Cable partial discharge online detection method based on non-calibration pulse current method

Abstract

The invention discloses a cable partial discharge on-line detection method based on a non-calibration pulse current method, which belongs to the field of power equipment partial discharge detection, and comprises the following steps of: designing four typical insulation defect models by combining actual operation and detection conditions of a cable, and respectively simulating corona discharge, suspension discharge, surface discharge and internal discharge; building an experimental platform, coupling partial discharge pulses by using a bushing sensor, and providing a phase synchronization signal; through the designed matching impedance circuit, the capacitance value of the bushing sensor can be measured. According to the function relationship established between the capacitance value and the discharge conversion coefficient, the partial discharge amplitude is rapidly estimated; a partial discharge pulse signal is collected by a pulse current method partial discharge sampling system, and a phase resolution partial discharge (PRPD) graph is constructed according to a phase value in combination with a power frequency synchronization signal.

Description

Technical Field

[0001] The invention discloses an online detection method for cable partial discharge based on a non-calibration pulse current method, and belongs to the field of partial discharge detection of power equipment. Background Art

[0002] Power cables offer advantages such as minimal external influences, reliability, durability, and a high rated operating temperature rating. They also enhance the urban environment and are widely used in power plants, substations, and power lines crossing railways, rivers, and communication lines, making them an indispensable component of urban and rural power supply networks. Partial discharge (PD) is a key indicator of cable insulation degradation, and timely and accurate detection and identification of PD is crucial for preventing cable failures. Traditional methods for PD identification, such as differential, directional coupling, electromagnetic coupling, capacitive coupling, inductive coupling, and ultra-high frequency (UHF) methods, have achieved some success in detecting PD in switchgear. However, these traditional measurement methods require the use of a standard calibration source to calibrate PD detection sensors, such as high-frequency current transformers (HFCTs). These methods are complex, have low accuracy, and can only be performed during a power outage, not online, making them difficult to meet real-time detection requirements. Therefore, finding a simple, convenient, and online PD detection method is crucial for cable PD detection. Summary of the Invention

[0003] The purpose of the present invention is to design a convenient and concise partial discharge detection method, and to propose an online detection method for cable partial discharge based on a non-calibrated pulse current method, which is characterized by comprising the following steps:

[0004] S1: Based on the actual operation and detection of cables, four typical insulation defect models are designed to simulate corona discharge, suspension discharge, surface discharge and internal discharge respectively. An experimental platform is built, and the casing sensor is used to couple the partial discharge pulse and provide a phase synchronization signal.

[0005] S2: The capacitance value of the casing sensor can be measured through the designed matching impedance circuit;

[0006] S3: Rapidly estimate the partial discharge amplitude based on the functional relationship between capacitance value and discharge conversion coefficient;

[0007] S4: The pulse current method partial discharge sampling system is used to collect the partial discharge pulse signal, combined with the power frequency synchronization signal, and a phase-resolved partial discharge (PRPD) map is constructed according to the phase value.

[0008] In step S1, four typical insulation defect models need to be designed. The upper ends of the four typical insulation defect models are connected to high voltage and the lower ends are grounded. The four models are then connected to a test bench. The power supply is boosted by a step-up transformer and then connected in series with a current-limiting resistor to protect the circuit. A bushing sensor is used to couple partial discharge pulses and provide a phase synchronization signal. Finally, a high-speed sampling device is used to collect partial discharge pulses through the bushing sensor.

[0009] In step S2, when measuring the PD signal, a matching impedance circuit is connected in parallel with the RC circuit in the charge indicator. For different charge indicators, the equivalent impedance of the matching impedance circuit must be low to maintain a relatively constant equivalent impedance across the entire parallel circuit. A corresponding impedance matching circuit must be designed to obtain the casing sensor's capacitance value.

[0010] In step S3, according to the IEC60270 standard, without connecting the switching device to high voltage, a standard calibration source is used to generate discharge pulses ranging from 500pC to 2nC to calibrate the acquisition circuit and obtain conversion coefficients at different capacitance values of 14, 20, 45, 50, 80, and 150pF.

[0011] There is a linear positive correlation between the pulse amplitude and the discharge amplitude. There is a conversion coefficient between the sensor response amplitude and the actual discharge amount of the partial discharge pulse.

[0012]

[0013] Different conversion coefficients are generated depending on the capacitance of the casing sensor. Previous methods required calibrating the sensor with a standard pulse source to obtain the conversion coefficient. This method uses an impedance matching circuit to directly obtain the sensor capacitance without interrupting power, thus simplifying the testing process. By performing multiple measurements with different capacitance values, the relationship between the conversion coefficient and the sensor capacitance can be determined, allowing for rapid estimation of cable partial discharge.

[0014] In step S4, the cable partial discharge pulse signal acquisition sensor, constructed in the previous steps, uses a high-speed sampling system to collect partial discharge pulses, obtaining the amplitude and discharge volume of each pulse. Phase information is then assigned to each pulse based on the coupled power frequency voltage signal. An appropriate number of pulses are selected to create a phase-resolved partial discharge map of the cable. This PRPD map can be used to determine whether the cable is defective and provides raw data for subsequent partial discharge type identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flowchart of the online detection method for cable partial discharge based on the non-calibrated pulse current method.

[0016] Figure 2-5 These are four typical insulation defect models designed.

[0017] Figure 6 These are the phase-resolved partial discharge (PRPD) maps of four typical partial discharge models.

[0018] Figure 7 This is a measured photo of a substation in Tianjin.

[0019] Figure 8 yes Figure 7 The three-phase polarity PRPD diagram corresponding to the substation shown. DETAILED DESCRIPTION

[0020] The present invention is not limited to the embodiments described below. All non-innovative work achievements made by researchers in this field based on the present invention fall within the scope of protection of the present invention. The present invention is further described below with reference to the accompanying drawings:

[0021] Figure 1 The figure shows a flow chart of the online detection method for partial discharge of cables based on the non-calibrated pulse current method. The steps include:

[0022] S1: Based on the actual operation and detection of cables, four typical insulation defect models are designed to simulate corona discharge, suspension discharge, surface discharge and internal discharge respectively. An experimental platform is built, and the casing sensor is used to couple the partial discharge pulse and provide a phase synchronization signal.

[0023] S2: The capacitance value of the casing sensor can be measured through the designed matching impedance circuit;

[0024] S3: Rapidly estimate the partial discharge amplitude based on the functional relationship between capacitance value and discharge conversion coefficient;

[0025] S4: The pulse current method partial discharge sampling system is used to collect the partial discharge pulse signal, combined with the power frequency synchronization signal, and a phase-resolved partial discharge (PRPD) map is constructed according to the phase value.

[0026] The specific contents of each process are as follows:

[0027] 1. Design insulation defect model and build experimental platform

[0028] In the actual operation and detection of cables, there are four typical discharges, so four insulation defect models are designed, such as Figure 2-Figure 5As shown, they correspond to internal discharge, suspended discharge, surface discharge and corona discharge respectively (the left side (a) is the discharge model structure diagram, and the right side (b) is the corresponding discharge model physical diagram). The study found that the bushing sensor embedded in the cable terminal switch cabinet can couple the local discharge pulse and provide the corresponding synchronization signal. Therefore, the sensor can be used to collect signals to realize the non-calibrated pulse current method for local discharge detection of cables. For different discharge insulation defects, the starting discharge voltage is slightly different: 5KV for internal discharge, 4KV for suspended discharge, 3.5KV for surface discharge, and 4.5KV for corona discharge. The experimental platform built is as follows Figure 2-Figure 5 As shown, a 220V AC power supply is used and connected to a 1:1000 step-up transformer. A current-limiting resistor protection circuit is then connected in series, and the insulation defect is connected to the circuit. Finally, the sampling device collects partial discharge pulses through the bushing sensor. The construction of the experimental bench complies with the IEC60270 standard.

[0029] 2. Sensor impedance matching circuit construction

[0030] An impedance matching circuit was designed based on the casing sensor. This circuit consists of two parts. The first part is used to obtain the casing sensor capacitance value, facilitating the subsequent calculation of the conversion coefficient and implementing non-calibrated pulse current measurement. The second part, consisting of a filter circuit and an amplifier circuit, is primarily used to condition the pulse signal obtained by the pulse current method, facilitating subsequent processing to generate accurate phase-resolved partial discharge (PRPD) images. The filter circuit has an equivalent impedance of approximately 100Ω, which is much smaller than the impedance of the charge indicator and ensures a constant impedance.

[0031] 3. Obtain the conversion factor

[0032] According to the IEC60270 standard, without connecting the switching device to high voltage, a standard calibration source is used to generate discharge pulses ranging from 500pC to 2nC to calibrate the acquisition circuit and obtain conversion coefficients for different capacitance values of 14, 20, 45, 50, 80, and 150pF.

[0033] There is a linear positive correlation between the pulse amplitude and the discharge amplitude. There is a conversion coefficient between the sensor response amplitude and the actual discharge amount of the partial discharge pulse.

[0034]

[0035] Different conversion coefficients are generated depending on the capacitance of the casing sensor. Previous methods required calibrating the sensor with a standard pulse source to obtain the conversion coefficient. This method uses an impedance matching circuit to directly obtain the sensor capacitance without interrupting power, thus simplifying the testing process. By performing multiple measurements with different capacitance values, the relationship between the conversion coefficient and the sensor capacitance can be determined, allowing for rapid estimation of cable partial discharge.

[0036] 4. PRPD map construction

[0037] The cable partial discharge pulse signal acquisition sensor constructed based on the above steps uses a high-speed sampling system to collect partial discharge pulses, obtain the amplitude and discharge amount of a single pulse, and at the same time, mark the phase information of each pulse according to the coupled power frequency voltage signal. After selecting an appropriate number of pulses, a phase-resolved partial discharge diagram of the cable is drawn, as shown in the figure. Figure 6 As shown in the figure (ad corresponds to the four types of internal, suspended, surface, and corona respectively). Based on the drawn PRPD map, it is possible to determine whether the cable has defects and also provide raw data for subsequent partial discharge type identification.

[0038] 5. Measured data analysis

[0039] For example Figure 7 As shown in the figure, an inspection was carried out at a substation in Tianjin, and suspended discharge was found.

[0040] The negative 1 switchgear of micro 41 was tested, and the three-phase PRPD spectrum was shown in Figure 8. Compared with the negative 3 switchgear of micro 41, the amplitude was attenuated. Therefore, the preliminary diagnosis result was that it was transmitted from the negative 3 switchgear.

[0041] The negative 3 switchgear of Micro 41 was tested, and the three-phase PRPD spectrum is shown in Figure 8. Compared with the adjacent switchgear, the discharge pulse amplitude at the red and yellow marks B is the largest, and both meet the characteristics of suspended discharge. The amplitudes of phases A and C are attenuated, but there is no obvious phase shift. Therefore, the preliminary diagnosis result is that there are two types of interphase suspended discharges in phase B of the negative 3 switchgear.

Claims

1. A cable partial discharge online detection method based on a non-calibrated pulse current method, characterized in that: The following steps are involved: S1: Based on the actual operation and detection of cables, four typical insulation defect models are designed to simulate corona discharge, suspension discharge, surface discharge and internal discharge respectively. An experimental platform is built, and the casing sensor is used to couple the partial discharge pulse and provide a phase synchronization signal. S2: The capacitance value of the casing sensor can be measured through the designed matching impedance circuit; S3: Rapidly estimate the partial discharge amplitude based on the functional relationship between capacitance value and discharge conversion coefficient; S4: The pulse current method partial discharge sampling system is used to collect the partial discharge pulse signal, combined with the power frequency synchronization signal, and a phase-resolved partial discharge (PRPD) map is constructed according to the phase value.

2. The method for online detection of cable partial discharge based on the non-calibrated pulse current method according to claim 1, characterized in that: Four typical insulation defect models were designed, and bushing sensors were used to collect partial discharge signals. The process is as follows: Four typical insulation defect models were designed. Their upper terminals were connected to high voltage and their lower terminals were grounded. They were then directly connected to the constructed experimental platform. The power supply was boosted by a step-up transformer and then connected in series with a current-limiting resistor for protection. Bushing sensors were used to couple partial discharge pulses and provide phase synchronization signals. Finally, a sampling device collected partial discharge pulses through the bushing sensors. The construction of the experimental platform complied with the IEC60270 standard.

3. The method for online detection of cable partial discharge based on the non-calibrated pulse current method according to claim 1, characterized in that: The designed impedance matching circuit can be used to measure the capacitance value of the casing sensor. The process is as follows: The pulse signal is connected from the charged indicator to the impedance matching circuit. The capacitance measurement part of the impedance matching circuit is composed of a capacitor with a larger capacitance. The voltage value on the capacitor is obtained through the voltage divider principle, and the capacitance value of the casing sensor is inferred.

4. The method for online detection of cable partial discharge based on non-calibrated pulse current method according to claim 1, characterized in that: The process of quickly estimating the partial discharge amplitude is as follows: According to the IEC60270 standard, without connecting the switching device to high voltage, a standard calibration source is used to generate discharge pulses ranging from 500pC to 2nC to calibrate the acquisition circuit and obtain conversion coefficients for different capacitance values of 14, 20, 45, 50, 80, and 150pF. There is a linear positive correlation between the pulse amplitude and the discharge amplitude. There is a conversion coefficient between the sensor response amplitude and the actual discharge amount of the partial discharge pulse. Different conversion coefficients are generated depending on the capacitance of the casing sensor. Previous methods required calibrating the sensor with a standard pulse source to obtain the conversion coefficient. This method uses an impedance matching circuit to directly obtain the sensor capacitance without interrupting power, thus simplifying the testing process. By performing multiple measurements with different capacitance values, the relationship between the conversion coefficient and the sensor capacitance can be determined, allowing for rapid estimation of cable partial discharge.

5. The method for online detection of cable partial discharge based on non-calibrated pulse current method according to claim 1, characterized in that: The pulse current method partial discharge sampling system is used to collect partial discharge pulse signals. Combined with the power frequency synchronization signal, a phase-resolved partial discharge (PRPD) map is constructed based on the phase value. The process is as follows: The cable partial discharge pulse signal acquisition sensor, constructed based on the aforementioned steps, utilizes a high-speed sampling system to collect partial discharge pulses, acquiring the amplitude and discharge volume of individual pulses. It also assigns phase information to each pulse based on the coupled power-frequency voltage signal. An appropriate number of pulses are selected to create a phase-resolved partial discharge map of the cable. This PRPD map can be used to determine whether the cable is defective and provides raw data for subsequent partial discharge type identification.

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