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
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
If you know more about this or have doubts please comment below
How to temporarily bypass the 220 volt low insulation system onboard a ship??
ReplyDeleteBetter you increse the set value... make it 4 or 5
DeleteWhat is the principle of dc injection type how it is detecting an earth fault??
ReplyDeleteIf there have two earth fault in two machinery how can we identifing
ReplyDeleteYou know that it is not easy to identify even if there is only one machinery showing earth fault.... 😃 using ohm meter it is not possible to say how many machines are in fault... Technically speaking with the 1st diagram in the article L3 is fault and L3 lamp is Dim... suppose 1st machinery L3 is fault and 2nd machinery L2 fault both L3 and L2 lamp will be Dim... if both machinery having L3 fault its not possible to find... Corrections accepted...
Delete