Delta Electronics VFD-M Series, User Manual

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Appendix CHow to Select the Right AC Motor Drive
|
Revision May 2008, ME14, SW V3.04 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=
) ( _ _ _ _ _
cos
kVA drive motor AC of capacity the
P k
M
≤
×
×
ϕ η
„ The motor capacity should be less than the capacity of AC motor drive
) ( _ _ _ _ _ 10 3
3
kVA drive motor AC of capacity the I V k
M M
≤ × × × ×
−
„ The current should be less than the rated current of AC motor drive(A)
) ( _ _ _ _ _ _ A drive motor AC of current rated the I k
M
≤ ×
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)
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