VLT ® 2000 Series How the VLT works I Factory-programmed optimization VLT Series 2000 has dynamic adaptation of the motor voltage and frequency. This ensures correct magnetisation of the motor, thus providing optimum dynamics, accuracy or efficiency. Start voltage increases the motor voltage at a given frequency. This increases the motor magnetization. The motor can yield a higher torque, but the disadvantage is that the motor losses are increased too. The result is a higher motor temperature. Excessive start voltage can cause a trip (cut-out). VLT has been designed for operation of the most common types of motors and loads.
Once parameters 103,104, 105, 107 and 108 have been set according to the motor type plate, your motor operation will be optimum in most cases. Start compensation changes the motor voltage as a function of the load. The voltage will increase with higher motor current. Over-compensation will overheat the motor and give the risk of instability and can cause trip (cut-out). As the name indicates, the function is most effective at low motor speed. Individual adaptation of VLT and motor is done via parameters 109-112. U/f ratio This describes the pre-programmed U/f characteristics which indicate the relation between motor voltage (U) and frequency (f).
The U/f ratio can be adjusted to ensure correct excitation of the motor, thereby helping to obtain optimal dynamism, accuracy or efficiency. Slip compensation adds both frequency and voltage and compensates for the varying slip at varying load so that the motor speed is kept constant at varying load. Over-compensation may make the speed increase at increasing load. This means motor overload and risk of unstable motor operation. Constant torque CT Par. 104 = Rated motor voltage Par. 105 = Rated motor frequency Par. 107 = Rated motor current Par. 108 = Motor no-load current Par. 109 = Start voltage Par. 110 = Start compensation Par. 111 = U/f ratio Par.
112 = Slip compensation 24 MG.20.B6.02 – VLT is a registered Danfoss trademark