Constant Torque Load
In this type of load, the load torque TL is independent of the speed n, and it remains constant or nearly constant at any speed. The load power, however, linearly increases with the increase in load speed. This includes conveyors, mixers, extruders, and feeding mechanisms for machinery.
Frictional loads, as well as gravity loads from cranes, hoists, and elevators, are all constant-torque loads. When a variable-frequency power supply drives a constant-torque load, it requires a sufficiently high torque output at low speeds and must have adequate overload capacity. If a long-term, stable speed operation at low speeds is necessary, consider the cooling capacity of standard squirrel-cage induction motors to prevent excessive motor temperature rise.
Constant Power Load
The characteristic of this type of load is that the required torque (TL) and speed (n) are generally inversely proportional, but their product, which is power, remains approximately constant. Spindles of metal cutting machine tools, rolling mills, paper machines, winding machines on film production lines, and unwinders all belong to constant power loads. The constant power nature of the load should be considered within a certain speed range. When the speed is very low, limited by mechanical strength, TL cannot increase indefinitely, and it transitions to a constant torque nature at low speeds. The constant power and constant torque regions of the load greatly influence the selection of transmission schemes. In constant flux adjustment of the motor, the output torque remains constant, which is constant torque adjustment; while in weak flux adjustment, the output torque is inversely proportional to the speed, which is constant power adjustment. If the range of constant torque and constant power adjustment of the motor is consistent with the range of the load's constant torque and constant power, which is referred to as "matching," the capacity of the motor and the inverter's capacity are both reduced. Ground power for aviation
Fluid Load
This type of load has a quadratic relationship between torque and rotational speed, and a cubic relationship between power and rotational speed. Various fans, pumps, and oil pumps fall under the category of typical fluid loads. By adjusting the speed of fluid loads through variable-frequency power supplies, air volume and flow rate can be regulated, leading to significant energy savings. Due to the rapid increase in demand power of fluid loads at high speeds, which is proportional to the cube of the load's rotational speed, it is not advisable to operate these loads beyond the frequency of the power supply. 400HZ power supply
