Why over current protection is important for VFD pump inverter?

Without proper current protection, the motor of a water pump might be damaged or even be burned because the electric current is higher than its rated handling ability. 

Variable frequency drive (VFD) / variable speed drive (VSD) Constant Pressure Booster Pump Inverter typically provides electronic overload protection for motors via their internal firmware. With proper setup and commissioning of the variable frequency drive (VFD) / variable speed drive (VSD) Constant Pressure Booster Pump Inverter parameters, the motor can be protected from overheating due to excessive load or other conditions that might cause the motor to run above its Full Load Amp rating. When an overload condition is detected it could lead the drive to give a warning or a fault.

Another method for protecting motors would be for the drive to monitor thermostat sensors that are placed in the motor and to use that feedback to warn or fault. The above methods are good for an application with a single motor on a drive, but in cases where multiple motors are connected to a variable frequency drive (VFD) / variable speed drive (VSD) Constant Pressure Booster Pump Inverter, motor overload protection needs to be handled a bit differently. In this case, individual motor overloads are required and if one of the motors is in an overload condition, that motor’s protection device should open a set of contacts that are wired back to a digital input on the drive so it can indicate there is a problem with one of the motors.

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Reference source: 

Rick Akey, senior application engineer, low-voltage drives groups, at ABB