The main switch of a Marine diesel generator often adopts a universal automatic air circuit breaker, which is also known as an automatic switch. The commonly used automatic switches on ships include: frame-type universal automatic switches and device-type automatic switches. The main switch of the generator is the connection component for the generator to be connected to the power grid. Under abnormal operation conditions, such as overload, short circuit in the power grid, or under-voltage of the generator, it can automatically disconnect the generator from the power grid. Therefore, it is both a switchgear and a protective device. The device type automatic air switch is generally used as a switchgear for branch circuits, load screens, lighting screens, etc. Different models of products have different protection functions, and generally have short-circuit protection and overload protection functions. There are many forms of main switches for Marine diesel generators manufactured both at home and abroad, and their structures vary. However, their basic principles are largely the same. Generally, they are composed of a single contact piece, an arc extinguishing device, a free trip mechanism, an operating mechanism and a protection device.
I. Contacts and arc Extinguishing Systems
When the contacts are cut off, a large current will generate an arc. Therefore, a complete contact system is necessary: consisting of main contacts, secondary contacts and arc contacts. The main contact bears the normal operating current of the circuit. The arc contact is set up to prevent the arc generated when the main contact is disconnected from the circuit from burning out the main contact. When closing the switch, the arc contact is connected first, followed by the secondary contact and the main contact in sequence. When the circuit is opened, the main contact opens first, followed by the secondary contact and the arc contact. The arc generated by the circuit opening is extinguished in the arc contact. Most automatic air circuit breakers use arc-extinguishing grilles for arc extinguishing.
II. Free Deduction Institutions
The function of the free trip mechanism is to keep the contacts intact and closed or open quickly. It is the connecting mechanism between the contact system and the operating transmission device. In the normal closed contact state, due to the action of the armature, the top rod moves upward in the opposite direction, colliding with the connecting rod contact point. The rigid connection of the four connecting rods is disrupted, and the tripping mechanism acts, causing the main contact to be in the open state. When the tripping occurs and it is necessary to close the switch again, the handle should be pulled down first to make the four-bar linkage mechanism in a rigid connection state and get ready for closing. Once it is necessary to close the switch, just push the handle up.
