Delta Electronics VFD-EL series, User Manual

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Appendix C How to Select the Right AC Motor Drive
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Revision 2016/03, 6ELE, V1.14
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
Selection Note
1.
When the AC Motor Drive is connected directly to a large-capacity power transformer (600kVA or above) or
when a phase lead capacitor is switched, excess peak currents may occur in the power input circuit and
the converter section may be damaged. To avoid this, use an AC input reactor (optional) before AC Motor
Drive mains input to reduce the current and improve the input power efficiency.
2.
When a special motor is used or more than one motor is driven in parallel with a single AC Motor Drive,
select the AC Motor Drive current
≥
1.25x(Sum of the motor rated currents).
3.
The starting and accel./decel. characteristics of a motor are limited by the rated current and the overload
protection of the AC Motor Drive. Compared to running the motor D.O.L. (Direct On-Line), a lower starting
torque output with AC Motor Drive can be expected. If higher starting torque is required (such as for
elevators, mixers, tooling machines, etc.) use an AC Motor Drive of higher capacity or increase the
capacities for both the motor and the AC Motor Drive.
4.
When an error occurs on the drive, a protective circuit will be activated and the AC Motor Drive output is
turned off. Then the motor will coast to stop. For an emergency stop, an external mechanical brake is
needed to quickly stop the motor.
Parameter Settings Note
1.
The AC Motor Drive can be driven at an output frequency up to 400Hz (less for some models) with the
digital keypad. Setting errors may create a dangerous situation. For safety, the use of the upper limit
frequency function is strongly recommended.
2.
High DC brake operating voltages and long operation time (at low frequencies) may cause overheating of
the motor. In that case, forced external motor cooling is recommended.
3.
Motor accel./decel. time is determined by motor rated torque, load torque, and load inertia.