Delta Electronics AC Motor Drive VFD-G, User Manual

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Appendix C How to Select the Right AC Motor Drive
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Revision July 2008, EG03, SW V1.06 C-3
Symbol explanation
M
P : Motor shaft output for load (kW)
η
: Motor efficiency (normally, approx. 0.85)
ϕ
cos
: Motor power factor (normally, approx. 0.75)
M
V : 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)
1 C
P
: Continuous motor capacity (kVA) P
C1
=KP
MnT
/
η
cos
S
k : Starting current/rated current of motor
T
n
: Number of motors in parallel
S
n
: Number of simultaneously started motors
2
GD
: Total inertia (GD
2
) calculated back to motor shaft (kg m
2
)
L
T : Load torque
A
t
: Motor acceleration time
N : Motor speed