Improper V/f curve selection is a common cause of overcurrent during low-speed operation, but it is often overlooked by field engineers.
TECO inverters provide multiple V/f curve selections. The default F0 or F1 is suitable for most general-purpose loads. When the load characteristics deviate from the default curve—for example, a constant-torque load that requires higher torque at low speed—it is necessary to switch to the corresponding curve or manually adjust the torque boost parameter.
Typical scenario: A TECO inverter drives a conveyor. It runs normally at no load, but reports an OC fault in the low-speed range after a load is applied. Inspection of the motor and cables shows no abnormality. It is finally determined that the V/f curve was set to the quadratic torque mode suitable for fans and pumps. At low speed, the output voltage is insufficient, causing the current to rise. Switching to the constant-torque curve solves the problem.
Commissioning recommendations: For applications with heavy starting loads (such as crushers, mixers, and extruders), in addition to adjusting the V/f curve, the torque compensation setting should also be checked. If the torque compensation setting is too high, it can cause excessive no-load current at low speed with no load, which may instead trigger a false alarm.