I believe that many of you have attended, at least once in your career, a Dry Dock period and noticed that during this time, because of the amount of planned maintenance to the vessel machineries, it is necessary for the vessel to be connected to the yard power supply.
Usually, Chief Engineer together with the Electrical Officer are involved in this process but it is imperious for every engineer to be familiar and proficient with the system and connecting procedure.
On the side of the emergency generator switchboard, there is a panel that can take electrical power supply wires during dry or retrofit docking. The shore cables enter the panel through a door that has been installed in the base of the panel. The connection to the power from shore is made via a moulded case circuit breaker (MCCB) to the bus tie line that connects the primary and secondary circuit breakers in the emergency switchboard.
The bus tie ACB at the main switchboard end of the bus tie line does not have undervoltage trips installed, and as a result, it will remain closed while shore power connection activities are being performed.
When the ship is being supplied by shore power the emergency switchboard can be supplied as normal through the main/emergency switchboard bus tie circuit-breakers.
The monitoring lamps for SHORE SOURCE (white lamp), SHORE MCCB CLOSED (green lamp), and SHORE MCCB OPEN (red lamp) for the shore supply are located on the shore power section of the emergency switchboard. Additionally, there is a SHORE MCCB ON lamp at the main switchboard bus tie panel E.
On the panel that controls the shore connection is installed a phase sequence monitoring system. Prior to turning on the shore power circuit-breaker, it is important to double check the phase sequence. Correct or incorrect phase sequence is shown by the SHORE POWER PHASE SEQUENCE indicator. If the phase sequence is correct for this vessel, the CORRECT lamp will be illuminated when the PHASE SEQUENCE TEST pushbutton is pressed. In the event of incorrect phase sequence, the WRONG lamp will be illuminated and the shore supply must be isolated and two supply phases changed over. The supply should then be reinstated and the phase sequence checked again. If there is a fault on the shore supply, both lamps will be illuminated.
When the shore supply has been connected at the box, it should be switched on ashore. The SHORE SOURCE indication lamps on the shore connection box will be illuminated.
The kilowatt/hour meter is provided on the shore connection box panel to measure and record the power consumed by the vessel when on shore supply. Interlocking is provided between the ship’s main diesel generator ACBs, the emergency generator ACB and the shore supply breaker. The shore supply breaker cannot be closed if any of the ship’s generator ACBs are closed. Conversely, none of the ship’s generator ACBs can be closed if the shore supply breaker is closed. This arrangement prevents the shore supply being paralleled with any other supply.
It is important to note that due to the location of the main and emergency switchboards, it may be helpful to set up personal communication, such as via UHF hand held radios, to reduce blackout time to a minimum.
The procedure for shore power connection is usually, maybe with some small exceptions, as follow:
- Isolate the emergency generator to ensure that it does not start, and set the engine control switch to MANUAL.
- Ensure that the shore connection circuit-breaker is open at the shore connection box. Supervise the connection of the shore power cables onto the bus bars inside the shore connection panel.
- Request the switching on of the shore supply from ashore. Confirm the presence of shore power and check the voltage. The SHORE SOURCE indicator should be illuminated at the shore connection panel.
- Check the phase sequence by pressing the PHASE SEQUENCE TEST pushbutton. The CORRECT lamp should illuminate.
- Isolate all non-essential services. Reduce the load at the main switchboard to the absolute minimum and ensure that only one diesel generator is on-load.
- Set the main switchboard GEN CONTROL switch on the synchronizing panel to the MANUAL position. This is to ensure that no main generators start when the vessel blacks-out.
- Open the running generator’s circuit breaker and the ship will blackout.
- Close the shore connection circuit-breaker at the shore connection panel; the SHORE MCCB CLOSED monitoring lamps will be illuminated.
- At the main switchboard, close the emergency switchboard tie line ACB. The main switchboard is now being supplied with shore power. Supply consumers as required.
- At the emergency switchboard close the bus tie breaker, which will have opened when the ship blacked-out, by turning the BUS TIE CONTROL switch (BC) to the CLOSE position.
- The emergency switchboard is now being supplied by shore power.
- Proceed to supply essential services such as fire detection, lighting, etc.
- If no maintenance is scheduled for the emergency generator, it may be returned to automatic standby by setting the control switch on the engine control panel to the AUTO position. It will then feed emergency lighting, etc, in the case of failure of the shore supply.
- The shore supply should be closely monitored to ensure that the rated current limit is not exceeded.
The procedure to transfer from shore supply to diesel generator supply is usually as described below:
- Isolate the emergency generator to ensure that it does not start.
- Isolate all non-essential services. Reduce the load at the main switchboard to the absolute minimum.
- Ensure that the main switchboard GEN CONTROL switch on the synchronizing panel is in the MANUAL position.
- Run up the selected main diesel generator on local control.
- At the main switchboard synchronizing panel, turn the SYNCHROSCOPE to the incoming generator’s position (DG1, DG2, DG3 or DG4).
- Adjust the frequency to 60Hz by means of the generator’s GOVERNOR control handle on the synchronizing panel.
- Open the breaker for shore power at the shore connection panel. The ship will blackout.
- Turn the relevant generator circuit breaker CONTROL switch to the CLOSE position. The circuit breaker closes and the generator supplies the main switchboard. The circuit breaker CLOSE indication at the relevant generator panel will be illuminated.
- Check the voltage and adjust the frequency to 60Hz. Supply main lighting, fire detection, etc.
- At the emergency switchboard, close the bus tie breaker, which will have opened when the ship blacked-out, by turning the BUS TIE CONTROL switch (BC) to the CLOSE position.
- Ensure that the emergency generator is returned to the normal automatic start condition.
If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries.
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