Appendix C How to Select the Right AC Motor Drive|VFD-B Series

„

The requirement of load capacity should be less than the capacity of AC

motor drive(kVA)

The requirement of load capacity=

k × PM ≤ the _ capacity _ of _ AC _ motor _ drive(kVA)

η × cosϕ

„

The motor capacity should be less than the capacity of AC motor drive

k × 3 ×VM × IM ×10−3 ≤ the _ capacity_ of _ AC _ motor _ drive(kVA)

„

The current should be less than the rated current of AC motor drive(A)

k × IM ≤ the _ rated _ current _ of _ AC _ motor _ drive( A)

Symbol explanation

P M

: Motor shaft output for load (kW)

η

: Motor efficiency (normally, approx. 0.85)

cosϕ : Motor power factor (normally, approx. 0.75)

V M

: Motor rated voltage(V)

I M

: Motor rated current(A), for commercial power

k

: Correction factor calculated from current distortion factor (1.05 - 1.1, depending

on PWM method)

PC1

: Continuous motor capacity (kVA)

k S

: Starting current/rated current of motor

n T

: Number of motors in parallel

n S

: Number of simultaneously started motors

GD 2

: Total inertia (GD2) calculated back to motor shaft (kg m2)

T L

: Load torque

t A

: Motor acceleration time

N

: Motor speed

Revision July 2008, BE16, SW V4.08 & V5.00

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