gefran VDI100 Series Instruction Manual page 196

07-15 Pre-excitation level
100~200 %
If a high starting torque is required for the application, especially for a large horsepower motors, the pre-excita-
tion operation can be used to pre-flux (magnetize) the motor.
Pre-excitation time (07-14)
When an operation command (forward or reverse) is activated, the inverter will automatically start pre-excita-
tion based on the time set in parameter 07-14.
The time for the flux to reach 100% is a function value of motor's electrical time constant (See figure 4.4.62).
Electrical time constant (quadratic by-pass circuit time constant) can be calculated by motor parameter setting
(group 02)
Electrical time constant T2=
Set the pre-excitation time (07-14) based on the electrical time constant T2
Pre-excitation initial level (07-15)
Use the pre-excitation initial level (07-15) to provide a higher excitation current during the pre-excitation time
(07-14), which will increase the speed and stability for motors.
In order to quickly magnetize the motor, reduce the pre-excitation time (07-14) and set the pre-excitation level
(07-15) to a high level.
If 07-15 is set greater than 100%, providing a high excitation current during the pre-excitation time (07-14), mo-
tor's magnetization time is shorted. When the setting reaches 200%, magnetization is reduced by roughly half.
A high pre-excitation level (07-15) might result in excessive motor sound during pre-excitation.
When the flux reaches 100%, pre-excitation current reverts back to 100% and pre-excitation is completed.
Code Parameter Name / Range
07-18 Minimum base block time
0.1~5.0 s
In case of a momentary power failure, the inverter continues to operate after the power has been restored
when parameter 07-00 is set to 1. Once the momentary power failure is detected; the inverter will automatically
shut down the output and maintain B.B for a set time (07-18).
It is expected that after the minimum base block time has expired the residual voltage to be almost zero.
When the momentary power failure time exceeds the minimum base block time (07-18), the inverter will auto-
matically perform a speed search upon return of power. Refer to the following figure 4.4.63.
196
Motor leakage inductance (02-17) + motor mutual inductance (02-18)
Motor rotor resistance (02-16)
Figure 4.4.62 Pre-excitation operation
Run
Command
Magnetic flux
and Excitation
current
100%
Motor
Speed
Pre-excitation Time
07-14
Excitation current
Pre-excitation initial Level (07-15)
t
Magnetic flux
t
t
VDI100 • Instruction manual