CN103176147A - 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 the 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 that causes thus is limited in a qualified scope, if the error when current signal is taken from and is subjected to direct current remanent magnetism to affect serious current transformer will to cause actual motion increases, current transformer affects significantly meter characteristic after producing remanent magnetism, double above than error under normal condition, 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 subjected to the damage of fault current, measure winding is easier to be 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 the 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 " technical requirement of protective current transformer, transient characterisitics " 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 that exists and the part that requires further improvement:

(1) AC method

Particular content is: apply sine wave AC voltage on the secondary terminals of current transformer, the 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 the saturation flux amount, then regulate exciting current, corresponding magnetic flux r is remanent magnetism when exciting current is zero, 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; Can not directly obtain the value of Secondary Winding direct current resistance in test process, 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, 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 secondary terminals charges, until in the loop, electric current reaches steady state value, then cut off direct supply, secondary inductance begins 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 the saturation flux amount, corresponding magnetic flux r is remanent magnetism when exciting current is zero, 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: with the primary side open circuit of current transformer, the electric charge that adopts capacitor from secondary terminals to the current transformer iron core excitation, applying a suitable DC voltage at secondary terminals charges, until in the loop, electric current reaches steady state value Im, measure time constant T in measuring process, T is carried out related operation 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 are 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: with the primary side open circuit of current transformer, the electric charge that adopts capacitor from secondary terminals to the 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 was saturated, corresponding magnetic flux s was the saturation flux amount, corresponding magnetic flux r is remanent magnetism when exciting current is zero, 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: 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 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, due to the non-vanishing volume situation of initial magnetic flux of ignoring 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 Novel 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 brought 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 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 is used for gathering the secondary side data of current transformer, and sends the data-signal that gathers to host computer;

Host computer is used for the data-signal that the receive data collecting unit gathers, and carries out data and processes, and 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 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, 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 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 gather 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.

Measuring method based on above-mentioned remanence of current transformer measuring system 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, is calculated Secondary Winding direct current resistance resistance R _CT

Step (2) judges whether current transformer has arrived the positive charge state of saturation, if arrived the 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 discharge operation, calculate the flux change amount φ in the positive charge operating process ₁

Step (3) judges whether current transformer discharges to be completed, if discharge is completed, 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 the reverse charging state of saturation, if arrived the 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 discharge operation, calculate the flux change amount φ in the reverse charging operating process ₃

Step (5) judges whether current transformer discharges to be completed, if discharge is completed, 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 the reverse charging operating process ₃, the remanence coefficient of calculating current transformer;

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

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, 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.

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 the positive charge operating process ₁Method as follows:

1) according to formula (2), obtain 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 that the direct current resistance preset value is 1, I _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,

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002912701800021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}$

（3）

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

The 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, 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 step (3) complete 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, 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 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), 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 remanence coefficient K _rComputing formula (10) obtains remanence coefficient K _rFor,

K _r=φ _r/φ _s （10）

With 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 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 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.

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 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

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

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

Host computer 14 is used for the data-signal that the receive data collecting unit gathers, and carries out data and processes, and 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 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, 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, 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 gather 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.

Need before test the first link 15 of current sensor 11 is 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, with the first input end 19 of measuring process operating unit, the second input end 20, the 3rd input end 21 respectively with data collecting card 13 output terminal 22,23,24 be connected, the 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 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, 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 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, 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, in host computer 14 control survey process operation unit the first relay 2 disconnect, the 3rd relay 8 closures, current transformer 29 is carried out discharge operation, calculate the flux change amount φ in the positive charge operating process ₁

Step (3) judges whether current transformer 29 discharges and completes, if discharge is completed, 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 chargings operations, calculate the flux change amount φ in 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, in host computer 14 control survey process operation unit the second relay 5 disconnect, the 3rd relay 8 closures, 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 to be completed, if discharge is completed, 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 the 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 shows.

Calculate Secondary Winding direct current resistance resistance R in 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 step (2) ₁Method as follows,

1) according to formula (2), obtain positive charge to exciting current I _mStablize the 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 the direct current resistance preset value is 1, I _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,

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002912701800021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}$

（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,

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{t_2}(U-R_{\mathrm{CT}}*I_m)\mathrm{dt}={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002912701800021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-{\&Integral;}_{t_0}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(11\right)$

In 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),

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002912701800021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-{\&Integral;}_{t_0}^{t_1}(R_{\mathrm{CT}}*I_m)\mathrm{dt}-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(13\right)$

By formula (2) Shi 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),

${\mathrm{\&Phi;}}_1={\&Integral;}_{t_0}^{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002912701800021.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}\mathrm{Udt}-\frac{R_{\mathrm{CT}}}{R}({\mathrm{\&Phi;}}_0-{\&Integral;}_{t_0}^{t_1}\mathrm{Udt})-{\&Integral;}_{t_1}^{t_2}(R_{\mathrm{CT}}*I_m)\mathrm{dt}---\left(3\right)$

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 step (3) complete 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 remanence 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 remanence coefficient K _rComputing formula (10) obtains remanence coefficient K _rFor,

K _r=φ _r/φ _s （10）

With 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.

Above demonstration 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 describes in above-described embodiment and instructions 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 (9)

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 is used for gathering the secondary side data of current transformer, and sends the data-signal that gathers to host computer;

Host computer is used for the data-signal that the receive data collecting unit gathers, and carries out data and processes, and 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 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, 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.

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 gather 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.

4. based on the measuring method of the remanence of current transformer measuring system of claim 1, it is characterized in that: comprise the following steps,

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

Step (2) judges whether current transformer has arrived the positive charge state of saturation, if arrived the 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 discharge operation, calculate the flux change amount φ in the positive charge operating process ₁

Step (3) judges whether current transformer discharges to be completed, if discharge is completed, 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 the reverse charging state of saturation, if arrived the 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 discharge operation, calculate the flux change amount φ in the reverse charging operating process ₃

Step (5) judges whether current transformer discharges to be completed, if discharge is completed, 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 the reverse charging operating process ₃, the remanence coefficient of calculating current transformer;

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

5. the measuring method of remanence of current transformer measuring system according to claim 4, is characterized in that: step (1) calculating Secondary Winding direct current resistance resistance R _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.

6. the measuring method of remanence of current transformer measuring system according to claim 4, is characterized in that: the flux change amount φ in the operating process of step (2) calculating positive charge ₁Method as follows:

1) according to formula (2), obtain positive charge to exciting current I _mStablize the 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 the direct current resistance preset value is 1, I _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,

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

（3）

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

7. the measuring method of remanence of current transformer measuring system according to claim 4, is characterized in that: the 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 step (3) complete the moment.

8. the measuring method of remanence of current transformer measuring system according to claim 4, is characterized in that: the 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.

9. the measuring method of remanence of current transformer measuring system according to claim 4, it 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), 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 remanence coefficient K _rComputing formula (10) obtains remanence coefficient K _rFor,

K _r=φ _r/φ _s （10）

With formula (4), formula (5), formula (8) and formula (9) substitution formula (10), obtain remanence coefficient K _rFor,

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

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