Section 4 Electric propulsion systems

4.1.1 This Chapter is to be read in accordance with the appropriate Chapters of Vol 2, Pt 9 Electrotechnical Systems and Vol 2, Pt 10 Human Factors.

4.1.2 Where the arrangements permit a propulsion motor to be connected to a generating plant having a continuous rating greater than the motor rating, means are to be provided to limit the continuous input to the motor to a value not exceeding the continuous full load torque for which the motor and shafts are approved.

4.1.3 The ventilation and cooling systems for electrical propulsion equipment are to be provided with monitoring devices arranged to operate an alarm if the temperature of the heated cooling medium exceeds a predetermined safe value. See also Vol 2, Pt 9, Ch 3, 7.2 Semiconductor converters 7.2.5.

4.1.4 The embedded temperature detectors required by Vol 2, Pt 4, Ch 5, 4.8 Propulsion motors – general 4.8.3 are to be arranged to operate an alarm if the temperature exceeds a predetermined safe value.

4.1.5 Propulsion motors, generators and converters are to be provided with means to prevent the accumulation of moisture and condensate when operating at low power levels, or when idle.

4.2.1 In general, for a ship to be assigned an unrestricted service notation, it is to have two independently driven propellers or other propulsion devices, each connected with at least one electric motor, where these form the sole means of propulsion.

4.2.2 For vessels where a propulsion device driven by electric motors is proposed as the sole means of propulsion, at least two effective, independent electric propulsion motors are to be provided and the system is to be designed in accordance with Vol 2, Pt 1, Ch 2 Requirements for Machinery and Engineering Systems of Unconventional Design. A Risk Assessment, in accordance withVol 2, Pt 1, Ch 3, 18 Risk Assessment (RA), is to identify components where a failure could cause loss of propulsion power or other essential services and the proposed arrangements for preventing and mitigating the effects of such a failure.

4.3.1 The propulsion system is to have sufficient power for manoeuvring the vessel and for going astern. With the ship travelling at her maximum service speed the propulsion equipment is to be capable of stopping and reversing the ship in an agreed time.

4.3.2 The propulsion system is to have adequate torque and power margins for all operating conditions including manoeuvring and rough weather with due regard to propeller and ship characteristics.

4.3.3 The electric power for the propulsion system may be derived from generating sets dedicated to propulsion duty or from a central power generation plant which serves both propulsion and ship service loads.

4.3.4 Where propulsion power is derived from a central, common, power plant the control system is to ensure a safe distribution of power between propulsion and ship services, with tripping of non-essential loads and/or reduction in propulsion power if necessary.

4.3.5 Where a central power generation system is employed, the number and rating of generator sets is to be such that with one set out of action the remaining sets are capable of providing all essential and normal ship service loads whilst maintaining an effective level of propulsion power.

4.3.6 Where, in a central power generation system, the electrical power requirements are normally supplied by two or more generating sets operating in parallel, on sudden loss of power from one set, the rating of the remaining set(s) in service is to be sufficient to ensure uninterrupted operation of essential services and an effective level of propulsion power.

4.3.7 Where a central power generation system is employed, means are to be provided to connect available generator sets to meet the power requirement of the electric propulsion system. Arrangements are to be in place to prevent generator sets being automatically disconnected during ship manoeuvres.

4.3.8 Where forced cooling is used on propulsion motors, it is to be possible to operate the motor at a defined reduced power level in the event of failure of the forced cooling.

4.3.9 Total harmonic distortion of the a.c. voltage waveform up to 10 per cent on electric propulsion circuits, not directly connected to the main source of electrical power, may be considered where details are submitted which demonstrate that the equipment and systems are capable of operating under such conditions. Where a higher value of THD is specified, see Vol 2, Pt 9, Ch 1, 2.1 Quality of power supplies (QPS) 2.1.4.

4.4.1 Propulsion control systems are to be stable throughout their normal operating range and arranged to attenuate any effects of cyclic propeller load fluctuations caused by wave action.

4.4.2 Control of propeller speed, and/or pitch, from zero to full ahead or astern is to be provided.

4.4.3 The control system is to ensure that there is no dangerous overspeeding of propulsion motors upon loss of load.

4.4.4 Interlocks are to be provided in the control system to ensure that ahead and astern circuits are not energised simultaneously.

4.4.5 Any single fault in either the propulsion machine excitation or power distribution systems is not to result in a total loss of propulsion power.

4.4.6 Control, alarm and safety systems for the propulsion system are to satisfy the requirements of Vol 2, Pt 9, Ch 7 Control, Alerts and Safety Systems and Vol 2, Pt 9, Ch 8 Programmable Electronic Systems.

4.4.7 Each control station is to be provided with an emergency stop function for the propulsion motor(s). The emergency stop function is to be independent of the normal control system.

4.4.8 The control system is to limit the propulsion power if the power available from the generator(s) is not sufficient to supply the demand level of propulsion power. In the event of a power limitation, there is to be a visual indication at the control stations.

4.4.9 Means are to be provided to identify the cause of propulsion motor power limitation or automatic reduction (e.g. excessive load torque, cooling failure, high temperature, power availability).

4.4.10 Alternative means of operation, independent of any remote system, are to be provided to permit effective control of the propulsion equipment for all intended functional requirements. The alternative control facility is to include all necessary protection and power limitation features.

4.4.11 Control systems are not to share hardware or data communication links with control, safety and alarm systems not associated with propulsion control, see also Vol 2, Pt 9, Ch 8, 5.2 Data communication links.

4.4.12 The factory acceptance test (FAT) of the propulsion control and power management system is to be carried out according to a FAT programme acceptable to LR. A reduced FAT programme for subsequent vessels in a series is subject to agreement by LR.

4.5.1 The requirements in this Section apply to systems provided with harmonic filters and are in addition to the requirements for harmonic filters in Vol 2, Pt 9, Ch 3, 4.11 Harmonic filtering and Vol 2, Pt 9, Ch 4, 4.13 Harmonic filters.

4.5.2 In the event of filter circuit failure, continued safe operation of the propulsion system is to be possible by following appropriate procedures specified by the manufacturer and/or system integrator. These procedures are to include any operational limitations, and they are to be kept on board and made available to the Surveyor on request.

4.6.1 Provision is to be made for protection against severe overloads, and electrical faults likely to result in damage to plant.

4.6.2 Propulsion motors are to be capable of withstanding, without damage, the thermal and mechanical effects of a short-circuit at the terminals.

4.6.3 Propulsion converters are to be capable of withstanding, without damage, the thermal and mechanical effects of a short-circuit at the terminals or connection to a propulsion motor with a stalled or locked rotor.

4.6.4 Electric motors of podded propulsion units, and/or propulsion motors having permanent magnet excitation, are to be provided with a protective device which, in the event of a short-circuit in the motor or in the cables between the motor and its circuit breaker, will instantaneously open the circuit breaker and, in motors with electromagnetic excitation, de-excite the motor. Motors with permanent magnet main excitation are to be provided with means to prevent further damage as a result of continued rotation after disconnection (e.g. shaft brake).

4.6.5 Safeguards for protecting propulsion equipment against damage resulting from earth faults are to be as specified by the equipment manufacturer. Where the fault current flowing is liable to cause damage to the electrical equipment, there are to be arrangements for interrupting the current automatically.

4.6.6 For the protection of electrical equipment and cables against overvoltages, means are to be provided for limiting the induced voltage when field windings and other inductive circuits are opened. Protective resistors and devices are to be sized to cater for the likely extreme operating conditions.

4.6.7 An alarm is to be initiated when the excitation system of electric generators providing propulsion power is overloaded such that damage due to heating could occur in the generator or its cabling.

4.6.8 Where, on stopping or reversing the propeller, regenerated energy is produced by the propulsion motor, this is not to cause a dangerous increase of speed in the prime mover or a dangerous overvoltage condition on the supply system. Where a central power generation system is used, then the voltage and frequency fluctuations are not to exceed the limits given in Vol 2, Pt 9, Ch 1, 2 System level requirements.

4.6.9 Dynamic braking resistors are to be suitably rated for their expected operation.

4.6.10 Loss of flow of air or liquid cooling of propulsion converters, where used, is to initiate an alarm at an attended control position. Loss of flow of air or liquid cooling is not to result in immediate damage to the propulsion converter, see Vol 2, Pt 9, Ch 3, 7.2 Semiconductor converters 7.2.4.

4.6.11 The system integrator is to determine the protection co-ordination required for high voltage propulsion transformers. Where primary protection is to be the only means of protection, evidence demonstrating that this is sufficient is to be submitted for consideration, see also Vol 2, Pt 9, Ch 4, 4.12 Protection of transformers 4.12.1.

4.6.12 Alarms and safeguards for electric propulsion equipment are indicated in Table 5.4.1 Electric propulsion equipment: Alarms and safeguards.

4.7.1 The main control station is to be provided with indicating instruments or other means of continuously monitoring the following:

1. a.c. systems

   1. The line current and excitation current of each generator, propulsion motor and propulsion transformer primary; and for each generator, the voltage, power and frequency.

   2. The winding, bearings and cooling system temperature of each generator, propulsion transformer and propulsion motor.

2. d.c. systems

   1. The armature voltage and current for each generator and propulsion motor and the current in each excitation circuit.

4.7.2 Each control station is to be provided with instruments to indicate:

1. propeller speed;

2. direction of rotation for a fixed pitch propeller or pitch position for a controllable pitch propeller;

3. visual indication of power limitation; and

4. the station in control.

4.8.1 Propulsion motors are to comply with the general requirements as specified within Vol 2, Pt 4, Ch 3, 6.1 General.

4.8.2 Shaft materials for electric propulsion motors are to comply with the Rules for Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials) and are to be manufactured under LR survey.

4.8.3 Propulsion motors that form part of the electrical propulsion systems are to have at least one embedded temperature detector (ETD) in each phase of the machine winding in locations which may be subjected to the highest temperature. Where there are two coil sides per slot the ETD’s are to be located between the insulated coil sides in the slot, see Vol 2, Pt 4, Ch 5, 4.1 General 4.1.4.

4.8.4 The adverse effect of voltage stresses on the winding insulation caused by the operation of switching devices is to be taken into account in the specification, design and installation of inverter fed induction motors.

4.8.5 A high bearing temperature alarm is to be provided where the electric propulsion motors are supplied with forced lubrication.

4.8.6 A low lubricating oil pressure alarm is to be provided for electric propulsion motors that are supplied with forced lubrication.

4.8.7 A high lubricating oil temperature alarm is to be provided for electric propulsion motors that are supplied with forced lubrication, see also Vol 2, Pt 4, Ch 5, 4.6 Protection of propulsion system 4.6.12 for second stage high temperature shutdown to prevent damage.

4.9.1 For propulsion motor ratings the applicable requirements of Vol 2, Pt 9, Ch 3, 6.2 Ratings are to be complied with.

4.9.2 Synchronous propulsion motors are to be capable of an overload power of not less than 10 per cent at their rated power factor for a period of 15 minutes without injurious heating.

4.10.1 For propulsion motor temperature rise the applicable requirements of Vol 2, Pt 9, Ch 3, 6.3 Temperature rise are to be complied with.

4.11.1 Machines are to withstand on test, without injury, the following momentary overloads:

1. The overload tests for propulsion machines will be specially considered for each installation.

4.12.1 For propulsion motor enclosures the applicable requirements of Vol 2, Pt 9, Ch 3, 6.5 Machine enclosure are to be complied with.

4.13.1 For survey and testing of propulsion systems the applicable requirements of Vol 2, Pt 9, Ch 1, 1.6 Surveys and Vol 2, Pt 9, Ch 3, 6.7 Survey and testing are to be complied with.