66 • Control Keypad
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7.8.3.2 Special Control for Synchronous Motors Excitation
In normal cases of synchronous motor starting, the HRVS-DN signals to motor’s excitation system to start via
the Up to Speed relay installed on the optional Relay PCB (via terminals 33, 34 & 35 I refer to
Figure 13 –
Control Module Input/Output
page 29).
The signal is initiated when:
The HRVS-DN is in Run
The Bypass is closed (End on Acceleration contact is closed) and 1 second time delay was elapsed.
Motor current is below 120% of FLA.
The parameters TURN BYPAS ON AT and MIN TIME TO BYPS are used for special cases where the sub-
synchronous current (at sub-synchronous speed) exceeds 120% of FLA.
These parameters are active only under the following conditions:
Optional Relay PCB is installed
When setting the RUN CONTACT DLY parameter, after reaching 120 seconds (maximum value) and
operator keeps pressing for additional 16 seconds the key.
The parameter TURN BYPAS ON AT determines motor current below which the soft starter goes into Run
condition and closes the End Of Acceleration relay.
The parameter MIN TIME TO BYPS must be set above the total acceleration time to sub-synchronous speed
assuring that Run condition can not be reached before the set time after the beginning of the starting process.
(sub-synchronous current can be observed when current ceases to decrease at the end of the acceleration)
This special feature is for synchronous motor starting applications where the motor current at asynchronous
speed may be at higher level than regular asynchronous motor starting conditions.
In this case the level of current at which the Run condition is being achieved can be programmed.
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