| In the marine AC power system,whether the insulation monitoring and insulation fault location are fast and accurate is related to the safety of the entire voyage.But nowadays ships tend to be large-scaled and automated,and the ship environment causes a higher incidence of single-phase grounding short-circuit faults in the power grid.At the same time,ensuring the safe and stable operation of capacitive equipment in the ship’s power system has also become an important issue for system operation.In addition to monitoring the insulation resistance of the power grid,it is also necessary to monitor the insulation dissipation factor of capacitive equipment.Due to the lack of intelligent insulation monitoring equipment in the marine power system,it is impossible to locate and repair the insulation degradation failure in time.There are serious fire alarms and interphase short-circuit accidents every year,which have a great impact on the safety and reliability of ships.With actual engineering application as the research background,the advantages and disadvantages of the existing technical solutions are compared.Refer to the standards IEC61557-8 and IEC 61557-9 to determine the design plan of this research.The research content is divided into the following four aspects:(1)Through theoretical analysis,the single frequency injection method is simulated based on Simulink.Through the simulation analysis and comparison between the single frequency method and the dual frequency method,the feasibility of the single frequency injection method to replace the existing dual frequency method in engineering practice is determined.At the same time,combined with discrete Fourier analysis,the specific steps of extracting low-frequency signal from the mixed signal of power frequency and low frequency are given.In order to obtain the current and voltage response of the low-frequency signal injection source acting alone,the low-frequency signal is sent to the STM32 single-chip microcomputer through the current and voltage transformers,and the fundamental wave is extracted through the discrete Fourier algorithm to obtain the low-frequency amplitude.Frequency injection method calculates the insulation resistance of the ship’s power grid to ground.(2)After analyzing the measurement method of the dielectric loss angle,use wavelet transform to select the appropriate wavelet basis to decompose and reconstruct the original voltage and current signals,filter out the harmonics in the ship power grid,and extract the basis of voltage and current.Choose the correlation function analysis method to calculate the dielectric loss angle of the capacitive device through the auto-correlation function and cross-correlation function of the fundamental voltage and current signals.Experiments show that the accuracy of the insulation loss angle calculated by this improved method is higher than that of the current commonly used methods,and it can better monitor the insulation of capacitive equipment in the ship’s power system,and find insulation faults in time.(3)With STM32 single-chip microcomputer as the development platform,the main part of the system is composed of 4 kinds of embedded devices: grid insulation monitoring device,fault location device,capacitive equipment insulation monitoring device,and protocol converter.The hardware system is modularized by making full use of chip characteristics and on-chip resources,referring to PCB design rules and then developing a complete insulation monitoring and fault location system including protocol converters.(4)Take STM32F407ZGT6 as the controller,transplant UCOS-Ⅲ embedded operating system,and carry out a modular design for the software system including the upper computer monitoring platform.The controller program uses C language as the programming language.The upper computer software is based on C#,and Microsoft Visual Studio is the development platform.The system monitors the insulation status of the ship’s power system in real time,and realizes the monitoring of the insulation resistance of the ship’s power grid to the ground,the monitoring of the dielectric loss factor of the capacitive equipment in the power system,insulation warning,insulation alarm,fault location,data upload,data storage and other functions.This research is of great significance to the safety and stability of ship power supply and the strategic demand for the localization of my country’s ship electronic equipment. |
