Section
16 Electric propulsion
16.1 General
16.1.1 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.
16.1.2 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
Pt 6, Ch 2, 10.2 Semiconductor converters 10.2.5.
16.1.4 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.
16.2 System design and arrangement
16.2.1 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.
16.2.2 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 Pt 7, Ch 14 Requirements for Machinery and Engineering Systems of Unconventional Design . The risk management 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.
16.3 Power requirements
16.3.1 The
propulsion system is to have sufficient power for manoeuvring the
vessel and for going astern. With the ship travelling at its maximum
service speed the propulsion equipment is to be capable of stopping
and reversing the ship in an agreed time.
16.3.2 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.
16.3.3 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.
16.3.4 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.
16.3.5 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.
16.3.6 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.
16.3.7 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.
16.3.8 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.
16.3.9 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.
16.4 Propulsion control
16.4.1 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.
16.4.2 Step-less
control of propeller speed, and/or pitch, from zero to full power
ahead or astern is to be provided.
16.4.3 The
control system is to ensure that there is no dangerous overspeeding
of propulsion motors upon loss of load.
16.4.4 Interlocks
are to be provided in the control system to ensure that ahead and
astern circuits are not energised simultaneously.
16.4.5 Any
single fault in either the propulsion machine excitation or power
distribution systems is not to result in a total loss of propulsion
power.
16.4.7 Each
control station is to be provided with an emergency stop function
for the propulsion motors. The emergency stop function is to be independent
of the normal control system.
16.4.8 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.
16.4.9 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).
16.4.10 Local
controls are to be provided, independent of any remote or automatic
system, to permit effective control of the propulsion equipment.
16.4.11 Control
systems are not to share hardware or data communication links with
control, safety and alarm systems not associated with propulsion control, see also
Pt 6, Ch 1, 2.11 Data communication links.
16.4.12 The factory acceptance test (FAT) of the propulsion control and power management system
is to be carried out according to a FAT program acceptable to LR. A reduced FAT program
for subsequent vessels in a series is subject to agreement by LR.
16.5 Harmonic filtering for propulsion
16.5.2 In the event of filter circuit failure, continued safe operation of the propulsion
system is to be possible by following appropriate procedures, as 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.
16.6 Protection of propulsion system
16.6.1 Provision
is to be made for protection against severe overloads, and electrical
faults likely to result in damage to plant.
16.6.2 Propulsion
motors are to be capable of withstanding, without damage, the thermal
and mechanical effects of a short-circuit at the terminals.
16.6.3 Electric
motors of podded propulsion units, and/or 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).
16.6.4 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.
16.6.5 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.
16.6.6 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.
16.6.7 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 Pt 6, Ch 2, 1.8 Quality of power supplies.
16.6.8 Dynamic
braking resistors are to be suitably rated for their expected operation.
16.6.9 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.
16.6.10 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
Pt 6, Ch 2, 10.2 Semiconductor converters 10.2.4.
16.6.11 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, then evidence demonstrating that this is sufficient is to be
submitted for consideration, see also
Pt 6, Ch 2, 6.12 Protection of transformers 6.12.1.
16.6.12 Alarms
and safeguards for electric propulsion equipment are indicated in Table 2.16.1 Electric propulsion equipment:
Alarms and safeguards.
Table 2.16.1 Electric propulsion equipment:
Alarms and safeguards
| Item
|
Alarm
|
Note
|
| Electric propulsion equipment
ventilation and cooling medium temperature
|
High
|
See
Pt 6, Ch 2, 16.1 General 16.1.2 and Pt 6, Ch 2, 16.3 Power requirements 16.3.8
|
| Electric propulsion transformer
winding temperature
|
High
|
See
Pt 6, Ch 2, 10.1 Transformers 10.1.12
|
| Electric propulsion generator
excitation
|
Overload
|
See
Pt 6, Ch 2, 16.6 Protection of propulsion system 16.6.6
|
| Electric propulsion generators and
motors winding temperature
|
High
|
See
Pt 6, Ch 2, 16.1 General 16.1.3
|
| Electric propulsion generator and
motor bearing temperature
|
1st stage high
2nd stage high
|
See
Pt 6, Ch 2, 9.1 General requirements 9.1.12
Safe shutdown to prevent damage
|
| Electric propulsion generator and
motor lubricating oil supply pressure
|
Low
|
See
Pt 6, Ch 2, 9.1 General requirements 9.1.13
|
| Electric propulsion generator and
motor lubricating oil temperature
|
1st stage high
2nd stage high
|
See
Pt 6, Ch 2, 9.1 General requirements 9.1.14
Safe shutdown to prevent damage
|
16.7 Instruments
16.7.1 The
main control station is to be provided with the following instruments:
-
a.c. systems:
-
an ammeter
for each generator, propulsion motor and propulsion transformer primary;
voltmeter, wattmeter and frequency meter for each generator and ammeter
for each excitation circuit; and
-
a temperature
indicator for each generator, propulsion transformer and propulsion
motor windings and bearings, the indicator is to read stator winding
temperature of the rotating machines, and cooling system temperature.
-
d.c. systems:
-
a voltmeter
and ammeter for each generator and propulsion motor; and
-
an ammeter
for each excitation circuit.
16.7.2 Each
control station is to be provided with instruments to indicate:
-
propeller speed;
-
direction of
rotation for a fixed pitch propeller or pitch position for a controllable
pitch propeller;
-
visual indication
of power limitation; and
-
indication of
station in control.
|