Research And Study On The Device For Measuring Capacitive Current Based On Scanning Frequency

Recently power cables in the distribution electric power network are used more than ever, and the capacitive current between lines and the ground is rose with the development of the city. It is recommended to install the Arc Suppression Coil when the capacitive current is greater than the permitted value 10 A in the distribution network. Just to know the exact value of capacitive current, the Arc Suppression Coil can do the right act.The paper has carried on deep studies to resonance ground system and compensation principles and analyzed various methods of capacitive current calculation of the automatic Arc Suppression Coil. The method of scanning frequency has been shown that it is more accurate than others and it can be used for all kinds of the Arc Suppression Coils, so the method of scanning frequency is chosen. The capacitive current measuring unit is composed of the signal generator and the controller. The signal generator is a voltage source inverter with IGBT, which produces square-wave output voltage with variable frequency. The four driving signals of IGBT are generated by the controller based micro-chip C8051F020. The controller is also used to sample the analog signals, to decide the resonance frequency, to show the result, and to communicate with computers.The simulative system is carried on in PSCAD/EMTDC. It is shown that the method of scanning frequency is feasible. The test is conducted in the laboratory and the result of the experimentation show that the calculation the capacitive current is vary approach to the real capacitive current and the time of the whole course is only 10 ms.