A hybrid system enables ships with variable power requirements to run at high propeller efficiency.
Hybrid Propulsion is simply the use of two (or more) different power sources to run the propellers.
Traditionally the majority of commercial vessels are equipped with either diesel engines or electric motors for running of the propellers. By combining these two power sources in one system we get a hybrid propulsion system. Additional energy carriers could be battery packs, gas engines, permanent magnet motors, or others.
The system configurations may vary from simple single screw systems to complex configurations with a large number of operational modes available. A hybrid propulsion system enables engines and propellers to run optimally over a wide power range.
The hybrid propulsion systems benefit of the best from two systems; the combination of electric propulsion and diesel drive.
A hybrid propulsion system based on one diesel engine and one frequency controlled electric motor is a simple and efficient solution. Combining a battery pack to the configuration will further increase the system flexibility and the ability to optimise the energy consumption during operation.
By using a Brunvoll gearbox with multiple PTO/PTI options, or a twin-in singel-out gearbox there are multiple possibilities to build the optimum system satisfying the right power requirement for the specific vessel.
All Brunvoll Hybrid Propulsion Systems are tailor made for the operation profile of the specific vessel, with any power source whether it is diesel, electric, battery or gas.
A Hybrid Propulsion system allows for the highest energy efficiency provided the right power sources are selected to serve the range of operational conditions from lying idle in port to the need for full power in heavy operations at sea.
A Brunvoll Hybrid Propulsion system consisting of two CP-Propellers driven by a "father and son" main engine combination at each of the twin-in single-out gearboxes, in addition to one combined generator/electric motor at each gearbox for PTO/PTI functionality. Such a system allows for numerous operation modes and efficient operation.
By adding batteries to the hybrid propulsion system the configuration can be designed for further profit from reduced fuel consumption, reduced running hours at the main engine and thereby reduced maintenance, higher redundancy, need for less power in the gen.sets, smoother operation of the gen.sets or main engine by using the batteries for peak shaving.
The Direct On-Line (DOL) starter consists of a contactor and a protection device such as a circuit breaker. The contactor is energized when the start button is pressed, and the full line voltage is connected to the motor. Motor is started with propeller in zero pitch position (IZP).
The star-delta starter method applies reduced voltage to the motor, thus reducing current, during startup. This method requires that both ends of motor winding terminals are available. When connected in star each winding has less voltage (1 / √3 ~ 60%), and thus will have reduced starting current and torque. When full speed is reached the motor is connected in delta, having full torque available. Propeller pitch can be increased, and load applied when motor is connected in delta. Motor is started with propeller in zero pitch position (IZP).
Auto-Transformer also applies reduced voltage in steps to the motor during startup. The transformer voltage ratio can be designed to the application, typically having a 50-70% motor voltage during startup. The motor consumes less current at a lower starting voltage. For example, with a 50% tap on the Auto-Transformer, the motor draws half its rated current, or about 25% of what it would draw with a DOL starter. Motor is started with propeller in zero pitch position (IZP).
An electronic soft starter is a starting device that controls the way electricity is provided to the motor by using active switching devices such as thyristors. The device works in both in-line and in-delta configuration modes in three-phase motors.
This starting method is ramping up the motor voltage in the starting sequence resulting in a reduced start-up current, allowing for a smooth and surge-free increase in motor torque. The voltage dips, stress, and wear and tear on the mechanical parts are all reduced as a result. Due to the thyristors there will be harmonic distortion of the current, and the influence on system voltage will depend on starting current and system impedance. Motor is started with propeller in zero pitch position (IZP).
This is an electronic-controlled approach for starting asynchronous motors smoothly. It controls the frequency and current for the motor with electronics inverter circuits, avoiding large startup current. The thruster system's mechanical parts will be protected from high load because of the smooth start-up, and the this will also reduce the load on generators during startup compared to line-starter options. Depending on required performance torque and current may be below nominal values during startup. This is the high-end solution for the starting the thrusters, giving benefits such as smooth start, better energy economy, reduced wear and tear and process optimization. Other benefits include motor speed stability during load changes and a longer motor life overall. Motor is started with propeller in zero pitch position (IZP).
Frequency converter starters may have different interface towards the main switchboard where 6-pulse rectifier is the most common, but both 12/24 pulse and Active Frontend (AFE) are used.6-pulse starters are the most common type, widely used due to the compact design and availability.The disadvantage with the 6-pulse starter is the increased THD during startup, particularly in smaller power system with large thrusters this might be an issue.
To mitigate the THD a 12 or 24 pulse transformer and rectifier may be chosen, typically used for larger thrusters in larger ships.
Frequency converter starters with active front end guarantees sinusoidal current and does not require a transformer. The AFE rectifier and LCL filter is more spacious than the 6-pulse rectifier and is suitable for high end solutions and ships with relatively small power system compared to thruster power.
Energy efficiency depends on a range of parameters from hull resistance, desired speed, power setup with fuel type, engine type and corresponding fuel diagram, configuration of the propulsion lines and systems, hydrodynamic conditions and operation profile, to name some of them.
Hybrid propulsion systems varies from simple systems with a few operation modes to the more sophisticated and complex systems with numerous running modes for a wide range of operations.
Any vessel with varying working conditions require flexible solutions in order to execute all tasks in the most efficient way.
Analyse the yearly operation profile of the vessel by how many days in the different conditions.
Evaluate the requirement for energy sources for the different tasks and design your system according to the ship’s actual service profile.
Brunvoll propellers are all designed to fit the specific vessel. Brunvoll bases its hydrodynamic expertise in propeller design on calculation methods of the latest hydrodynamic theories and tank test results.
In a CP-propulsion system reducing zero pitch loss is essential, which means to use minimum of energy just to rotate the propellers without giving thrust to the vessel.
Selected Brunvoll references
Brunvoll CP-Propulsion System including Integrated Costa Propulsion (ICP), Rim Driven Thruster (RDT), Tunnel Thrusters and Control System
Brunvoll CP-Propulsion System with nozzle, rudder and steering gear, Tunnel Thruster and Control System
Brunvoll CP-Propulsion System, Tunnel Thrusters, Retractable Azimuth Thrusters and Control System