Section 5 Design and Construction

5.1.1 This Chapter is to be read in conjunction with the requirements of Pt 5 Main and Auxiliary Machinery and Pt 6 Control, Electrical, Refrigeration and Fire of the Rules for Ships.

5.1.2 Means are to be provided to monitor and record system disturbances such as: voltage spikes, voltage drops, common mode noise, high frequency noise, power failures, surges and other conditions that could result in a hazard. The Risk Assessment required by Ch 1, 4.2 Risk Assessment, is to determine the level required, considering the needs of the Operators and all persons who carry out maintenance. It is to include, but not be limited to:

• the location and maintainability of the monitoring equipment;
• the level of monitoring required, such as the frequency, type and display of information; and
• who the system is to alert and how they are to be alerted.

5.1.3 d.c. connections are to be designed to prevent arc flash incidents occurring, due to high resistance connections forming as a result of corrosion.

5.1.4 Arc protection and arrangements are to be in accordance with Pt 6, Ch 2, 8 Protection from electric arc hazards within electrical equipment of the Rules for Ships.

5.1.5 To prevent permanent damage to connected equipment from voltage spike or surges, the voltages are to be limited using arrestors or by another recognised method, where it is deemed necessary by the system designer or LR.

5.2.1 In general nominal system voltages for both a.c. and d.c. are not to exceed:

• 1000 V a.c. and 1500 V d.c. for generation and power distribution;
• 500 V a.c. or d.c. for cooking and heating equipment permanently connected to fixed wiring;
• 250 V a.c. or d.c. for lighting, heaters in cabins, crew’s and embarked personnel’s rooms, and other applications not mentioned above.

Voltages greater than those mentioned in this Section will be subject to special consideration.

5.2.2 Converters are to be selected to withstand the voltage ripple levels present on the d.c. bus. For every system, the following voltage parameters are to be defined:

• maximum non-repetitive peak,
• maximum repetitive peak,
• maximum repetitive peak-to-peak.

5.2.3 Distribution systems supplying consumers through semi-conductor converting equipment are to ensure galvanic isolation and ground separation.

5.2.4 Where consumers are supplied via converters which are connected to both sides of a d.c. bus capable of being split, arrangements are to be provided to eliminate the risk of current being supplied back to the d.c. bus through flyback diodes.

5.2.5 Generators and loads connected to the d.c. bus via converters are to facilitate connection and removal of generators and consumers in a stable manner.

5.2.6 Where a bi-directional flow of power may occur, the distribution system is to withstand the power variations being introduced. The level of bi-directional flow allowed is to be specified by the system designer.

5.2.7 Where Pulse Width Modulation converters are to be used, the voltage rate of rise times are to be evaluated. Rotating machinery, surge protective devices, cable insulation and motor windings are to be designed accordingly.

5.3.1 In addition to the requirements of Pt 6, Ch 2, 5.3 Isolation and switching of the Rules for Ships, d.c. systems are to comply with the following requirements.

5.3.2 The system is to be designed to prevent damage to the converter when switching under load.

5.3.3 Where essential services are required by Pt 5 Main and Auxiliary Machinery of the Rules for Ships to be duplicated, these are to be served by individual circuits, separated in their switchboard or section board and throughout their length as widely as is practicable without the use of common feeders, protective devices, control circuits or controlgear assemblies, so that any single fault will not cause the loss of both services.

5.3.4 WhereCh 1, 5.3 Isolation and switching 5.3.3 is applicable, the distribution system is to be split into at least two independent systems, or to be separated by protection devices providing overcurrent protection, including short circuit. The protective devices used are to be selective, ensuring faults are not transmitted further, and independent of the direction of current flow.

5.3.5 Interlocks are to be provided which will prevent access to capacitors until their voltage level has reduced to below the safe extra low voltage level (50V); this is to ensure safety of personnel during maintenance.

5.3.6 Where fuses are used in the system, appropriate labelling is to be provided detailing the type of replacement fuses to be fitted.

5.4.1 Insulated d.c. systems are to be provided with earth fault monitoring, detection and alarm capable of detecting earth faults up to and including the connected loads. Information is to be submitted demonstrating that the selected monitoring devices are fit for purpose. See also, Pt 6, Ch 2, 5.4 Insulated distribution systems.

5.5.1 In addition to the requirements of Pt 6, Ch 2, 10.2 Semiconductor converters of the Rules for Ships, converting equipment is to comply with the following requirements.

5.5.2 Converting equipment mentioned in this Section can be of conversion type d.c./a.c., a.c./d.c., d.c./d.c., and can be of the controlled (e.g. Active Front End (AFE)) or non-controlled type (e.g. Diode Supply Unit (DSU)).

5.5.3 Converters are to be provided with visual means of status indication to include, but not limited to:

• Power available at the input;
• Power at output;
• Temperature; and
• Overload.

This is a minimum list of indicators and alerts for a converter; additional indicators, alerts and shutdowns may be necessary as determined through the Risk Assessment the d.c. distribution system required by Ch 1, 4.2 Risk Assessment. If certain indicators and alerts are not applicable, sufficient evidence shall be produced to support the claim (e.g. Risk-Based Analysis such as FMECA).

5.5.4 Converters supplying electrical power to the d.c. distribution bus and consumers are to be capable of delivering the required currents for the time required to enable current-time discrimination of protective devices. The electrical supply is to be automatically restored following fault clearance.

5.5.5 Converter software development is to be carried out in accordance with Pt 6, Ch 1, 2.10 Programmable electronic systems - General requirements of the Rules for Ships.

5.5.6 Converters are to be capable of handling voltage and current spikes from the d.c. bus under all normal and reasonably foreseeable abnormal conditions without sustaining any damage or tripping, so far as is reasonably practicable.

5.5.7 Converters supplying essential services are to automatically restart and connect to the d.c. bus after a blackout as specified in Pt 6, Ch 2, 2.2 Number and rating of generators and converting equipment 2.2.3 of the Rules for Ships.

5.5.8 Where converters are equipped with internal capacitors which can contribute significantly to the short-circuit level of the system, the contribution is to be accounted for in the design of the protection and distribution system.

5.5.9 The recharging of the converter internal capacitors during and after short circuit is to be managed to minimise the risk of capacitor and converter component damage due to inrush currents.

5.5.10 Where capacitors are connected to a converter output, the output is to be charged by the converter or by external chargers to a level which will minimise the risk of damage to the capacitors before connecting them to the d.c. bus.

5.5.11 Converters arranged to operate in parallel are to be capable of stable load sharing up to maximum load, including temporary overloads.

5.5.12 Converters are not to be used as the final protective device for short circuit in lieu of dedicated protective devices such as fuses or circuit breakers; unless evidence is provided demonstrating that the converter will remain within the specified safe operational specification under all normal and reasonably foreseeable abnormal operating conditions.

5.5.13 Where converters are arranged to provide protection against electrical faults as specified in Ch 1, 5.5 Converting equipment 5.5.12, a disconnector or switch disconnector is to be provided to enable safe isolation of the convertor from its incoming supplies.

5.5.14 Converters are to be protected from permanent damage as a result of short circuits or overload currents on their input or output terminals.

5.6.1 Short-circuit calculations are to be carried out and a justification for the method applied is to be submitted for review.

5.6.2 Where fuses are implemented to limit the fault current in the converter, the activation of the protection is not to influence the redundant consumers or cause loss of other single consumers as required by Pt 6, Ch 2, 5.2 Essential services of the Rules for Ships, nor shall it influence the redundant power source required by Pt 6, Ch 2, 2.2 Number and rating of generators and converting equipment of the Rules for Ships.

5.6.3 Fuses used to protect distribution converters are to be of the bolted type. Where alternative arrangements are proposed, it is to be demonstrated that protection system’s selectivity is not adversely affected as a result of an increased connection resistance.

5.7.1 A minimum of two voltmeters indicating the d.c. bus voltage are to be provided. Where the main d.c. bus can be separated into sections there is to be at least one voltmeter per section. An ammeter is to be provided for each converter supplying the d.c. bus.

5.7.2 The meters required by Ch 1, 5.7 Instrumentation 5.7.1 are to be located and arranged such that they may be viewed at a single operating position. In addition meters may be required at additional locations to mitigate hazards identified by the risk assessment required by Ch 1, 4.2 Risk Assessment.

5.7.3 Instrumentation for generators is to be provided in accordance with Pt 6, Ch 2, 7.11 Instruments for alternating current generators of the Rules for Ships.

5.8.1 Cables and busbars for d.c. systems are to be selected and installed in accordance to Pt 6, Ch 2, 11 Electric cables, optical fibre cables and busbar trunking systems (busways) of the Rules for Ships.

5.8.2 Cables are to be selected to meet the intended vessel life taking into account all reasonably foreseeable electrical effects such as, but not limited to, skin effect or partial discharge, age degradation and operating environment.

5.9.1 Batteries connected to and charged by the d.c. bus are to be protected against all effects of electrical faults in the system.

5.9.2 Batteries connected to and charged by the d.c. bus are to be so located and provided with arrangements allowing for the safe isolation of their terminals and the reduction of voltages to a safe level during maintenance. Proposals for alternative arrangements providing an equivalent level of safety will be subject to special consideration.

5.9.3 Batteries are to be connected to the distribution system by protection devices which provide overcurrent protection, including short circuit. The protective devices used are to be selective, ensuring faults are not transmitted further, independent of the direction of current flow.

5.10.1 The shortest distances between conductive d.c. parts; between conductive d.c. parts and earth in air or along the surface of an insulating material, are to be suitable for the rated voltage, having regard to:

• the nature of the insulating material;
• the transient over voltages developed by switching and fault conditions;
• the environment into which the assembly is installed.

5.10.2 Assemblies are to be verified, in accordance with IEC 61439-1, Low-voltage switchgear and controlgear assemblies, including an impulse voltage test, or another relevant national or international standard acceptable to LR.