doublelinetoground

Double line-to-ground fault, abbreviated as double line-to-ground (DLG) fault, is a type of electrical fault in a three-phase power system where two phase conductors are simultaneously shorted to ground at a common point. This fault involves ground current and affects two phases, making it more severe than a single-line-to-ground fault but typically less severe than a three-phase fault. It commonly arises in networks with grounding schemes that allow a low-impedance path to ground, and can be triggered by insulation failure, conductor damage, lightning, or external faults.

Electrically, a double line-to-ground fault is analyzed using symmetrical components, involving positive, negative, and zero sequence networks. The fault creates a connection among these networks through the ground, distributing currents and voltages among the three phases in a characteristic way. The fault current magnitude depends on the source impedance, line and transformer impedances, and the grounding impedance at the fault location. In general, the currents in the two faulted lines are significant and the post-fault voltages on all three phases become unbalanced. The exact values are determined by solving the network equations for the positive, negative, and zero sequence networks.

Modeling and analysis are common in power system studies, such as short-circuit calculations, protective relay settings, and stability assessments. Engineers use symmetrical components to predict voltage recovery, fault current levels, and the impact on equipment ratings.

Protection and mitigation involve protective relays and automatic circuit breakers designed to detect abnormal current flow and isolate the faulted section. Overcurrent, distance, and ground-fault relays are commonly employed, with coordination ensuring rapid clearance of the fault while minimizing disruption to the rest of the system. Grounding quality and insulation integrity influence the likelihood and severity of DL-G faults.