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Chapter 8Appendix C How to Select the Right AC Motor Drive
2.3 When it is running continuously
×
k
Symbol explanation
P
: Motor shaft output for load (kW)
M
η
: Motor efficiency (normally, approx. 0.85)
ϕ
cos
: Motor power factor (normally, approx. 0.75)
V
: Motor rated voltage (V)
M
I
: Motor rated current (A), for commercial power
M
k
: Correction factor calculated from current distortion factor (1.05-1.1, depending on
PWM method)
P
: Continuous motor capacity (kVA)
C
1
k
: Starting current/rated current of motor
S
n
: Number of motors in parallel
T
n
S
: Number of simultaneously started motors
: Total inertia (GD
2
GD
T
: Load torque
L
t
A
: Motor acceleration time
: Motor speed
N
Revision August 2008, SE09, SW V2.61
The requirement of load capacity should be less than the capacity of the AC
motor drive(kVA)
The requirement of load capacity is
×
k
P
M
≤
the
_
capacity
η
ϕ
×
cos
The motor capacity should be less than the capacity of AC motor drive
×
×
×
×
k
3
V
I
10
M
M
The current should be less than the rated current of AC motor drive(A)
≤
I
the
_
rated
M
2
) calculated back to motor shaft (kg m
_
of
_
AC
_
motor
−
≤
3
the
_
capacity
_
current
_
of
_
AC
_
drive
(
kVA
)
_
of
_
AC
_
motor
_
_
motor
_
drive
2
)
|VFD-S Series
drive
(
kVA
)
(
A
)
C-3
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