The main switch of marine diesel generators often uses a universal automatic air circuit breaker, also known as an automatic switch. Commonly used on ships are: frame type universal automatic switch and device type automatic switch. The main switch of the generator is the connecting component for the generator to be connected to the power grid. Under abnormal operating conditions, such as overload, power grid short circuit, generator undervoltage, etc., it can automatically disconnect the development motor from the power grid. Therefore, it is both a switching device and a protective device. Device type automatic air switches are generally used as switch appliances for branches, 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 and structures of main switches for marine diesel generators manufactured domestically and internationally, but the basic principles are similar. Generally, they are composed of a single contact, an arc extinguishing device, a free release mechanism, an operating mechanism, and a protection device.
1、 Contact and arc extinguishing system
When the contact is cut off, the current is likely to generate an arc, so it is necessary to have a complete contact system: composed of the main contact, auxiliary contact, and arc contact. The main contact bears the normal working current of the circuit, and the arc contact is set to prevent the arc generated when the main contact disconnects the circuit from burning the main contact. When closing, the arc contact is first connected, followed by the secondary contact and the main contact. When opening, the main contact is first disconnected, followed by the auxiliary contact and arc contact. The arc generated by the circuit breaking is extinguished in the arc contact. Automatic air circuit breakers mostly use arc extinguishing barriers for arc extinguishing.
2、 Free release mechanism
The function of the free release mechanism is to keep the contact intact and close or quickly disconnect., It is the connecting mechanism between the contact system and the operating transmission device. In the normal closed state of the contact, due to the action of the armature, the top rod moves upwards in reverse, hitting the connecting rod contact point, and the rigid connection of the four connecting rods is damaged. The release mechanism acts, causing the main contact to be in a disconnected state. When the switch needs to be closed again after tripping, the handle should be pulled down first to form a rigid connection state for the four link machine, and the switch should be prepared. Once the switch needs to be closed, simply push the handle up.
