ABS Rules for Integrated Power Systems (IPS)

Mike Roa, American Bureau of Shipping

Abstract: This paper will provide an overview of the American Bureau of Shipping (ABS) Rules and for integrated power systems (IPS). The paper will include a review and comparison of the key requirements from the ABS Steel Vessel Rules (for commercial ships) and the ABS Naval Vessel Rules (for military ships) for integrated electric propulsion systems. The paper will explain how to apply the ABS propulsion redundancy notations (R1, R2, R1-S, R2-S) and dynamic positioning system (DPS) notations (DPS-0, DPS-1, DPS-2, and DPS-3) to vessels with integrated electric propulsion systems. Various military and commercial electric propulsion and integrated power system architectures will be examined and contrasted, and the merits and rationale behind the different approaches will be explained. The paper will also provide a brief summary of other standards for electric propulsion systems such as IEEE Standard 45 (2002), IEEE Recommended Practice for Electrical Installations on Shipboard, Clause 31. Electric propulsion and maneuvering system and IPS power electronics conversion equipment standards such as the new IEEE Standard P-1662 - Guide for the Design and Application of Power Electronics in Electrical Power Systems on Ships and the IEC Publication 60146 Series, Semiconductor converters - General requirements and line commutated converters. This paper will provide guidance on the development of Rules and proposed changes to the ABS Steel Vessel Rules and Naval Vessel Rules. The paper will emphasize that ABS is always looking for feedback from industry on ways to improve the clarity of the Rules, capture new technology and lessons learned from shipbuilding programs. ABS has extensive experience with electric propulsion going back as far as the T-2 tankers of World War II fame to modern day electric propulsion designs on many Military Sealift Command (MSC), National Oceanic and Atmospheric Administration (NOAA), and U.S. Navy ships. These designs include various MSC and NOAA oceanographic research vessels, the T-AKE dry cargo ships, the new T-AGM 25 missile range instrumentation ship, and the most advanced integrated power system using electric drive on the DDG-1000 ZUMWALT class destroyers. Purpose: The purposes of this paper are to provide: (a) Background and Summary: Provide a brief history

and background regarding the Naval Sea Systems Command (NAVSEA) and the American Bureau of Shipping (ABS) collaboration to produce the ABS Naval Vessel Rules (NVR) for Integrated Power Systems on U.S. Navy ships. Explain the origin of the requirements that were created for Integrated Power Systems NVR.

(b) Comparison between commercial and military

rules: Provide a brief explanation of the comparison table between Steel Vessel Rules (commercial) and Naval Vessel Rules (military) requirements for electric propulsion vessels. Identify the major differences between what is required by commercial practice and the requirements that have been adopted by the military. Explain the goals, rationale, and benefits of each approach.

(c) Industry Feedback: Summarize industry feedback received from industry partners on the commercial and military approaches to Integrated Electric Drive. This section will identify improvements and recent rule changes that have been made to the SVR and NVR regarding integrated electric drive. Provide a summary of recent industry feedback and suggested changes.

Background and Summary:

During 1990s, U.S. Government initiated a streamlining of government regulations which led to the evaluation of all military standards and specifications (MIL-STDs and MIL-SPECs). Additionally, the Department of Defense (DOD) Procurement Reform policies began to encourage maximum use of commercial standards and commercial-off-the-shelf (COTS) equipment. DOD began promoting the use of commercial standards and specifications wherever possible and, consequently, the U.S. Navy General Specifications for Shipbuilding were cancelled in 1998.

ABS worked on the evaluation of MIL-SPECs and

MIL-STDs throughout the 1990s with NAVSEA. It was recognized early that ABS has long history of classing Naval Auxiliaries to commercial Steel Vessel Rules and ABS was tapped as a potential resource and partner in this effort to create new technical shipbuilding standards for the Navy. ABS and the Navy began to work as a team to respond to the need for a new process to maintain and apply baseline technical criteria. Accordingly, ABS proceeded with development of Naval Vessel Rules as a joint effort with the Naval Sea Systems Command (NAVSEA).1 NAVSEA and ABS jointly developed and implemented a set of Naval Vessel Rules to be used in the design, construction, maintenance, and modernization of non-nuclear naval surface combatant ships.

After many years of success in applying the ABS ship

classification process to many Sealift and Naval Auxiliary programs, the Navy and ABS decided to collaborate in order to address the lower risk aspects (hull structures, stability, mechanical, electrical) of designing and certifying naval combatant ships. This allows in-house Navy engineering resources to be focused more on the higher risk mission related aspects of combatants while maintaining technical control via close collaboration with ABS on the Naval Vessel Rules, the foundation for the process. The Navy retains technical authority but uses ABS as a partner to administer the Naval Vessel Rules and verify compliance with the rules as part of the traditional ABS class process.

The Naval Vessel Rules, as tailored by approved

alternatives, are currently being applied to the USS FREEDOM (LCS-1), USS INDEPDENDENCE (LCS-2),

1 Naval Vessel Rules: A NAVSEA/ABS Partnership for the Future RADM Paul S. Sullivan USN, Howard Fireman, Ray Finney and Glenn Ashe, ASNE Day Conference 2004, Naval Engineering: Transforming Maritime Defense and Sea Power June 28-29, 2004 Hyatt Regency Crystal City, Arlington, Virginia.

978-1-4244-3439-8/09/$25.00 ©2009 IEEE 1

and USS ZUMWALT (DDG-1000) shipbuilding programs. The NVR will be applicable to all future U.S. Navy non-nuclear surface combatants. As per the Rules, the Naval Technical Authority (NTA) will remain in the lead role for certification of integrated power systems. Many aspects of the design will be reviewed and approved by both ABS and NTA. Commercial Steel Vessel Rules (SVR) Requirements for Integrated Power Systems

The baseline commercial rules for electric propulsion systems are fairly straightforward and focus on requiring the system design to meet a minimum baseline criterion for propulsion system safety. These rules can be applied to systems where power for ship’s loads and propulsion are derived from the same source (integrated power systems) or where electrical power for propulsion and ship’s loads are provided from separate sources (segregated electrical propulsion plants). The latter method is a legacy design which is rarely used, however, the rules have been retained in the event that a design calls for the use of dedicated propulsion generators.

The rules also have optional provisions for providing

additional propulsion redundancy in order to achieve a redundancy notation (R1, R2, R1-S, or R2-S). The selection of these optional redundancy notations is at the discretion of the vessel owner. In some areas of the world (i.e. Prince William Sound), the local port state authority will require vessels transiting the area to have a standby tugboat to provide assistance or a redundant propulsion system as an alternative to the standby tugboat. The requirements came about as a result of some incidents where lack of propulsion and steering redundancy resulted in a marine casualty. The naval rules also have an additional R2-N notation which includes some minimum survivability criteria (expressed in terms of extent of damage) that a vessel must with able to withstand and maintain propulsion and steering.

Finally, for vessels equipped with Dynamic Positioning

Systems (DPS), the ABS Steel Vessel Rules have some optional requirements for vessels that use integrated electrical plants to support dynamic positioning of the vessels. An example would be an electric propulsion ship equipped with electrically powered motor drive thrusters which are used in tandem for dynamic positioning of the vessel. The DPS criterion is similar to the redundancy criterion; it’s basically an optional set of notations (DPS-0, DPS-1, DPS-2, DPS-3). The notation indicates the general level of fault tolerance provided by the dynamic positioning system and the appropriate notation is selected by the owner to meet the mission requirements. The maximum environmental conditions (Sea State, Winds, and Current) are also specified by the owner in order for ABS to determine the safe operating envelope that the vessel may operate in.

The following paragraphs provide a high level summary of the basic requirements associated with the various levels of classification of vessel with integrated electrical propulsion systems and the various optional redundancy and dynamic positioning notations. Baseline Requirements - SVR Part 4, Chapter 8, Section 5, Electric Propulsion Systems Para. 5.1 - General • Describes how to apply the electric propulsion rules

• Acknowledges consideration of alternative recognized standards

• Provides list of electric propulsion system plans and data required to be submitted to ABS

Para. 5.3 – System Design General • Explains purpose of requirements • Defines integrated electric propulsion system as a

system where a common set of generators supplies power to vessel service loads as well as propulsion loads.

• Generating Capacity • Requires integrated propulsion system generating plant

to have sufficient capacity to carry vessel service load and supply propulsion power for at least 7 knots or ½ design speed (whichever is the lesser) with one generator out of service.

Power Management System • Requires integrated propulsion system to be provided

with automatic power management for load sharing, blackout prevention, and maintaining power to essential services and minimum propulsion loads, load shedding, and propulsion power limiting.

Regenerative Power • Requires that regenerative power shall not cause

voltage and frequency disturbances to exceed specified limitations

Harmonics • Requires harmonic distortion calculation to be

performed at all locations throughout the system • Harmonic distortion is not allowed to exceed the

specified limits • Where these limits are exceeded, equipment must be

designed for operation at the higher level of distortion Para. 5.5 - Electric Power Supply Systems Propulsion generators • For segregated plants, allows propulsion power to be

derived from a single propulsion generator • For integrated plants, generators sets must also comply

with same criteria as propulsion generators • Single system - single propulsion generator supplying a

single propulsion motor requires redundant excitation systems for the generator and motor.

• Multiple systems – where multiple propulsion generators, converters, or motors are provided, they are to be arranged such that one unit can be taken out of service (electrically disconnected) without preventing operation of the other units.

• Excitation systems – redundant excitation is required such that in case of failure in one excitation system, propulsion is maintained to support at least 7 knots or ½ design speed

• Features for other services – addresses situations where propulsion generators are used to support services other than propulsion (dredging, cargo oil pumps, etc.)

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Propulsion Excitation • Each exciter to be on a separate feeder, fitted with

overload protection • Field circuits provided with a means of suppressing

voltage rise when field switch is opened • Ship service generator connection – excitation is to be

from generator side of breaker Para. 5.7 - Circuit Protection Setting • Overcurrent devices are set sufficiently high to prevent

operation due to normal transients occurring during maneuvering, or heavy seas, broken ice.

DC Propulsion circuits • Fuses not allowed • provided with overload relays to open field circuits • protected from reversal of rotation Excitation circuits • Overload protection not allowed for opening excitation

circuit Magnetic fluxes • Means provided for selective tripping or rapid reduction

to prevent over-currents from harming the plant Semiconductor converters • Overvoltage protection - Means provided to prevent

excessive overvoltages with visual and audible alarms • Overcurrent protection - provided to prevent

permissible current from being exceeded • Short-circuit protection - Fuses provided for short-

circuit protection with visual and audible alarms • Filter circuits - Fuses provided for filter circuits with

visual and audible alarms Para. 5.9 - Protection for Earth Leakage Main propulsion circuits • Means for earth leakage detection provided with

audible and visual alarms Excitation circuits • Means for earth leakage detection provided in

excitation circuits of propulsion machines AC Systems • AC propulsion circuits provided with earthing detector

alarm or indicator • Neutral current limiting required for systems with

earthed neutral to prevent neutral current from exceeding 20 amps upon an earth to ground fault

• Unbalance relay required to open generator and motor field circuits upon an unbalanced fault

DC Systems • Earthing detector to be provided

• Provisions to prevent damage due to overloads, overcurrents, or faults

• Protective equipment capable of being set high enough to prevent operation due to normal transients occurring during maneuvering, or heavy seas, broken ice.

Para. 5.11 - Propulsion Control • This section discusses propulsion control and

monitoring requirements which is beyond the scope of this technical paper.

Para. 5.13 - Instrumentation at the Control Station • This section addresses control station instrumentation

for propulsion control systems which is beyond the scope of this technical paper.

Para. 5.15 - Equipment Installation & Arrangements General • Addresses general safety measures, accessibility,

connections, and creepages and clearances for propulsion equipment

Accessibility and Facilities for Repairs • Addresses measures for accessibility for repairs,

renewal of parts, facilities for support of shaft to permit maintenance and bearing replacement, slip-coupling design to permit removal

Semiconductor converters • Installed away from radiant heat sources with adequate

circulation of air • Immersed-type converters use non-flammable liquids • Converters with forced cooling arranged to prevent

operation unless cooling system is on-line • Minimum enclosure rating IP22 • Designed to allow removal of converter stacks without

disassembly of entire unit Propulsion cables • Splices and joints not permitted • Terminals sealed from air or moisture • Cable ends to be sealed during installation until

permanently attached • Cable supports designed for short circuit, spaced les

than 36 inches apart, arranged to prevent chaffing Para. 5.17 - Equipment Requirements Material Tests • Materials for thrust shafts, line shafts, propeller shafts,

generator/motor shafting, coupling bolts, fan shrouds, and centering/retaining rings

• Major castings to be surface inspected • Welding to meet applicable Rules Temperature rating • Specifies temperature rise limits for electric propulsion

rotating machinery Protection against Moisture Condensation

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• Means to prevent moisture condensation of prime movers

Capability

• Adequate overloading and build-up capacity to supply power required during transitional changes

• Capable of absorbing regenerative power without tripping during crash-back (full ahead to full astern)

• Speed control • Governor provided to maintain steady-state speed

+/- 5 % through entire speed range • Manual controls provided where required to

control propeller speed • Parallel operation - generator governors to permit

stable operation through entire speed range • Protection for Regenerated Power

• Braking resistors or ballast consumers provided to absorb regenerated power and reduce motor speed

• Alternatively, regenerated power to be limited by control system

Rotating Machines for Propulsion (generators and motors) • Ventilation and Protection

• Designed to prevent personnel injury or entrance of foreign matters

• Dampers required in air ducting • Fire extinguishing

• Fixed system required for enclosed machines • Self-extinguishing insulation may be provided as

an alternative • Air coolers

• Two means of circulation • Heat exchangers to have double walled tubes • Visual and audible alarms provided for water

leakage • Temperature sensors

• To be provided in windings of machines over 500 kW

Propulsion Generators

• Excitation from rotating exciters, static exciters, or MG sets

• Excitation power from machine being excited or from any other generating unit

DC Propulsion Motors

• Rotors – rated for overspeed up to limits of overspeed device setting

• Overspeed protection – provided to prevent overspeed during light loading

Electric Couplings

• Addresses general requirements, accessibility, temperature ratings, excitation, controls, and nameplates

Semiconductor Converters for propulsion • General – addresses standard of construction (IEC

60146 Series) and cooling system design. • Testing and Inspection

• Tested per IEC 60146 or other recognized standard.

• Type tests to include the Insulation Test, Light Load & Function Test, Rated Current Test, Power Loss, Temperature Rise Test and checking the Auxiliary Devices, Properties of the Control Equipment and Protective Devices.

• Routine Tests are to include the Insulation Test and Light Load & Function Test and checking the Auxiliary Devices, Properties of the Control Equipment and Protective Devices.

• Forced cooling – details requirements for cooling systems including temperature monitoring, audible and visual failure alarms, and automated propulsion motor power reduction to prevent overheating

• Additional requirements – addresses special criteria for liquid cooled semiconductor converters including alarms for leak detection and containment of leakage.

Reactors and Transformers for Semiconductor Converters • Addresses general construction criteria, voltage

regulation, and high temperature alarms Switches • Addresses general design, generator and motor

switch design (air break or oil-break), and field switches

Propulsion cables • Addresses minimum conductor sizes, allowable

insulation materials, and metallic sheathing, inner wiring, and testing (dielectric and insulation tests).

Para. 5.19 – Trials

• Addresses Sea Trial testing including duration runs, maneuvering tests, crash back tests, test of operation of protective devices, and stability tests for control.

• All tests required to demonstrate each item of the

electric plant as well as the electric propulsion system as a whole are to be performed

Propulsion Redundancy Notations • Applicability:

• For vessels equipped with propulsion and steering systems designed to provide enhanced reliability and availability through functional redundancy.

• Vessels must have ACCU Notation as a pre-requisite for propulsion redundancy Notations.

• Objective: • Minimize risk associated with loss of propulsion

or steering capability. • Notations R1, R1-S, R2, R2-S. • Plus notations apply additional weather criteria.

Notation RI • Multiple propulsion machines (e.g. diesel engine, gas

turbine, steam turbine, electric motor) • Single propulsor (e.g. propeller, azimuthing thruster) • Single steering system (e.g. steering gear, rudder)

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Notation R2 • Multiple propulsion machines (e.g. diesel engine, gas

turbine, steam turbine, electric motor) • Multiple propulsors (e.g. propeller, azimuthing thruster) • Multiple steering systems (e.g. steering gear, rudder) Notation R1-S • Multiple propulsion machines arranged in separate

spaces to prevent fire or flood from affecting both machines.

• Single propulsor. • Single steering system. Notation R2-S • Multiple propulsion machines arranged in separate

spaces to prevent fire or flood from affecting both machines.

• Multiple propulsors arranged in separate spaces to prevent fire or flood from affecting both machines..

• Multiple steering systems arranged in separate spaces to prevent fire or flood from affecting both machines.

Single Failure Criteria: • Applicable for all of the notations (R1, R2, R2-S, and

R2-S) • Upon a single failure, propulsion can be maintained or

restored in 2 minutes. • Capable of advancing the vessel at a speed of at least

1/2 its design speed or seven knots, whichever is less. • Capable of maintaining that speed for 36 hours with

vessel fully loaded. The plus (+) notation: • Upon a single failure, propulsion can be maintained or

restored in 2 minutes. • Capable of maneuvering into orientation of least

resistance to weather. • Capable of maintaining position such that the vessel

will not drift for 36 hours with the severest loading condition.

• Possible in weather conditions up to wind speed of 17 m/s (33 knots) wave height of 4.5 m (15 ft), 7.3 seconds mean period.

Impact on Electrical System Design: • Main switchboard must be capable of being sub-divided • Fault on switchboard must cause automatic isolation. • Essential circuits arranged to meet single failure criteria

previously described (1/2 design speed or 7 knots). • “S” notations require further segregation. Impact on Fire Safety: • Propulsion machines and auxiliary systems arranged to

minimize common damage due to a localized fire. • Vital auxiliary service systems to be grouped and

separated as far as practicable. • Electrical cables supplying redundant equipment are to

exit switchboard and be routed to the equipment as far as practicable.

Test and Trial

• During the sea trial, the propulsion and steering capability are to be tested in accordance with an approved test program to verify compliance with this section.

Fault Simulation Test • Simulation tests for the redundancy arrangements are to

be carried out to verify that, upon any single failure, the propulsion and steering systems remain operational, or the back-up propulsion and steering systems may be speedily brought into service.

Dynamic Positioning Notations What is dynamic positioning? • A system which integrates the controls of propulsion,

azimuthing thrusters, and, in some cases, steering gear • Provides manual position control and automatic

heading control to maintain position and heading under specified maximum environmental conditions.

What type of vessels use Dynamic Positioning? • Offshore Supply Vessels (OSVs) to maintain station

adjacent to offshore drill rig. • Oceanographic Research Vessels - To maintain a

precise heading while plotting ocean depth. • Diving Support Vessels - To maintain a location of an

area where divers must work (moon pool). • Icebreakers - While creating a seaway. Environmental conditions: • Strictly dictated by the owner’s requirements. • May vary based on intended service of the vessel. • May vary based on intended location of the vessel. • Generally expressed in terms of Sea State, Winds, and

Current. Notation DPS-0: • Most basic system. • No redundancy. • Centralized Manual position control provided (joystick) • Automatic heading control (autopilot) provided. Notation DPS-1: • No redundancy. • Provides automatic position and heading control. • Provides Independent manual position control

(joystick) with automatic heading control (autopilot). Notation DPS-2: • Capable of maintaining position and heading with a

single fault. • Provides automatic position and heading control. • Provides Independent manual position control

(joystick) with automatic heading control (autopilot). Notation DPS-3: • Capable of maintaining position and heading with a

single fault AND loss of a compartment due to fire or flood.

• Provides automatic position and heading control.

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• Provides Independent manual position control (joystick) with automatic heading control (autopilot).

Sea Trials • Upon completion and installation of the dynamic

positioning system, complete performance tests are to be carried out to the Surveyor’s satisfaction at the sea trials. The schedule of these tests is to be designed to demonstrate the level of redundancy established in the FMEA. Where practicable, the test environment is to reflect the limiting design operating conditions. Otherwise, external forces designed to simulate the design environmental forces are to be applied.

DP Requirements - Impact on Power Generation and Distribution System Power Generation System DPS-2 Notation: • Generators and distribution systems sized and arranged

such that, in the event of single fault, sufficient power remains available to supply the essential loads and maintain the vessel position

• Essential services are to be arranged such that, with any single fault, sufficient power remains available to supply essential loads and maintain position

DPS-3 Notation:

• Generators and their distribution systems arranged in

separate compartments so that, if any one compartment is lost due to fire or flood, sufficient power is available to maintain position.

• Essential services are to be arranged so that upon loss of any single compartment, sufficient power remains available to supply the essential loads and maintain position

Power Management System • For DPS-2 and DPS-3 notations, power management

systems are is to be provided to ensure that sufficient power is available for essential operations, and to prevent loads from starting while there is insufficient generator capacity.

• At least two power management systems are to be provided, to account for the possible failure of either power management system. Consideration will be given to techniques such as shedding of non essential loads or interfacing with control system to provide temporary thrust reduction to ensure availability of power.

• For DPS-3 notation, the power management systems are to be located and arranged such that no single fault, including fire or flood in one compartment, will render all the power management systems inoperable.

The following table summarizes the carriage

requirements associated with the various DPS notations.

Table 1 - Summary of Carriage Requirements for DPS Notations

DPS Notation Items DPS-0 DPS-1 DPS-2 DPS-3

Power Generation and Distribution System

No Redundancy No Redundancy Redundancy Redundancy

Power management System No No Yes (2) Yes (2) UPS No Yes (1) Yes (2) Yes (3) Thruster System No Redundancy No Redundancy Redundancy Redundancy Automatic Control Systems N/A 1 2 3 Independent Manual Position Control with Automatic heading control

1 1 1 1

Manual Thruster Control System (for each Individual Thruster)

Yes Yes Yes Yes

Emergency Shutdowns for each thruster

Yes Yes Yes Yes

Position Reference (GPS) 1 2 3 3 Gyro Compass 1 2 3 3 Wind Sensors 1 2 3 3 Consequence Analyzer No No Yes Yes FMEA required? No No Yes Yes Military Naval Vessel Rules (NVR) Requirements for Integrated Power Systems

The following paragraphs provide a high level summary of requirements for electric propulsion and integrated power systems that are specified in the ABS Naval Vessel Rules. Source of Electrical Power • Criteria for number and capacity of power sources • Power quality requirements for system-user interface

(MIL-STD-1399, Section 300)

• Transformer and converter capacity requirements • Location and separation of power sources • Recovery time (90 seconds) to restore or maintain

power after loss of any generator • Switchboard number and location, major functions,

required modes of operation, method of interconnection Power to Essential Services • All essential services to be provided with two

independent sources of power • List of essential services defined; includes loads

required for propulsion, steering, safety, firefighting, damage control, mission systems, etc..

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• Selection criteria for bus transfer devices (MBTs, ABTs, SABTs)

Ship Survivability

• Outlines the major design factors that must be considered to preserve the ability for the ship and ship systems to meet mission requirements after damage and flooding.

• Separation of main generators • Arrangements of power supply to essential services • Separation of redundant distribution system cabling

Main Distribution System

• Defines the allowed standard types of distribution systems and cabling methods

• Ungrounded and grounded distribution systems • Zonal distribution systems • Assignment and division of switchboard feeders • Arrangements/locations of distribution equipment

including load centers, MCCs, distribution panels, etc. • Separation of main cableways and feeders • Cable selection criteria, allowable voltage drop

Rotating Machines

• Defines which equipment standards must be complied with for generator sets, motors, and motor- generators

• Specifies method for determining ratings, overload/over current capabilities, short circuit capability

• Detailed construction requirements for generators and propulsion motors

• Performance requirements for generator governor frequency control, voltage regulation, load sharing

• Provides testing requirements and test schedule for rotating machinery intended for essential services

Distribution Equipment, Switchboards, and Motor Controllers

• Sets forth standards of construction for distribution equipment and components

• Detail construction requirements for switchgear, enclosures, bus bars, protective devices, transfer switches, disconnecting devices, internal wiring, hand rails, instrumentation, electric plant controls, motor starters, motor control centers, etc.

• Defines certification and testing requirements for essential distribution equipment

Transformers and Converters

• Provides standards of construction for frequency changers, rectifier power supplies, and transformers

• Defines transformer rating criteria, temperature rise, cooling medium, moisture protection, testing

• Defines semiconductor converter general requirements, cooling arrangements, accessibility

Electric Propulsion

• Requires additional Plans and data to be submitted • Electric power supply system arrangements including

criteria for number and rating of power sources • Propulsion circuit and equipment protection

• Propulsion control • Propulsion equipment design, installation, and testing • Shipboard testing and Sea trials

Integrated Power Systems

• Additional plans and data and special reports • Basic requirements and terminology, Concept of

operations, IPS System control • Specifies a zonal distribution system. • Energy storage capability to meet platform survivability

and ride through and recovery requirements. • Generator sizing – number and rating of power sources;

additional sizing criteria for multiple mission profiles • Power Quality at system user interfaces, propulsion

bus, and generator/distribution bus • Installation, Testing, Shore power, Dark ship recovery,

Environmental, Survivability, Reliability and Maintainability, Safety, Grounding, Bonding, Shielding

• IPS Failure Modes and Effects Analysis required Comparison between commercial and naval rules Commercial and naval integrated power systems requirements differ mainly due to the level of redundancy and fault tolerance and survivability required for warships as opposed to commercial ships.

Naval Approach

The current naval approach utilizes an elaborate zonal distribution system with multiple independent power sources in multiple zones to ensure maximum survivability. The naval rules require four key characteristics to be met:

The number and complexity of distribution level connections

crossing construction boundaries are minimized Distribution levels are consistent with physical and electrical

boundaries and hence are consistent with modular ship construction

System Control is distributed among electrical zones equipment to enhance survivability.

Localization, isolation, reconfiguration, and recovery from faults are performed automatically.

While not strictly required to be considered an

integrated power systems, the current trend on naval IPS vessels is to utilize a zonal approach with a DC distribution system which distributes power to the various loads via converters within each zone. The zonal approach also prevents faults from affecting multiple zones by isolating the disturbance so it only affects the impacted zone. The zonal approach requires all loads within each zone to be powered from a source within the same zone. The zonal architecture reduces the number of longitudinal cable runs along the length of the vessel thereby reducing the number of penetrations through fire/flooding boundaries and this increases the survivability of the vessel. The only penetrations through the zones are the port and stbd DC buses which allow for power to be transferred from zone to zone. These buses are separated port and stbd and high and low to ensure maximum probability of survival in the event of battle damage. A typical IPS system zonal architecture is depicted in figures (1) and (2) as follows:

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Figure (1) – Comparison of Conventional System with Zonal System Shipwide

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Figure (2) – Comparison of Conventional System with Zonal System - Intrazonal

Essential services are supplied with redundant sources within the same zone and are arranged for automatic transfer between the 2 sources through auctioneering diode devices built into power conversion modules (PCMs) that act like bus transfer devices to automatically switch to the alternate source upon a loss of the normal source. Power conversions modules also provide for power conditioning throughout the distribution system also enable the system to maintain higher levels of power quality through the use of techniques such as active filtering. The auctioneering devices within the PCMs provide for seamless switching between

normal and alternate sources thereby ensuring a rapid transfer to the alternate source which prevents disturbances during switching events from affecting sensitive loads. Finally, the system is provided with intelligent autonomous zonal controllers that serve to provide automated power management and coordination of power flow between the zones as well as automatic fault recovery and system reconfiguration during failure scenarios. Figure (3) provides a high level block diagram of the typical military IPS architecture.

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Figure (3) Typical Naval IPS Architecture

Commercial Approach Commercial vessels with integrated electric propulsion typically take a much simpler radial distribution approach to system arrangements and do not employ nearly as many conversion devices. Usually all power sources are co-located and are connected to a single main switchboard which feeds propulsion loads as well as ship service loads. If ship service loads require a different voltage, then transformers or converter banks are usually provided between the propulsion bus and the ship service bus. A single dedicated self-contained emergency power source is required with its own separate switchboard to supply emergency loads. The emergency power source and its respective switchboard are required to be located away from the main machinery spaces and above the main deck to ensure its availability in the event of a machinery space fire or flooding. With respect to propulsion redundancy, typical commercial systems just need to meet some basic fault tolerance level such as at least two power sources sized to carry the at-sea load with one unit out of service and dual-excitation for electric propulsion, and redundant auxiliary services fed by opposite sides of the main

switchboard. Integrated electric propulsion system generating plants are required to have sufficient capacity to carry the vessel service load and supply propulsion power for at least 7 knots or ½ design speed (whichever is the lesser) with one generator out of service.

Where a redundancy notation is specified, the system must also survive a single major equipment failure to maintain ½ design speed or 7 knots (whichever is the lesser) within two minutes as dictated by the appropriate redundancy notation. Additional higher “S” notations require separation of major electric propulsion equipment to allow the system to survive loss of an entire space. With respect to control and automation, the rules for commercial based systems only address those systems directly related to electric propulsion and associated auxiliaries from a single centralized location such as an Engineer’s Operating Station (EOS) with remote bridge control. Figures (4) and (5) show typical example arrangements of commercial integrated electric drive systems.

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Figure (4) Basic Power Generation and Distribution System (on a modern merchant ship)

Emergency Generator

660V / 440 V

Transformer

440 Volts

660 Volts

440 Volts

660 Volts

440 Volts

Main Switch Board

Auxiliary Switch Board

Emergency Switch Board

Mot

ors

Figure (5) - The Power Plant Concept

The Power Plant Concept

Source: http://www.marine-electricity.com/Web%20Links/Papers/Seminar%20Paper.htm

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In some cases, the differences in way the systems are

designed are due to the inherent differences in the purpose of military and commercial vessels. Additionally, military and commercial vessel owner-operators have different motivations and priorities in the design objectives to be applied to the integrated power system design.

Differences in the Technical Requirements

During drafting of the NVR, ABS started with Navy

requirements and ABS Steel Vessel Requirements and drafted hybrid requirements in the following areas to support military requirements:

GENERAL SHIPBUILDING SPECIFICATION (G.S.S) REQUIREMENTS - Adopted selected parts of G.S.S. that were considered essential items for naval combatants. Examples: • Low-smoke, halogen free cable to meet MIL-DTL-

24643 for US Navy • Power quality to meet MIL-STD-1399, Section 300 • Automatic and manual transfer switches for essential

services • Casualty power system • Bumpless transfer between ship and shore power • Installation methods to meet DOD-STD-2003 GOVERNMENT STANDARDS - Adopted Military specifications and standards for various electrical equipment with provision to allow other recognized standards approved by the Naval Technical Authority. COTS EQUIPMENT CRITERIA - Special equipment design, installation, and testing requirements added for COTS switchboards, power panels, and circuit breakers.

SHIPBOARD TESTS – Greatly expanded requirements to include systems and equipment testing per GSS Section 095-300. HIGH VOLTAGE SYSTEMS – Added more detailed requirements based on comments received from NAVSEA . ELECTRIC PROPULSION – Adopted selected recommendations from IEEE Std 45 (2002) for equipment design, installation, testing. ZONAL DISTRIBTION SYSTEMS – Added definition and requirements for zonal distribution systems. INTEGRATED POWER SYSTEMS (IPS) – Added new section for IPS which was drafted from the Navy’s latest performance specification for integrated power systems. This spec included unique IPS generator plant sizing criteria and defined required system control functions. EMERGENCY POWER SOURCE - Replaced requirements to install a commercial style emergency power source with requirements for all essential services to be supplied by two independent sources of power. SHIP SURVIVIABILITY– Added new section and requirements for Ship Survivability adopted from NAVSEA Design Practices and Criteria Manual. PROTECTIVE DEVICE SETTINGS AND TYPES – Added detailed criteria for protective device settings and types.

The following table summarizes some of the major

differences between the military and commercial requirements for integrated power systems.

Table (2) – Comparison Table, Commercial and Military Integrated Power System Requirements

CRITERIA STEEL VESSEL RULES NAVAL VESSEL RULES

Number and Rating of Main Generators (General criteria)

The number and capacity of generating sets is to be sufficient under normal seagoing conditions with any one generator in reserve to carry those electrical loads for essential services and for minimum comfortable conditions of habitability.

The number and capacity of power sources shall be sufficient, under normal sea-going conditions with any one source in reserve and the other sources operating at no greater than 95% maximum capacity (when generators are operating in parallel), to carry those electrical loads for essential and non-essential services, critical mission loads, minimum comfortable conditions of habitability and additional electric margin as specified by the NTA.

Number and Rating of Main Generators (Electric Propulsion and IPS ships)

Generating Capacity - Requires integrated propulsion system generating plant to have sufficient capacity to carry vessel service load and supply propulsion power for at least 7 knots or ½ design speed (whichever is the lesser) with one generator out of service.

For any Naval vessel with Electric Propulsion: With the highest rated source out of service, the remaining propulsion power shall be sufficient to provide for a speed of not less than 7 knots or 1/2 of the design speed of the vessel, whichever is the greater, unless otherwise specified by the Naval Technical Authority. For combatant vessels with Integrated Power Systems: The overall generating plant capacity shall be based on either max speed powering requirement or sustained speed power requirement (as specified by the Naval Technical Authority) plus the maximum of either Condition I Battle or Condition III Cruise ship service electrical load and service life electrical load growth margin. The electric plant capacity shall also include design and build margins.

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CRITERIA STEEL VESSEL RULES NAVAL VESSEL RULES

Essential Services Essential Services are those considered necessary for: Continuous operation to maintain propulsion and steering (primary essential services); Non-continuous operation to maintain propulsion and steering and a minimum level of safety for the vessel’s navigation and systems including safety for dangerous cargoes to be carried (secondary essential services); and Emergency services as described in 4-8-2/5.5 (each service is either primary essential or secondary essential depending upon its nature).

i. navigation, propulsion and maneuvering of the vessel;

ii. essential services as described in 3-2-3/3.1; iii. maintaining a minimum level of safety, such

as providing for lighting, ventilation of propulsion machinery space, interior and radio communications, manually operated alarms, fire safety systems, bilge and ballast services, damage control systems;

iv. maintaining a minimum level of safety with regard to the cargoes carried,

v. critical mission services including all critical mission related systems, such as weapons systems, firefighting systems, and control and communication systems.

Number and Rating of Transformers/Converters

Where transformers and/or converters form a part of the vessel’s electrical system supplying essential services and services necessary for minimum comfortable conditions of habitability, as defined in 4-8-1/7.3.3 and 4-8-1/7.3.4, the number and capacity of the transformers and/or converters are to be such that, with any one transformer or converter, or any one single phase of a transformer out of service, the remaining transformers and/or converters or remaining phases of the transformer are capable of supplying power to these loads under normal seagoing conditions.

Detailed sizing criteria is provided, sizing depends on the application: Three phase power transformers (high voltage) used to supply 450 volt, 60 hertz, load center switchboards: (1) For load center switchboards supplying loads where determination of a specific demand factor is possible, the total load shall be based on the sum of each individual load multiplied by a demand factor. Additional criterion applies for load centers feeding complementary loads. Total is adjusted for service life load growth. (2) For load center switchboards supplying a diversity of loads of such character that determination of a reasonably accurate demand factor is not possible, the connected kW load, neglecting spare circuit breakers, shall be increased by the percent specified by the NAVSEA design manual criteria for on non fixed loads, for service life load growth, and multiplied by a demand factor.

Emergency Power Source

Requires independent self contained emergency power source for a limited list of emergency loads required for communications, steering, fire-fighting, dewatering, etc.

No emergency power source is required. All essential services are required to be supplied by two independent power sources.

Redundancy Notations (R1, R2, R1-S, R2-S)

Upon a single failure, capable of advancing the vessel at a speed of at least 1/2 its design speed or seven knots, whichever is less.

With one main generator (power source) out of service, propulsion may be at reduced power sufficient to provide for a speed of not less than 7 knots or 1/2 of the design speed, whichever is the greater.

Power Quality

Permanent Transient Frequency ±5% ±10% (5 s) Voltage +6% to −10% ±20% (1.5 s) The total harmonic distortion (THD) in the voltage waveform in the distribution systems is not to exceed 5% and any single order harmonics not to exceed 3%. Other higher values may be accepted provided the distribution equipment and consumers are designed to operate at the higher limits.

MIL-STD-1399, Section 300, Type I Power Quality – has more stringent criteria for voltage and frequency tolerances as follows: Permanent Transient Frequency ±3% ±4% (2 s) Voltage +5% ±16% (2 s) Also, mil spec has additional power system characteristics (i.e. harmonic distortion, unbalances, modulation) Note: NVR provides alternatives where a system cannot meet MIL-STD-1399 spec; (see special requirements clause for exceptions and the requirement for a power quality report to be submitted for NTA review where the electric power quality differs from that of MIL-STD-399, Section 300)

Transfer Switches

Only the vital automation systems for vessels classed ACC or ACCU Notation required to be provided with automatic transfer switches.

All essential services must be provided with automatic or manual transfer switches (depending on the nature of the load).

Grounding Allows both grounded and ungrounded distribution systems.

Electric distribution systems shall be ungrounded except as otherwise required (i.e. local limited grounding for special power, COTs equipment, electronics, isolated receptacles, high voltage systems)

Equipment and Cabling Standards

In general, electrical equipment is to be designed, constructed and tested to a national, international or other recognized standard and in accordance with requirements of this section.

Same requirement as SVR, however, some equipment is required to meet military specifications/standards; NTA must approve any alternative standards.

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CRITERIA STEEL VESSEL RULES NAVAL VESSEL RULES

Survivability None Maximum separation of the main generators and frequency conversion equipment. For essential loads:

• Two independent sources of power shall be provided from separate sources to the equipment.

• Support services to essential loads shall be supplied from the same power sources serving the essential load.

• Non-redundant distribution equipments shall be located adjacent to the equipment they serve and the connecting cables shall be kept to minimal length and run as directly as possible.

Separation of distribution systems such that: • Redundant distribution cable runs shall maintain

adequate separation, port and starboard plus minimum, where possible, two deck separation, throughout the entire cable run.

• Redundant user systems shall be supplied from two or more separate distribution systems to preclude loss of all capability with a single power loss

• Essential loads shall be isolated from non-essential loads to accommodate load shedding during an electrical system casualty

Distribution System Main and emergency distribution systems must be separated. Cabling to duplicated essential services (i.e. propulsion lube oil pumps, steering pumps) is required to be kept separate and fed from opposite sides of the main bus.

The zonal electrical distribution system will partition the ship into electrical zones. Each zone will receive power from two independent sources via the port and starboard cableways. Zones containing essential loads will have not less than two load centers separated to obtain the greatest survivability practicable.

Differences in the Review and Approval Process In addition to the differences in technical requirements for commercial and naval integrated power systems, there are also major differences in the design review and approval process. Mainly, the requirements differ in the quantity of plans and data required to be submitted, how often the drawings need to be submitted, and the time required for getting a design approved . The commercial approach is typically cost restricted and the systems developer and/or shipyard will proceed with detail design, get the design to a sufficiently mature point in the process, and submit the drawings for ABS review and approval. Typically, the drawings are sufficiently developed to allow all technical comments to be closed and final approval granted within 2 to 3 rounds of submittals. The naval rules require systems plans and data to be submitted to the Bureau and the Naval Technical Authority for approval at the completion of each of the following design phases: conceptual, feasibility, preliminary, contract, detail, delivery, and post construction (as-built). This results in the approval process being spread out over several phases versus a final review of ready to build drawings and ABS is much more involved at the earlier stages of design on military projects. With regards to the review time required, commercial projects typically do not employ as many unique features or developmental items as military projects, and the overall system architecture is much less complex. Accordingly, the design process timeline is much shorter because fewer special studies are required and the simplicity of the design does not require as extensive of a review. Finally, the military tends to make more changes as the design develops while commercial projects are fairly stable once a design has been approved in concept.

Rationale for the Differences

The main reasons for these differences between commercial and naval requirements in the area of integrated power systems are:

• A higher level of survivability required for naval

integrated power systems. • Military integrated power systems power plants must

support more operational scenarios and must be designed with more flexibility to allow many types of loading scenarios.

• Higher level of complexity of naval integrated power systems to provide for better fault tolerance, power quality, and faster switchover times to recover from failures.

• The need for the capability of autonomous distributed control which requires more interfaces and more integration and a higher level of automation in order to support automated zonal power management, multiple schemes of scenario based load shedding, and automatic fault recovery.

• Higher level of integration with other shipboard supporting systems

• Need to design for a longer life cycle and allow for modifications and upgrades since the Navy is more likely to upgrade or modify systems more frequently.

• Greater need for commonality and standardization across the fleet to support human performance, reduced manpower, reduced training, eliminate human error, and reduced maintenance.

• The use of developmental technology to support future electric warship weapons systems as opposed to off-

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the-shelf technology typically employed on standardized electric propulsion designs on merchant vessels

Other Recognized Standards for Integrated Power Systems and Power Electronics

In addition to class society rules, there also are several key standards in the areas of marine integrated power systems and power electronics. A summary of the scope of these additional standards is as follows: IEEE Standard 45 (2002), IEEE Recommended Practice for Electrical Installations on Shipboard, Clause 31. Electric propulsion and maneuvering system - provides recommendations covering general specifications, testing, installation, operation, and maintenance of electric propulsion systems. Although these recommendations relate specifically to the electric propulsion equipment, they also address mechanical equipment where required for the successful functioning of the entire system. It should be noted that the IEEE is in the process of updating this publication and will soon be coming out with a new release. IEEE Standard P-1662 - Guide for the Design and Application of Power Electronics in Electrical Power Systems on Ships - This standard applies to power electronics components and systems on ships and similar applications. It summarizes current electrical engineering methods and practices for applying power electronics in electrical power systems on ships and describes analytical methods, preferred parameters and performance characteristics from a common frame of reference for reliable integrated marine electrical power systems. It should be noted that this is a relatively new standard that is still going through the balloting process. IEC 60146 Series, Semiconductor converters - General requirements and line commutated converters - This International Standard specifies the requirements for the performance of all electronic power converters and electronic power switches using controllable and/or non-controllable electronic valves. The electronic valves mainly comprise semiconductor devices, i.e. diodes and various types of thyristors and transistors, such as reverse blocking or conducting thyristors, turnoff thyristors, triacs and power transistors. The devices may be controlled by means of current, voltage or light. Non-bistable devices are assumed to be operated in the switched mode. This standard is primarily intended to specify the requirements applicable to line commutated converters for conversion of a.c. power to d.c. power or vice versa. Parts of this standard are applicable also to other types of electronic power converters. It should be noted that this standard is currently invoked by both ABS Naval Vessel Rules and ABS Steel Vessel Rules as recognized standard for the design, construction, and testing of semi semiconductor converters. Future Challenges

One of the greatest challenges faced by a classification society is to be able to look far enough ahead in areas of rapidly changing technology in order to ensure that appropriate criteria are in place to support introduction of that new technology into the world’s fleets while maintaining the safety of the vessels. The expanding application of electronic and electrical systems in ships and offshore structures has been a continuing focal point for ABS rule development over the last several decades.

The advances in power electronics and networking have opened new opportunities to optimize ship designs. The application of integrated power systems to ships both in the commercial and military arenas allows for better use of installed horsepower and increased flexibility in ship arrangements. In these uncertain times of fuel costs, the integrated electric plant also offers the potential for reducing operating costs by taking advantage of large engines operating at their optimum fuel rates.

As mentioned earlier, the primary concerns of the regulatory bodies and the classification process is the safety of personnel and navigational safety. This focuses the rules mainly on propulsion and steering which in a conventional ship were separate from the electric plant. Even cases of electric propulsion, the design and equipment have been addressed as a separate system. The integrated power system challenges societies such as ABS to blend our rule requirements in order to maintain the same confidence levels in the safety of the overall ship design.

The implementation of integrated power systems varies significantly between the typical commercial application and newer military applications. These differences are directly related to the survivability requirements of the ships. For commercial applications the focus is on surviving equipment failures while maintaining safety of the crew and safety of navigation. The military requirements for survivability go far beyond the commercial concerns as for a military combatant the ship must survive significant physical damage and still maintain is ability to perform its mission, i.e to fight. To achieve this higher level of survivability the more complex aspects of the DC zonal distribution system are justified. However, the added complexity introduces many challenges to regulatory bodies and classification societies to adapt proven design concepts to the new system architectures without over specifying the design.

For example, power conversion devices in the commercial world are normally part of a single user system and are treated as part of that system in terms of essentiality to the ship. But many of the power conversion devices in the military zonal distribution architecture are primary to the source of electrical power for the ship and as such need to be addressed more as sources than as loads in terms of reliability and design. But to apply the full distribution requirements individually to each zone of a zonal distribution system will lead to over design of the ship. One of the challenges for rule development is how much of the complexity of the typical zonal distribution system needs to be required for classification. The current Naval Vessel Rules have incorporated ALL of the design features of the DC zonal architecture. However, as they are applied to such programs as the DDG-1000, there are several areas that client feedback has demonstrated that the NVR is overly restrictive. ABS has instituted a feedback process of Justification and Technical Determination (JTD) documentation to address these concerns both from the individual project aspect and also to impact the continuing rule development process for the NVR.

Another example is in the area of network controls and the use of networks to replace many previously stand alone systems. Where commercial rules require segregation of monitoring and control from safety protection systems, new ship designs are using the concept of Total Ship Computing Environment (TSCI) to provide a robust network that is capable of supporting many of these functions using essentially the same hardware but in a manner that maintains the survivability of the older stand alone systems. The challenge of such network solutions from a classification

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perspective is how to assure the capabilities of the network under fault conditions. Due to the pervasive use of networks and subnetworks for control and monitoring and protection (safety systems), the challenge is to determine how far down in the scheme do the reliability and redundancy rule requirements need to reach. At the lower levels the software implementation is a proprietary item critical to a vendor maintaining their competitive advantage in the marketplace. Rule requirements for full disclosure of the details of this software to assure reliability can become major issues in the overall ship design. Potential Areas for Further Rule Development

Based on recent client feedback and lessons learned from applying the rules on various commercial and government electric ship projects, the following topics have been identified as possible areas for future rule development:

Power Electronics Equipment Standards – Marine criteria is provided in IEC 60146 and the new IEEE P-1662. Other industries such as railway, utility companies, and industrial drives have much more experience in this area than the marine industry. ABS needs to leverage off these industries and adopt appropriate best practices for marine power electronics equipment while maintaining the required degree of safety. Sizing criteria for Converters and Transformers - Current legacy DOD design data sheets that use traditional load factor methodology for estimating loads may result in enormously over sized converters on a vessel where the converters form an integral part of the distribution system. There is a need to adopt more intelligent methods (such as stochastic estimation principles2) for estimating loads to ensure proper sizing of distribution converters so the system can service the load efficiently in all operating modes. Medium Voltage Direct Current Distribution (MVDC) Systems– Similar to power electronics, this is another new area for the marine industry. MVDC has not been used extensively on ships. Need to leverage lessons learned from other industries and draft better requirements to address special concerns. Implementation of new Rules for Software quality assurance and testing: As these requirements are fairly new to classification societies, the marine industry may require specialized training to ensure compliance with the new criteria. While US Navy has an established industry support contractor infrastructure and organization to perform software certification, class societies may need some time to reach an equivalent level. Superconductors, Fuel Cells, Permanent Magnet Motors - New rules and requirements need to be drafted to ensure that these advanced technologies are implemented safely where intended for marine service. The marine environment requires special considerations and where these technologies form part of an essential system for propulsion, safety and reliability will have to be carefully assessed as the technology is unproven in marine applications. Zonal Systems Architecture and Integrated Fight Through Power (IFTP) – For naval vessels, lessons learned from DDG-1000 has shown that the requirements for zonal

2 Electric Ship Technologies Symposium, 2007. ESTS apos;07. IEEE Volume , Issue , 21-23 May 2007

systems need to be stand alone from the criteria specified for Integrated Power Systems to avoid confusion. IPS criteria for electric propulsion will be separated from the criteria for zonal distribution. Additionally, the rules for Integrated Fight Through Power (IFTP) type system architecture need to be drafted to address key requirements to allow the vessel’s electrical systems to withstand battle damage and continue operating in order to enable the vessel to fight through a casualty and continue to perform critical missions. Application of Redundancy Notations to Electric Propulsion Vessels – It has been suggested that more guidance should be provided on the requirements for how to apply the redundancy notations on vessels with integrated electric drive. The IEEE Std 45 Handbook offers specific guidance in this area. More examples and illustrations could be added to the rules to clarify how the rules apply to the unique approaches that can be taken on integrated electric drive systems such as tandem rotor arrangements or azimuthing motor driven thrusters and pods. Specific proposed rules for tandem rotor arrangements include adding criteria for: (a) Each set of windings must be adequately protected from short circuit in order to limit the fault energy level and duration such that the fault is limited and interrupted in time to prevent a short circuit in one set of windings from having an incapacitating effect on the other. (b) Each set of windings must be electrically and physically segregated such that a fire or short circuit in one set of windings will not have an incapacitating effect on the other. (c) A failure of one set of windings will not result in propulsion performance inferior to that required by 7.1 or 7.2, as applicable. (d) A single failure in the primary (master) motor drive control system will result in automatic changeover to the secondary (slave) motor drive control system. (e) The winding insulation is "self-extinguishing" and will not support a flame after removal of the source of heat. Sizing Of Auxiliary Cooling Fans/Blowers Inside Electric Propulsion Equipment – There is a need to clarify criteria for required size and quantity of auxiliary cooling fans/blowers on electric propulsion equipment such as transformers, converters, and drives. The redundancy notations require maintaining full propulsion upon failure of propulsion auxiliary equipment such as cooling water pumps, lube oil pumps, or fuel oil pumps. This requirement drives designers to design propulsion auxiliary systems with a sufficient number and rating of standby units to support full propulsion upon loss of one auxiliary piece of equipment. However, in many drive and transformer designs, all of the internal cooling fans or blowers are required to achieve rated power (typically there are no standby fans or blowers). Not being able to make full power after a loss of auxiliary equipment does not meet the intent of the redundancy notations and this should be accounted for in the design of the propulsion drives or transformers on vessels with R1 or R2 notations. Continuity of Power (30 second criteria for ship service power restoration): The ABS Steel Vessel Rules and USCG regulations should be clarified with regards to the criteria for restoration of main power during single generator operations. Currently the rules require main (ship service) power to be restored within 30-45 upon loss of a single

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generator (the standby ship service generator is required to automatically restore power to the main bus in 30-45 seconds). This requirement is not difficult to achieve on a vessel with conventional direct diesel or gas turbine propulsion where the ship service generator sets are typically not very large and can be safely automatically started and connected within the specified time period of 30-45 seconds. However, for integrated electric drive plants, where larger generator sets are required (usually a few megawatts) in order to supply both propulsion power and ship service power, this requirement becomes a challenge because most large diesel or gas turbine engines cannot be safely automatically started, connected the bus, and loaded with 30-45 seconds. Additionally, the rules and USCG regulations are not explicit in terms of how much propulsion power needs to be available within 30-45 seconds. The criteria should be quantified to specify precisely how much propulsion power needs to be available in 30-45 seconds. It is not clear if the intent was to just restore ship service power for propulsion auxiliaries or is the intent to restore sufficient propulsion power as required to make a minimum speed (i.e. 7 knots). This requirement applies an unfair penalty on designers of integrated electric drive vessels as there are no rules or regulations imposed on conventional propulsion plants to restore propulsion power to any specified level within 30-45 seconds. Conclusions:

While much headway has been made in the area of

rules and requirements for integrated electric propulsion, there are several potential areas for improvement to be made. Due to emerging technologies in the areas of power electronics, computer based systems, and networks, maintaining rules and requirements that address the adaptation of modern technologies are a major challenge to the regulatory bodies and class societies.

As part of the overall effort to create the Naval Rules,

ABS has gained much knowledge from the Navy in terms of the specialized requirements that are needed to address the unique needs on integrated electric warships such as the widespread use of converters as part of a DC zonal distribution scheme and distributed control versus centralized control. Much collaboration has occurred as part of the overall effort to improve these rules. Further work is needed to address lessons learned from recent naval shipbuilding programs and achieve the goals of the Navy to codify the requirements for future naval surface combatants. The Navy, USCG, ABS, and industry need to continue to work on improving and establishing new rules and requirements for both commercial and military integrated electric propulsion systems.

Several forums currently exist to support these efforts

including the annual ABS rules update process, ABS industry panels, IEEE standards committees, ASNE and SNAME technical symposiums, and the newly formed National Shipbuilding Research Program (NSRP) Electrical Technologies Panel. The current issues addressed in this paper should be prioritized in terms of impact and significance and proposed changes to the rules to resolve these issues should be drafted and submitted on a periodic annual basis to continually improve the requirements for integrated electric propulsion systems.

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