Theory:Reed Relay Usage:Protective Size:Miniature Protect Feature:Epoxy Contact Load:High Power
Speed relay (speed relay) is also called reverse connection brake relay. Its main structure is composed of three parts: rotor, stator and contacts.
The speed relay is mainly used in the control circuit of three-phase asynchronous motor reverse braking, and its task is to generate a rotating magnetic field opposite to the actual rotor rotation direction after the phase sequence of the three-phase power source is changed, thereby generating a braking torque. Therefore, the motor is quickly reduced in speed under braking. Send a signal immediately when the motor speed is close to zero, cut off the power and stop it (otherwise the motor will start in the opposite direction)
Its rotor is a permanent magnet, connected to the motor or mechanical shaft, and rotates as the motor rotates. The rotor is similar to the squirrel-cage rotor, with short-circuit bars inside, and it can also rotate around the axis of rotation. When the rotor rotates with the motor, its magnetic field cuts with the stator short-circuit bar, generating induced potential and induced current, which is the same as the working principle of the motor, so the stator rotates as the rotor rotates. When the stator rotates, the lever is driven, and the lever pushes the contact to close and break it. When the direction of rotation of the motor changes, the rotation of the rotor and stator of the relay also changes. At this time, the stator can touch another set of contacts to make it open and close. When the motor stops, the contacts of the relay return to the original static state.
Since the relay works coaxially with the motor, no matter whether the motor rotates forward or reverse, one of the two normally open contacts of the electrical appliance is closed, and the motor is ready to be braked. Once the braking starts, the interlocking contacts of the control system and the spare closed contacts of the speed relay form a motor phase sequence reverse connection (commonly known as reverse phase) circuit to make the motor stop under the reverse connection brake. When the rotation speed of the motor is close to zero, the normally open contact of the brake of the speed relay is cut off, thereby cutting off the power supply and ending the braking state of the motor.
Speed relays are widely used. They can be used to monitor the internal combustion engines of ships and trains, as well as gas, water and wind turbines. They can also be used in the paper industry, foil production and textile production. In the application of marine diesel engines and many diesel generator sets, the speed relay serves as a secondary safety circuit, and when an emergency occurs, the engine is quickly shut down.