Chapter 8Appendix C How to Select the Right AC Motor Drive
|VFD-S Series
C-2 Revision August 2008, SE09, SW V2.61
C.1 Capacity Formulas
1. When one AC motor drive operates one motor
The starting capacity should be less than 1.5x rated capacity of AC motor drive
The starting capacity is
)(_____5.1
375cos973
2
kVAdrivemotorACofcapacitythe
t
NGD
T
Nk
A
L
×≤
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×+
××
×
ϕη
2. When one AC motor drive operates more than one motor
2.1 The starting capacity should be less than the rated capacity of the AC motor drive
Acceleration time
≦
60 seconds
The starting capacity is
()
[]
()
)(_____5.11
cos
111 kVAdrivemotorACofcapacitythek
n
n
Pknn
Nk
sCss
T
s
T
×≤+=+
×
×
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−−
ϕη
Acceleration time
≧
60 seconds
The starting capacity is
()
[]
()
)(_____1
cos
111 kVAdrivemotorACofcapacitythek
n
n
Pknn
Nk
sCss
T
s
T
≤+=+
×
×
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎣
⎡
−−
ϕη
2.2 The current should be less than the rated current of the AC motor drive(A)
Acceleration time
≦
60 seconds
)(______5.111 AdrivemotorACofcurrentratedthek
n
n
In SM
T
S
T
×≤++
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
−
Acceleration time
≧
60 seconds
)(______11 AdrivemotorACofcurrentratedthek
n
n
In SM
T
S
T ≤++
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
−
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