Section 4 Electrical system

4.1.1 ‘Dead transfer’ arrangements are to be provided that permit transfer between operation using ship sources of electrical power and an external electrical power supply by disconnecting one from the ship distribution system and then connecting the other to the dead system.

4.1.2 Additional arrangements for connecting ship sources of electrical power and an external electrical power supply in parallel temporarily to transfer load from one to the other only are permitted, provided these are in accordance with Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.3 to Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.9.

4.1.3 Means to automatically synchronise a ship source of electrical power with an external electrical power supply and connect them in parallel for load transfer when requested by operating staff are to be provided.

4.1.4 Means to automatically transfer load between a ship source of electrical power and an external electrical power supply following their connection in parallel, are to be provided. The load transfer is to be completed in as short a time as practicable without causing machinery or equipment failure or operation of protective devices and this time is to be used as the basis for defining the Transfer Time Limit required by Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.5.

4.1.5 When transferring of load between ship sources of electrical power and an external electrical power supply exceeds a defined Transfer Time Limit then, arrangements are to be such that:

• the transfer is aborted;
• load is removed from the ship sources of electrical power or external electrical power supply that was intended to take the load; and then
• the Connection Circuit-Breaker is opened.

An alarm is to be provided at a machinery control station that is attended when connected to an external electrical power supply when the Transfer Time Limit is exceeded and is to indicate the return to previous operating conditions.

4.1.6 The Transfer Time Limit referred to in Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.5 may be adjustable to match the ability of an external electrical power supply to accept and shed load. Setting of the Transfer Time Limit is to be demonstrated to the attending Surveyor at Surveys and Trials, see Pt 7, Ch 13, 6.1 General.

4.1.7 An external power supply may only be connected in parallel with a single ship source of electrical power. Arrangements are to be provided to ensure that this requirement is satisfied before and during parallel connection. Details of alternative proposals may be submitted for consideration.

4.1.8 Arrangements provided to adjust ship sources of electrical power to allow connection in parallel and transfer of load are not to cause machinery or equipment failure, operation of protective devices or damage under normal conditions or in the event of a failure.

4.1.9 Where load reductions are required to transfer load they are not to result in loss of essential services or the loss of availability of emergency services. Means are to be provided to readily make necessary load reductions and re-instate supplies following transfer.

4.2.1 Arrangements for operating from external supplies are to be sufficiently rated to supply the following:

• essential services normally required in port;
• emergency services;
• services required to ensure ready availability of non-operating main and auxiliary machinery;
• services required to prevent damage to cargo or stores; and
• the services required for the Defined Operations.

The schedule of loads required by Pt 6, Ch 2, 1.3 Documentation required for supporting evidence 1.3.3 is to incorporate operation when connected to an external electrical power supply.

4.2.2 The maximum electrical step load switched on or off is not to cause the power supply quality to exceed the parameters given in Pt 6, Ch 2, 1.8 Quality of power supplies or failure when connected to an external electrical power supply in accordance with the defined requirements, see Pt 7, Ch 13, 3.1 General 3.1.10.

4.2.3 Consideration is to be given to providing means to inhibit automatically the connection of large motors, or the connection of other large loads, that the arrangements are not rated to supply when connected to an external electrical power supply having the defined minimum apparent power or current capacity, see Pt 7, Ch 13, 3.1 General 3.1.10 and Pt 6, Ch 2, 6.9 Load management 6.9.4.

4.3.1 Where an external electrical power supply is not arranged to operate in parallel with ship sources of electrical power, the connection to the external electrical power supply is to be provided with a Connection Circuit-Breaker arranged to open simultaneously, in the event of short-circuit, overload or undervoltage, all insulated poles.

4.3.2 Where an external electrical power supply is arranged to operate in parallel with ship sources of electrical power during load transfer, the connection to the external electrical power supply is to be provided with a Connection Circuit-Breaker arranged to open simultaneously, in the event of a short-circuit, an overload or an undervoltage, all insulated poles. This circuit-breaker is to be provided with reverse power protection with time delay, selected or set within the limits of 2 per cent to 15 per cent of full load to a value fixed in accordance with the rating defined in the Design Statement; a fall of 50 per cent in the applied voltage is not to render the reverse power mechanism inoperative, although it may alter the amount of reverse power required to open the circuit breaker.

4.3.3 The electrical system, including short-circuit protective device rating, is to be suitable for the highest prospective fault level at the point of installation. The short-circuit current calculations required by Pt 6, Ch 2, 1.2 Documentation required for design review 1.2.6 are to identify the system state that would result in the highest prospective fault level. The highest prospective fault level may occur during parallel connection with an external power supply and the resulting combination of:

1. ship sources of electrical power, taking into account Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.7; and

2. an external electrical power supply having the defined maximum permitted prospective fault level, see Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.7.

Details of alternative proposals may be submitted for consideration.

4.3.4 The connection circuit is to be arranged such that contamination due to the products of arcing as a result of a fault in the Connection Circuit-Breaker enclosure on the external power supply side will not result in essential or emergency services not being available when supplied by ship sources of electrical power.

4.3.5 Initial connection of an external electrical power supply to the ship switchboards or converter equipment to connect to ship loads is to be arranged to be made by closing of the Connection Circuit-Breaker only.

4.3.6 Converter equipment used to connect an external electrical power supply to the ship electrical system is to ensure that a supply that would result in damage is not applied to the connected ship electrical systems in the event of a failure.

4.3.7 The voltage and time delay settings of the Connection Circuit-Breaker undervoltage release mechanism( s) are to be selected to ensure that the discriminative action required by Pt 6, Ch 2, 6.1 General 6.1.1 is maintained.

4.3.8 Means are to be provided to prevent closure of the Connection Circuit-Breaker when a connected external electrical power supply has a different phase rotation or has a voltage or frequency that does not match the ship electrical system rating within the tolerances defined by Pt 6, Ch 2, 1.8 Quality of power supplies 1.8.2 or Pt 6, Ch 2, 1.8 Quality of power supplies 1.8.5. Signals are to be provided, where necessary, to allow comparison with ship electrical system characteristics.

4.3.9 For high voltage connections means are to be provided to ensure the circuit breaker cannot be closed when any of the following conditions exist:

• one of the earthing switches is closed (shore-side/ship-side);
• the safety circuit is not established;
• emergency-stop facilities are activated;
• ship or shore control, alarm or safety system self-monitoring diagnostics detect an error that would affect safe connection;
• the data-communication link between shore and ship is not operational, where applicable;
• the permission from the ship is not activated;
• the HV supply is not present;
• equipotential bonding is not established (via equipotential bond monitoring devices where utilised, or via manual override);
• the cabinet door is in the open position; or
• cable plugs both shore and ship are not fully inserted into the socket.

4.3.11 Connection power circuits are to be provided with protection against earth faults in accordance with Pt 6, Ch 2, 6.4 Protection against earth faults.

4.4.1 External electrical power supply connections are to be provided with instruments and devices on board equivalent to those required for alternating current generators by Pt 6, Ch 2, 7.11 Instruments for alternating current generators 7.11.1 where synchronising is not provided, or by Pt 6, Ch 2, 7.11 Instruments for alternating current generators 7.11.2 to Pt 6, Ch 2, 7.11 Instruments for alternating current generators 7.11.3 where synchronising for load transfer is provided. See also Pt 6, Ch 2, 7.11 Instruments for alternating current generators and Pt 6, Ch 2, 7.12 Instrument scales.

4.4.2 Means are to be provided to ensure that a source of electrical power or electrical power supply can only be connected to other live parts when synchronised. See also Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.2 for temporary parallel connection for load transfer.

4.4.3 The arrangements are to prevent Connection Equipment power conductors being made live by connecting to the ship electrical system.

4.4.4 The simultaneous connection of a ship source of electrical power and external electrical power supply to the same dead part of the electrical system is to be prevented.

4.4.5 For high-voltage connections, suitable means are to be provided to earth the connection power circuit so that it is discharged and so maintained that it is safe to touch.

4.4.6 Means provided to connect a connection power circuit to earth are to be arranged such that the circuit may only be earthed when it is isolated.

4.4.7 Interlocking arrangements are to be provided to prevent the connection of a high-voltage external power supply to a switchboard connected to earth using the means required by Pt 6, Ch 2, 7.8 Earthing of high-voltage switchboards.

4.5.1 When the ship main source of electrical power is shutdown and failure of the connected external electrical power supply occurs, the Connection Circuit-Breaker is to be arranged to automatically open followed by:

1. connection of the emergency source of electrical power to emergency services in accordance with Pt 6, Ch 2, 3.3 Emergency source of electrical power in passenger ships 3.3.1 or Pt 6, Ch 2, 3.4 Emergency source of electrical power in cargo ships 3.4.1 as applicable; and

2. automatic connection of the transitional source of electrical power to emergency services in accordance with Pt 6, Ch 2, 3.3 Emergency source of electrical power in passenger ships 3.3.1 or Pt 6, Ch 2, 3.4 Emergency source of electrical power in cargo ships 3.4.1 as applicable; and

3. automatic starting and connecting to the main switchboard of the main source of electrical power and automatic sequential restarting of essential services, in as short a time as is practicable. See also Pt 7, Ch 13, 2.1 General requirements 2.1.3 and Pt 6, Ch 2, 2.2 Number and rating of generators and converting equipment 2.2.3.

Failures include loss of power, disconnection, phase failure and quality of supply outside the tolerances given in Pt 6, Ch 2, 1.8 Quality of power supplies 1.8.2 or Pt 6, Ch 2, 1.8 Quality of power supplies 1.8.5.

4.5.2 An alarm is to be provided at a machinery control station that is attended when connected to an external electrical power supply to indicate activation of the automatic power supply failure response required by Pt 7, Ch 13, 4.5 Ship power restoration 4.5.1. The alarm is to indicate the failure that caused the activation.

4.5.3 The automatic power supply failure response required by Pt 7, Ch 13, 4.5 Ship power restoration 4.5.1 is to be inhibited during the 'dead transfer' required by Pt 7, Ch 13, 4.1 Electrical Load Transfer 4.1.1 but arrangements are to permit personnel to readily revert to operation from ship sources of electrical power if the 'dead transfer' to the external electrical power supply is not completed.