Appendix C How to Select the Right AC Motor Drive|VFD-B Series
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=
k×N
973 ×η × cosϕ
⎜⎜⎝⎛TL
+
GD 2
375
×
N
tA
⎟⎟⎠⎞
≤ 1.5 × the _ capacity
_ of
_
AC
_ motor
_ drive(kVA)
2. When one AC motor drive operates more than one motor
2.1 The starting capacity should be less than the rated capacity of AC motor drive
Acceleration time ≦60 seconds
The starting capacity=
k×N
η × cosϕ
[nT
+
ns(ks
− 1)] =
⎡
PC1⎢⎢1 +
⎢⎣
ns
nT
(ks
)⎤
−1
⎥
⎥
⎥⎦
≤ 1.5 × the _ capacity _ of
_
AC
_ motor _ drive(kVA)
Acceleration time ≧60 seconds
The starting capacity=
[ ] k × N
η × cosϕ
( ) nT + ns ks − 1
( ) =
⎡
PC1⎢⎢1 +
⎢⎣
ns
nT
⎤
ks
−
1
⎥
⎥
≤
the
_
capacity
_
of
⎥⎦
_ AC _ motor _ drive(kVA)
2.2 The current should be less than the rated current of AC motor drive(A)
Acceleration time ≦60 seconds
nT
+
IM
⎢⎡1+
⎣
nS
nT
⎜⎝⎛
kS
1− ⎟⎠⎞
⎤
⎥
⎦
≤ 1.5 × the _ rated
_ current _ of
_
AC
_ motor
_ drive( A)
Acceleration time ≧60 seconds
nT
+
IM
⎢⎡1+
⎣
nS
nT
⎜⎝⎛
kS
1− ⎟⎠⎞
⎤
⎥
⎦
≤
the _ rated
_ current _ of
_
AC
_ motor
_ drive( A)
2.3 When it is running continuously
C-2
Revision July 2008, BE16, SW V4.08 & V5.00