Study On The On-line Insulation Monitoring System For Power Cable Above 66kv Voltage Levels

Cross-linked polyethylene high-voltage cables whose insulation characteristics affect the security of power net directly are used widely because of their favorable insulation characteristics. At present, the study of insulation on-line measurement becomes a hotspot. Therefore, it is important to develop an insulation on-line measurement system to monitor the state of 66kV and upwards levels cables.In the process of research, the mathematics model of cable's insulation system, signal extraction method and signal synchronous sample, feasible algorithm of harmonic method and dielectric loss calculating method are studied at first. Base on all kinds of measuring method, the technologies of harmonic analysis and quasi-synchronous are used in measuring tanδof dielectric. By analyzing the relationship between phase ground current and total ground current of split phase shield cables, the conversion formulae between ground phase currents and main insulation currents are derived out when incomplete commutating and complete commutating, thereby phase ground currents of different phases are picked up successfully. At last, the whole measurement system is developed, and the data analysis soft is compiled.In order to prove that the on-line monitoring system can be used at practice, the simulation experiment is carried out. The results of test show that the precision of tanδis±0.1%, the precision and the range of ground current are 0.1 A and 0～10A respectively. Therefore, it can be seen that the on-line monitoring system can be used by practice.