Delta VFD022B21A - Page 245

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
P
: Motor shaft output for load (kW)
ӯ
: Motor efficiency (normally, approx. 0.85)
M
cos
: Motor power factor (normally, approx. 0.75)
MV
: Motor rated voltage(V)
M
I
: 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
T
: Load torque
At
: Motor acceleration time
N : Motor speed