When It Is Running Continuously; Symbol Explanation - Delta Electronics AC Motor Drive VFD-EL User Manual

2.3 When it is running continuously

k

Symbol explanation

P : Motor shaft output for load (kW)
M
: Motor efficiency (normally, approx. 0.85)
η
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
: Starting current/rated current of motor
k
S
n
: Number of motors in parallel
T
n
: Number of simultaneously started motors
S
: Total inertia (GD
2
GD
: Load torque
T
L
t
: Motor acceleration time
A
N : Motor speed
Revision August 2008, 2ELE, V1.02
Appendix C How to Select the Right AC Motor Drive|
The requirement of load capacity should be less than the capacity of AC
motor drive(kVA)
The requirement of load capacity=
×
k P
M
≤
the _
η ϕ
×
cos
The motor capacity should be less than the capacity of AC motor drive
× × × ×
k 3 V I
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
capacity _ of _ AC
− ≤
3
10 the _ capacity
_ current _ of _
_ motor _ drive ( kVA
_ of _ AC _ motor
AC _ motor _ drive
2
)
)
_ drive ( kVA )
( A )
C-3