CN1397806A - Large-size magnetic core sensor and anti-interference method for discriminating directional coupling pulse - Google Patents

Abstract

The invention discloses a large-diameter magnetic core type current sensor and an anti-interference method for directional coupling pulse polarity and amplitude identification, which is suitable for a transformer partial discharge on-line monitoring system, and is arranged at the flange of the transformer high-voltage outlet bushing base , coupling the partial discharge signal through the high-voltage outgoing line. After winding the coil around the magnetic core, connect high-pass filter capacitors and sampling resistors in series at both ends of the coil. The sensitivity of the series circuit is greater than that of the parallel circuit, and it has a good filtering effect on low-frequency signals. The semi-enclosed sensor shell made of metal can effectively suppress electromagnetic interference in the space while coupling the high-voltage outlet signal, and can prevent rain, dust, etc., and improve the anti-interference ability and vibration resistance of the coil. Through the anti-interference method of directional coupling pulse polarity and amplitude identification, the software can confirm and compare the polarity or amplitude of the pulses collected by the two sensors installed at the casing flange and at the end screen of the casing to identify Partial discharge and external disturbances.

Description

Large-diameter magnetic core sensor and anti-interference method for directional coupling pulse identification

1. Technical field

The invention relates to an on-line monitoring of the insulation state of large-scale electric equipment, in particular to a large-diameter magnetic core type current sensor and an anti-interference method for identifying directional coupling pulses.

2. Background technology

1. On-line monitoring of partial discharge of power transformers

In the existing on-line monitoring system for partial discharge of power transformers, a small-diameter magnetic core current sensor with an inner diameter of less than 50mm is used to couple discharge signals from the end screen grounding wire, neutral point grounding wire, and core grounding wire, and the non-magnetic core The type current sensor extracts the discharge signal from the high-voltage bushing, suppresses the on-site interference and identifies the internal discharge pulse of the transformer through differential, digital filtering and other measures, so as to obtain more realistic discharge information.

2. Sensor technology

In order to make pulse identification from the partial discharge signal of the coupling transformer at the high-voltage outlet terminal and the signal coupled with the ground wire at the end of the bushing, in the past, it was limited to the large-diameter magnetic core current sensor with high processing difficulty and high cost, and only the non-magnetic core current sensor was used. . The sensor is composed of Rogowski coil with non-magnetic material as the core, parallel resistance and capacitance, shielding box and so on.

The non-magnetic core sensor has serious distortion of the partial discharge signal, and can only meet the lower sensitivity requirements, but it is difficult to meet the requirements of pulse polarity identification. And because non-magnetic material is used as the core, according to the coil inductance calculation formula L=(μhln(R/r))/2π, compared with the magnetic core sensor, since the μ value is much smaller than the magnetic core, the sensitivity is low. much.

3. Pulse recognition anti-jamming technology

In order to identify the discharge pulse from the inside of the transformer, according to the principle of differential and polarity identification, in the past, a differential circuit or logic gate circuit was used to differentially amplify the two signals or judge the polarity of the pulse to identify discharge and interference.

Due to the different transmission paths, the two comparison signals have different sizes and waveforms. The differential circuit can only remove the interference of certain frequency components. The logic gate circuit often malfunctions for the oscillating waveform, which makes the monitoring system unable to identify the discharge pulse normally and loses The significance of online monitoring.

If the large-scale power equipment in operation, such as transformers and generators, fails, it will have disastrous consequences for the power system and even the national economy and people's livelihood. On-line monitoring of partial discharge of power equipment can effectively monitor the operation status of power equipment and improve the level of safe operation.

When the pulse current method is used to monitor the partial discharge of power transformers online, severe electromagnetic interference greatly reduces the sensitivity and reliability of the monitoring, and sometimes even makes the measurement impossible. Therefore, one of the key technologies for on-line partial discharge monitoring is how to suppress interference in order to detect real partial discharge signals. (1) Signal coupling

For the suppression of interference, the signal source should be analyzed first. According to the simulation analysis of the partial discharge of large power transformers, the high voltage lead wire is the best monitoring point. In order to couple the high-voltage lead signal, the sensor needs to be installed on the base of the high-voltage bushing. Its size is large, and the diameter of the bushing base above 110KV exceeds 210mm.

At the same time, the software is used to confirm and compare the signals collected from the high-voltage lead and the end-screen lead of the high-voltage bushing to identify the polarity of the discharge pulse [Luo Bing et al, A new method of noise suppression for on-line monitoring partial discharge in transformers .ISH-1995, 5587-2], or pulse amplitude identification can be used to remove interference and only record real discharge pulses.

The existing small-diameter magnetic core sensor [Borisi H, et al.Application of Rogowiski Coils for Partial Discharge Decoupling and noise suppression ISH.1987, 42.02] has excellent performance. The signals are comparable and consistent, so as to carry out pulse identification and amplitude identification, prompting the applicant to try the development of a large-diameter magnetic core sensor. (2) Pulse discrimination and anti-jamming

In view of the fact that the differential amplification and polarity identification methods implemented by hardware circuits in the past are difficult to effectively identify discharge pulses on site, in order to effectively suppress interference and identify partial discharge signals from inside the transformer, the applicant conducted in-depth research and proposed a virtual instrument-based The anti-jamming method of directional coupling pulse polarity and amplitude identification by software identification, which makes full use of the functions of the software, will help to improve the reliability and accuracy of pulse identification.

3. Contents of the invention

One object of the present invention is to provide a large-diameter magnetic core current sensor; another object of the present invention is to provide an anti-interference method for identifying directional coupling pulses of large-diameter magnetic core sensors.

In order to achieve the above object, the technical solution adopted in the present invention is that the large-diameter magnetic core current sensor consists of a Rogowski coil, a filtering and sampling unit, an electromagnetic shielding It is composed of a box, etc., and its characteristic is that the whole magnetic core is composed of a plurality of strip ferrite cores, which are connected by two open magnetic cores to make it a closed shape; High-pass filter capacitor and sampling resistor; the sensitivity of the series circuit is greater than that of the parallel circuit. At the same time, the capacitor C has a good filtering effect on low-frequency signals. According to the simulation analysis and actual test, the appropriate parameters such as capacitance, resistance and coil turns can be determined;

In order to effectively suppress electromagnetic interference in space and improve the anti-interference ability and vibration resistance of the coil, a semi-closed sensor housing is made of metal plates. At the same time, in order to ensure that the signal to be detected will not be shielded, the inner side of the housing is designed as an open type. , so that the coupled signal can enter the coil smoothly.

Some other features of the present invention are that the two open magnetic cores are butted together to form a closed shape, which is a square in the Chinese character "Hui", a hexagonal in the Chinese character "Hui" or a circle in the Chinese character "Hui".

The suitable parameters such as capacitance, resistance and number of coil turns are as follows: the capacitance value is set at 0.01 μF, the resistance is 1 KΩ, and the number of coil turns is 37 turns.

A large-diameter magnetic core current sensor and an anti-interference method for identifying the polarity and amplitude of directional coupling pulses is characterized in that two large-scale magnetic core current sensors, one large and one small, are installed on each phase of the high-voltage winding, According to the similarities and differences between the large and small sensors at the high-voltage bushing in the same phase and the end screen of the bushing coupled to the external interference signal and the pulse polarity of the internal discharge signal, identify the partial discharge signal that occurs inside the transformer, and confirm and compare the two by computer software. The polarity or amplitude of the pulse collected by each sensor can be used to identify partial discharge and external interference; proceed as follows:

1) Polarity identification

According to the similarities and differences between the large and small sensors at the high-voltage bushing in the same phase and the end screen of the bushing coupled to the external interference signal and the pulse polarity of the internal discharge signal, the partial discharge signal that occurs inside the transformer can be identified;

The pulse polarity identification virtual instrument based on the sensor with good α response and the software phase compensation technology can better identify the internal discharge signal of the transformer; first, the computer will continuously collect the signals of at least 50 power frequency cycles, which are respectively from the high voltage A large sensor at the base of the casing and a small sensor from the end screen of the casing. Then, the software divides the signal collected in each power frequency cycle into several data segments of equal time length. The length of the data segment can be adjusted according to the test and field conditions. The signal and the signal of the grounding wire at the end screen of the bushing are first suppressed by periodic interference and background noise interference, and then the polarities of the waveforms of the two signals in the same time period are respectively obtained in the virtual pulse recognition instrument, and the polarity is the same or the same Different judgments, the same polarity is interference, remove it; the different polarity is discharge, record it;

2) Amplitude identification

A specially wound Rogowski coil is used to couple the partial discharge signal at the bottom of the high-voltage bushing close to the flange, and judge whether it is a partial discharge signal or external electromagnetic interference according to the voltage at both ends of the coil; this method connects the middle tap of the Rogowski coil to the transformer Connect the measuring terminals of the end screen of the bushing; connect the measuring terminals of the end screen with a small resistance to ground; the capacitance C of the bushing and the capacitance C _z of the end screen to ground form a capacitive voltage divider, C ₁ << C ₂ , so that R ₁ and R ₂ , R _s , are all at low potential, the Rogowski coil is connected with the measuring terminal of the end screen of the high-voltage bushing to form a directional coupling circuit; U(1)=Uc+U1, U(2)=Uc-U2=Uc-U1, at this time U(1)>U(2); if the current I is reversed, then U(1)<U(2); thus comparing U(1) and U(2) can clearly distinguish the partial discharge signal from the external electromagnetic Interference is distinguished.

The programming content of the software is: first, the computer will continuously collect signals of at least 50 power frequency cycles, which are _respectively from _the ground voltage U( 1) and U(2). Then, the software divides the signal collected in each power frequency cycle into several data segments of equal time length. The length of the data segment can be adjusted according to the test and field conditions. Under each data segment, the signal from the large sensor After periodic interference and background noise interference are suppressed, the volts of the voltages of the two signals in the same time period are respectively obtained in the virtual pulse recognition instrument, and the amplitudes are compared. If U(1)>U(2), it is regarded as an interference signal and removed; if U(1)<U(2), it is regarded as a discharge signal and the data is stored.

The sensitivity of the large-diameter magnetic core type current sensor of the present invention can reach 100pC, the response bandwidth is 80K-5MHz at -3db, the resolution is 5μs, and has good linearity.

Utilizing the directional coupling polarity identification and amplitude identification method of the large-diameter magnetic core type current sensor of the present invention, the partial discharge signal can be accurately identified in the following ranges: the time length is 200ns～100μs, the amplitude is 1mV～5000mV, and the time delay is less than 500ns alpha response signal.

4. Description of drawings

Fig. 1 is a schematic diagram of a large-scale magnetic core type sensor (Rogowski's structure) of the present invention, wherein (a) is a schematic structural diagram of a magnetic core, and (b) a schematic structural diagram of a coil;

Fig. 2 is the schematic diagram of amplitude discrimination of the present invention;

Figure 3 is a waveform diagram of the sensor response on the high voltage bushing;

Fig. 4 is a sensor response waveform diagram on the casing end screen;

Figure 5 is a schematic diagram of analog interference and discharge wiring;

Figure 6 is a waveform diagram of the laboratory simulated interference and the actual discharge sensor coupled to it.

5. Specific implementation

In order to understand the present invention more clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings and the embodiments completed by the inventor according to the technical solution of the present invention.

1. Large-diameter magnetic core current sensor

Referring to Figure 1 and Figure 2, the large-diameter magnetic core sensor uses a segmented combination to make the magnetic core. It consists of Rogowski coil with ferrite core, filtering and sampling unit, electromagnetic shielding box and so on.

As shown in Figure 1(a), the entire magnetic core is composed of multiple strip ferrite cores, which are connected by two open magnetic cores to form a closed "back" square, hexagonal, circular and other shapes. . The relative magnetic permeability of the magnetic core is much higher than that of non-magnetic core materials, which ensures the high sensitivity of the sensor.

After the coil is wound around the magnetic core, see Figure 1(b), and a high-pass filter capacitor and sampling resistor are connected in series at both ends of the coil. The sensitivity of the series circuit is greater than that of the parallel circuit. At the same time, the capacitor C has a good filtering effect on the low-frequency signal. According to the simulation analysis and actual test, the appropriate parameters such as capacitance, resistance and coil turns can be determined. (Taking the sensor installed on the base of the 110KV high-voltage bushing as an example, the capacitance value is set to 0.01μF, the resistance is 1KΩ, and the number of coil turns is 37 turns.)

In order to effectively suppress electromagnetic interference in space and improve the anti-interference ability and vibration resistance of the coil, a semi-closed sensor shell is made of metal plate, and the shell of the sensor is directly grounded, which has a good shielding effect on electric and magnetic interference. At the same time, in order to ensure that the signal to be detected will not be shielded, the inner side of the shell is designed to be open, so that the coupled signal can enter the coil smoothly.

2. Anti-jamming method using large-diameter magnetic core sensor for directional coupling pulse identification

Two large-diameter magnetic core current sensors are installed in each phase of the high-voltage winding, and the large and small sensors at the same-phase high-voltage bushing and the end screen of the bushing are coupled to the external interference signal and the pulse pole of the internal discharge signal. Identify the partial discharge signal inside the transformer, and use computer software to confirm and compare the polarity or amplitude of the pulses collected by the two sensors to identify partial discharge and external interference; follow the steps below:

(1) Polarity identification

The principle of polarity identification is that according to the similarities and differences between the large and small sensors at the high-voltage bushing in the same phase and the end screen of the bushing coupled to the external interference signal and the pulse polarity of the internal discharge signal, the partial discharge signal that occurs inside the transformer can be identified.

The pulse polarity identification virtual instrument based on the large-diameter magnetic core current sensor with good α response and the software phase compensation technology of the present invention can better identify the internal discharge signal of the transformer. First, the computer will continuously collect signals of at least 50 power frequency cycles, which are respectively from the large sensor at the base of the high voltage bushing and the small sensor at the end screen of the bushing. Then, through computer software, the signal collected in each power frequency cycle is divided into several data segments of equal time length. The length of the data segment can be adjusted according to the test and field conditions. The signal of the lead wire and the signal of the grounding wire at the end of the bushing are suppressed by periodic interference and background noise interference, and then the polarity of the waveforms of the two signals in the same time period are respectively obtained in the virtual pulse recognition instrument, and the polarity is the same Or different judgments, the same polarity is interference, remove it; the different polarity is discharge, record it.

(2) Amplitude identification

The principle is shown in Figure 2. It uses a specially wound Rogowski coil to couple the partial discharge signal at the bottom of the high voltage bushing near the flange, and judges whether it is a partial discharge signal or external electromagnetic interference according to the voltage at both ends of the coil. This method connects the center tap of the Rogowski coil to the measuring terminal at the end of the transformer bushing. A small resistor is connected to the terminal string of the last screen to ground. The bushing capacitor C and the last screen-to-ground capacitor C _z form a capacitive voltage divider, C ₁ << C ₂ , so that R ₁ , R ₂ , and R _s are all at low potential. The Rogowski coil is connected with the measuring terminal at the end screen of the high-voltage bushing to form a directional coupling circuit. When the current I of the directional coupling circuit in Fig. 1 is in the direction shown in the figure, U(2)=Uc+U1, U(2)=Uc-U2=Uc-U1. At this time U(1)>U(2); if the current I is reversed, then U(1)<U(2). Thus comparing U(1) and U(2) can clearly distinguish the partial discharge signal from the external electromagnetic interference.

The sensitivity of the large-diameter magnetic core type current sensor of the present invention can reach 100pC, the response bandwidth is 80K-5MHz at -3db, the resolution is 5μs, and has good linearity.

Utilizing the directional coupling polarity identification and amplitude identification method of the large-diameter magnetic core type current sensor of the present invention, the partial discharge signal can be accurately identified in the following ranges: the time length is 200ns～100μs, the amplitude is 1mV～5000mV, and the time delay is less than 500ns alpha response signal.

Example: The test on the #2 main transformer of a certain power plant is as follows: In the off-line state, according to the national standard GB7354-87, a pulse with a rising edge of 45ns and a charge of 1000pC was injected between the high-voltage outlet terminal of phase A and the transformer shell. Figures 3 and 4 are the time-domain responses of the two sensors in phase A displayed by a 500MHz bandwidth oscilloscope (Tektronix TDS3052). The signals coupled to the two sensors not only have a high signal-to-noise ratio, but also have a good α response. The maximum pulse amplitudes received are 0.3V and 0.8V respectively, and the time delay is 20ns, which creates necessary conditions for subsequent processing of pulse signals such as polarity identification and acquisition of effective amplitude information.

It can be seen from Figures 3 and 4 that for the simulated pulse interference signal from outside the transformer, the first wave polarity of the signals coupled to the two sensors is the same, so it is judged as an interference signal, which can be eliminated by software judgment.

With the help of virtual instruments, the schematic diagram of the anti-jamming method test circuit for directional coupling pulse polarity and amplitude identification is shown in Figure 5. In the figure, sensors a and b are respectively a large rectangular sensor and a small circular sensor, and the input of the square wave is the size It is an analog pulse of 1000pc. When the positive end of the square wave is connected to point 1, the square wave simulates interference; when the positive end of the square wave is connected to point 2, the square wave simulates transformer discharge.

Connect the positive end of the square wave to points 1 and 2 respectively, and the waveforms of the large and small sensors obtained in the oscilloscope are shown in Figure 6. (a) is the signal coupled by the large sensor when simulating interference, the time axis length is 10 μs, and the amplifier attenuates 100 times; (b) is the signal coupled by the small sensor when simulating interference, the time axis length is 10 μs, and the amplifier attenuation is 1000 times; (c) is the signal coupled by the large sensor during the simulated discharge, the time axis length is 20 μs, and the amplifier attenuation is 1000 times; (d) is the signal coupled by the small sensor during the simulated discharge, the time axis length is 20 μs, and the amplifier attenuation is 1000 times.

It can be seen from Figure 6 that when the disturbance is simulated, the direction of the pulse coupled to the large and small sensors is the same; on the contrary, when the discharge is simulated, the direction of the pulse coupled to the large and small sensor is opposite. Moreover, when both are interference pulses, the maximum peak values of the two oscillation pulses have the same polarity; when both are discharge pulses, the maximum peak values of the two oscillation pulses have different polarities. As a result, the software can better identify discharges and disturbances.

As mentioned above, using the present invention to monitor partial discharges of large transformers, transformers, generators, etc. in the power system on-line can reduce accidents and ensure safe and stable operation of the power system, thereby obtaining huge economic benefits.

Claims (4)

1. a large size magnetic-core type current sensor is characterized in that, is that Rogovski coil, filtering and sampling unit, the electromagnetic screen box of magnetic core constitutes by adopting sectionally assembled ferrite;

Whole magnetic core is made up of a plurality of strip FERRITE CORE, is docked by two open magnetic cores and makes it to be close-shaped;

Described filtering and sampling unit are, after magnetic core winds coil, at coil two ends polyphone high-pass filtering capacitor C and sampling resistor R; The sensitivity of series circuit is greater than parallel circuit, and capacitor C has good filter action to low frequency signal simultaneously, according to simulation analysis and actual tests, can determine parameters such as suitable electric capacity, resistance and coil turn;

The electromagnetic screen box is made semi-enclosed shell with sheet metal, the inboard of shell is designed to open, makes coupled signal can enter coil smoothly.

2. large size magnetic-core type current sensor according to claim 1 is characterized in that, described two open magnetic cores dock make it to be sealing be shaped as " returning " word square or " returning " word hexagon or " returning " word circle.

3. large size magnetic-core type current sensor according to claim 1 is characterized in that parameters such as described suitable capacitor C, resistance R and coil turn are: the value of capacitor C is decided to be 0.01 μ F, and resistance R is 1K Ω, and coil turn is 37 circles.

4. the anti-interference method differentiated of large size magnetic-core type current sensor and directional couple pulse polarity amplitude, it is characterized in that, install small one and large one two with large size magnetic-core type current sensor at every phase high pressure winding, big according to homophase bushing place and bottom shielding of bushing place, little sensor is coupled to the similarities and differences of external interference signals and internal discharge signal pulse polarity, identification occurs in the local discharge signal of transformer inside, by computer software confirm and relatively two sensor acquisition of size to the polarity or the amplitude of pulse differentiate shelf depreciation and external interference; Carry out according to the following steps:

1) polarity is differentiated

According to the large and small sensors coupled at homophase bushing place and bottom shielding of bushing place the similarities and differences, occur in the local discharge signal of transformer inside with identification to external interference signals and internal discharge signal pulse polarity;

Pulse polarity based on large size magnetic-core type current sensor with good α response and software phase compensation technology is differentiated virtual instrument, can discern transformer internal discharge signal preferably; At first, computing machine is the signal of at least 50 power frequency periods of continuous acquisition, and these signals are respectively from the large sensor of bushing base position and from the little sensor at bottom shielding of bushing place.Then, software is the data segment of several equal time length with the signal segmentation that collects in each power frequency period, the length of data segment can be adjusted according to test and field condition, under each data segment, signal and the signal elder generation process PERIODIC INTERFERENCE of bottom shielding of bushing ground wire and the inhibition that ground unrest disturbs from the transformer high-voltage lead-in wire, in virtual pulse recognition instrument, obtain the polarity of two paths of signals waveform in the identical time period afterwards respectively, and carry out the identical or different judgement of polarity, what polarity was identical is to disturb, and removes it; What polarity was different is discharge, notes;

2) amplitude is differentiated

Adopt Rogowski coil close flange place coupling local discharge signal bottom bushing of special coiling, and judge that according to the size of coil both end voltage local discharge signal still is external electromagnetic interference (EMI); This method couples together the centre tap of Rogowski coil and bushing shell for transformer end screen measurement terminal; Low resistance grounding of end screen measuring junction substring; Capacitance of bushing C and end screen ground capacitance C _zForm capacitive divider, C ₁＜＜C ₂, make R ₁, R ₂, R _s, all be in electronegative potential, Rogowski coil and bushing end screen measurement terminal link up and constitute the directional couple circuit; U (1)=Uc+U1, U (2)=Uc-U2=Uc-U1, U (1)＞U (2) at this moment; If electric current I is reverse, then U (1)＜U (2); U (1) relatively thus) and U (2) just can be clearly local discharge signal and external electromagnetic interference (EMI) be distinguished and come;

The workout content of described software is: at first, computing machine is the signal of at least 50 power frequency periods of continuous acquisition, and these signals are respectively from the large sensor up-sampling resistance R of bushing base position ₁, R ₂On voltage-to-ground U (1) and U (2), then, software is the data segment of several equal time length with the signal segmentation that collects in each power frequency period, the length of data segment can be adjusted according to test and field condition, under each data segment, from the signal elder generation process PERIODIC INTERFERENCE of large sensor and the inhibition of ground unrest interference, in virtual pulse recognition instrument, obtain the volt value of two paths of signals voltage in the identical time period afterwards respectively, and carry out amplitude relatively; If U (1)＞U (2) then thinks undesired signal, remove it; If U (1)＜U (2) thinks discharge signal, the storage data.

Images