Ungrounded power system overview

This system must be monitored with specific device to meet specific applications, such as hospital, naval applications, heavy industries, railways, nuclear power plants and other critical ones, where safety and continuity of service must be ensured even in case of earth fault. Lastly, this system is chosen in certain cases because it can facilitate preventive and corrective maintenance operations.

The system transformer’s neutral is isolated from earth, or connected through a specific impedance, while the electrical load frames are earthed. So, in case a first fault occurs, there is no loop for shorting current to flow, allowing the system to continue to operate normally without hazard to people and equipment. However, the faulty circuit must be detected and repaired before a second fault occurs. Because this system can tolerate an initial fault, maintenance operations have to be conducted as soon as possible to prevent the system trip in case a second earth fault occurs.