Appendix C How to Select the Right AC Motor Drive_VFD-B Series
Revision 10/2005, BE13, SW V4.08 C-3
2.3 When it is running continuously
The requirement of load capacity should be less than the capacity of AC motor drive(kVA)
The requirement of load capacity=
d
u
u
MK
cos
MPk
the capacity of AC motor drive (kVA)
The motor capacity should be less than the capacity of AC motor drive
duuuu
3
103 MM IVk the capacity of AC motor drive (kVA)
The current should be less than the rated current of AC motor drive(A)
du MIk the rated current of AC motor drive(A)
Symbol explanation
M
: Motor shaft output for load (kW)
ӯ
: Motor efficiency (normally, approx. 0.85)
cos
: Motor power factor (normally, approx. 0.75)
MV
: Motor rated voltage(V)
M
: Motor rated current(A), for commercial power
k
: Correction factor calculated from current distortion factor (1.05 - 1.1, depending on PWM
method)
1CP
: Continuous motor capacity (kVA)
Sk
: Starting current/rated current of motor
Tn
: Number of motors in parallel
Sn
: Number of simultaneously started motors
2
GD
: Total inertia (GD
2
) calculated back to motor shaft (kg m
2
)
L
: Load torque
At
: Motor acceleration time
N : Motor speed
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