Definition: Arcing ground is the surge, which is produced if the neutral is not connected to the earth. The phenomenon of arcing ground occurs in the ungrounded three-phase systems because of the flow of the capacitance current.The capacitive current is the current flow between the conductors when the voltage is applied to it. The voltage across the capacitances is known as the phase voltage. During the fault, the voltage across the capacitance reduces to zero in the faulted phase, while in the other phases the voltage is increased by the factor of √3 times.
Arcing Ground Phenomena
In a three phase line, each phase has a capacitance on earth. When the fault occurs on any of the phases, then the capacitive fault current flows into the ground. If the fault current exceeds 4 – 5 amperes, then it is sufficient to maintain the arc in the ionised path of the fault, even though the fault has cleared itself.
The capacitive current over 4 to 5 ampere flows through the fault give rise to an arc in the ionised path of the fault. With the formation of the arc, the voltage across it becomes zero, and therefore the arc is extinguished. The potential of the fault current restored due to which the formation of a second arc takes places. The phenomenon of intermitting arcing is called the arcing grounding.
The alternating extinction and reignition of the charging current flowing in the arc build up the potential of the other two healthy conductors due to the setting of the high-frequency oscillations. The high-frequency oscillations are superimposed on the network and produce the surge voltage as high as six times the normal value. The overvoltage damages the healthy conductor at some other points of the system.
How to Eliminates Arcing Ground?
The surge voltage due to arcing ground can remove by using the arc suppression coil or Peterson coil. The arc suppression coil has an iron cored tapped reactor connected in neutral to ground connection.
The reactor of the arc suppression coil extinguishes the arcing ground by neutralising the capacitive current. The Peterson coil isolates the system, in which the healthy phases continue supplies power and avoid the complete shut down on the system till the fault was located and isolated.