Ship Earth Fault Indicators Working With simple Diagram



Earth Fault Indicators
          Ships 440V and 220V isolated system should have insulation indicators in order to indicate the presence of earth fault in the system. Generally two types of earth fault indicators are fitted onboard, Earth fault indication Lamps and An instrument showing Insulation with respect to the earth (Ohm meter). 


Earth Fault Indication Lamps
          This is the cheapest and older method using from many years. In this system 3 lamps are connected to three phases as shown in the figure below



         If there is no earth fault in the system the three light will glow equally with equal brightness. If there is an earth fault occur in one of the line, suppose L3 the lamp connected in that line L3 off or dim and the other two lamps glow brighter. This is because if there is an earth fault the potential difference between the earth and line become zero so there wont be any current flow ie, lap on that line off. 

Earth Fault Indicator Using Ohm Meter
           This instrument is very sensitive as compared to earth fault indication lamps. It shows the value of insulation resistance directly in Kohm or Mohm. It is incorporated with visual and audible alarm. Insulation resistance is measured by a small DC voltage injected in to the system. Below you can see a simple circuit diagram,




Actual Diagram of Ship Earth Fault System Incorporating both Earth Fault Indication Laps and Ohm Meter 

You Can Answer Following Questions
> Explain working principle of earth fault indication lamps with diagram
> How to test earth fault indicating system
> Explain Earth fault indicator using ohm meter
> Draw actual diagram of ship earth fault indication system



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