The Development Of Testing System For Harmonic Component In Loss Current Based On FPGA And Current Comparator

XLPE power cables are increasingly being used in the transmission and distribution lines,which has become the main Urban Power System.The water tree aging has been XLPE power cable insulation threat which affects the safety of the line.In order to ensure the safe operation of XLPE power cable,it is necessary to diagnose its insulating state,and particularly important to develop a set of insulating state testing system which can adapt to the industrial field applications and easy operation.The testing system of loss current harmonic component which our research group developed has been proved to be an effected test system in the practical application of engineering.However,its operation is complex,and its test time is long,also brings troubles to the operator.For above reasons,it is necessary to develop a set of easy-operated testing systeme based on the test system developed early.A design scheme using the method of controllable compensation current to achieve the balance of current comparator firstly proposed in this article,to greatly simplify the operation of the equipment.In this design scheme,the voltage signals and the unbalanced current signals from current comparator are collected into the control system by signal acquisition unit,then compenzation current signal is calculated by the system with the determined algorithm,the compenzation current signals generated by the voltage-controlled current source connected with the compensation coils of current comparator.The compensation effect is determined by the output of the detection coil,and the balance of the current comparator can be achieved through continuously correction of the compensation current signal.According to the ampere-turns balance principle,the real information of the current from test product are calculated out.Above processes are done automatically by the control system,to realize the automatic test of harmonic components.After developing above design program,the algorithm producing controllable compensation current was puted forward.In the algorithm,the nonlinear model of the product to be measured is set up in FPGA,and the nonlinear model parameters are caculated based on the excitation voltage and unbalanced current signals.The compenzation current signal is produced through real-time operating system as the output of the FPGA nonlinear model with the input of the excitation voltage.The correctness of the calculation method is verified by simulation.After the software algorithm was laid down well,software programming of the FPGA and real-time controller were developed by Lab VIEW software platform.Combined with the software systems and hardware,the test system is set up.Finally,using standard capacitor as test product,the validation experiments of test system was done.Confirmatory tests confirmed that the design of the test system is feasible.Because of test error,the test system needs to be further revised and improved.