Mitsubishi Electric FR-A700 Series, Technical Manual

Page: 449 / 550

483
SELECTION
S
E
LECTION
3
3.1.2 Rated inverter capacity
(common)
Rated capacity of the inverter is calculated based on the
rated output current.
The rated output current is a current value which the
inverter can output continuously at the rated output
voltage. The inverter must always be used at no more than
this current value.
The overload capacity is defined as the permissible value
of a current beyond the rated output current of the inverter.
The overload capacity of the
is 150%
for one minute and of the is 120% for one minute.
At a start or for instantaneous overload, the inverter must
be used at not more than the overload capacity.
The capacity of the inverter is classified by the rated motor
output (kW). This rated capacity applies to the operation of
one general-purpose squirrel-cage induction motor of two
to six poles especially when there are no limits on
acceleration time and starting torque. The suitable capacity
must be selected when running a special motor or driving
several motors in parallel by one inverter, or when an
operation pattern or load torque has been specified.
(1) Operation of one motor
*When the inverter is used continuously at rated torque
at 50Hz, note the permissible continuous torque of
the motor. For more information, refer to the catalog
of the corresponding inverter series.
(2) Operation of two or more motors
When two or more motors are connected to one
inverter and the output side magnetic contactor is
used to start
/
stop the motors during inverter
operation, the inverter capacity selection depends
on how to start the motor.
1) Simultaneous start
When two or more motors are always switched
ON-OFF at the same time, select the inverter to
satisfy the following condition:
2) Sequential start
When motors are started from the first one
When the current limit function is activated, the
frequency changes abruptly. In a sequential start,
therefore, the speeds of the motors already
started change suddenly.
Therefore, select according to the machine
specifications.
• When the fast-response current limit function of
the inverter is utilized to minimize the inverter
capacity
Select the FR-A720-5.5K inverter rated at (6.0A
three motors 1.1 = 19.8A) or more and
having current limit function.
• When it is not desired to affect the motors already
started
Select the FR-A720-18.5K inverter rated at (6.0A
two motors 1.1+48.4A = 61.1A) or more and
having current limit function.
common
Rated inverter capacity (kVA)
=
Rated
output
voltage (V)
Rated output
current (A)
10
-3
Select the inverter to satisfy the following condition:
Rated inverter output current
≥
rated motor current 1.1
(The current that flows when a standard motor is
driven by the inverter is about 1.1 times larger than
the current that flows when the motor is run with the
commercial power supply.)
A700 E700 D700
F700
common
common
Inverter
MC
IM
1
IM
2
MCCB
Rated inverter output current
≥
Sum of rated currents of all motors 1.1
[Example] Operation of three SF-JR 1.5kW 4-pole
motors (rated current 6.0A, starting current
48.4A)
Select the FR-A720-5.5K inverter rated at
(6.0A three motors 1.1 = 19.8A) or
more and having current limit function.
• When the fast-response current limit function
of the inverter is utilized to minimize the
inverter capacity
Rated inverter output current
≥
sum of rated currents of all motors 1.1
• When it is not desired to affect the motors
already started
(The point is to make selection so that the
current limit function is not activated)
Rated inverter output current
≥
sum of rated currents of motors already
started
1.1
+ Motor starting current of motor started last *
* Motor starting current: Select the inverter so that
the starting current of the motor is 6 to 8 times
greater than the rated current of the motor.
[Example] Operation of three SF-JR 1.5kW 4-pole
motors (rated current 6.0A, starting current
48.4A)
MC1
MC2
Inverter IM
1
IM
2
MCCB