Delta Electronics VFD-VE Series User Manual
Appendix C How to Select the Right AC Motor Drive|
Revision August 2008, 03VE, SW V2.04
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
C.2 General Precaution