Shore Power Switchboard Integration

The shore interface may follow a common standard, but the vessel's distribution system has its own ratings, protection settings, earthing arrangement and control logic. Adding shore power means checking how each of those behaves with a new incoming source, not simply adding another breaker to the board.

From the connection point to the transformer

In one common high-voltage arrangement, the shore cable reaches a shore connection switchboard on board, typically at 6.6 or 11 kV, and a transformer steps the supply to the vessel's distribution voltage. Where the vessel's own system is high voltage, or the connection is low voltage, the arrangement differs and an onboard transformer may not be needed. At this stage the physical checks are space and weight, the cable route through the vessel, and the siting of high-voltage equipment in spaces that were not designed around it.

Where a transformer is part of the arrangement, its rating and impedance influence the voltage drop and the fault current available downstream. The earthing arrangement also has to be checked across the interface: a transformer can separate the shore and ship systems electrically, while an arrangement without one requires the two sides to be reconciled directly. The final arrangement depends on the vessel and the shore supply.

The shore incoming breaker

The shore supply reaches the main switchboard through an incoming breaker and is treated as one more source beside the generator incomers. Three things are checked at its position. Is there a spare way of the right size, or room to add a section? Can the busbars carry the shore supply current with the board loaded and sectioned as it is in port? And what is the fault level with the shore supply connected? These are the checks set out under switchboards and power distribution, applied to a new source of supply.

One key check is fault level. The existing board and breakers were selected for the sources originally connected to it. A shore supply through a transformer may provide a lower or higher fault contribution than the generators, so breaking capacity and protection performance have to be checked for each operating mode. If shore and generator sources are intentionally paralleled during a controlled transfer, their contributions are also checked for that period.

Protection that works on two different sources

Protection that coordinates correctly on generator supply does not automatically coordinate on shore supply, because the source impedance has changed. Downstream coordination is checked against the vessel's feeders, while upstream coordination needs data from the terminal or port-side protection. That boundary is an interface between two systems, not a setting that can be decided from the ship alone.

Earth-fault protection depends on the earthing arrangement. On an insulated distribution system, a first earth fault is normally detected and alarmed rather than cleared immediately. The shore source may use a different arrangement, so the fault path and the devices expected to operate in each mode have to be analysed before equipment and settings are fixed.

Interlocking and transfer

Unless the sources are synchronised for a controlled parallel transfer, interlocking must prevent shore supply and generators from being connected to the same busbar at the same time. The chosen transfer method determines the additional control, synchronising and protection work.

• Open-transition transfer: the generator source is disconnected before the shore breaker closes. It is simpler to interlock, but there is an interruption to the normal supply during changeover, so essential and restart-sensitive loads have to be considered.
• Closed-transition transfer: a generator is synchronised with the shore source, load is transferred, and the generator breaker then opens. This can avoid an interruption, but it requires synchronising equipment and logic, an agreed limit on parallel time, and a fault-level check for the parallel period.

Further interlocks cover the connection itself, so that the high-voltage plugs cannot be handled live and the connection sequence can only run in the safe order. An emergency shutdown that opens the shore supply is part of the same scheme.

How the PMS handles the shore source

A power management system normally manages generator availability against the load on the bus. With shore power connected, it also has to recognise the shore incomer, its available capacity and the response to loss of shore supply. Depending on the vessel, that can include starting a standby generator, limiting load or shedding non-essential consumers. Shore-supply status, measurements and alarms also have to reach the monitoring system. This is automation and control work carried out together with the switchboard changes.

Frequency and voltage

If the shore supply frequency differs from the vessel's, frequency conversion is needed somewhere between the grid and the ship's busbar, either ashore or on board. That location should be settled against the ports the vessel actually uses because an onboard converter changes space, cooling and equipment scope. Voltage compatibility is handled through the connection and transformer arrangement for the shore voltages the vessel is expected to meet.

Work that requires a dead board

A significant part of the retrofit may be prepared while the main switchboard remains in service: equipment foundations, cable routes, the transformer and the shore connection switchboard, subject to the vessel's permits and arrangement. The final busbar connection is different. Adding the incoming section or breaker and making the bus connection requires the affected section to be safely isolated, and the operational impact depends on whether the board can be sectioned.

Interlock and transfer testing also needs to be planned with the yard or terminal because both the vessel sources and the shore source may be required. The sequence follows the logic described under testing and commissioning: dead-circuit checks, controlled energisation, functional verification of protection and interlocks, and the designed transfer sequence under the conditions required for commissioning.

The drawings have to reflect the new source

The single-line diagram records the new source, transformer where fitted, incoming breaker and protection. The related control drawings carry the interlocking and transfer logic. A modification of this kind normally goes to the vessel's class society for review, so the submission set and review time are planned before the installation window. Our guide to IEC/IEEE 80005-1 on the ship side covers the shore-connection standard, while what an AMP retrofit involves sets out the wider conversion scope.