Section 7 Electrical systems

7.1.1 The electrical installation is to be designed, constructed and installed in accordance with the requirements of Vol 2, Pt 4, Ch 3, 7.2 General arrangements.

7.1.2 Where the thruster units are electrically driven, the relevant requirements, including surveys, of Vol 2, Pt 9 Electrotechnical Systems are to be complied with.

7.2.1 Where a central power generation system is employed, the requirements of Vol 2, Pt 4, Ch 5, 4.3 Power requirements 4.3.5 are to be complied with.

7.2.2 For azimuth thrusters, the generating and distribution system is to be so arranged that after any single failure, steering capability can be maintained or regained within a period not exceeding 45 seconds, and the effectiveness of the steering after such a fault will not be reduced by more than 50 per cent. This may be achieved by the parallel operation of two or more generating sets, or alternatively when the electrical requirements may be met by one generating set in operation, on loss of power, the automatic starting and connecting to the switchboard of a standby set, provided that this set can restart and run a thruster with its auxiliaries.

7.2.3 The failure of one thruster unit or its control system is not to render any other thruster inoperative.

7.3.1 Azimuth thruster auxiliaries and controls are to be served by individual circuits. Services that are duplicated are to be separated throughout their length as widely as is practicable and without the use of common feeders, transformers, converters, protective devices or control circuits.

7.4.1 Where the auxiliary services and thruster units are supplied from a common source, the following requirements are to be complied with:

1. the voltage regulation and current sharing requirements defined in Vol 2, Pt 9, Ch 2, 6.4 Generator control 6.4.2 and Vol 2, Pt 9, Ch 2, 6.4 Generator control 6.4.7 are to be maintained over the full range of power factors that may occur in services;

2. auxiliary equipment and services are to operate with any waveform distortion introduced by converters without deleterious effect. (This may be achieved by the provision of suitably filtered/converted supplies).