What is a Shaft Generator? Automatic Control of the Shaft Generators

When the order is issued for the main engine to operate at a constant speed corresponding to the correct frequency, and if the load on the distribution network is not in excess of the maximum permissible load on the shaft generator, and if no alarm is operative on the shaft generator, this combination of conditions is indicated on the control panel by the "shaft generator ready" lamp lighting up.

The generator then rotates at the correct speed although without excitation, i. e. it generates no voltage.

If the change-over switch on the control panel is set to the "shaft generator on" position the generator will be excited and will generate a voltage. When about 85% of the normal voltage is attained, control of excitation shaft generator will be taken over by the voltage regulator in the switchgear.

The diesel-driven generator or generators supplying the distribution network are then synchronized to the shaft generator by the synchronizing unit in the shaft generator unit. When the generators are running in synchronism, the shaft generator breaker will receive a closure signal from the automatic control equipment.

What is a Shaft Generator?

Shaft generators are devices used on ships to produce electrical power. They are typically mounted on the main propulsion shaft of a vessel and convert mechanical energy from the rotating shaft into electrical energy. Here's an overview of how they work and their benefits:

How Shaft Generators Work

1. Connection to Propulsion Shaft:

   • Shaft generators are mechanically connected to the main propulsion shaft. As the ship's engine drives the propulsion shaft to turn the propeller, it also drives the shaft generator.

2. Energy Conversion:

   • The mechanical energy from the rotating shaft is converted into electrical energy by the generator. This process is similar to how traditional generators work, where a rotating magnet (rotor) inside a coil of wire (stator) induces an electrical current.

3. Power Distribution:

   • The electrical power generated is then distributed to the ship’s electrical grid, supplying power to various systems on board, including lighting, navigation equipment, and other electrical devices.

Benefits of Shaft Generators

1. Fuel Efficiency:

   • Shaft generators help improve overall fuel efficiency by reducing the need to run auxiliary diesel generators while the ship is sailing, as the main engine provides the necessary power to both propel the ship and generate electricity.

2. Reduced Emissions:

   • Using shaft generators can lead to lower emissions since they reduce the reliance on auxiliary engines, which typically run on diesel fuel.

3. Operational Cost Savings:

   • By generating power from the main engine, the operational costs can be reduced due to less fuel consumption and maintenance requirements compared to running separate auxiliary generators.

4. Space and Weight Savings:

   • Integrating a shaft generator system can save space and reduce the overall weight of the vessel since it minimizes the need for additional power generation equipment.

5. Reliability and Redundancy:

   • Shaft generators provide an additional source of power, enhancing the redundancy and reliability of the ship's electrical supply system.

Types of Shaft Generators

• Direct Drive Shaft Generators:

  • These are directly connected to the propulsion shaft and operate at the same speed as the shaft.

• Gear-Driven Shaft Generators:

  • These use a gearbox to adjust the rotational speed, allowing the generator to operate at a different speed than the propulsion shaft, which can be beneficial for optimizing generator performance.

• Variable Speed Shaft Generators:

  • These are designed to operate efficiently at varying speeds, often using power electronics to manage the frequency and voltage of the generated electricity.

Applications

• Commercial Ships:

  • Shaft generators are commonly used in commercial vessels such as cargo ships, tankers, and container ships, where energy efficiency and cost savings are crucial.

• Naval Vessels:

  • They are also employed in naval ships to ensure a reliable and efficient power supply for critical systems.

Shaft generators play a vital role in modern maritime operations by enhancing energy efficiency, reducing operational costs, and supporting environmental sustainability.

When the shaft generator is in service and no alarm is operative, a shut-down signal will be applied to all diesel-driven generators. These generators will be unloaded, and the circuit breakers will then trip the generators from the distribution network. The diesel engines will then be stopped.

A synchronizing alarm will be initiated if the shaft generator is not synchronized to the network within about one minute. Other alarms in the equipment indicate high voltage, high frequency, low voltage and low frequency.

All alarms can be delayed by an adjustable period ranging between 1 second and 60 seconds. If a shaft generator alarm should become operative the number of diesel-driven units necessary to replace the shaft generator will then be started immediately and will be synchronized to the network. When a sufficient number of diesel-driven units are in service, the shaft generator will be unloaded and its circuit breaker will be tripped.

If no diesel-driven unit is synchronized to the network after an adjustable time delay, the shaft generator breaker will trip and black out will occur. The time delay for tripping the shaft generator circuit breaker can be set at any value between about 1 second and 60 seconds. The black out will last only about 1 second, since the necessary number of diesel-driven units are already in service, although not synchronized to the network.

In automatic electrical power plants using shaft generator additional shaft generator control unit is installed for automatic change over of the power supply between the shaft generator and the diesel-driven generators.

The shaft generator unit provides the following functions:

1. Excitation of the shaft generator.
2. Synchronization to the distribution network and closure of the circuit breaker.
3. Unloading and shutting-down of the diesel-driven generators operating in parallel
4. In the event of an alarm on the shaft generator, changing over from this generator to the stand-by generators.
5. Switching a diesel-driven generator onto the distribution network and unloading of the shaft generator when "Shaft generator off" is requested.
6. Field suppression on the shaft generator after tripping.