The Research Of Automatic Compensation Measurement Of Arc Suppression Coil Based On Variable Frequency Method

Single phase ground fault is one of the most common in mid-voltage power system. With the development of our country’s power grid, the proportion of cable in transmission and distribution has been increased. The single phase ground fault will produce larger capacitive current in the failure point which will prejudice the arc suppressing. This phenomenon may generate the arc grounding over-voltage and result to interphase short circuit. Most of the medium voltage distribution network in our country has adopt arc-suppression coil grounded way to compensate the capacitive current in the failure point, the measuring of capacitive current determines the accuracy of arc-suppression coil’s compensation.In this paper, the principle of resonant grounding has been intensive studied and several methods of the tracking compensation of arc suppression has been well analyzed and compared. The variable frequency has the advantages of high accuracy, quick response and wide range of application coverage, this design is based on the variable frequency method. On the basis of intense research of variable frequency method, Building the10kV power distribution system model in the platform of PSCAD/EMTDC. Combine the model of grounding transformer, sweep signal generator and the phase detection part, the simulation experiment has been carried and verified the feasibility of variable frequency method.Based on above discussions, a capacitive current measuring system based on System-on-chip single chip---C8051F020has been developed. The measurement system includes two parts of host computer and lower machine. Lower machine includes the sweep frequency generator, phase detection part and control circuit of C8051F020. The design of sweep frequency generator is based on the DDS chip AD9850. The implementation of phase detection function is centered on AD8302. The build of host computer software is based on the C/S architecture. The client interface is coded by C#and the database server is built by SQL Server.The experiment of measuring system is carried out in laboratory with the simulation circuit. The result shows that the measuring time is within10s and the measurement error is not greater than3.3%. The experiment verified the accuracy and real-time of the capacitive current measuring system.The development of capacitive current measuring system can be directly applied to pre-set type arc-suppression coil. After being transformed according to diffrerent adjustment principle, the measuring system can be applied to post-set type arc-suppression coil.