CN115389807B - Transformer neutral point direct current sensor based on fluxgate - Google Patents
Transformer neutral point direct current sensor based on fluxgate Download PDFInfo
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- CN115389807B CN115389807B CN202211321759.0A CN202211321759A CN115389807B CN 115389807 B CN115389807 B CN 115389807B CN 202211321759 A CN202211321759 A CN 202211321759A CN 115389807 B CN115389807 B CN 115389807B
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- G01—MEASURING; TESTING
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- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention relates to a transformer neutral point direct current sensor based on a fluxgate, which comprises a magnetic core, a winding assembly and a signal processing circuit assembly, wherein the magnetic core is provided with a magnetic core coil; the magnetic core and winding assembly comprises an annular magnetic core I and an annular magnetic core II; the primary winding I and the secondary winding I are wound on the annular magnetic core I, and the primary winding II is wound on the annular magnetic core II; the signal processing circuit component consists of an open-loop self-oscillation inductance type magnetic flux gate circuit, an alternating current magnetic flux compensation circuit and a zero magnetic flux driving circuit. The invention provides a direct current extraction scheme under the condition of mixing alternating current and harmonic current, a closed loop is constructed to realize direct current zero magnetic flux of an annular magnetic core I, and the voltage output by a direct current zero magnetic flux circuit can be conveniently converted into the direct current to be detected through a formula.
Description
Technical Field
The invention belongs to the research field of power grid direct current bias current tests, and particularly relates to a transformer neutral point direct current sensor based on a fluxgate.
Background
The direct current transmission mostly adopts a single-pole earth return operation mode during fault. Under the condition, a large amount of direct current can indirectly invade an alternating current power grid through the ground, so that a transformer winding passes direct current magnetic biasing current with different numbers of amperes to dozens of amperes, and an iron core of the transformer is in a saturated working state. In order to warn the dc magnetic bias risk of the transformer, a dc current sensor needs to be installed at the neutral point of the transformer.
When the power system normally operates, a certain amount of alternating current and harmonic current can flow through the neutral point of the transformer. Under the condition that direct current invades an alternating current power grid, a neutral point of the transformer can not only pass through the direct current, but also the alternating current and harmonic current can influence the measurement result of the direct current.
At present, an open Hall type current sensor is mainly adopted for testing the direct current of the neutral point of the transformer. The open Hall type current sensor is divided into a circular structure and a square structure. The inner diameter of the circular structure is within 8cm, while the long side of the square structure does not exceed 10cm. The open hall type current sensor has an excessively small opening size and is therefore greatly restricted in use. The open-loop Hall sensor is not only inconvenient to install, but also has certain electric shock risk for operating personnel in the installation process. If the opening size of the Hall sensor needs to be further enlarged, the measurement precision of the Hall sensor is greatly reduced, and the requirement of engineering application cannot be met. Therefore, a large-sized transformer neutral point direct current sensor needs to be developed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a transformer neutral point direct current sensor based on a fluxgate.
The technical scheme adopted by the invention is as follows: the transformer neutral point direct current sensor based on the fluxgate comprises a magnetic core and winding assembly, a signal processing circuit assembly and an output assembly;
the magnetic core and winding assembly comprises an annular magnetic core I and an annular magnetic core II; the primary winding I and the secondary winding I are wound on the annular magnetic core I, and the primary winding II is wound on the annular magnetic core II;
the signal processing circuit component consists of an open-loop self-oscillation inductance type magnetic flux gate circuit, an alternating current magnetic flux compensation circuit and a direct current zero magnetic flux driving circuit; the output of the open-loop self-oscillation inductance type magnetic flux gate circuit is connected with the primary winding I and also used as the input of a unit gain inverter of the alternating current magnetic flux compensation circuit; the alternating current magnetic flux compensation circuit is used for offsetting alternating current magnetic flux in the annular magnetic core I; the output signal of the alternating current magnetic flux compensation circuit is used as the input of the direct current zero magnetic flux driving circuit;
the open-loop self-excited oscillation inductive fluxgate circuit comprises an inductor of a primary winding I, a comparator, an exciting current sampling resistor I, a threshold voltage zero setting resistor I and a threshold voltage zero setting resistor II, wherein one end of the inductor of the primary winding I, the negative input end of the comparator and one end of the exciting current sampling resistor I are connected in common, the other end of the exciting current sampling resistor I is grounded, the positive input end of the comparator is connected with one end of the threshold voltage zero setting resistor I and one end of the threshold voltage zero setting resistor II in common, the other end of the threshold voltage zero setting resistor I is grounded, and the other end of the threshold voltage zero setting resistor II is connected with the other end of the inductor of the primary winding I and the output end of the comparator in common;
the alternating current magnetic flux compensation circuit is composed of a unit gain phase inverter, a primary winding II, an exciting current sampling resistor II and a high-pass filter, wherein the input end of the unit gain phase inverter is connected with the output end of the comparator, the output end of the unit gain phase inverter is connected with one end of the primary winding II, the other end of the primary winding II is connected with one end of the exciting current sampling resistor II and the input end of the high-pass filter in a common mode, and the other end of the exciting current sampling resistor II is grounded;
the direct-current zero-magnetic-flux driving circuit consists of an adder, a low-pass filter, a proportional integrator, a power amplifier and an inductor of a secondary winding I, wherein one channel input of the adder is connected with one end of the inductor of a primary winding I and one end of an exciting current sampling resistor I in a common mode; the input of the other channel of the adder is connected with the output end of the high-pass filter, the output end of the adder is sequentially connected with the low-pass filter, the proportional integrator, the power amplifier and the inductor of the secondary winding I in series, and the direct-current zero-magnetic-flux driving circuit flows through the secondary compensation current to offset a direct-current magnetic field generated by a primary side detected direct-current component, so that direct-current zero magnetic flux is realized;
the output assembly consists of a digital voltmeter and an output sampling resistor, one end of the output sampling resistor is connected with the output end of the secondary winding I, the other end of the output sampling resistor is grounded, and the digital voltmeter is connected with the two ends of the measuring resistor;
calculating the DC current of the neutral point of the transformer from the voltage measured by the digital voltmeterI dc The method of (1) is as follows:
in the formula (I), the compound is shown in the specification,
for maximum error of measured DC current, U is the voltage measured by digital voltmeter, K 1 Is the proportional constant of a proportional integrator, K 2 Is the amplification factor of an amplifier, R S1 Sampling resistors I, R for exciting current S2 Sampling resistors II, R for exciting current 1 Zero setting of the resistance I, R for the threshold voltage 2 Zero setting of the resistance II, I for the threshold voltage S For compensating the current for the secondary side, R M To measureResistance, N 1 Is the number of turns of the primary winding I, N 2 Number of turns of primary winding II, N 3 The number of turns of the secondary winding I.
Further preferably, the annular magnetic core I and the annular magnetic core II are of a movable open-loop and closed-loop structure.
Preferably, the annular magnetic core I is wound on the primary winding I and the secondary winding I, the annular magnetic core II is wound on the primary winding II and the secondary winding II, the annular magnetic core I and the annular magnetic core II are respectively embedded on two sides of the annular soft plastic, one section of the annular magnetic core I, the annular magnetic core II and the annular soft plastic is cut off at the position without the winding to form a connecting joint, the connecting joint is in a closed-loop structure when being clamped with the annular opening main body part, and the connecting joint is in an open-loop structure when being taken down.
Preferably, the annular magnetic core I and the annular magnetic core II are embedded in the two sides of the annular soft plastic, and then an annular epoxy outer sleeve is sleeved outside the annular soft plastic, an opening is cut in the corresponding part of the connecting joint of the annular epoxy outer sleeve, and the epoxy outer sleeve at the connecting joint part is arranged.
Further preferably, the connecting joint is cut into a clamping groove structure, and the clamping groove structure is clamped with the cut annular opening main body part.
Preferably, the output assembly is composed of a digital voltmeter and an output sampling resistor, one end of the output sampling resistor is connected with the output end of the secondary winding I, the other end of the output sampling resistor is grounded, and the digital voltmeter is connected with two ends of the measuring resistor. The number of turns N of the primary winding I 1 =1000, number of turns of primary winding ii N 2 =1000, number of turns N of secondary winding i 3 =500。
The invention constructs a magnetic core and winding assembly and a signal processing circuit assembly, wherein the signal processing circuit assembly consists of an open-loop self-excited oscillation inductance type magnetic flux gate circuit, an alternating current magnetic flux compensation circuit and a direct current zero magnetic flux driving circuit; the output signal of the excitation flux compensation circuit (namely the output signal of the low-pass filter) is used as the input of the direct current zero flux driving circuit, and the measured direct current error signal controls the proportional-integrator to drive the power amplifier to output the secondary side compensation current for offsetting the direct current magnetic field generated by the primary side measured direct current, thereby forming a closed loop circuit to realize the direct current zero flux. The direct current of the neutral point of the transformer can be calculated by measuring the voltage drop on the resistor, and the maximum error of measurement is only 4mA.
Drawings
Fig. 1 is a schematic diagram of a transformer neutral point dc current sensor based on a self-oscillating inductive flux gate circuit.
Fig. 2 is a dc current waveform of a transformer with a slowly varying neutral point obtained by field measurement.
Detailed Description
It should be noted that, in the present application, the embodiments and features of the embodiments may be combined with each other, and the present invention will be described in detail with reference to the accompanying drawings and embodiments.
For better understanding of the present invention, the following examples are provided to further illustrate the present invention, and the examples described are only a part of the present invention, but the present invention is not limited to the following examples. Various changes or modifications may be effected therein by one skilled in the art and such equivalents are intended to be within the scope of the invention as defined by the claims appended hereto.
Referring to fig. 1, the transformer neutral point direct current sensor based on the fluxgate comprises a magnetic core and winding assembly, a signal processing circuit assembly, and an output assembly.
The core and winding assembly consists of 2 toroidal cores and 3 windings. Annular magnetic core IC 1 And a toroidal core IIC 2 All are circular magnetic cores (radius 0.2m, cross section size 20mm multiplied by 2 mm) made of high permeability amorphous alloy material Metglas 2714A. 3 windings (Primary winding IW) 1 Primary winding IIW 2 Secondary winding iw 3 ) Is an enameled wire coil with the diameter of 0.2 mm. Annular magnetic core IC 1 And a toroidal core IIC 2 Are completely the same in physical properties and geometrical dimensions; primary winding iw 1 Respectively has N turns 1 =1000, primary winding IIW 2 N turns of 2 =1000, secondary winding iw 3 N turns of 3 =500. Primary winding IW 1 and secondary winding IW 3 wind in the ringC-shaped magnetic core 1 The above. Primary winding IIW 2 Wound around a toroidal core IIC 2 The above.
For convenient field installation, annular magnetic core IC 1 And a toroidal core IIC 2 In a movable open-closed loop configuration, a toroidal core IC 1 Winding primary winding iw 1 And secondary winding iw 3 Annular magnetic core IIC 2 Winding primary winding IIW 2 Rear, toroidal core IC 1 And a toroidal core IIC 2 Are respectively embedded at two sides of the annular soft plastic and are provided with annular magnetic cores IC 1 Annular magnetic core IIC 2 The annular soft plastic is cut off at a winding-free part to form a connecting joint, the connecting joint is preferably cut into a clamping groove structure, and the clamping groove structure is clamped with the cut annular opening main body part; the connecting joint is of a closed-loop structure when being clamped with the annular opening main body part, the connecting joint is of an open-loop structure when being taken down, and the open-loop and closed-loop structure realizes the open installation and closed measurement of the magnetic core. Annular magnetic core IC 1 And a toroidal core IIC 2 The back of the ring-shaped soft plastic is sleeved with a ring-shaped epoxy outer sleeve which is also provided with a cut opening at the corresponding part of the connecting joint and an epoxy outer sleeve at the connecting joint part. Primary winding iw 1 Secondary winding iw 3 Primary winding IIW 2 The testing host is led out through a connecting wire and connected with the testing host, and a signal processing circuit assembly and an output assembly are integrated in the testing host.
The signal processing circuit component consists of an open-loop self-oscillation inductive magnetic flux gate circuit, an alternating current magnetic flux compensation circuit and a direct current zero magnetic flux driving circuit.
The open-loop self-oscillation inductive fluxgate circuit is composed of a primary winding iw 1 Inductance L 1 A comparator (model is OP 284), an exciting current sampling resistor IR S1 （3.3k 
) Threshold voltage zero setting resistor IR 1 （5.1k 
) And threshold voltage zero setting resistor IIR 2 （19.6k 
) Is composed of a primary winding iw 1 Inductance L 1 One end of the comparator, the negative input end of the comparator and the exciting current sampling resistor IR S1 One end of the resistor is connected in common, and an exciting current sampling resistor IR S1 The other end of the comparator is grounded, and the positive input end of the comparator and the threshold voltage zero setting resistor IR 1 And a threshold voltage zero setting resistor IIR 2 One end of the resistor is connected in common, and the threshold voltage zeroing resistor IR 1 The other end of the resistor is grounded, and a threshold voltage zero setting resistor IIR 2 The other end of (1) and the primary winding IW 1 Inductance L 1 The other end of the comparator is connected with the output end of the comparator in common. The output of the open-loop self-excited inductance oscillating circuit is connected with the primary winding IW 1 In addition, the input voltage is used as the input of a unity gain inverter of the alternating current magnetic flux compensation circuit.
The AC flux compensation circuit comprises a unity gain inverter (model AD 744) and a primary winding IIW 2 Exciting current sampling resistor IIR S2 （10k 
) And a high-pass filter (type: UAF 42), wherein the input end of a unit gain inverter (type: AD 744) is connected with the output end of the comparator, and the output end of the unit gain inverter is connected with the primary winding IIW 2 One end of (1), primary winding IIW 2 The other end of the resistor and an excitation current sampling resistor IIR S2 One end of the high-pass filter is connected with the input end of the high-pass filter in common, and the exciting current sampling resistor IIR S2 And the other end of the same is grounded. AC flux compensation circuit for canceling annular magnetic core IC 1 Of the alternating magnetic flux component.
The direct current zero magnetic flux driving circuit consists of an adder (model number is SN74LS 283), a low-pass filter (model number is UAF 40), a proportional integrator (model number is SN85LS164, a proportionality coefficient K1= 1.0), a power amplifier (model number is UAF42, an amplification factor K2= 10000.0) and a secondary winding I W 3 Inductor (2)L 3 . One channel input of adder and primary winding IW 1 Inductance L 1 One end of, an excitation current sampling resistor IR S1 One ends of the two are connected together; the other channel input of the adder is connected with the output end of the high-pass filter, and the output end of the adder is sequentially connected with the low-pass filter, the proportional integrator, the power amplifier and the secondary winding I W in series 3 Inductance L 3 The DC zero-flux drive circuit passes through the secondary compensation current I S The device is used for offsetting a direct current magnetic field generated by the primary side direct current to be measured, thereby realizing direct current zero magnetic flux.
Exciting current sampling resistor IIR S2 Voltage signal v on sn2 After passing through a high-pass filter, the high-pass filter is connected with an excitation current sampling resistor R S1 Voltage signal v on sn1 Added by an adder, the output signal v of which sn12 As an input signal to the low pass filter. The high-pass filter is mainly used for inhibiting the interference of the direct current magnetic field of the environment background.
Output signal v of AC flux compensation circuit dc (i.e. the output signal of the low pass filter) as the dc zero flux drive circuit input,
representing the measured dc current error signal. DC error signal control proportional-integrator drive power amplifier output secondary side compensating current I S The primary side DC current compensation circuit is used for offsetting DC magnetic flux generated by primary side measured DC current, thereby forming a closed loop circuit to realize DC zero magnetic flux.
The output assembly consists of a digital voltmeter and an output sampling resistor, one end of the output sampling resistor is connected with the secondary winding I W 3 The other end of the output sampling resistor is grounded, the digital voltmeter is connected with the two ends of the measuring resistor to measure the voltage at the two ends of the output sampling resistor, and the primary side measured current (large current) is accurately converted into secondary side compensation current I according to a certain proportion through the direct current zero magnetic flux driving circuit S (small current), while the secondary side compensates for the current I S It is easy to measure the resistance R M （0.5k 
) Converted into a voltage signal and then measured by a digital voltmeter (model number SN85LS 164). The secondary compensation current I obtained from the measurement is known as the conversion ratio S The primary side measured current is obtained through calculation easily, and the primary side measured current is the neutral point direct current of the transformer, so that the precise measurement of the neutral point direct current of the transformer is realized. The waveform of the slowly varying dc current at the neutral point of the transformer obtained from one of the case site measurements is shown in fig. 2, and the sampling frequency of the digital voltmeter is 10Hz to maintain the tracking measurement of the dc current at the neutral point of the slowly varying transformer.
The method has the greatest advantage that the measured voltage signal can be used for reversely deducing the neutral point direct current waveform of the transformer, so that the non-contact measurement of the current is realized. Calculating transformer neutral point DC current from voltage measured by digital voltmeterI dc The method of (1) is as follows:
in the formula (I), the compound is shown in the specification,
for maximum error of measured DC current, U is the voltage measured by digital voltmeter, K 1 Is the proportional constant of a proportional integrator, K 2 Is the amplification factor of an amplifier, R S1 Sampling resistors I, R for exciting current S2 Sampling resistors II, R for exciting current 1 Zero setting of the resistance I, R for the threshold voltage 2 And a threshold voltage zero setting resistor II.
The invention not only provides a calculation formula of the neutral point direct current of the transformer, but also provides an estimation formula of the maximum measurement error of the neutral point direct current of the transformer, and a measurement result with satisfactory engineering can be obtained on site.
When the transformer neutral point direct current sensor based on the fluxgate works normally, the closed-loop system is in a direct current zero-flux state, the measured current of the alternating current flux compensation circuit is equivalent to zero, the average value of the alternating current in the primary winding is zero, namely the output signal of the low-pass filter is zero, the induced voltage on the secondary winding is zero, and the direct current error signal is zero, namely the system is in an ampere-turn balance state. The alternating current/harmonic current of the neutral point of the transformer causes that the alternating current exciting current of the alternating current flux compensation circuit is not zero, and the alternating current exciting current offsets with the alternating current component output by the open-loop self-oscillation inductive magnetic flux gate circuit through the adder, so that the influence of the alternating current component and the harmonic current component on a direct current measurement result is avoided.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art. It is within the spirit of the invention that conventional alternatives according to the prior art be made within the spirit of the invention.
Claims (6)
1. The transformer neutral point direct current sensor based on the fluxgate comprises a magnetic core and winding assembly, a signal processing circuit assembly and an output assembly; the method is characterized in that:
the magnetic core and winding assembly comprises an annular magnetic core I and an annular magnetic core II; the primary winding I and the secondary winding I are wound on the annular magnetic core I, the primary winding II is wound on the annular magnetic core II, the annular magnetic core I and the primary winding I form an inductance element of an open-loop self-excited nonlinear inductance oscillating circuit, the annular magnetic core II and the primary winding II form an inductance element of an alternating current magnetic flux compensation circuit, and the annular magnetic core I and the secondary winding I form an inductance element of a direct current zero magnetic flux driving circuit;
the signal processing circuit component consists of an open-loop self-oscillation inductance type magnetic flux gate circuit, an alternating current magnetic flux compensation circuit and a zero magnetic flux driving circuit; the output of the open-loop self-oscillation inductance type magnetic flux gate circuit is connected with the primary winding I and is also used as the input of a unity gain inverter of the alternating current magnetic flux compensation circuit; the alternating current magnetic flux compensation circuit is used for offsetting alternating current magnetic flux in the annular magnetic core I; the output signal of the alternating current magnetic flux compensation circuit is used as the input of the direct current zero magnetic flux driving circuit;
the open-loop self-excited oscillation inductive fluxgate circuit comprises an inductor of a primary winding I, a comparator, an exciting current sampling resistor I, a threshold voltage zero setting resistor I and a threshold voltage zero setting resistor II, wherein one end of the inductor of the primary winding I, the negative input end of the comparator and one end of the exciting current sampling resistor I are connected in common, the other end of the exciting current sampling resistor I is grounded, the positive input end of the comparator is connected with one end of the threshold voltage zero setting resistor I and one end of the threshold voltage zero setting resistor II in common, the other end of the threshold voltage zero setting resistor I is grounded, and the other end of the threshold voltage zero setting resistor II is connected with the other end of the inductor of the primary winding I and the output end of the comparator in common;
the alternating current magnetic flux compensation circuit is composed of a unit gain phase inverter, a primary winding II, an exciting current sampling resistor II and a high-pass filter, wherein the input end of the unit gain phase inverter is connected with the output end of the comparator, the output end of the unit gain phase inverter is connected with one end of the primary winding II, the other end of the primary winding II is connected with one end of the exciting current sampling resistor II and the input end of the high-pass filter in a common mode, and the other end of the exciting current sampling resistor II is grounded;
the direct-current zero-magnetic-flux driving circuit consists of an adder, a low-pass filter, a proportional integrator, a power amplifier and an inductor of a secondary winding I, wherein one channel input of the adder is connected with one end of the inductor of a primary winding I and one end of an exciting current sampling resistor I in a common mode; the input of the other channel of the adder is connected with the output end of the high-pass filter, and the output end of the adder is sequentially connected with the low-pass filter, the proportional integrator, the power amplifier and the inductor of the secondary winding I in series;
the output assembly consists of a digital voltmeter and an output sampling resistor, one end of the output sampling resistor is connected with the output end of the secondary winding I, the other end of the output sampling resistor is grounded, and the digital voltmeter is connected with the two ends of the measuring resistor;
calculating transformer neutral point DC current from voltage measured by digital voltmeterI dc The method of (1) is as follows:
in the formula (I), the compound is shown in the specification,
for maximum error of measured DC current, U is the voltage measured by digital voltmeter, K 1 Is the proportional constant of a proportional integrator, K 2 Is the amplification factor of an amplifier, R S1 Sampling resistors I, R for exciting current S2 Sampling resistors II, R for exciting current 1 Zero setting of the resistance I, R for the threshold voltage 2 Zero setting of the threshold voltage resistance II, I S For compensating the current for the secondary side, R M For measuring resistance, N 1 Is the number of turns of the primary winding I, N 2 Number of turns of primary winding II, N 3 The number of turns of the secondary winding I.
2. The fluxgate-based transformer neutral point direct current sensor according to claim 1, wherein: the annular magnetic core I and the annular magnetic core II are of a movable open-loop and closed-loop structure.
3. The fluxgate-based transformer neutral point direct current sensor according to claim 2, wherein: the annular soft plastic is characterized in that the annular magnetic core I is wound around the primary winding I and the secondary winding I, the annular magnetic core II is wound around the primary winding II, the annular magnetic core I and the annular magnetic core II are respectively embedded on two sides of the annular soft plastic, one section of the annular magnetic core I, the annular magnetic core II and the annular soft plastic is cut off at a winding-free position to form a connecting joint, the connecting joint is in a closed-loop structure when being clamped with the annular opening main body part, and the connecting joint is in an open-loop structure when being taken down.
4. The fluxgate-based transformer neutral point direct current sensor according to claim 3, wherein: the annular magnetic core I and the annular magnetic core II are embedded in the two sides of the annular flexible plastic, and then are sleeved with annular epoxy outer sleeves, openings are cut in the corresponding parts of the connecting joints of the annular epoxy outer sleeves, and the epoxy outer sleeves at the positions of the connecting joints are arranged.
5. The fluxgate-based transformer neutral point direct current sensor according to claim 3, wherein: the connecting joint is cut into a clamping groove structure, and the clamping groove structure is clamped with the cut annular opening main body part.
6. The fluxgate-based transformer neutral point direct current sensor according to claim 1, wherein: the number of turns of the primary winding I is N 1 =1000, number of turns of primary winding II N 2 =1000, number of turns N of secondary winding i 3 =500。
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