Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on prot...Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.展开更多
The problem of controlling a single-input-single-output plant without prior knowledge of high frequency gain sign is addressed by using the model reference robust control approach.A switching method is proposed based ...The problem of controlling a single-input-single-output plant without prior knowledge of high frequency gain sign is addressed by using the model reference robust control approach.A switching method is proposed based on a monitoring function so that after a finite number of swi- tchings the tracking error converges to zero exponentially.Furthermore,it is shown that if some initial states of the closed-loop system are zero,only one switching is needed.展开更多
A compact high-voltage repetitive nanosecond pulse generator(HRNPG)was developed for studying the technology of repetitive nanosecond pulse technology and its related application.The HRNPG mainly consists of a repetit...A compact high-voltage repetitive nanosecond pulse generator(HRNPG)was developed for studying the technology of repetitive nanosecond pulse technology and its related application.The HRNPG mainly consists of a repetitive charging module,a Tesla transformer and a sharpening switch.With its voltage lower than 1 kV,the primary repetitive charging circuit comprises two fast thyristors as its low-voltage switches.The spiral Tesla transformer acts as the main step-up component,and its peak transformation ratio is designed to be more than 100.A self-breakdown spark switch,i.e.the sharpening switch,is used to sharpen the output of the transformer and to generate nanosecond pulses.The HRNPG prototype is capable of generating pulses of 100 kV in peak with rise time 30 ns and the maximum repetition rate of 500 Hz on a 6 k load.Experimental results show,without any magnetic core,the developed Tesla transformer prototype can easily output high voltage while keeping itself small in size and light in weight,which is of significance for the compactness and portability of the pulse generator.The N2-insulated spark switch operated well at voltage close to 100 kV and the repetition rate within several hundreds of hertz.展开更多
文摘Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.
基金Supported by National Natural Science Foundation of P.R.China(60174001)National Natural Science Foundation of Beijing(4022007)
文摘The problem of controlling a single-input-single-output plant without prior knowledge of high frequency gain sign is addressed by using the model reference robust control approach.A switching method is proposed based on a monitoring function so that after a finite number of swi- tchings the tracking error converges to zero exponentially.Furthermore,it is shown that if some initial states of the closed-loop system are zero,only one switching is needed.
基金Project supported by National Natural Science Foundation of China （51107049）.
文摘A compact high-voltage repetitive nanosecond pulse generator(HRNPG)was developed for studying the technology of repetitive nanosecond pulse technology and its related application.The HRNPG mainly consists of a repetitive charging module,a Tesla transformer and a sharpening switch.With its voltage lower than 1 kV,the primary repetitive charging circuit comprises two fast thyristors as its low-voltage switches.The spiral Tesla transformer acts as the main step-up component,and its peak transformation ratio is designed to be more than 100.A self-breakdown spark switch,i.e.the sharpening switch,is used to sharpen the output of the transformer and to generate nanosecond pulses.The HRNPG prototype is capable of generating pulses of 100 kV in peak with rise time 30 ns and the maximum repetition rate of 500 Hz on a 6 k load.Experimental results show,without any magnetic core,the developed Tesla transformer prototype can easily output high voltage while keeping itself small in size and light in weight,which is of significance for the compactness and portability of the pulse generator.The N2-insulated spark switch operated well at voltage close to 100 kV and the repetition rate within several hundreds of hertz.
