When a wound rotor induction motor (WRIM) is started from stand, the torque that is generated by the current must be higher than the load starting inertia to induce the rotation of the motor. The required load torque depends on each application and its specifications as the mass of the moved parts, inertia and friction values and materials within the application are affecting the operation.
Without a starting resistor the rotor current would reach up to 7 x rated current which would negatively influence the supply grids. It is possible to generate a smoother starting curve which protects electrical as well as mechanical components and assures a smooth startup of the system. Therefore, Liquid Resistance Starters (LRS) are commonly used to start up WRIM motors in industrial environments.
For liquid starters, the electrolyte solution of Na2CO3 acts as resistor, which in turn depends on the soda concentration. By changing the distance between upper and lower electrodes, the resistance is reduced smoothly. In addition, the fluid acts as a store of heat energy, which occurs during start-up, and this is slowly released to the atmosphere via the tank surface (optional heat exchanger can also be used). This system is predominantly used where the process does not require speed control and the application requires a very high starting torque. The robust design guarantees high operational reliability and long service.
The liquid starters FExxxx comply with:
They conform to Low Voltage Guideline 2006/95/EG of the European Parliament and are therefore suitable for installation in