Toshiba VF-A7 instruction manual Explanation of terms, Overload stallSoft stall

1)Setting the electronic thermal protection characteristics parameter the motor overload protection level #1 



and

The electronic thermal protection characteristics selection parameter  is used to enable or disable the motor overload trip function () and the soft stall function. The motor overload trip function () needs to be selected with the parameter , while the inverter overload trip function () is always activated.

Explanation of terms

Overload stall(Soft stall):

The function of automatically lowering the output frequency before the motor overload trip function  is activated when the inverter detects that an excessive load is applied to the motor. (Lowers maximum about 48Hz when base frequency is 60Hz.) This function enables the inverter to

output a frequency commensurate with the load current so that the motor can keep running without tripping. This function is useful for such loads as fans, pump and blowers, which have the square reduction torque characteristic that the current passed decreases as the rotating speed falls.

Note) Do not use this overload stall function for loads with a constant torque characteristic (e.g., a belt conveyer to which a constant load current is always passed regardless of their speed).

[A general-purpose motor (other than motors intended for use with inverters)]

When a motor is operated in a frequency range below its rated frequency, its cooling efficiency drops. To prevent the motor to overheat because of this, the overload detecting point is advanced when the inverter is used for a general-purpose motor.

■Setting the electronic thermal protective function 

Set value	Overload protection		Overload stall
	protect		not	stall
	protect		stall
	not	protect	not	stall
	not	protect	stall

■Setting the motor overload protection level #1 

When the inverter is used for a motor with a capacity or a current rating smaller than that of the inverter, it is necessary to adjust the motor overload protection level #1 parameter  to the rated current of the motor.

Output current reduction rate [%]

 ×1.0

 ×0.6

0
	30	Output frequency [Hz]

Note) The motor overload starting level is fixed at 30 Hz. If necessary, set  at ～.

(See the next page for the setting procedure.)

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