Definition and Function

The shaft grounding device is an important safety equipment in the ship shaft system, mainly used to safely introduce the accumulated electrostatic charges on the shaft system into the earth (for ships, it is the hull), and prevent the harm caused by static electricity accumulation. At the same time, it can also reduce the electrochemical corrosion of the shaft system. During the operation of a ship, due to various factors such as friction and liquid flow, the shaft system is prone to static electricity. If this static electricity is not released in a timely manner, it may cause dangerous situations such as fires and explosions.

Structural composition

Grounding brush component:

This is the core part of the shaft grounding device. Grounding brushes are usually made of materials with good conductivity and wear resistance, such as graphite, and their shapes are generally block shaped or brush shaped. The electric brush is in close contact with the surface of the shaft system, and the elastic deformation of the electric brush ensures a good electrical connection with the shaft system, thereby conducting static electricity on the shaft system. The electric brush is installed on the brush holder, which can fix the position of the electric brush and ensure that the electric brush can continuously and stably contact during the rotation of the shaft system.

Grounding cable:

The grounding cable is used to connect the grounding brush and the grounding point of the ship's hull. The material of cables is generally copper or other conductive materials, and their cross-sectional area should be determined based on factors such as the size of the electrostatic current that may be generated by the shaft system to ensure safe and rapid introduction of static electricity into the ship's hull. The two ends of the cable are firmly connected to the grounding brush and the grounding point of the ship, usually through reliable methods such as welding, crimping, or bolt connection.

Insulation monitoring components (optional):

In some complex shaft grounding devices, insulation monitoring components are also equipped. It is mainly used to monitor the insulation status between the shaft system and the hull. When the insulation resistance is lower than the set value, an alarm is issued to remind the crew to check whether the grounding device is working properly. Insulation monitoring components usually include insulation resistance monitoring devices, which determine the insulation condition by measuring the resistance between the shaft system and the hull.

working principle

When static electricity is generated during the operation of the shaft system, the electrostatic charges will be distributed on the surface of the shaft system. Due to the close contact between the grounding brush and the shaft system, and the good conductivity of the brush, electrostatic charges will be conducted to the grounding cable through the brush. Grounding cables transport electrostatic charges to the hull, which acts as a massive conductor to safely release static electricity into surrounding media such as seawater. If there is an insulation monitoring component, it will monitor the insulation resistance between the shaft system and the hull in real time. When the insulation resistance decreases due to some reasons (such as brush wear, cable damage, etc.), the monitoring component will send a signal to indicate the possibility of poor grounding.

advantage

Effective electrostatic protection: The shaft grounding device can promptly guide the static electricity generated on the shaft to the ground, avoiding the accumulation of static electricity and effectively preventing dangerous events such as fires and explosions caused by static electricity, ensuring the safety of the ship. Especially for ships transporting flammable and explosive goods (such as oil tankers transporting petroleum), the electrostatic protection function of the shaft grounding device is crucial.

Reduce electrochemical corrosion: By grounding the shaft system, the potential difference between the shaft system and the surrounding medium (such as seawater) can be balanced, reducing the occurrence of electrochemical corrosion. Electrochemical corrosion can cause damage to the metal structure of the shaft system and shorten its service life, while grounding devices can alleviate this problem to some extent.

Disadvantages and countermeasures

Electric brush wear problem: Grounding electric brushes are prone to wear during long-term contact and relative motion with the shaft system. Once the electric brush is severely worn, it may lead to poor contact and affect the effectiveness of electrostatic conduction. The response measures include regularly checking the wear of the electric brush and replacing it in a timely manner when the wear exceeds a certain limit. At the same time, brush materials with better wear resistance can be selected, or the structure and installation method of the brush can be optimized to extend its service life.

Risk of grounding cable damage: Grounding cables may be damaged due to mechanical damage, corrosion, and other reasons. For example, during ship vibrations or collisions with external objects, cables may be squeezed or scratched. The countermeasure is to regularly inspect the appearance and connection of the cables, and replace or repair damaged cables in a timely manner. At the same time, protective measures should be taken during the cable laying process, such as using protective sleeves, to prevent the cable from being damaged.

Application scenarios

Various types of ship shaft systems: Almost all ship shaft systems require the installation of shaft grounding devices. Whether it is a cargo ship, passenger ship, oil tanker or warship, as long as the shaft system may generate static electricity during operation, grounding devices are needed to ensure safety. Especially on ships transporting flammable and explosive liquids such as oil tankers and chemical tankers, shaft grounding devices are indispensable safety facilities.