Low isolation or electrical earth fault signal is a critical issue which requires a quick responses; either to find the earth fault or rectify it cause. Mostly all ships generates 440 V , 220 V , 110V or less, and may likely develop low isolation fault since the earthed ship distribution system is equivalent to a short-circuit of a single earth acting across the generator through the vessel hull.
In all ships, the earthing monitor or indicator are provided manly 440 V and 220 V. The earth fault monitor can be either three set of indicator lamps with gauge or an instrument (always calibrated in maga ohms or kilo ohms) to show the system IR value to earth fault. This monitor are installed in ship engine room control panel, where all engineers can easy observe it condition.
What is the working principle of electrical earth lamp?
The 3 phase A.C system indication lamps and gauges are provided to monitor or check healthy of all connected electrical equipments (such as electrical motors, sockets, lights, electronics, etc). When an earth fault occurs on any of the three phase conductor, it lamp will go dim, while other two the have higher voltage will became brighter and if a gauge indicator is attached, then you will see it rise more than zero. Normally in a good condition ( when no earth fault found) the lamp always glow with equal half brilliance and gauge indicator steady on zero.
The earth could be either the cable is grounded, touching another phase, water in between and an object connecting both phase). In such case, it’s a risk to operators ( easily to get electric shock, got your equipment damage, electrical fire out break due to over heating of the conductor, etc).
How to solve electrical earth fault?
When a fault alarm or lamp indicated, first question you have to answer is what voltage?. Let’s say you have 440v lamp indicated, that means one or more electrical motors ( such as vent motor, water, fuel or oil pump motor, etc) that has power input of 440v to be check. Switch them off one by one to figure out the line in question. Since ship equipments are more, all 220v are group in a on single distribution panel (for 220), while 440v can be directly connected with the help of a breaker.
If during troubleshooting, eventually got the line affected ( once the light glow as explained above), then, keep the equipment off and run a test to understand the actual fault. Sometimes it maybe difficult to find in case a cable has broken inside. In such case, full cable renewal will be very recommended.
What are risk behind ship earth or low isolation fault?
As earlier said, there are several risks involved when an electrical equipment has low isolation or earthing. They could be loss of life or invalid, electrical fire outbreak, lossing your expensive equipment.
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The 3 phase lamp indicator as discussed earlier are very old system for determining whether an electrical equipment connection is faulty base on it voltage feed or all is good condition. It also act as a safety precautions to help show when an issue arise. Though this lamps indicators has it disadvantage( they are not very sensitive or instantly indicate fault,may fail to indicate the presence of a high impedance earth fault,lamp may be faulty, etc). Therefore it’s always attached with instrument type earth fault indicator gauges.
It’s important to always pay proper attention to all of the above mentioned to be on the safe side.
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