Fuji Electric frenic mini series, Руководство пользователя

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G-6
V/f control
The rotating speed N of a motor can be stated in an
expression as
) s 1 (
p
f 120
N
− ×
×
=
where,
f: Output frequency
p: Number of poles
s: Slippage
On the basis of this expression, varying the output
frequency varies the speed of the motor. However,
simply varying the output frequency (f) would
result in an overheated motor or would not allow
the motor to demonstrate its optimum utility if the
output voltage (V) remains constant. For this
reason, the output voltage (V) must be varied with
the output frequency (f) by using an inverter. This
scheme of control is called V/f control.
Variable torque load
A squared torque load is characterized by:
1) A change in the required torque in proportion to
the square of the number of revolutions per minute.
2) A power requirement that decreases in
proportion to the cube of the decrease in the
number of revolutions per minute.
55 . 9
) m N ( Torque ) rpm ( speed Rotating
) kW ( power quired Re
•
×
=
Related function code: F37
Applications: Fans and pumps
Voltage and frequency variations
Variations in the input voltage or frequency within
permissible limits. Variations outside these limits
might cause an inverter or motor to fail.