One of the most important applications of industrial resistors is to control of motors used in compressors, blowers, cranes, forklifts, lift trucks, conveyors, and etc. This equipment is used to start different types of high-power DC and AC motors. The Motor starter device limits the inrush current of the motor and adjusts its torque-speed characteristic.
- In wound rotor induction motors, the motor starter is connected to the rotor slider rings by star connection and using reducing resistance steps, it provides a soft start for the engine. This equipment is used in engines with high starting torque.
- In the squirrel cage induction motors, the motor starter is located on the stator winding supply path and reduces the startup current by reducing the startup voltage. In this case, using reducing resistance steps, a smooth startup for the engine is provided.
- In starting with the star-triangle connection, the engine is started by the star connection and then converted to triangle state. In this method, to reduce the spark and to create a balance in the electromotive force of the return, the motor starter is added to the circuit, which eventually causes the engine to start smoothly.
- In DC series motors, the motor starters are located in the path of the winding and armature, reducing the voltage and start-up current. As a result, the inrush torque decreases and with the reduction of the resistance steps, the engine starts up smoothly.
Main specifications of the Motor Starter
Main Specifications of Motor Starting are mainly rated voltage, rated power, rated resistance and number of steps. In order to calculate the inrush current limited by the motor starter, the NEMA standard, in accordance with the location of the motor application, introduces the NEMA Resistor Class parameter, which based on that and the main motor specification (including rated current, frequency, pole number and rotor speed) one can compute total resistance, resistance of each step and the rated power of the resistor.
Paarsun Co. designs and manufactures motor starters by taking into account the above parameters as well as the duty cycle, allowed temperature rise according to the standard, the type of cooling and vibrations existing in the system.