Study On DC Arc Fault Characteristics And On-line Monitoring System Of PV System

In the DC side of the photovoltaic system,DC fault arc is generated by failure connection,poor contacts and insulation failure of cables.Existing protection facilities,such as fuses and circuit breakers,cannot actively disconnect the arc circuit,and the arc will continue to burn,which leads to fire disaster.In order to guarantee the safe and reliable operation of the PV system,eliminate the arc in the bud,the arc fault characteristics are studied by experiments in both lab and field,and an on-line monitoring system is developed.In this paper,a DC arc generator and arc fault experiment platform was set up,and arc experiments were conducted in laboratory and photovoltaic field respe ctive.In the laboratory,the main factors influencing arc characteristics are analyzed by the control variable method,the data show that current and gap distance were the main factors changing arc characteristics,however the DC voltage may decide whethe r arc is generated and maintained or not.And the characteristics of arc R-I,V-I and P-I are studied.Four kinds of arc faults are simulated in field experiment,they are two series faults and parallel faults.We found that: 1)Regardless of the current and the electrode spacing,after the arc occurs,the branch current and voltage change are different,but the commonality is the current fluctuation in the time domain intensifies,and the harmonic amplitude in the range of 40kHz~80kHz in the frequency spectrum increases;2)All arc faults can be detected by the current signal through the inlet line of the junction box,The series fault arc can be extinguished by the method of disconnecting the loop,while isolating the parallel arc fault is not available be cause of an extra arc branch bypass the junction box.A DC arc fault On-line monitoring system is developed,which mainly includes arc detection module,power supply module,main control module,GPRS module,bluetooth module.Finally,this system was tested in field,it is proved that the system can quickly and effectively detect and identify both series and parallel arc fault types as to take corresponding protective measures or alarm timely,the maximum response time of all kinds of fault is less than 100 ms,far less than the UL1699 B regulations on arcing time of arc detection devices.At the same time,the sudden change of environmental factors such as shadow occlusion and light intensity may not trigger protection device.In conclusion,in this paper,the characteristics of dc fault arc are studied by means of experiments,and a DC arc fault On-line monitoring system is developed.This system can detect and alarm quickly when an arc fault occurs in PV system,so as to promote the safe and reliable operation of PV system.