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Practical Marine Electrical Knowledge: Program 8. Electric Propulsion & High Voltage Practice
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Practical Marine Electrical Knowledge: Program 8. Electric Propulsion & High Voltage Practice

Recent Advances in Electric Propulsion and Safety

Overview of Electric Propulsion in Modern Shipping

  • The program discusses recent advancements in electric propulsion, emphasizing the importance of understanding electrical systems upon joining a ship.
  • Diesel-electric propulsion is currently predominant, with gas turbine-electric likely to gain popularity in the future, especially for cruise liners.

Power Requirements on Modern Ships

  • Modern ships require substantial electric power not just for propulsion but also for hotel services like air conditioning, lifts, and telecommunications.
  • A modern cruise liner may need over 40 megawatts of power compared to the average ship's requirement of 1 to 3 megawatts.

High Voltage Generation and Safety Procedures

  • Power generation typically occurs at 6.6 kilovolts, stepping down to lower voltages for auxiliary services; some vessels operate at 11 kilovolts.
  • Rigorous safety procedures are essential when working with high voltage circuits; documentation must be meticulously filled out and countersigned.

Permit to Work Process

  • The Chief Electric Technical Officer (Seto) must complete a permit to work order before conducting insulation tests on high voltage circuits.
  • An electrical isolation certificate is issued detailing where circuits will be isolated and locked off; keys are secured in a lockout box.

Isolation and Testing Procedures

  • Circuit breakers are isolated by switching them to test positions and confirming they are dead using high voltage test prods.
  • Portable earth leads are connected for operator safety during testing; insulation resistance tests measure between phases and earth connections.

Finalizing Maintenance Tasks

  • After completing all tests listed on the permit, additional earth leads are removed, panel doors locked, and warning signs taken down.

Power Management Systems in Marine Propulsion

Overview of Power Types and Management

  • Various types of power systems are utilized in marine propulsion, including air type, SF6 gas field type, and vacuum interrupter type.
  • A Power Management System (PMS) is essential for controlling the distribution of power to meet varying demands efficiently and safely.

Load Management and Automation

  • The PMS can limit propulsion load to ensure full power availability for hotel services; it sequences generators evenly for optimal fuel economy.
  • Control during startup is managed from the Engine Control Room (ECR), with transfer capabilities to the bridge for navigation commands.

Synchronization Techniques

  • Synchro phasing of propellers minimizes hull vibration, particularly important for cruise ships; requires propeller shaft speeds within 5 RPM.
  • This synchronization technique is not employed in heavy seas due to potential speed fluctuations when propellers emerge from water.

Electric Marine Propulsion Benefits

  • Electric propulsion allows diesel engines driving AC generators to be arranged flexibly, saving space while optimizing fuel economy by sequencing operations.
  • Most marine propulsion motors are AC; configurations may include induction motors linked to controllable pitch propellers or DC motor drives in specialized vessels.

Variable Speed Drive Technology

  • Modern developments include variable speed drive technology using static converters that provide variable frequency AC to synchronous motors.
  • Safety measures like interlocking key systems ensure proper grounding before accessing high-voltage areas; permits and isolation certificates are mandatory.

Converter Operations and Efficiency

  • Propulsion transformers step down voltage from 6.6 kV mains to 3 kW; converters transform fixed frequency input into variable frequency output.
  • Thyristors are used in converters, allowing controlled current flow but requiring specific conditions for operation; they generate heat that must be dissipated effectively.

Advanced Converter Technologies

  • Frequency converters can switch between AC/DC/AC or AC/AC modes, utilizing a three-phase synchro converter design for efficient energy management.
  • Computers control each converter per propulsion motor, ensuring smooth operation with redundancy through multiple computers tracking normal operations.

Synchronous Motor Functionality

Understanding Synchronous Motors and Their Control

Basics of Synchronous Motor Operation

  • The speed of a synchronous motor is calculated using the formula: n = F times 60/P , where:
  • n = revolutions per minute (RPM)
  • F = frequency of three-phase supply currents to the stator
  • P = pairs of poles in the stator winding, equal to rotor poles.
  • The variable frequency from the converter directly controls rotor shaft speed. Required torque ( T ) is proportional to both magnetic flux ( Φ ) and stator current ( I ).

Direction Control and Motor Configuration

  • To reverse shaft rotation, the propulsion computer stops forward speed and switches converter thyristors into a reversed sequence.
  • Propulsion motors feature two separate three-phase stator windings positioned 30 degrees apart, creating a 12-pulse torque that minimizes shaft vibration.

Emergency Operations and Power Management

  • In emergencies, it’s possible to operate as a half motor with reduced power output; however, this increases vibration and voltage harmonic disturbances.
  • A synchronous motor generates internal back EMF which assists in commutation at normal speeds but becomes ineffective at low speeds (10% or less).

Low-Speed Operation Challenges

  • At low speeds, thyristors on the network bridge are switched off briefly to regain control. Discrete current pulses are applied to maintain rotation direction.
  • Current switching converters introduce voltage disturbance harmonics into the main supply network, potentially causing malfunctions or overheating in other circuits.

Harmonic Disturbances and Safety Procedures

  • Harmonics can be observed as spikes on AC supply voltage waveforms when running without harmonic filters due to faults.
  • Strict safety procedures must be followed for fault investigation in high-voltage areas, requiring multiple approvals before work begins.

Maintenance Protocol for Electrical Systems

  • Maintenance involves disconnecting breakers and applying temporary earth connections for safe discharge of harmonic capacitors before testing them.
  • Capacitor readings should meet expected tolerances; deviations indicate potential issues needing resolution for optimal waveform performance.

Additional Electrical Systems Overview

  • Besides high-voltage systems (6.6 kV), there are also circuits operating at lower voltages (440 V and 220 V), necessitating special protection relays.
  • Periodic maintenance testing by outside contractors ensures accuracy of electrical circuit equipment through calibrated tests during major refits.

Advanced Testing Techniques

  • Testing includes verifying vacuum interrupter circuit breakers under high voltage conditions to ensure insulation integrity against arcing during operation.

Introduction of Special Observation Ports

Enhancements in Safety and Monitoring

  • The introduction of special observation ports at the back of high-voltage cabinets allows for thermal observation without compromising safety.
  • A digital stills camera is utilized to provide a standard visual reference, ensuring comprehensive documentation.
  • Both types of images (thermal and standard) are incorporated into the contractor's report, enhancing clarity and accountability.

Electrical Propulsion in Ships

Understanding High Voltage Power Generation

  • Recognition of the growing application of electrical propulsion for ships highlights its importance in modern maritime technology.
  • Large power requirements necessitate high voltage power generation, emphasizing rigorous safety procedures associated with high voltage (HV).

Electric Propulsion Technology Overview

Key Components and Operations

  • Electric propulsion technology relies on thyristors within computer-controlled frequency converters for efficient operation.
  • The operation and control action of synchronous motors are reviewed, showcasing their role in electric propulsion systems.
  • Pulsed mode operation is essential at low running speeds, indicating specific operational requirements for effective performance.

Fault-Finding Procedures and Testing Techniques

Ensuring Reliability in Electrical Systems

  • A fault-finding procedure was followed to locate issues within a high voltage harmonic filter, demonstrating systematic troubleshooting methods.
  • Testing techniques for protection relays were examined to ensure reliability and safety in electrical systems.

Conclusion and Further Learning Resources

Recommendations for Continued Study

  • Viewers are encouraged to watch the program again for better understanding and retention of complex topics discussed.
Playlists: Practical Marine Electrical Knowledge
Video description

This is Program 8 of VIDEOTEL series on Practical Marine Electrical Knowledge. Designed to assist sea-going personnel in their understanding of the safe operation, testing and maintenance of ships electrical equipment and services. Examines practical electrical maintenance and fault-finding procedures on board various ship types. The series is made up of 8 programs. This program highlights recent advances of electric propulsion together with high voltage operation, safety and testing. There are many system variations around. So, it's most important that you become familiar with the components of the electrical system and the layout of the main switchboard immediately you join a ship. Pay attention to the layout of the emergency switchboard. This study will pay dividends during a blackout or when troubleshooting in cause of major breakdown. Electric Propulsion & High Voltage Practice Electrical Safety Golden Rule is: Before any work is done on the electrical installation, first, isolate the circuit by removing the supply fuses or locking the circuit-breaker in the open position. So, then the circuit cannot be energized accidentally. Then, post a warning sign to alert others that the circuit is being worked down. Then prove the circuit dead with voltmeter or approved line tester. ______________________________ This video series explains a ship's electrical system, including its generation plant, switchboards and distribution network. Electrical safety and safe working practice are stressed throughout with the significance of circuit faults and the various forms of protective switchgear. Based on book "Practical Marine Electrical Knowledge" which covers every aspect of a ships electrical system and includes correct operation, safety, testing, UMS requirements and standards for Classification Society Surveys. ______________________________ Timeline of Program 8. Electric Propulsion & High Voltage Practice: 00:00 Video Intro 00:42 Content 00:51 Introduction 01:12 Use of electric motors for propulsion 01:30 Power on cruise ships 01:57 Central power station 02:13 Average ship requirements 02:18 Modern cruise ship requirement 02:25 High voltage power generation 02:52 High voltage operation safety procedures 3:00 Documentation to fill out 3:40 Electrical Isolation Certificate 3:55 Warning sign before starting the electrical job 4:18 Safety precautions 4:24 Circuit-breaker removal 4:40 Using high voltage test prod 5:19 Safety requirements 5:35 Circuit-breaker installing back 5:49 Completion of Electrical Isolation Certificate 6:00 HV equipment to test 6:40 HV equipment isolation test 7:06 Circuit-breaker earth 7:47 After all tests 8:29 Power generation 8:34 Woodward electronic governor 8:47 Main 6.6 kV switchboard 9:15 Type of circuit-breakers 9:25 AVR, synchronizing panel, excitation control unit 9:39 Power management system 10:17 Main use of generating power 10:23 Ship’s propulsion control 10:56 Synchrophasing of propellers 11:33 Main benefit of electric propulsion 12:03 On the non-driving end 12:22 Marine propulsion motors 12:57 Static converters 13:08 Interlocking 13:34 Propulsion step-down transformers 13:59 Converter 14:20 Thyristors 15:40 Cooling 15:57 Frequency converter types 16:11 Three-phase synchro converter 16:57 Computer 17:32 Rotor magnetic poles 17:44 Speed of rotation 18:09 Variable frequency 18:15 Torque 18:28 Direction 18:49 Stator windings 19:02 In an emergency 19:19 Field 19:35 DC field current 19:52 Exciter AC supply 20:12 At normal speed 20:25 At very low shaft speed 20:47 At low speed 20:57 Need of encoders 21:17 Use of current switching converters 21:56 Harmonics 22:10 Harmonic filters 22:24 Permit-to-Work 22:59 Firstly – Safety Notice 23:21 Releases 23:51 In the filter room 24:01 Test of capacitors 24:24 Main and auxiliary power 24:53 Special protection relays 25:13 Calibrated test equipment 25:38 Testing of vacuum interrupted circuit-breaker 26:02 Check for local hot spots 26:27 Thermal observation 26:41 Report 26:52 Conclusion ______________________________________ Made by VIDEOTEL 1999 archive #marine #electrical knowledge