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Electric Propulsion Plant

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24.1 The requirements of this section relate to propulsion equipment and electromagnetic slip couplings essential for the safe operation of the vessel.

24.2 Where the arrangements permit a propulsion motor to be connected to a generating plant having a continuous rating greater than the motor rating, means shall be provided to limit the continuous input to the motor to a value not exceeding 5% overload in torque, based on the continuous full-load torque for which the motor is designed.

24.3 For the purpose of inspection and maintenance, provision shall be made for access to stator winding and armature coils and for the withdrawal and replacement of the coils of dc machines and of salient-pole ac machines.

24.4 Pressure or gravity lubrication systems shall be fitted with a low oil pressure alarm and shall be provided with an alternative means of lubrication as follows:

  1. an automatically operated stand-by pump;
  2. an automatic gravity supply reservoir; or
  3. oil rings.

24.5 In excitation circuits there shall be no automatic circuit-opening devices except those affording short-circuit or phase-failure protection for the main propulsion circuit.

24.6 The torque available in the propulsion motors for manoeuvring shall be reasonably in excess of the trailing action of the propeller, to enable the latter to be stopped or reversed in a reasonable time when the vessel is travelling at maximum service speed.

24.7 For dc systems, arrangements for generator and motor excitation shall be such that, if the motor excitation circuit is opened by a switch or contactor, the generator excitation is simultaneously interrupted or the generator voltage is immediately reduced to zero.

24.8 Adequate torque margin shall be provided in ac propulsion systems to guard against the motor pulling out of synchronism under normal service conditions, including rough weather and on a multiple-screw vessel when turning.

24.9 Where the system might result in overspeeding of the propulsion motor in the event of loss of load, overspeed protection devices arranged to interrupt the supply of power shall be provided and the rotating parts shall be suitably constructed to prevent damage due to temporary overspeeding.

24.10 Effective means shall be provided in generators and motors to prevent the accumulation of moisture due to condensation such as heating the windings, either electrically or otherwise, when they are idle for appreciable periods.

24.11 All important circuits, instruments and apparatus shall be clearly labelled for identification.

24.12 Suitable interlocks shall be provided to prevent damage to the plant as a result of incorrect switching such as the opening of switches or contactors not intended to be operated while carrying current.

24.13 Where electric, pneumatic or hydraulic aid is used for normal operation, failure of such aid shall not result in interruption of power to the propeller shaft and any such device shall be capable of purely manual operation without delay.

24.14 Provision shall be made for protection against severe overloads, excess currents and electrical faults, likely to result in damage to the plant.

24.15 The protective equipment shall be capable of being so set as not to operate on the overloads or excess currents likely to be experienced in a heavy seaway or when manoeuvring.

24.16 The main propulsion circuit shall be provided with ground leakage indicating devices that will operate when the insulation resistance is 100,000 ohms or less.

24.17 Excitation circuits shall be provided with lamps, voltmeters or other suitable means to indicate continuously the state of the insulation of the excitation circuits under running conditions.

24.18 For dc equipment operating at voltages exceeding 500 volts and for all ac equipment, both audible and visual ground alarms shall be fitted:

  1. the alarms shall operate automatically on the occurrence of a ground fault but the operation of such devices shall not interrupt the power supply;
  2. a switch may be provided for switching off the audible device but in such cases the visual alarm shall remain switched on until the fault has been cleared; and
  3. where a ground connection is used for the operation of the indicator, the arrangement shall be such that the ground circuit is opened automatically in order to stop the circulation of fault current.

24.19 Access doors for switchgear and control gear operating at voltages in excess of 50 volts shall be either interlocked to prevent access while such parts are alive or be provided with a lock, the key of which shall be kept in a place accessible only to authorized personnel.

24.20 For the protection of the field windings and cables, means shall be provided for limiting the voltage induced when the field circuits are opened.

24.21 Where excitation is obtained direct from the auxiliary bus-bars, means shall be provided to limit the voltage induced at the bus-bars when the auxiliary generator circuit breaker or the distribution circuit breaker opens.

24.22 Shunt resistors which are connected across the field circuit of synchronous propulsion motors when they are functioning as a synchronous motor shall be suitably insulated for the voltage induced when manoeuvring and shall be amply rated.

24.23 Where separately driven direct-current generators are connected electrically in series, means shall be provided to prevent reversal of the direction of rotation of any of them on the failure of the driving power of the prime mover.

24.24 Contactors and switches used for reversing the rotation of the propulsion motors shall be provided with means for opening them forcibly if they should inadvertently be left closed and they shall be so interlocked mechanically as to prevent the circuits for ahead and astern rotation being closed simultaneously.

24.25 An audible alarm device shall be provided for machines having enclosed-ventilating systems, arranged to operate in the event of the temperature of the heated air exceeding the predetermined safe value.

24.26 Electric slip couplings shall be of substantial and rigid construction, and shall be enclosed, ventilated or otherwise provided with substantial wire or mesh screen to prevent injury to personnel or the entry of foreign material.

24.27 Electric slip couplings, including their exciters when tested under rated load conditions shall have temperature rises not exceeding the limits given in Table 16-1 of Section 16.

24.28 When the coupling is fitted with an integral fan, the temperature-rise limits given above shall not be exceeded when operating continuously at 70% full load speed, rated torque and rated full-load excitation.

24.29 Shafting materials for motors and generators above 375 kW which are essential to the safety of the ship shall be submitted in accordance with Schedule VI Part II Div. II of the Marine Machinery Regulations

24.30 Electronic governors controlling the speed of a propulsion unit shall have two power supplies, one of which shall be a battery; in the event of a “normal” supply failure the governor shall be automatically transferred to the alternative battery power supply; an audible and/or visual alarm shall be provided in the main machinery control area to indicate that the governor has transferred to the battery supply; the prime-mover shall be equipped with a separate overspeed device to prevent runaway if a failure should render the governor inoperative; the alternative battery supply shall be arranged for trickle charge to ensure the battery is always in a fully charged state; each governor shall be protected separately so that a failure in one governor will not cause failure in other governors; a mechanical back-up governor may be provided in lieu of the alternative battery supply; the mechanical governor shall be of a suitable type and shall automatically assume control of the engine in the event of electronic governor failure.

24.31 Alternating-current propulsion generators shall be provided with means for obtaining the temperatures of the stationary windings; a minimum of one embedded temperature detector per phase is to be provided for this purpose on the hot end of the machine; the temperatures are to be indicated at a convenient location, preferably the generator control panel.

25. Additional Requirements for AC Supply Systems with Voltages of 1 kV and Above

NOTE: FOR THE PURPOSES OF THIS SECTION, “HIGH VOLTAGE” MEANS VOLTAGES OF l kV AND ABOVE

25.1 The main switchboard shall be in at least two independent sections, each supplied by at least one generator and so arranged that duplicated essential services are supplied from separate switchboard sections.

25.2 Distribution systems shall be three-phase, 3-wire and may be operated with the neutral either insulated or grounded.

25.3 Where the system neutral is insulated, the dielectric strength of all electrical equipment is to be sufficient to withstand any possible transient over-voltage to ground.

25.4 Where the system neutral is grounded, the connection to ground shall be made through a resistor which is capable of limiting ground fault current to a value not greater than the full load current of the largest connected generator and not less than 3 times the minimum current required to operate any ground-fault monitoring or protection device; the neutral impedance shall be chosen so that the transient over voltages caused by a fault are kept to a minimum.

25.5 A neutral grounding resistor shall be provided for each section of the system that can operate independently.

25.6 A disconnecting means shall be fitted in each generator ground connection to permit complete isolation of the generator for maintenance purposes.

25.7 Transformer primary neutrals shall not be grounded except when all generators are disconnected and power is being supplied from shore.

25.8 A means of visually and audibly indicating any system ground fault shall be fitted.

25.9 A suitable disconnecting means shall be provided on the supply side of fuses used for the protection of instrument potential transformers.

25.10 Terminal boxes and cable termination spaces shall be of sufficient size to accommodate cable glands and terminations while maintaining minimum cable bending radii.

25.11 High voltage and low voltage cable connections shall not be accommodated in the same terminal box.

25.12 Where practicable, all high voltage cable connections shall be covered with a suitable insulating material, otherwise, phases are to be separated from ground and from each other by barriers of suitable insulating material.

25.13 High voltage equipment shall be so constructed and located that live parts are inaccessible to unauthorized persons.

25.14 Permanent legible warning notices shall be attached to high voltage equipment and at the entrances to compartments where high voltage equipment is housed; such notices shall carry the wording “DANGER HIGH VOLTAGE” and “DANGER HAUT TENSION”.

25.15 Where a transformer is located in a compartment which forms the enclosure of the transformer, the door of the compartment shall be provided with a means to prohibit unauthorized access and interlocked with the transformer primary circuit breaker so that the circuit breaker is tripped when the door is opened and cannot be closed while the door is open.

25.16 Compartments housing high voltage equipment and work areas surrounding the equipment shall be adequately illuminated and provided with a means of exit which shall be kept clear of all obstructions.

25.17 High voltage cables shall not be run in the same wireway as cables for use in systems operating at voltages less than l kV.

25.18 High voltage cables shall be readily identifiable and shall be clearly marked at each side of all bulkhead or deck penetrations with the wording “DANGER HIGH VOLTAGE” and “DANGER HAUT TENSION”.

25.19 High voltage cables shall not be installed in elevator shafts and where practicable, shall not be run through accommodation spaces.

25.20 Where single conductor cables are used, precautions shall be taken to prevent the flow of induced circulating currents in the sheath or armour and the cables shall be transposed at intervals of approximately 16 metres.

25.21 For switchgear assemblies l kV and over, the most recent edition of CSA Standard C.22.2 No. 31, shall be used as criteria for construction, installation and testing.

25.22 High voltage cables associated with systems operating at 2 kV and above are to be terminated in accordance with the most recent edition of Canadian Electrical Code Part 1.

25.23 For control apparatus, the most recent edition of CSA Standard C22.2 No. 14, shall be used as criteria for construction, installation and testing.

25.24 For transformers, the most recent edition of CSA Standard C9, shall be used as criteria for construction, installation and testing.

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Date modified:
2010-01-18