Working principle and main function of speed relay

Speed relay, speed relay, also known as reverse brake relay. Its main structure is composed of rotor, stator and contact. The speed relay is mainly used in the control circuit of reverse connection braking of three-phase asynchronous motor. Its task is to generate a rotating magnetic field opposite to the actual rotor rotation direction when the phase sequence of three-phase power supply is changed, thus generating braking torque. Therefore, the speed of the motor can be reduced rapidly under braking. Send a signal immediately when the motor speed is close to zero, cut off the power supply and stop it, or the motor will start in the opposite direction.

1、 Operating principle of speed relay

Its rotor is a permanent magnet, connected with the motor or mechanical shaft, and rotates with the motor rotation. The rotor is similar to the squirrel-cage rotor, with a short circuit bar inside, which can also rotate around the rotating shaft. When the rotor rotates with the motor, its magnetic field is cut with the stator short circuit bar to produce the induced electromotive force and induced current, which is the same as the working principle of the motor, so the stator rotates with the rotor.

When the stator rotates, it drives the lever, which pushes the contact to make it close and open. When the rotation direction of the motor changes, the rotation direction of the rotor and stator of the relay also changes. At this time, the stator can touch another group of contacts to make them open and close. When the motor stops, the contact of the relay will return to the original static state.

Working principle and main function of speed relay

2、 Main functions of speed relay

1. The speed relay is mainly used in the control circuit of reverse connection braking of three-phase asynchronous motor. Its task is to generate a rotating magnetic field opposite to the actual rotor rotation direction when the phase sequence of three-phase power supply is changed, thus generating braking torque. Therefore, the speed of the motor can be reduced rapidly under braking. Send a signal immediately when the motor speed is close to zero, cut off the power supply and stop it (otherwise the motor starts in the opposite direction).

2. The speed relay is widely used to monitor the internal combustion engine of ships and trains, as well as gas, water and wind turbines. It can also be used in the paper industry, foil production and textile industry. In the application of marine diesel engines and many diesel generator sets, the speed relay, as a secondary safety circuit, quickly shuts down the engine when an emergency occurs.