CN215678525U - Anti-direct-current-component two-stage current transformer for electric energy meter and calibrating device thereof - Google Patents
Anti-direct-current-component two-stage current transformer for electric energy meter and calibrating device thereof Download PDFInfo
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Abstract
The utility model provides a direct-current component resistant two-stage current transformer for an electric energy meter and a calibrating device thereof. Comprising a main core T1Auxiliary iron core T2Compensation coil NBPrimary coil N1And a secondary coil N2Compensating coil NBWound around a main core T1The main iron core and the auxiliary iron core are distributed in parallel, and the main iron core and the auxiliary iron core are wound with a secondary coil N together2And a primary coil N1(ii) a Compensation coil NBPolar terminal and secondary coil N2Is connected with the polar end of the compensating coil NBNon-polar terminal and secondary coil N2Are connected. The auxiliary iron core with strong saturation resistance is used as the iron core of the first-stage current transformer of the two-stage current transformer, the requirement of the current transformer on the accuracy under the condition of direct current magnetic biasing is met, the auxiliary iron core and the compensation coil wound on the main iron core form the second-stage current transformer together, the second-stage current transformer is used for reducing the error of the current transformer, and the design size of the main iron core can be reduced under the same error precision.
Description
Technical Field
The utility model relates to a direct-current component resisting two-stage current transformer for an electric energy meter and a direct-current component resisting current transformer calibrating device, and belongs to the technical field of electric energy metering.
Background
The current transformer is a key component in the watt-hour meter and is mainly used for measuring the actual current flowing through. In recent years, the phenomenon of direct current magnetic bias becomes more serious, so that people are promoted to increase the research strength on the effect, and scientific countermeasures are also appeared in succession. The current transformer with the function of resisting the direct current component adopts a composite iron core structure, has higher alternating current measurement accuracy, and can control the influence quantity of the direct current component and the even harmonic in an alternating current circuit on the watt-hour meter within the standard requirement.
When the external environment temperature changes, the internal impedance of the secondary coil changes accordingly. The larger the internal impedance of the secondary coil is, the larger the internal impedance variation of the secondary coil caused by temperature change is, which results in the larger error variation of the anti-dc current transformer, so that the error of the anti-dc current transformer is deviated much from that of the anti-dc current transformer when the anti-dc current transformer operates at the limit temperature.
The current transformer is used inside the electric energy meter to carry out isolation measurement on three-phase current, and the precision of the electric energy meter can be directly influenced by the error of the current transformer. Errors in the pure sine wave current measurement and the half-wave current measurement are required according to the requirement of electric energy meter verification regulations, and therefore a corresponding detection device is required to carry out error test on the current transformer. Because the error of the current transformer under the sine current and the half-wave current has larger difference, the grade of the current transformer under the sine current is generally 0.2 grade to 0.02 grade; and the specific difference error limit value is +/-3% under the half-wave current, and the angular difference limit value is +/-500'. When the measured angular difference is large, the specific difference and the angular difference obtained by measuring with the transformer calibrator of the rectangular coordinate system have large systematic principle errors, so that the error of the current transformer needs to be measured in a polar coordinate mode.
SUMMERY OF THE UTILITY MODEL
The utility model aims to overcome the defects of the prior art and provides a direct-current component resistant two-stage current transformer and a direct-current component resistant current transformer calibrating device for an electric energy meter, which can simultaneously meet the accurate measurement of the current transformer in alternating current and half-wave states.
In order to achieve the above object, the present invention provides a dc component resistant two-stage current transformer for an electric energy meter, comprising a main core T1Auxiliary iron core T2Compensation coil NBPrimary coil N1And a secondary coil N2Compensating coil NBWound around a main core T1The main iron core and the auxiliary iron core are distributed in parallel, and the main iron core and the auxiliary iron core are wound with a secondary coil N together2And a primary coil N1；
Compensation coil NBPolar terminal and secondary coil N2Is connected with the polar end of the compensating coil NBNon-polar terminal and secondary coil N2The non-polar ends of the two are connected;
wherein, the main iron core T1And an auxiliary core T2Nested inside and outside each other, primary coil N1And a secondary coil N2Simultaneously wound on the main iron core and the auxiliary iron core,
or, the main iron core T1And an auxiliary core T2Stacked one above the other, primary coil N1And a secondary coil N2And simultaneously wound on the main iron core and the auxiliary iron core.
Preferably, including the secondary coil internal impedance Z2Compensating coil internal impedance ZBAnd external load impedance Z, secondary coil N2Internal impedance Z of series secondary coil2And external load impedance Z, compensation coil NBInternal impedance Z of series compensation coilBThen is connected in parallel and externally connected on the load impedance Z.
Preferably, the secondary winding N2And the primary coil N1The turn ratio of the compensation coil N is equal to the rated current ratio of the current transformerBAnd a secondary coil N2The number of turns is the same.
Preferably, the main iron core is an iron core with initial permeability higher than 50000Gs/Oe, and the iron core with initial permeability higher than 50000Gs/Oe is a permalloy iron core or an ultracrystalline iron core.
Preferably, the auxiliary iron core is a constant permeability saturation resistant iron core, which is a cobalt-based amorphous iron core, a tension annealed nanocrystalline iron core, or an air-gap-processed silicon steel sheet iron core.
The calibrating device comprises a fluxgate sensor T1, a sampling resistor R1, a signal amplifier A1, a filter A2, an A/D collector A6 and a DSP digital signal processor A7, wherein the sampling resistor R1 is connected in series between a K1 pin of the fluxgate sensor T1 and a K2 pin of the fluxgate sensor T1, the signal amplifier A1 is connected in parallel to the resistor R1, the output end of the signal amplifier A1 is electrically connected with the input end of the filter A2, the output end of the filter A2 is electrically connected with the input end of the A/D collector A6, and the output end of the A/D collector A6 is electrically connected with the DSP digital signal processor A7.
Preferably, the current transformer comprises a sampling resistor R2, a signal amplifier A4, a filter A5, an inverting amplifier A3 and a load resistor RL, wherein a pin S1 of a current transformer CTx with direct current component to be tested is electrically connected with a non-inverting input end of the inverting amplifier A3, a pin S2 of the current transformer CTx with direct current component to be tested is electrically connected with the inverting input end of the inverting amplifier A3 after being connected with the load resistor RL in series, and the non-inverting input end of the inverting amplifier A3 is grounded;
the inverting input end of the inverting amplifier A3 is electrically connected with the output end of the inverting amplifier A3 after being connected with the sampling resistor R2 in series, the output end of the inverting amplifier A3 is electrically connected with the input end of the signal amplifier A4, the output end of the signal amplifier A4 is electrically connected with the input end of the filter A5, and the output end of the filter A5 is electrically connected with the input end of the A/D collector A6.
Preferably, the load circuit comprises a plurality of relays, the load resistor RL comprises a plurality of resistors, the resistors are sequentially connected in series, and each resistor is connected with a relay of a normally closed contact in parallel.
Preferably, the load resistor RL includes a1 Ω resistor, a2 Ω resistor, a4 Ω resistor, an 8 Ω resistor, a 16 Ω resistor, a 32 Ω resistor, a 64 Ω resistor, and a 128 Ω resistor, and the 1 Ω resistor, the 2 Ω resistor, the 4 Ω resistor, the 8 Ω resistor, the 16 Ω resistor, the 32 Ω resistor, the 64 Ω resistor, and the 128 Ω resistor are arranged in series;
the relay comprises eight relays, wherein a1 omega resistor, a2 omega resistor, a4 omega resistor, an 8 omega resistor, a 16 omega resistor, a 32 omega resistor, a 64 omega resistor and a 128 omega resistor are respectively connected with a relay with a normally closed contact in parallel.
Preferably, the fluxgate sensor T1 is wound by 1 turn on the primary winding as the 100A current output range; the fluxgate sensor T1 is wound with 10 turns of the primary winding as the 10A current output range; the fluxgate sensor T1 has a primary winding wound 100 turns as a 1A current output range.
Preferably, the sampling resistor R1 and the sampling resistor R2 are high precision low temperature drift resistors.
The utility model achieves the following beneficial effects:
the application provides electric energy meter is with anti direct current component doublestage current transformer adopts the iron core of the supplementary iron core that anti saturation capacity is strong as doublestage current transformer's first order current transformer, is used for satisfying the requirement of current transformer degree of accuracy under the direct current magnetic biasing condition on the one hand, and on the other hand plays the auxiliary action, constitutes second grade current transformer together with the compensation coil of coiling on the main iron core, is used for reducing current transformer's error, consequently can reduce the design size of main iron core under the same error precision.
Meanwhile, the error change of the double-stage current transformer manufactured by the structure caused by the internal impedance change of the secondary coil can be ignored when the double-stage current transformer operates at different limit temperatures. The problem that the error variation of the current transformer is increased due to the change of the internal impedance of the secondary coil when the anti-direct current transformer operates at different limit temperatures in the prior art is solved.
The iron core with strong anti-saturation capacity is used as the auxiliary iron core of the double-stage current transformer, and the fundamental wave precision of the double-stage current transformer is improved by 1-2 orders of magnitude under the premise that the main iron core with high initial magnetic permeability is the same.
The application provides a pair of anti direct current component doublestage current transformer calibrating installation for electric energy meter, direct measurement current transformer's primary current signal and secondary current signal, the ratio difference and the angular difference that obtain through handling. The problem that when the angular difference of the current transformer is more than 100' by the existing difference measurement method, the obtained specific difference has obvious system principle errors is solved, and the accurate measurement of the direct-current component resistant double-stage current transformer for the electric energy meter in alternating current and half-wave states can be simultaneously met.
The application provides electric energy meter is with anti direct current component doublestage current transformer adopts the iron core of the supplementary iron core that anti saturation capacity is strong as doublestage current transformer's first order current transformer, is used for satisfying the requirement of current transformer degree of accuracy under the direct current magnetic biasing condition on the one hand, and on the other hand plays the auxiliary action, constitutes second grade current transformer together with the compensation coil of coiling on the main iron core, is used for reducing current transformer's error, consequently can reduce the design size of main iron core under the same error precision. Meanwhile, the error change of the double-stage current transformer manufactured by the structure caused by the internal impedance change of the secondary coil can be ignored when the double-stage current transformer operates at different limit temperatures. The problem that the error variation of the current transformer is increased due to the change of the internal impedance of the secondary coil when the anti-direct current transformer operates at different limit temperatures in the prior art is solved.
Drawings
FIG. 1 is a functional schematic of the present application;
FIG. 2 is a diagram illustrating an inside-outside nesting structure in the first embodiment of the present application;
FIG. 3 is a top-bottom stacked structure of the second embodiment of the present application;
FIG. 4 is a schematic diagram of the operation of a prior art anti-DC component current transformer;
FIG. 5 is a functional block diagram of the present invention;
FIG. 6 is a schematic diagram of the calculation of the current transformer ratio difference and phase difference;
fig. 7 is a circuit diagram of the load RL.
Detailed Description
The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The following examples are only for illustrating the technical solutions of the present application more clearly, and the protection scope of the present application is not limited thereby. In addition, if a description of "a," "an," "two," etc. is referred to in this application, it is used for descriptive purposes only and not for purposes of indicating or implying relative importance or implicit ly indicating a number of technical features indicated. Thus, a feature defined as "a", "an", or "two" may explicitly or implicitly include at least one of the feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present application.
Example one
As shown in fig. 2, a main core T wound with a compensation coil1And an auxiliary core T2The primary coil is uniformly wound on the main iron core and the auxiliary iron core, and is electrically connected with the resistor for the electric energy meterA primary current terminal of the direct current component double-stage current transformer; the secondary coil is uniformly wound on the main iron core and the auxiliary iron core;
the compensation coil is uniformly wound on the main iron core, and the number of turns of the compensation coil is the same as that of the secondary coil.
Further, the present embodiment includes the secondary coil internal impedance Z2Compensating coil internal impedance ZBAnd external load impedance Z, secondary coil N2Internal impedance Z of series secondary coil2And external load impedance Z, compensation coil NBInternal impedance Z of series compensation coilBThen connected in parallel to the external load impedance Z.
The polar end of the secondary coil is connected with the polar end of the compensation coil to serve as the polar end of the secondary current of the direct-current component resisting double-stage current transformer for the electric energy meter, and the non-polar end of the secondary coil is connected with the non-polar end of the compensation coil to serve as the non-polar end of the secondary current of the direct-current component resisting double-stage current transformer for the electric energy meter;
further, the secondary coil N2And the primary coil N1The turn ratio of the secondary winding is equal to the rated current ratio of the current transformer, and the secondary winding N2And the compensation coil NBAre equal.
An iron core made of a constant magnetic permeability material with strong anti-saturation capacity is used as an auxiliary iron core, and a primary coil and a secondary coil are wound on the auxiliary iron core to form a first-stage current transformer. An iron core made of a high initial magnetic permeability material is used as a main iron core, and a primary coil, a secondary coil and a compensation coil are wound on the main iron core to form a second-stage current transformer. The primary coil wound on the auxiliary iron core and the primary coil wound on the main iron core are the same coil, and the secondary coil wound on the auxiliary iron core and the secondary coil wound on the main iron core are the same coil. The number of turns of the compensation coil on the main iron core is equal to that of the secondary coil. Thus, a two-stage current transformer is formed by the two-stage transformers.
Because doublestage current transformer's error is the negative value of first order and second grade current transformer error product, like this application under fundamental wave operating condition, its error will be than having 1 ~ 2 orders of magnitude less than when not having first order current transformer, and supplementary iron core has played the effect that reduces the fundamental wave error. When the primary working current contains a large direct-current component and a half-wave component, the auxiliary iron core of the first-stage current transformer can play a main role in reducing errors under the condition that the main iron core of the second-stage current transformer is seriously saturated, so that the errors of the auxiliary iron core meet the requirements specified by related regulations.
In addition, the internal impedance of the secondary coil changes along with the change of the external environment temperature, the error of the current transformer has a direct relation with the internal impedance of the secondary coil, and the error of the current transformer also changes along with the change of the external environment temperature. The problem is solved fundamentally, and the error influence of the change of the internal impedance of the secondary coil along with the temperature change on the direct-current component resistant double-stage current transformer for the electric energy meter can be ignored.
Fig. 1 is a working schematic diagram of an anti-dc component two-stage current transformer for an electric energy meter provided by the present application. Wherein T is1Is a main iron core, T2As an auxiliary core, N1Is a primary coil, N2Is a secondary coil, NBFor compensating the coil, Z is the external load impedance, Z2Is the internal impedance of the secondary coil, ZBTo compensate for coil internal impedance, I1For the primary current of a current transformer, I2For the current flowing in the secondary coil of the current transformer, IBFor compensating the current flowing in the coil for the current transformer, I2NIs the current transformer secondary current.
The first-stage current transformer of the anti-DC component two-stage current transformer for the electric energy meter consists of a primary coil N1Auxiliary iron core T2And a secondary coil N2Composition of external load impedance Z and secondary coil internal impedance Z2And constitute the secondary load impedance of the first stage current transformer. The magnetomotive force equation is
Wherein I01Excitation current generated for the first stage current transformer, hence the first stageThe error produced by the stage current transformer is
The secondary current transformer of the anti-DC component two-stage current transformer for the electric energy meter consists of a primary coil N1Secondary coil N2Main iron core T1And a compensation coil NBComposition, primary coil N1And a secondary coil N2Combining the primary coil of the second stage with an external load impedance Z and an internal compensation coil impedance ZBAnd the secondary load impedance of the second-stage current transformer is formed. The magnetomotive force equation is
Wherein I02The excitation current for the second stage current transformer, the error produced by the second stage current transformer being
For the whole DC component resistant two-stage current transformer for the electric energy meter, the secondary output current is
The magnetomotive force equation is
Therefore, the error of the anti-DC component double-stage current transformer for the whole electric energy meter is the negative value of the error product of the first-stage current transformer and the second-stage current transformer,
fig. 4 is a schematic diagram of the operation of a current transformer with anti-dc component in the prior art. Wherein, T1And T2Respectively a common iron core with high initial permeability and an anti-saturation iron with constant permeabilityA core.
Under the condition of power frequency, compared with the anti-DC component current transformer provided by the prior art in FIG. 4, the error of the anti-DC component current transformer is equal to the error epsilon of the second-stage current transformer of the anti-DC component two-stage current transformer for the electric energy meter2Are equal. And the error of the anti-DC component two-stage current transformer for the electric energy meter is epsilon ═ epsilon1ε2Because of e1Is substantially in the order of 10-1～10-2Therefore, the precision of the anti-direct-current component double-stage current transformer for the electric energy meter is improved by 1-2 orders of magnitude compared with the original anti-direct-current component current transformer in the prior art, and the accuracy is higher.
Under the condition of direct current magnetic biasing, the main iron core is saturated under the condition, and the main iron core cannot play an excitation role in the direct current component resisting two-stage current transformer for the electric energy meter, so that the auxiliary iron core with strong saturation resisting capability plays a main role at the moment, the excitation current is provided by the auxiliary iron core, and the error is determined by the magnetic performance of the auxiliary iron core.
Under the condition of extreme temperature operation, the error of a general current transformer is influenced by the change of the internal impedance of a secondary coil, so that the error of the current transformer is seriously deviated from the normal temperature. The error of the anti-direct-current component double-stage current transformer for the electric energy meter is mainly determined by the error of the second-stage current transformer, the impedance change of a secondary coil caused by the temperature change only affects the error of the first-stage current transformer, and the error influence on the double-stage current transformer is extremely small, so that the error influence of the temperature change on the anti-direct-current component double-stage current transformer for the electric energy meter is small.
At power frequency, the exciting current for the prior art anti-dc component current transformer provided in fig. 4 is basically composed of the main core T1The main iron core needs to provide a secondary induction potential of
Error is affected by secondary coil impedance Z2The temperature influence of (2) causes the error variation of the anti-direct-current component current transformer to be increased. The exciting current of the anti-direct-current component two-stage current transformer for the electric energy meterThe secondary induction potential required to be provided by the main iron core when the current is at the power frequency is
Due to the fact that
Therefore, it is not only easy to use
To produce
Is borne by the auxiliary core. Therefore, the change of the impedance of the secondary coil caused by the direct-current component resisting double-stage current transformer at the limit temperature can be ignored for the power frequency error of the direct-current component resisting double-stage current transformer for the electric energy meter.
Fig. 2 is an internal and external nested structure diagram of the direct-current component resistant two-stage current transformer for the electric energy meter, the compensation coil is uniformly wound on the main iron core, the main iron core on which the compensation coil is wound is placed on the inner side or the outer side of the auxiliary iron core, and the main iron core and the auxiliary iron core are stacked together to wind the primary coil and the secondary coil. Connecting the polar end of the compensating coil with the polar end of the secondary coil to be used as the secondary polar end of the anti-direct-current component two-stage current transformer for the electric energy meter; and the non-polar end of the compensating coil and the non-polar end of the secondary coil are connected to be used as the secondary non-polar end of the direct-current component resisting two-stage current transformer for the electric energy meter.
Table 1 shows the ratio difference and the phase difference between the dc component resistant two-stage current transformer for an electric energy meter provided by the present application and the dc component resistant current transformer in the prior art in two operating states of normal temperature and extreme high temperature (+85 ℃). The rated transformation ratio of the two current transformers is 5(60) A/2mA, and the technical parameters of a common iron core with high initial permeability and an anti-saturation iron core with constant permeability are kept consistent. Under the condition of power frequency, error data of the two current transformers at normal temperature are compared, and the ratio difference and the phase difference of the direct-current component resisting double-stage current transformer for the electric energy meter are smaller than those of the existing direct-current component resisting current transformer. The high temperature and normal temperature data of the two current transformers are compared, it can be seen that the ratio variation caused by the temperature of the anti-direct current component current transformer in the prior art is about 0.01%, the angular difference variation exceeds 2 ', the anti-direct current component double-stage current transformer for the electric energy meter can control the ratio variation within 0.01%, the angular difference variation does not exceed 0.4', the accuracy of power frequency operation is improved, and the error influence quantity of the temperature variation on the anti-direct current component double-stage current transformer for the electric energy meter is reduced.
TABLE 1
The rated current ratio of the current transformer refers to the ratio of primary current and secondary current of the current transformer, which is a term of art in the transformer industry.
The main iron core primary coil, the main iron core secondary coil, the compensation coil, the auxiliary iron core primary coil and the auxiliary iron core secondary coil are coils, the main iron core, the auxiliary iron core, the main iron core primary coil, the main iron core secondary coil, the compensation coil, the auxiliary iron core primary coil and the auxiliary iron core secondary coil are large in the types which can be adopted in the prior art, the technical personnel in the field can select the proper type according to actual requirements, and the embodiment is not exemplified one by one.
Example two
Fig. 3 is a top-bottom stacking structure diagram of the direct-current component resistant two-stage current transformer for the electric energy meter, the compensation coil is uniformly wound on the main iron core, the main iron core on which the compensation coil is wound is placed above or below the auxiliary iron core, and the main iron core and the auxiliary iron core are stacked together to wind the primary coil and the secondary coil. Connecting the polar end of the compensating coil with the polar end of the secondary coil to be used as the secondary polar end of the anti-direct-current component two-stage current transformer for the electric energy meter; and the non-polar end of the compensating coil and the non-polar end of the secondary coil are connected to be used as the secondary non-polar end of the direct-current component resisting two-stage current transformer for the electric energy meter.
EXAMPLE III
As shown in fig. 5, the calibrating apparatus for the dc component resistant current transformer for the electric energy meter comprises a fluxgate sensor T1, a sampling resistor R1, a signal amplifier a1, a filter a2, an a/D collector A6 and a DSP digital signal processor a7, wherein the sampling resistor R1 is connected in series between a pin K1 of the fluxgate sensor T1 and a pin K2 of the fluxgate sensor T1, the signal amplifier a1 is connected in parallel to the resistor R1, an output terminal of the signal amplifier a1 is electrically connected to an input terminal of the filter a2, an output terminal of the filter a2 is electrically connected to an input terminal of the a/D collector A6, and an output terminal of the a/D collector A6 is electrically connected to the DSP digital signal processor a 7.
Furthermore, the current transformer comprises a sampling resistor R2, a signal amplifier A4, a filter A5, an inverting amplifier A3 and a load resistor RL, wherein a pin S1 of the current transformer CTx for the direct-current component of the electric energy meter to be tested is electrically connected with an inverting input end of the inverting amplifier A3, a pin S2 of the current transformer CTx for the direct-current component of the electric energy meter to be tested is electrically connected with a non-inverting input end of the inverting amplifier A3 after being connected with the load resistor RL in series, and the inverting input end of the inverting amplifier A3 is grounded;
the inverting input end of the inverting amplifier A3 is electrically connected with the output end of the inverting amplifier A3 after being connected with the sampling resistor R2 in series, the output end of the inverting amplifier A3 is electrically connected with the input end of the signal amplifier A4, the output end of the signal amplifier A4 is electrically connected with the input end of the filter A5, and the output end of the filter A5 is electrically connected with the input end of the A/D collector A6.
Further, the load resistor RL includes a plurality of resistors, the plurality of resistors are connected in series in sequence, and each resistor is connected in parallel with a relay with a normally closed contact.
Further, as shown in fig. 7, in the present embodiment, the load resistor RL includes a1 Ω resistor, a2 Ω resistor, a4 Ω resistor, an 8 Ω resistor, a 16 Ω resistor, a 32 Ω resistor, a 64 Ω resistor, and a 128 Ω resistor, and the 1 Ω resistor, the 2 Ω resistor, the 4 Ω resistor, the 8 Ω resistor, the 16 Ω resistor, the 32 Ω resistor, the 64 Ω resistor, and the 128 Ω resistor are connected in series;
the relay comprises eight relays, wherein a1 omega resistor, a2 omega resistor, a4 omega resistor, an 8 omega resistor, a 16 omega resistor, a 32 omega resistor, a 64 omega resistor and a 128 omega resistor are respectively connected with a relay with a normally closed contact in parallel.
Further, in the present embodiment, the fluxgate sensor T1 has a primary winding wound by 1 turn, which is taken as the 100A current output range; the fluxgate sensor T1 is wound with 10 turns of the primary winding as the 10A current output range; the fluxgate sensor T1 has a primary winding wound 100 turns as a 1A current output range.
Further, in the present embodiment, the sampling resistor R1 and the sampling resistor R2 are high-precision low-temperature drift resistors.
The components of the current sensor include a1 Ω resistor, a2 Ω resistor, a4 Ω resistor, an 8 Ω resistor, a 16 Ω resistor, a 32 Ω resistor, a 64 Ω resistor, a 128 Ω resistor, a fluxgate sensor T1, a sampling resistor R1, a signal amplifier a1, a filter a2, an a/D collector A6, a DSP digital signal processor a7, a sampling resistor R2, a signal amplifier a4, a filter A5, an inverting amplifier A3, and a load resistor RL.
The primary current of the direct-current component resistant two-stage current transformer CTx for the electric energy meter to be measured is measured by adopting a fluxgate sensor T1, the T1 outputs the primary current according to the turn ratio relation, the secondary current is connected with a sampling resistor R1 and is converted into voltage to be measured, the secondary current passes through a load resistor RL, and then the sampling resistor R2 of an inverting amplifier A3 is adopted to convert the secondary current into voltage to be measured. The voltage on R1 is transmitted to a/D collector a6 via amplifier a4 and filter a5, synchronized with the voltage on R2 by amplifier a1 and filter a 2. The data acquired by the A/D acquisition unit A6 is read by the DSP A7 for Fourier analysis, and the ratio difference and the phase difference of the measured mutual inductor are calculated by trigonometric function operation and a ratio difference and angle difference formula. Wherein the primary and secondary current signals comprise alternating and half-wave signals. The primary winding of the fluxgate sensor T1 can be wound for 1 turn as the 100A current output range, and then continuously wound for 9 turns as the 10A current range, and then continuously wound for 90 turns as the 1A current range;
as shown in fig. 7, the load resistance RL is controlled by 8 relay switches, the relays are normally closed contacts, and the opening or closing of the switches is directly controlled by a binary system, so that a required load resistance value is obtained.
The method comprises the steps of reading, carrying out Fourier analysis, and simultaneously calculating by a trigonometric function operation and a ratio difference and angle difference formula to obtain a ratio difference and a phase difference of a tested mutual inductor, wherein the calculation process belongs to the prior art, and is not specifically explained in the embodiment.
Fig. 6 is a schematic diagram of calculation of a ratio difference and an angle difference of a conventional current transformer. The existing conventional current transformer calibrating device mostly adopts a comparison and difference measurement method, compares the primary and secondary current difference values with a current standard value, and calculates to obtain a ratio difference and a phase difference. As shown in fig. 6, phasor oa represents the primary current signal, phasor ob represents the secondary current signal, phasor ab represents the difference between the primary and secondary currents, phasor oc represents the projection of phasor ob on oa, and δ represents the angular difference between vectors oa and ob. The phasor oa is equal in length to the phasor ob.
When the anti-direct current split two-stage current transformer is in an alternating current running state, the angle difference is small enough (the angle difference of 0.2 stage transformer is less than 50'). When δ ≈ 50', the line segment ab ≈ radian ab ≈ angular difference δ according to an approximation principle. The results were consistent with both direct and differential measurements.
When the anti-direct current branch double-stage current transformer is in a half-wave operation state, the angular difference is large (larger than 100'), and the specific difference and the angular difference obtained by the measurement of a rectangular coordinate system have system errors. As shown in fig. 6, when δ is 600', the specific difference f is 0.0%. Angular difference delta calculated according to the principle of the differential method1Sum ratio difference f1。
Through the calculation, when the angular difference is 600', the specific difference obtained by the difference measurement method has a system error of-1.519%; according to the relationship in Table 2, when the angular difference is 50', the difference in the difference-measuring method ratio is-0.011%; the time ratio difference at 300' was-0.381% different; at 1000', the ratio difference is not only-4.2%, but also-1.4%. Therefore, when the angular difference of the transformer is more than 100', the method is not suitable for error test by using the transformer calibrator of the rectangular coordinate system.
TABLE 2 differences between the actual error and the ratio and angular differences of the differential method when the ratio difference is 0.00%
When the direct-current-component-resistant two-stage current transformer for the electric energy meter is used for measuring pure sine wave current, the results of a difference measuring method and a direct measuring method are not greatly different. However, when the half-wave current is measured, the angular difference is about 300', and the specific difference obtained by measuring the transformer calibrator with the rectangular coordinate system has a large system principle error, so that the error of the current transformer is measured by a direct measurement method.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (10)
1. The direct-current-component-resistant two-stage current transformer for the electric energy meter is characterized by comprising a main iron core T1Auxiliary iron core T2Compensation coil NBPrimary coil N1And a secondary coil N2Compensating coil NBWound around a main core T1The main iron core and the auxiliary iron core are distributed in parallel, and the main iron core and the auxiliary iron core are wound with a secondary coil N together2And a primary coil N1；
Compensation coil NBPolar terminal and secondary coil N2Is connected with the polar end of the compensating coil NBNon-polar terminal and secondary coil N2The non-polar ends of the two are connected;
wherein, the main iron core T1And an auxiliary core T2Nested inside and outside each other, primary coil N1And a secondary coil N2Simultaneously wound on the main iron core and the auxiliary iron core,
or, the main iron core T1And an auxiliary core T2Stacked one above the other, primary coil N1And a secondary coil N2And simultaneously wound on the main iron core and the auxiliary iron core.
2. The dc component resistant two-stage current transformer for electric energy meter according to claim 1, characterized by comprising a secondary coil internal impedance Z2Compensating coil internal impedance ZBAnd external load impedance Z, secondary coil N2Internal impedance Z of series secondary coil2And external load impedance Z, compensation coil NBInternal impedance Z of series compensation coilBThen is connected in parallel and externally connected on the load impedance Z.
3. The dc component resistant two-stage current transformer for electric energy meter according to claim 1, wherein the secondary winding N is a secondary winding2And the primary coil N1The turn ratio of the compensation coil N is equal to the rated current ratio of the current transformerBAnd a secondary coil N2The number of turns is the same.
4. The direct-current-component-resistant two-stage current transformer for the electric energy meter according to claim 1, wherein the main iron core is an iron core with initial permeability higher than 50000Gs/Oe, and the iron core with initial permeability higher than 50000Gs/Oe is a permalloy iron core or an ultracrystalline iron core.
5. The direct-current-component-resistant two-stage current transformer for the electric energy meter according to claim 1, wherein the auxiliary iron core is an anti-saturation iron core with constant magnetic permeability, and the anti-saturation iron core with constant magnetic permeability is an iron core made of cobalt-based amorphous material, a nanocrystalline iron core subjected to tension annealing treatment or a silicon steel sheet subjected to air gap treatment.
6. The calibrating device for the anti-direct-current component current transformer for the electric energy meter based on claim 1 is characterized by comprising a fluxgate sensor T1, a sampling resistor R1, a signal amplifier A1, a filter A2, an A/D collector A6 and a DSP digital signal processor A7, wherein the sampling resistor R1 is connected in series between a K1 pin of the fluxgate sensor T1 and a K2 pin of the fluxgate sensor T1, the signal amplifier A1 is connected in parallel to the resistor R1, an output end of the signal amplifier A1 is electrically connected with an input end of the filter A2, an output end of the filter A2 is electrically connected with an input end of the A/D collector A6, and an output end of the A/D collector A6 is electrically connected with the DSP digital signal processor A7.
7. The calibrating device for the anti-direct-current component current transformer of the electric energy meter according to claim 1, which comprises a sampling resistor R2, a signal amplifier A4, a filter A5, an inverting amplifier A3 and a load resistor RL, wherein the pin S1 of the anti-direct-current component double-stage current transformer CTx for the electric energy meter to be tested is electrically connected with the non-inverting input end of the inverting amplifier A3, the pin S2 of the anti-direct-current component double-stage current transformer CTx for the electric energy meter to be tested is electrically connected with the inverting input end of the inverting amplifier A3 after being connected with the load resistor RL in series, and the non-inverting input end of the inverting amplifier A3 is grounded;
the non-inverting input end of the inverting amplifier A3 is electrically connected with the output end of the inverting amplifier A3 after being connected with the sampling resistor R2 in series, the output end of the inverting amplifier A3 is connected with the input end of the signal amplifier A4, the output end of the signal amplifier A4 is electrically connected with the input end of the filter A5, and the output end of the filter A5 is electrically connected with the input end of the A/D collector A6.
8. The calibrating device for the anti-DC-component current transformer of the electric energy meter according to claim 7, which comprises a plurality of relays,
the load resistor RL comprises a plurality of resistors which are sequentially connected in series, and each resistor is connected with a relay of a normally closed contact in parallel.
9. The calibrating device for the direct current component resistant current transformer of the electric energy meter according to claim 8, wherein the load resistance RL comprises a1 Ω resistance, a2 Ω resistance, a4 Ω resistance, an 8 Ω resistance, a 16 Ω resistance, a 32 Ω resistance, a 64 Ω resistance and a 128 Ω resistance, and the 1 Ω resistance, the 2 Ω resistance, the 4 Ω resistance, the 8 Ω resistance, the 16 Ω resistance, the 32 Ω resistance, the 64 Ω resistance and the 128 Ω resistance are arranged in series;
the relay comprises eight relays, wherein a1 omega resistor, a2 omega resistor, a4 omega resistor, an 8 omega resistor, a 16 omega resistor, a 32 omega resistor, a 64 omega resistor and a 128 omega resistor are respectively connected with a relay with a normally closed contact in parallel.
10. The calibrating device of the anti-DC-component current transformer for the electric energy meter as claimed in claim 7, wherein the fluxgate sensor T1 is wound by 1 turn at the primary winding as the 100A current output range; the fluxgate sensor T1 is wound with 10 turns of the primary winding as the 10A current output range; the fluxgate sensor T1 has a primary winding wound by 100 turns as a 1A current output range; the sampling resistor R1 and the sampling resistor R2 are high-precision low-temperature drift resistors.
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