Study On The Current Transformer Energy-absorbing Source Combined With Super Capacitor And Lithium Battery

The transmission line is a very important element of the power grid, it has a greatnegative effect on the power grid when it breaks down. On-line monitoring technologyis used to guarantee the safety of the transmission line. The transmission line is featuredwith high voltage and often locates in complex environment, therefore, the problem ofsupplying a suitable source for the monitoring device is one of the barriers to thedevelopment of on-line monitoring technology.This paper is based on the summary of existing sources and some previousresearch achievements, a new current transformer(CT) energy-absorbing sourcecombined with super capacitor and lithium battery is developed to supply source for theremote monitoring system of lightning counter. The source can supply stable DCvoltage for monitoring device by the management of energy which is absorbed by CTfrom transmission line through electro-magnetic induction. Equivalent circuit model ofCT is established and electro-magnetic relationship is researched when CT transferspower to load. Influence factors on CT’s output power are analyzed to keep CTabsorbing energy efficiently by parameters matching. Hardware circuit is designedbased on the principle of power-supplying classification and lithium battery is used asstandby source. Good adaptation of the source is achieved by making it work indifferent conditions along with the changes of line current. Super capacitor is used tolimit CT’s induced voltage to prevent iron core saturated, it also supplies instantaneoushigh power to meet the requirement of communication module of monitoring device.Lithium battery is used to supply standby power to eliminate the energy-absorbingdead-zone of the source when line current is low. Switching tube and relays can adjustsource’s working conditions automatically to adapt the wide-range of current line.Modules of over-voltage protection, over-current protection and lithium protectionensure safety of the source when it works.The source’s different working conditions were test in simulation experiment, theresults were as follows: when line current changed from0A to800A, the iron corewould not be saturated, the source could supply2.5W power with stable DC5V output.For example, when line current was less than70A, the source can supply power with thesupplementary of lithium battery (lithium battery could supply power at most2hoursindependently if transmission line was outage); when line current was more than70A,the source could supply power independently through super capacitance without lithium battery. In addition, the source could supply12W instantaneous high power.In conclusion, when line current changes in a wide range, the newly developed CTenergy-absorbing power source can supply stable power and instantaneous high powerfor monitoring device with eliminated energy-absorbing dead-zone.