In theory,due to the fact that the grounding wire PE of wind turbine and the N-line(directly grounded)of the Y-shaped wiring on the low-voltage side of the box-type transformer share the grounding body,when the wind t...In theory,due to the fact that the grounding wire PE of wind turbine and the N-line(directly grounded)of the Y-shaped wiring on the low-voltage side of the box-type transformer share the grounding body,when the wind turbine is struck by lightning,the lightning current is directly conducted to the N-line on the low-voltage side of the box-type transformer(invasion mode of transformer synonym end).At the same time,conducted overvoltage pulse is generated in the three-phase winding on the low-voltage side,and coupled to the high-voltage side of the box-type transformer(Δconnection)to generate coupling overvoltage pulse.After investigation,the existing regulations on the tripping rate of power lines have not taken into account the impact of wind turbines being struck by lightning on line tripping,and the mechanism is still unclear.In order to further analyze the causes of lightning tripping of collection line circuit breakers in wind farms,it is necessary to study the physical process of how lightning current is conducted(coupled)to the collection line through the box-type transformer after lightning strikes on the wind turbines.In this paper,the test method of"conduction and coupling test of lightning current invading transformer N-line",and the waveform parameters(polarity,phase,amplitude,and transformation ratio)of the primary and secondary windings of the box-type transformer when lightning current invades the transformer N-line are introduced.It can provide assistance for operation and maintenance personnel to analyze the reasons for lightning tripping of 35 kV line circuit breakers in wind farms.展开更多
In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous p...In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.展开更多
For actively modulated In-line Sagnac interferential all optic fiber current transformers (AOFCTs), the accuracies are directly affected by the amplitude of the modulation signal. In order to deeply undertand the func...For actively modulated In-line Sagnac interferential all optic fiber current transformers (AOFCTs), the accuracies are directly affected by the amplitude of the modulation signal. In order to deeply undertand the function of the modulator, a theoretical model of modulation effect to AOFCTs is built up in this paper. The effect of the amplitude of the modulation signal to the output intensity of AOFCTs is theoretically formulated and numerical calculated. The results show that the modulation voltage variation could affect the output accuracies significantly. This might be some references on the investigation for practical applications of AOFCTs.展开更多
The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is...The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is the Hall direct measurement principle.The transformer has the following three characteristics:firstly, the effect of the remnant field of the iron core on the measurement is decreased;secondly,because the temperature compensation is adopted,the transformer has good temperature charactreristic;thirdly,be cause the wavelet transfomation technology is adopted,the transformer has the capacity of good antijanming.展开更多
The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic int...The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic interference resistance.However,the high cost of the all-fiber optical transformer limits its promotion and application in engineering.This paper proposes a design scheme of an independent double acquisition loop for the all-fiber optical current transformer based on the single optical path.Firstly,based on the closed-loop control mode and open-loop control mode,the twochannel sampling signal demand for relay protection,and the independent dual-acquisition loop design scheme of the all-fiber optical current transformer are proposed.Secondly,the reliability and economic feasibility of the scheme are demonstrated by an analysis of system failure and cost.The results show that the scheme can actualize the acquisition function of two independent all-fiber optical current transformer products on a single all-fiber current transformer in an integrated manner,which greatly reduces the cost of the all-fiber optical current transformer in engineering applications.展开更多
An optical fiber transmitting photoelectric coupling current transformer has been developed. In the environment of high voltage and electromagnetic fields, this device is characterized by high insulation, high reliabi...An optical fiber transmitting photoelectric coupling current transformer has been developed. In the environment of high voltage and electromagnetic fields, this device is characterized by high insulation, high reliability, small mass and high anti-interference. The structure design and operating principle of the system are introduced, measurement errors are analyzed and experimental results are given.展开更多
Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is use...Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is used to establish a calculation model,at the same time mainly considers the excitation characteristics of the transformer,the transient model of the circuit breaker,and the model of high voltage transformer,and calculated the inrush current with transformer switch-in with load in this plan.During system debugging in the plan,the two sets of main transformers passed the closing and opening test,and the data of inrush current in the test are recorded and analyzed.The simulation calculation and measured data show that the results are consistent.The simulation calculation also shows that it is not recommended to perform on-load closing of the transformer except for special circumstances,because of the influence of hysteresis characteristic when the transformer was switched in with load or the terminal voltage of the transformer resumed normal level from a low one after an external near-end fault was cleared,which various transformer differential protection using the characteristics of inrush to implement block scheme may mal-operate.展开更多
In this article,a new type current transformer was developed using an active-passive circuit to improve low frequency response of the system without impairing high frequency response.The active-passive current transfo...In this article,a new type current transformer was developed using an active-passive circuit to improve low frequency response of the system without impairing high frequency response.The active-passive current transformer with In-flange was fabricated.Theoretical analysis,numerical simulations and experimental results are given.展开更多
In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then t...In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then the nature of the magnetizing current due to energizing a power transformer at no-load is explained. The first generation of methods used to disable the protective relay system during inrush current, namely the Desensitizing and Tripping Suppressor, is introduced. The second generation, the harmonic restraint method and the waveform-based restraint method with their different versions, is explained. Then we will explore thoroughly the fictitious equivalent resistance method as an example of the third generation of model type restraining or blocking methods. Finally, a comparison between these methods and conclusion is carried out.展开更多
The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EM...The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EMD, then define and compute the projection area on X-axis of each IMF—, the specific gravity of SIMF—, and the maximum of —. We can get a new scheme of transformer-protection based on comparing the difference between inrush and fault current. Theoretical analysis show that the method can precisely discriminate inrush and fault current, fault clearance time is about 20ms. Moreover, it is convenient to achieve and hardly be affect by not-periodic component.展开更多
This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency c...This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.展开更多
This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The desi...This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.展开更多
The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as h...The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as high as ten times its rated current. This could cause many problems from mechanical stress on transformer windings to harmonics injection, and system protection malfunction. There have been numerous researches focusing on calculation and mitigation of the transformer inrush current. With the development of smart grid, distributed generation from independent power producers (IPPs) is growing rapidly. This paper investigates the inrush current due to black start of an IPP system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software. The study demonstrates that a single genset is capable of energizing a group of transformers since the overall inrush current is slightly above the inrush of the transformer directly connected to the generator. In addition, a simple method is proposed to mitigate the inrush current of the transformers using an auxiliary transformer.展开更多
The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination o...The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.展开更多
Preventive maintenance in the transformer is performed through a dif-ferential relay protection system,and it protects the transformer from internal and external faults.However,the Current Transformer(CT)in the differ...Preventive maintenance in the transformer is performed through a dif-ferential relay protection system,and it protects the transformer from internal and external faults.However,the Current Transformer(CT)in the differential protec-tion system mal-operates during inrush currents.CT saturates due to magnetizing inrush currents and causes false tripping of the differential relays.Moreover,iden-tification of tripping in protection relay either due to inrush current or internal faults needs to be diagnosed.For the above problem,continuous monitoring of transformer breather and CT terminals with thermal camera helps detect the trip-ping in relay due to inrush or internal fault.The transformer’s internal fault leads to high breathing process in the transformer breather,never for inrush currents.During inrush currents,CT temperature is increased.Continuous monitoring of breather and CT of the transformer through thermal imaging and radiometric pix-els detect the causes of CT saturation and differentiates maloperation.Hybrid wavelet threshold image analytics(HWT-IA)based radiometric pixels analysis of the transformer breather and CT after de-noising provides an accurate result of about 95%for identification of the false tripping of differential protection system of transformer.展开更多
This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission chara...This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.展开更多
We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology fo...We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers(HFCTs).The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal.Firstly,by studying the working principle of HFCTs,we summarize that the bandwidth of the selected signal acquisition device should be at least 100 MHz to ensure measurement accuracy.Secondly,Gauss pulse and square wave pulse are generated to determine the effects of different sources.The measurement results indicate that Gauss pulse is more suitable for pulse injection method,and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion.Finally,the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods.The measurement results show a remarkable consistency between two methods.However,pulse injection method requires the simpler operation and lias a higher resolution,obviously improving the measurement efficiency and bet ter displaying the details of the transfer impedance curves.展开更多
基金Supported by the Real-time Monitoring of Strong Electromagnetic Pulse Protection(Lightning)Effect and Grounding Resistance for Guangdong Yuedian Zhuhai Biqing Bay Sea Wind Farm(SFC/ZHW-ZX-FW-24-023)the Research on Key Technologies of Lightning Intelligent Protection System for Guangdong Energy Hehe Sea Wind Farm(SFC/QZW-ZX-XF-24-020).
文摘In theory,due to the fact that the grounding wire PE of wind turbine and the N-line(directly grounded)of the Y-shaped wiring on the low-voltage side of the box-type transformer share the grounding body,when the wind turbine is struck by lightning,the lightning current is directly conducted to the N-line on the low-voltage side of the box-type transformer(invasion mode of transformer synonym end).At the same time,conducted overvoltage pulse is generated in the three-phase winding on the low-voltage side,and coupled to the high-voltage side of the box-type transformer(Δconnection)to generate coupling overvoltage pulse.After investigation,the existing regulations on the tripping rate of power lines have not taken into account the impact of wind turbines being struck by lightning on line tripping,and the mechanism is still unclear.In order to further analyze the causes of lightning tripping of collection line circuit breakers in wind farms,it is necessary to study the physical process of how lightning current is conducted(coupled)to the collection line through the box-type transformer after lightning strikes on the wind turbines.In this paper,the test method of"conduction and coupling test of lightning current invading transformer N-line",and the waveform parameters(polarity,phase,amplitude,and transformation ratio)of the primary and secondary windings of the box-type transformer when lightning current invades the transformer N-line are introduced.It can provide assistance for operation and maintenance personnel to analyze the reasons for lightning tripping of 35 kV line circuit breakers in wind farms.
文摘In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.
文摘For actively modulated In-line Sagnac interferential all optic fiber current transformers (AOFCTs), the accuracies are directly affected by the amplitude of the modulation signal. In order to deeply undertand the function of the modulator, a theoretical model of modulation effect to AOFCTs is built up in this paper. The effect of the amplitude of the modulation signal to the output intensity of AOFCTs is theoretically formulated and numerical calculated. The results show that the modulation voltage variation could affect the output accuracies significantly. This might be some references on the investigation for practical applications of AOFCTs.
基金ThispaperissupportedbyNationalNatureScienceFoundationofChina (No 60 1760 2 0 )
文摘The wavelet transformation is applied to the high current transformer.The high current transformer elaborated in the paper is mainly applied to the measurement of AC/DC high current.The principle of the transformer is the Hall direct measurement principle.The transformer has the following three characteristics:firstly, the effect of the remnant field of the iron core on the measurement is decreased;secondly,because the temperature compensation is adopted,the transformer has good temperature charactreristic;thirdly,be cause the wavelet transfomation technology is adopted,the transformer has the capacity of good antijanming.
基金supported by the National Natural Science Foundation of China (No. U1866203)
文摘The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic interference resistance.However,the high cost of the all-fiber optical transformer limits its promotion and application in engineering.This paper proposes a design scheme of an independent double acquisition loop for the all-fiber optical current transformer based on the single optical path.Firstly,based on the closed-loop control mode and open-loop control mode,the twochannel sampling signal demand for relay protection,and the independent dual-acquisition loop design scheme of the all-fiber optical current transformer are proposed.Secondly,the reliability and economic feasibility of the scheme are demonstrated by an analysis of system failure and cost.The results show that the scheme can actualize the acquisition function of two independent all-fiber optical current transformer products on a single all-fiber current transformer in an integrated manner,which greatly reduces the cost of the all-fiber optical current transformer in engineering applications.
文摘An optical fiber transmitting photoelectric coupling current transformer has been developed. In the environment of high voltage and electromagnetic fields, this device is characterized by high insulation, high reliability, small mass and high anti-interference. The structure design and operating principle of the system are introduced, measurement errors are analyzed and experimental results are given.
文摘Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is used to establish a calculation model,at the same time mainly considers the excitation characteristics of the transformer,the transient model of the circuit breaker,and the model of high voltage transformer,and calculated the inrush current with transformer switch-in with load in this plan.During system debugging in the plan,the two sets of main transformers passed the closing and opening test,and the data of inrush current in the test are recorded and analyzed.The simulation calculation and measured data show that the results are consistent.The simulation calculation also shows that it is not recommended to perform on-load closing of the transformer except for special circumstances,because of the influence of hysteresis characteristic when the transformer was switched in with load or the terminal voltage of the transformer resumed normal level from a low one after an external near-end fault was cleared,which various transformer differential protection using the characteristics of inrush to implement block scheme may mal-operate.
文摘In this article,a new type current transformer was developed using an active-passive circuit to improve low frequency response of the system without impairing high frequency response.The active-passive current transformer with In-flange was fabricated.Theoretical analysis,numerical simulations and experimental results are given.
文摘In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then the nature of the magnetizing current due to energizing a power transformer at no-load is explained. The first generation of methods used to disable the protective relay system during inrush current, namely the Desensitizing and Tripping Suppressor, is introduced. The second generation, the harmonic restraint method and the waveform-based restraint method with their different versions, is explained. Then we will explore thoroughly the fictitious equivalent resistance method as an example of the third generation of model type restraining or blocking methods. Finally, a comparison between these methods and conclusion is carried out.
文摘The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EMD, then define and compute the projection area on X-axis of each IMF—, the specific gravity of SIMF—, and the maximum of —. We can get a new scheme of transformer-protection based on comparing the difference between inrush and fault current. Theoretical analysis show that the method can precisely discriminate inrush and fault current, fault clearance time is about 20ms. Moreover, it is convenient to achieve and hardly be affect by not-periodic component.
文摘This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.
基金Project supported by the National Natural Science Foundation of China （Grant No.50447006）
文摘This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.
文摘The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as high as ten times its rated current. This could cause many problems from mechanical stress on transformer windings to harmonics injection, and system protection malfunction. There have been numerous researches focusing on calculation and mitigation of the transformer inrush current. With the development of smart grid, distributed generation from independent power producers (IPPs) is growing rapidly. This paper investigates the inrush current due to black start of an IPP system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software. The study demonstrates that a single genset is capable of energizing a group of transformers since the overall inrush current is slightly above the inrush of the transformer directly connected to the generator. In addition, a simple method is proposed to mitigate the inrush current of the transformers using an auxiliary transformer.
文摘The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.
文摘Preventive maintenance in the transformer is performed through a dif-ferential relay protection system,and it protects the transformer from internal and external faults.However,the Current Transformer(CT)in the differential protec-tion system mal-operates during inrush currents.CT saturates due to magnetizing inrush currents and causes false tripping of the differential relays.Moreover,iden-tification of tripping in protection relay either due to inrush current or internal faults needs to be diagnosed.For the above problem,continuous monitoring of transformer breather and CT terminals with thermal camera helps detect the trip-ping in relay due to inrush or internal fault.The transformer’s internal fault leads to high breathing process in the transformer breather,never for inrush currents.During inrush currents,CT temperature is increased.Continuous monitoring of breather and CT of the transformer through thermal imaging and radiometric pix-els detect the causes of CT saturation and differentiates maloperation.Hybrid wavelet threshold image analytics(HWT-IA)based radiometric pixels analysis of the transformer breather and CT after de-noising provides an accurate result of about 95%for identification of the false tripping of differential protection system of transformer.
文摘This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.
文摘We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers(HFCTs).The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal.Firstly,by studying the working principle of HFCTs,we summarize that the bandwidth of the selected signal acquisition device should be at least 100 MHz to ensure measurement accuracy.Secondly,Gauss pulse and square wave pulse are generated to determine the effects of different sources.The measurement results indicate that Gauss pulse is more suitable for pulse injection method,and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion.Finally,the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods.The measurement results show a remarkable consistency between two methods.However,pulse injection method requires the simpler operation and lias a higher resolution,obviously improving the measurement efficiency and bet ter displaying the details of the transfer impedance curves.
