discharge process of step (3) ₂, according to formula (4), obtaining, 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 discharged in step (3) the moment.

Flux change amount φ in the described calculating reverse charging of step (4) operating process ₃, according to formula (5), obtaining, 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 ₄for the moment of reverse charging state of saturation.

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

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

φ _s=φ _r-φ ₂ （6）

Wherein, φ _rfor 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 remanence coefficient K _rcomputing formula (10), obtains remanence coefficient K _rfor,

K _r=φ _r/φ _s （10）

By formula (4), formula (5), formula (8) and formula (9) substitution formula (10), obtain remanence 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 thermometrically method of the present invention, by increasing reverse charging to this process of current transformer state of saturation, eliminate the remanence coefficient measuring error of the non-vanishing generation of the initial magnetic flux unshakable in one's determination of current transformer, greatly improved the accuracy that current transformer measures remanence coefficient.

More than show and described ultimate principle of the present invention, principal character and advantage.The technician of the industry should understand; the present invention is not restricted to the described embodiments; that in above-described embodiment and instructions, describes just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.The claimed scope of the present invention is defined by appending claims and equivalent thereof.

Claims (5)

1. remanence of current transformer measuring method, is characterized in that: comprises the following steps,

The first relay closes in step (1) PC control measuring process operating unit, to the operation of current transformer positive charge, calculates Secondary Winding direct current resistance resistance RCT;

Step (2) judges whether current transformer has arrived positive charge state of saturation, if arrived positive charge state of saturation, the first relay disconnection, the 3rd relay closes in PC control measuring process operating unit, current transformer is carried out to discharge operation, calculate the flux change amount φ 1 in positive charge operating process;

Step (3) judges whether current transformer has discharged, if discharged, in PC control measuring process operating unit, the second relay closes, the 3rd relay disconnect, and to current transformer reverse charging operation, calculate the flux change amount φ 2 in discharge process;

Step (4) judges whether current transformer has arrived reverse charging state of saturation, if arrived reverse charging state of saturation, the second relay disconnection, the 3rd relay closes in PC control measuring process operating unit, current transformer is carried out to discharge operation, calculate the flux change amount φ 3 in reverse charging operating process;

Step (5) judges whether current transformer has discharged, if discharged, in PC control measuring process operating unit, the 3rd relay disconnects;

Step (6), according to the flux change amount φ 2 in discharge process and the flux change amount φ 3 in reverse charging operating process, is calculated the remanence coefficient of current transformer,

The method of the remanence coefficient of described calculating current transformer is as follows,

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

φs＝φr﹣φ2 (6)

Wherein, φ r is remanence of current transformer;

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

-φs＝-φr﹣φ3 (7)

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

φs＝﹣(φ2+φ3)/2 (8)

φr＝(φ2﹣φ3)/2 (9)

4) according to remanence coefficient Kr computing formula (10), obtain remanence coefficient Kr and be,

Kr＝φr/φs (10)

By formula (4), formula (5), formula (8) and formula (9) substitution formula (10), obtain remanence coefficient Kr and be,

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

Step (7) host computer is preserved the remanence coefficient of the current transformer calculating and is shown.

2. remanence of current transformer measuring method according to claim 1, is characterized in that: step (1) is calculated Secondary Winding direct current resistance resistance RCT, according to formula (1), obtains

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

Wherein, I1 is that in the operating process of current transformer positive charge, exciting current Im stablizes Current Transformer Secondary side current value when constant, and U1 is that in the operating process of current transformer positive charge, exciting current Im stablizes current transformer secondary side magnitude of voltage when constant.

3. remanence of current transformer measuring method according to claim 1, is characterized in that: the method that step (2) is calculated the flux change amount φ 1 in positive charge operating process is as follows:

1) according to formula (2), obtain positive charge and stablize the flux change amount Φ 0 when constant to exciting current Im,

${\mathrm{\&Phi;}}_0={\&Integral;}_{t_0}^{t_1}(U-R*I_m)\mathrm{dt}---\left(2\right)$

Wherein, R is that direct current resistance preset value is that 1, Im is exciting current, and U is the voltage at Current Transformer Secondary terminal two ends, the initial time that t0 is positive charge, moment when t1 is constant for stablizing as exciting current Im;

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

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(3\right)$

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

4. remanence of current transformer measuring method according to claim 1, is characterized in that: the flux change amount φ 2 in the described calculating discharge process of step (3), according to formula (4), obtain, and 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, t3 be discharged in step (3) the moment.

5. remanence of current transformer measuring method according to claim 1, is characterized in that: the flux change amount φ 3 in the described calculating reverse charging of step (4) operating process, according to formula (5), obtain, and 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, t4 is the moment of reverse charging state of saturation.