By LCdr NS Wickramasinghe BSc Hons (E & E Eng) MSc (HRM) AMIE (I) AMIE (SL) C Eng (I)

Earthed & Insulated Distribution Systems 2

NER Earthed Power Distribution System When Star point of three phase power generation system is Earthed onboard a ship it is called EARTHED Power distribution system. It must be done through a Neutral Earth Resistor (NER) to limit the fault current below the generator rated current to avoid the service interruption. 3

Insulated Power Distribution System When Star point of three phase power generation system is not connected to earth is call INSULATED power distribution system 4

NER Earth Fault in Earthed Power Distribution System Large Fault Current Ground Fault An earth fault occurs in earthed power distribution system, it creates a flow of high current. That current will be short circuited the circuit at that moment. A circuit breaker or a circuit protection device tripping mechanism works and disconnect the fault current and ensure the safety of persons and equipment. 5

Earth Fault in Insulated Power Distribution System No Fault Current An earth fault occurs in insulated power distribution system, it does not creates a flow of fault current. Therefore we won’t be able to see any power failure due to a one earth fault onboard ship. Ground Fault 6

Earth Fault in Insulated Power Distribution System 7 No Fault Current If a fault occur in same phase at two different locations on an insulated systems the system will not be disconnected or circuit breakers will not be operated

Earth Fault in Insulated Power Distribution System If an Earth fault occur in two different phases on an insulated systems the system be disconnected or circuit breakers will be operated 8

Purpose of Insulated Distribution Systems According to SOLAS regulations neutral insulated systems to be used in cargo area, pump rooms & tankers to avoid explosion hazards due to stray earth current. In a Neutral earthed system a single earth fault would have caused heavy earth current to flow and operate the tripping mechanisms Even with a single earth fault essential services onboard a ship will continue to operate 9

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