ETO ETO Exam papers 📅 Mar 2021

Exam Question

With Respect to Insulated and Earthed Neutral systems used on board

(a) Discuss the Advantages and Disadvantages of both the Insulated and Earthed systems used onboard (8)

(b) Discuss the consequences of Earth fault in an earthed distribution system (4)

(c) What would be the Ohmic Value of the NER to limit the earth fault to the full load rating of a 2 MW. 0.8 pf, 3.3KV, 3 Phase A C. generator? (4)

Reference Answer

(a) Advantages of Insulated system:
The priority requirement on board ship is to maintain continuity of the electrical supply to essential equipments in the event of a single earth fault occurring. Because of supply is totally isolated from ship’s hull, there is no closed path, hence no current will flow to earth on occurring of single earth fault and equipments will continue to run. Short circuit will happen if double earthing happens in two different places in same phase.
Fault current is negligible in insulated system.
Disadvantages of Insulated system:

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