A shore supply is required so that the ships generators and their prime movers can be shut down for major overhaul during a dry dock period.
Requirements/Checks
- There must be a suitable connection box conveniently located to accept the shore supply cable. The connection box is sometimes located at the entrance to the accommodation or in the emergency generator room.
- The connection box must have suitable input and output terminals to accept the shore supply cable including an earthing terminal to earth the ship’s hull to the shore earth.
- For an AC supply, a phase sequence indication to be fitted to indicates correct supply phase sequence.
- A voltmeter to indicate polarity of D.C. shore supply.
- A data plate giving details of the ship’s electrical system (voltage and frequency) and showing the method for connecting the shore supply cable.
- Ship generators are disconnected from the MSB.
- The connection box must have a circuit breaker or an isolation switch and fuses to protect the cable linking the connection box to the main switch board.
- The frequency and voltage of shore supply matches with the ships electrical distribution system.
- Check the IR of shore cable and shore connection box.
- Take the energy meter readings both at shore as well as at ship.
Safe Connection Procedure
After terminal connections are made, before closing the breaker phase sequence is checked with the indication to ensure that motor will not run in the wrong direction. The indication lamp shows availability of shore power at the switch board and the supply breaker is closed after the ship’s alternator are disconnected.
Overload protection is provided by the supply breaker or an isolating switch and fuses. There is usually a lamp to show that the supply is On, together with a voltmeter and ammeter.
The phase sequence indicator may be arranged as two lamps connected as an unbalanced load across the 3phase via resisters and capacitors. The sequence is right when the right side lamp is bright and the other is dark. An alternative PSI is a rotary pointer driven by a small 3phase induction motor.
