CN104267241A - High-frequency current partial discharge signal acquisition sensor - Google Patents

Abstract

The invention discloses a high-frequency current partial discharge signal acquisition sensor, which belongs to the field of sensors. The object of the present invention is to achieve a high-frequency current partial discharge signal acquisition sensor capable of receiving tiny signals by improving the Rogowski coil. The current-carrying wire of the present invention passes through the Rogowski coil, and the voltage and current are induced on the coil, and the voltage and current pass through the resistance to convert the current into a voltage; the coil is wound around the magnetic core, and then leads to the ground through the integral resistance; Its circuit connection is: M is the mutual inductance of the coil, Ls is the self-inductance of the coil, Rs is the equivalent resistance of the coil, Cs is the equivalent stray capacitance of the coil, R is the integral resistance of the coil; the primary side current After the current transformer is transformed to the secondary side, the secondary side is connected in series through the inductance Ls, the resistance Rs, and the integral resistance R, and the equivalent stray capacitance Cs of the coil is connected in parallel at both ends of the integral resistance R. The invention increases the self-inductance L of the coil, reduces the size and number of turns of the coil, and reduces the stray capacitance C, thereby improving the performance of the coil.

Description

High Frequency Current Partial Discharge Signal Acquisition Sensor

technical field

The invention belongs to the field of sensors. the

Background technique

A Rogowski coil is a toroidal coil wound uniformly on a non-ferromagnetic material. The output signal is the differential of the current with respect to time. Through a circuit that integrates the output voltage signal, the input current can be truly restored. The coil has the characteristics of real-time measurement of current, fast response, no saturation, and almost no phase error, so it can be applied to relay protection, thyristor rectification, frequency conversion speed regulation, resistance welding and other signal distortions and electric furnaces, Short-circuit test, lightning signal acquisition and other high-current occasions. However, the partial discharge signal is a tiny current signal, and ordinary Rogowski coils cannot sense this tiny current at all. the

Contents of the invention

The object of the present invention is to achieve a high-frequency current partial discharge signal acquisition sensor capable of receiving tiny signals by improving the Rogowski coil. the

The current-carrying wire of the present invention passes through the Rogowski coil, and the voltage and current are induced on the coil, and the voltage and current pass through the resistance to convert the current into a voltage; the coil is wound around the magnetic core, and then leads to the ground through the integral resistance; Its circuit connection is: M is the mutual inductance of the coil, Ls is the self-inductance of the coil, Rs is the equivalent resistance of the coil, Cs is the equivalent stray capacitance of the coil, R is the integral resistance of the coil; the primary side current After the current transformer is transformed to the secondary side, the secondary side is connected in series through the inductance Ls, the resistance Rs, and the integral resistance R, and the equivalent stray capacitance Cs of the coil is connected in parallel at both ends of the integral resistance R. the

According to the equivalent circuit, the circuit equation can be listed as:

(3.1)

(3.2)

(3.3)

The meanings of relevant parameters in the above formula are shown in formula (3.1), from formula (3.2) and formula (3.3):

(3.4)

Laplace transform and simplify equations (3.1) and (3.4), we get: (3.5)

Under zero initial conditions, the transfer function G(s) of the system is:

(3.6)

Under the action of a sinusoidal steady-state signal, there are:

(3.7)

According to formula (3.7), we can get:

(3.8)

Therefore, the amplitude-frequency characteristic of the current coupler is:

(3.9)

The equivalent circuit of the current coupler is similar to the high-frequency small-signal parallel resonant circuit, and the high-frequency small-signal parallel resonant circuit is used

According to the theoretical analysis of the vibration circuit, the frequency band of the current coupler can be obtained as:

Lower limit frequency:

(3.10)

Upper limit frequency:

(3.11)

Working frequency band:

(3.12)

When fh>>fl, there are:

(3.13)

From formula (3.13), it can be seen that Ls should be as large as possible, and Rs and R should be as small as possible.

The invention increases the self-inductance L of the coil, reduces the size and number of turns of the coil, and reduces the stray capacitance C, thereby improving the performance of the coil. Metal soft magnetic materials have higher saturation magnetic induction, Curie temperature and basic permeability, but lower coercive force. However, its volume resistivity is low and high-frequency eddy current loss is large, so it is generally suitable for low-frequency applications. The magnetic properties of ferrite soft magnetic materials are generally lower than those of metal soft magnetic materials, but their volume resistivity is several orders of magnitude higher than that of metal soft magnetic materials. The high frequency loss is small, suitable for high frequency use, and its price is low. Ferrite soft magnetic material has the characteristics of high permeability, low loss, high saturation magnetic induction, high cut-off frequency, high stability, etc., and is widely used in the production of high-frequency inductor coil cores to improve the self-inductance of the coil and reduce its volume. the

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a schematic circuit diagram of the present invention;

Fig. 3 is the frequency spectrum of the HFCT sensor of the present invention.

Detailed ways

The current-carrying wire 3 of the present invention passes through the Rogowski coil, and the voltage and current are induced on the coil 1, and the voltage and current pass through the resistance to convert the current into a voltage; the coil 1 is wound around the magnetic core 4, and then leads to the ground through the integrating resistor 2; the other end Connect to the analog input terminal of the conditioning circuit; its circuit connection is: M is the mutual inductance of the coil, Ls is the self-inductance of the coil, Rs is the equivalent resistance of the coil, Cs is the equivalent stray capacitance of the coil, R is the integral of the coil Resistor; the primary side current is transformed to the secondary side through the current transformer, and the secondary side is connected in series through the inductance Ls, the resistance Rs, and the integral resistance R, and the equivalent stray capacitance Cs of the coil is connected in parallel at both ends of the integral resistance R. the

According to the equivalent circuit, the circuit equation can be listed as:

(3.1)

(3.2)

(3.3)

The meanings of relevant parameters in the above formula are shown in formula (3.1), from formula (3.2) and formula (3.3):

(3.4)

Laplace transform and simplify equations (3.1) and (3.4), we get: (3.5)

Under zero initial conditions, the transfer function G(s) of the system is:

(3.6)

Under the action of a sinusoidal steady-state signal, there are:

(3.7)

According to formula (3.7), we can get:

(3.8)

Therefore, the amplitude-frequency characteristic of the current coupler is:

(3.9)

The equivalent circuit of the current coupler is similar to the high-frequency small-signal parallel resonant circuit, and the high-frequency small-signal parallel resonant circuit is used

According to the theoretical analysis of the vibration circuit, the frequency band of the current coupler can be obtained as:

Lower limit frequency:

(3.10)

Upper limit frequency:

(3.11)

Working frequency band:

(3.12)

When fh>>fl, there are:

(3.13)

From formula (3.13), it can be seen that Ls should be as large as possible, and Rs and R should be as small as possible.

The present invention is further described below:

The partial discharge signal acquisition sensor is a wide-band transformer, and its model is a Rogowski coil with a high-frequency magnetic core, that is, a feed-through current transformer with a high-frequency magnetic core. The structure is shown in the figure below. The basic principle is to make the partial discharge pulse current of the outer shielding layer of the cable form an induced current pulse in the secondary winding through the change of the magnetic field, and then collect the pulse voltage signal through the integrating resistor, so as to judge whether there is partial discharge in the cable, and whether there is partial discharge in the cable. the size of.

The self-integrating Rogowski coil directly adopts the integrating resistance, and has a high frequency response. It is an ideal means for measuring nanosecond pulse and large current signals, and is widely used at home and abroad. The measurement principle and equivalent circuit are shown in the figure, where M is the mutual inductance of the coil, Ls is the self-inductance of the coil, Rs is the equivalent resistance of the coil, C is the equivalent stray capacitance of the coil, R is the integral resistance of the coil . the

According to the equivalent circuit, the circuit equation can be listed as:

(3.1)

(3.2)

(3.3)

The meanings of relevant parameters in the above formula are shown in formula (3.1), from formula (3.2) and formula (3.3):

(3.4)

Laplace transform and simplify equations (3.1) and (3.4), we get: (3.5)

Under zero initial conditions, the transfer function G(s) of the system is:

(3.6)

Under the action of a sinusoidal steady-state signal, there are:

(3.7)

According to formula (3.7), we can get:

(3.8)

Therefore, the amplitude-frequency characteristic of the current coupler is:

(3.9)

The equivalent circuit of the current coupler is similar to the high-frequency small-signal parallel resonant circuit, and the high-frequency small-signal parallel resonant circuit is used

According to the theoretical analysis of the vibration circuit, the frequency band of the current coupler can be obtained as:

Lower limit frequency:

(3.10)

Upper limit frequency:

(3.11)

Working frequency band:

(3.12)

When fh>>fl, there are:

(3.13)

From the above analysis, it can be seen that in the case of a certain magnetic core material and coil size, in order to make the working frequency band of the Roe-type coil as wide as possible, the upper limit frequency should be as large as possible and the lower limit frequency should be as small as possible. From formula (3.13), it can be seen that Ls should be as large as possible, and Rs and R should be as small as possible. In the case of a certain coil size, Ls can be increased by increasing the magnetic permeability μ and the number of coil turns N. However, the nature of the magnetic material determines that when the magnetic permeability μ increases, its operating frequency will decrease. In addition, increasing the winding diameter can reduce Rs, but this is mutually restricted with increasing the number of coil turns N. The sensitivity of the working frequency band of the Rogowski coil is also closely related to the integrating resistance R. The increase of the integral resistance can increase the sensitivity of the sensor, but at the same time it will lead to a decrease in the frequency bandwidth. Therefore, if the Rogowski coil sensor has a wide operating frequency band and a certain response sensitivity, it is necessary to select an optimal combination of integrating resistance R and coil turns N after determining the core material and its size.

Soft magnetic materials are mainly divided into two categories: metal soft magnetic materials and ferrite soft magnetic materials. The partial discharge signal is a tiny current signal, and ordinary Rogowski coils cannot sense this tiny current at all. The purpose of choosing magnetic materials is to increase the self-inductance L of the coil, reduce the size and number of turns of the coil, and reduce the stray capacitance C, thereby improving the performance of the coil. Metal soft magnetic materials have higher saturation magnetic induction, Curie temperature and basic permeability, but lower coercive force. However, its volume resistivity is low and high-frequency eddy current loss is large, so it is generally suitable for low-frequency applications. The magnetic properties of ferrite soft magnetic materials are generally lower than those of metal soft magnetic materials, but their volume resistivity is several orders of magnitude higher than that of metal soft magnetic materials. The high frequency loss is small, suitable for high frequency use, and its price is low. Ferrite soft magnetic material has the characteristics of high permeability, low loss, high saturation magnetic induction, high cut-off frequency, high stability, etc., and is widely used in the production of high-frequency inductor coil cores to improve the self-inductance of the coil and reduce its volume. the

Through comparative experiments, under the existing conditions of this design, the final selected sensor parameters are: the magnetic core material is nickel zinc, the coil is about 15 turns, and the integral resistance is 100-150 ohms. the

Through the previous description, the basic parameters of the Rogowski coil can be determined, but if it is used directly, it must be affected by many external disturbances such as stray electromagnetic fields. Therefore, a shielding body that can effectively shield external stray electromagnetic fields is required outside the coil. It should also be noted that in order to allow the main magnetic field of the measured current to enter the coil, it is necessary to leave a 1mm wide gap inside the shielding case. The material of the shielding shell can be made of iron, and the outside is plated with silver, which can effectively shield the electric field and low-frequency magnetic field. But at this time, a 1mm wide slit must be opened in the direction of the coil section. This is to increase the reluctance, and the shielding shell does not form a loop, so as to prevent the magnetic field of the measured current from being concentrated on the shielding shell and unable to enter the coil. . The material of the shielding shell can also be made of copper or aluminum, so that there is no need to open a gap in the direction of the cross section of the coil because of its high magnetic permeability. In this paper, an aluminum shielding shell is used to cover the coil, and the semi-circular coils are respectively installed in the corresponding semi-circular metal shielding boxes, finally forming a split-type circular ring structure. the

Claims (1)

1. A high-frequency current partial discharge signal acquisition sensor, characterized in that: the current-carrying wire (3) passes through the Rogowski coil, and a voltage and current are induced on the coil (1), and the voltage and current pass through a resistor to convert the current into a voltage; the coil (1) Wrap around the magnetic core (4), and then lead to the ground through the integral resistor (2); the other end is connected to the analog input terminal of the conditioning circuit; the circuit connection is: M is the mutual inductance of the coil, Ls is the self-inductance of the coil , Rs is the equivalent resistance of the coil, Cs is the equivalent stray capacitance of the coil, R is the integral resistance of the coil; the primary side current is transformed to the secondary side through the current transformer, and the secondary side passes through the inductance Ls, the resistance Rs, the integral The resistance R is connected in series, and the equivalent stray capacitance Cs of the coil is connected in parallel at both ends of the integrating resistance R; According to the equivalent circuit, the circuit equation can be listed as: (3.1) (3.2) (3.3) The meanings of relevant parameters in the above formula are shown in formula (3.1), from formula (3.2) and formula (3.3): (3.4) Laplace transform and simplify equations (3.1) and (3.4), we get: (3.5) Under zero initial conditions, the transfer function G(s) of the system is: (3.6) Under the action of a sinusoidal steady-state signal, there are: (3.7) According to formula (3.7), we can get: (3.8) Therefore, the amplitude-frequency characteristic of the current coupler is: (3.9) The equivalent circuit of the current coupler is similar to the high-frequency small-signal parallel resonant circuit, and the high-frequency small-signal parallel resonant circuit is used According to the theoretical analysis of the vibration circuit, the frequency band of the current coupler can be obtained as: Lower limit frequency: (3.10) Upper limit frequency: (3.11) Working frequency band: (3.12) When fh>>fl, there are: (3.13) From formula (3.13), it can be seen that Ls should be as large as possible, and Rs and R should be as small as possible.