Mitsubishi Electric FR-A700 Technical Manual page 458

3.2.4 Efficiency
(common)
(1) Finding the overall efficiency
MCCB
P (IN)
INV
P : Inverter input power [kW]
INV (IN)
P : Motor input power [kW]
M (IN)
P : Motor output power [kW]
M(OUT)
Inverter efficiency
INV ..........
the inverter itself and is found by the following formula
from the inverter input power P
input power P .
M(IN)
P
M (IN)
= 100 [%]
INV
P
INV (IN)
Motor efficiency ............... Indicates the efficiency of
M
the motor driven by the inverter and is found by the
following formula:
P
M(OUT)
100[%]
M =
P
M(IN)
Overall efficiency .............. Indicates the efficiency of
T
the inverter and motor combined and is found by the
following formula:
P
M (OUT)
= =
T INV
M
P
INV(IN)
common
Inverter
IM
P
Motor
P (IN)
M
Indicates the efficiency of
and the motor
INV (IN)
100[%]
(2) Motor efficiency
The motor efficiency in (1) is further developed as
indicated by the following formula:
(OUT)
M
=
M
Main motor losses are iron loss, stator copper loss and
rotor copper loss. When the load torque decreases, the
ratio of the above losses to the output power increases,
reducing the efficiency. Similarly, if the load torque remains
the same, the decrease in output frequency results in
reduced efficiency.
The reduction in motor terminal voltage (i.e. inverter output
voltage) decreases the motor torque. The increase in
motor slip and rotor copper loss decreases the motor
efficiency.
492
P P
M(OUT) M(OUT)
100
P
P + motor loss
M (IN) M(OUT)
SELECTION
100[%]