Maintenance of a Ship’s Main Electricity Distribution at Sea
Ship Earth Fault Maintainance
A ship’s electrical distribution system serves to transmit electrical power to all the components that are connected to the ship. The main component of a ship’s electrical distribution system is the main switchboard which conveys power to the motor starter groups. Motor starter groups are part of the main board, the distribution boards and the section boards. High Voltage and Low Voltage are distribution sections of the system and are interconnected by transformers (Maes, 2004). Grounding is an electrical term used to define a reference point in the electrical circuits from which all voltages are measured. The earth point forms a solid connection to the earth and has no resistance to electric current due to its massive section and its mass. The earth normally forms the ground. However, because on boards a ship the earth is absent, the hull of the ship then becomes the reference point from which all voltages are measured and is the ship’s ground (Maes. 2004).
There are three types of an electrical fault that is experienced in a ship’s electrical distribution system. These include an earth fault, an open circuit fault and a short circuit fault. An earth fault is an electric fault that occurs when the insulation protecting a component is lost and therefore there is current that is allowed to flow to the earth potential. This is caused by either wear of the insulation or breakdown. Earth faults when not detected and corrected are likely to cause electrical shocks to personnel or fire to the ship. In order to mitigate the dangers that may arise due to the electric shock and fire cause by the earth fault, it is recommended that the metal parts that are part of the ship are earthed. This helps in preventing the ship from attaining high amounts of voltage with respect to the earth which is considered dangerous.
An open circuit is a type of electrical fault that is caused when the phase conductor is interrupted. The interruption can be wholly or even partial. An open circuit is normally caused by breaks present in the wire and also due to bad connections. The effects of this type of electrical fault vary depending on the type of type of interruption on the conductor. When the phase conductor is totally interrupted the open circuit can lead to ashes. When the phase conductor is interrupted the open circuit can lead to heat loss. Open circuits also lead to overload as they cause the three phase to now solely run on two phases.
There are three types of electrical faults that be experienced in general. An earth fault, an open circuit fault and a short circuit fault (Maes, 2004). An earth fault occurs when the insulation is lost and current flows to earth potential. It is normally caused by the insulation breaking down or being worn out or presence of a loose wire that acts as a live conductor to contacting the enclosed earthed metal. It causes fire or electric shock. Earthing of metal enclosure or metal parts that carry no currents is encouraged as a preventive measure. Open circuit results from total or partial interruption of a phase conductor. It is caused by bad connections or breaks present in the wire. It leads to flashes or high heat. Short circuits are caused by connections of two phase conductors. This can be due to loss of insulation, human error or presentation of a situation considered as abnormal. It causes release of a large current amount and this is often accompanied by explosions
A ship has an electrical distribution system that has a high voltage and low voltage component. The High Voltage component is 6.6kV and the low voltage component is 690V. The ship’s electrical distribution system has experience an electrical fault that is an earth fault. The earth fault is reported to be on the low voltage component. The main cause of the earth fault that is reported is investigated using the procedure outlined by Vance (2014) as illustrated below.
An electrical officer is on board a ship as they are qualified to handle the machinery and equipment that are present on board. The ship is designed to alert the electrical officer when there is a problem that has occurred in the ship that needs to be attended to. Such equipments include ammeters or alarms. When an earth fault occurs, there is an alarm that goes off to alert on this. Ground fault detection equipments and ground fault ammeters are also present in a ship and these help to detect the specific reason why the alarm went off. On checking the two and noting that it is due to a ground fault, necessary steps are then taken.
First, the common trip reset button is activated. The common trip button is located on the Low Voltage switchboard. The activation of the common trip button serves to have the system reset (Electrical O&M Manual). The alarm trip reset button also enables an individual to know how genuine is the fault that has caused the alarm to go off. Once the reset button has been activated it remains in a depressed position until the problem has been solved.
The general idea is to isolate the cause of the problem. The electrical officer therefore proceeds by first of all shutting down all the equipment and the solar panels individually only leaving the battery switch on. The positive battery cable is then disconnected and then the meter reading is set to DC and to read in volts. A meter reading between the cable and the battery terminal is taken and if the reading is 12 volts or if there is any reading at all then this authenticates the problem by indicating that there is actually a leak.
This is noted and therefore the electrical officer tests whether this leak is due to the battery. The battery switch is switched off and then the meter reading is checked. A meter reading present when battery is off is an indication that the leak is due to the battery. This requires the electrical officer to rewire and concurrently reroute everything when supporting the highest possibility. Having done this, the battery switch is then switched off when the meter is connected and then the meter is disconnected. The meter is checked to see if there is a reading. In this particular case, there was a reading and this led to the conclusion that the leak is due to the system and not the battery.
The electrical officer then switches the battery switch on again. At this stage when this is done, the meter is connected. The electrical officer studies the fuse as well as the breaker channel. The breakers are then closed and the fuses are pulled. The meter is checked for a reading. If there is no reading then the fuse after therefore breakers are closed then this implies that this was the cause of the fault. However, in this case a reading still was on the meter and therefore the breakers or the system panel was the cause of the leak.
The electrical officer then sets the meter to read in ohms. Then electrical officer removes the breaker, one after the other while testing across each breaker’s terminal. Having the breaker off should note and infinite reading on the meter and this would mean that the leak is on the breaker. The electrical officer on this ship still noted a reading and this could only mean that it is the system panel that was the cause on this.
Therefore, the electrical officer has to identify which machinery has the leak attributed to it. This can be easily done by isolating each machinery and checking if there is still a leak. However, this method isn’t practically as a ship is underway. Isolation might prove to be dangerous especially when one is required to isolate critical component like a steering gear (Balasubramanian, 2011). It is however easy to conduct a changeover and have the running machinery be replaced with the stand by machinery. After the electrical officer did this for this ship, he checked the earth fault indicator and noted the cause of the leak to be a contactor 6Q15 which is a steering gear point. Indeed isolation of each component would have proved to be dangerous in this case.
With the cause of the setting off of the alarm detected, the common trip reset button is then simply released by twisting and unlocking the head (Electrical O&M Manual)
Safety Checks Procedures and Permits to Work
There are a lot of precautions that are to be taken when on board a ship. These are referred to as safety checks. These precautions are set out in order to reduce the accidents that can occur due to carelessness or mistakes as the results will be fatal. The safety checks procedures are outlined as follows (Electrical O&M Manual).
There is limited access allowed to the switch room. This is because there is a lot of different technical equipment that require technical personnel with the know how to handle it. In case of a fault, the critical equipment should not be removed as this may be hazardous to the ship. Simply a changeover from the running machinery to the stand by machinery is carried out. However, when machinery is broken down and the ship is not underway, the machinery should be isolated and replaced. It is compulsory to have a backup power system which is the secondary power system. This ensures that incase of failure on the main power system the normal operations still carry on. All the switches and circuits require to be switched off when necessary.
There are other bits that are still part of safety checks procedures. These include ensuring all doors are firmly shut and secured. Observing cleanliness of the switch room as well as the plant areas. Ensuring there are no obstructions or equipments loosely lying around in the switch rooms and the plant area and also keeping tools and equipment away and in a safe area.
A permit to work is a written document that is required before any maintainance work is carried out in a ship. The maintainance work is specifically after an assessment has been done and it has been noted that it is not possible to follow the normal safe practices. It specifies the extent of work to be done, the timescale and the precautions to be taken.
A ship has maintainace work now and then. Maintainace can be preventive, condition-based or break down (Munir, 2006).. Preventive is scheduled by the manufacturer. Tests are done to check on the normal working conditions of the machinery. They include Tests of Time between overhauls, tests on centrifugal filter cleaning, test on cylinder overhaul and big end bearing inspection. Lifting tools are necessary for dismantling. Condition-based maintainace consists of inspections and include tests such as visual, vibration, pressure, temperature, load, electrical and water tightness (GMM, 2001). Calibration and measuring equipment is used. Break down maintainance is carried out in the case of a breakdown and tests and equipment are based on the nature of the breakdown. Before maintainance the circuit switch should be off and crank doors sealed shut. After maintainance, it is necessary to check on the LV and HV systems. Check for anomalies in the connections, temperature changes, meter reading and earth fault relay.
The fault that occurred in the ship was an earth fault and if not checked could lead to an electric shock or a fire.
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