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| SOFT STARTERS | |
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What advantages does the by-pass contactor provide to soft starters? |
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Silicon controlled rectifiers (SCR), which are part of the
power circuit of soft starters, generate an enormous amount
of heat, equal to 1.2W multiplied by the amps consumed
during ramp up, multiplied by the number of phases
controlled. The by-pass contactor, incorporated in the ADX…B and ADX..BP versions up to 245A, or to be externally mounted for the other ADX versions up to 1200A and predisposed for the complete control of the by pass, provides to exclude the power circuit once the motor starting is completed and then disconnects the SCRs. In this way, dissipation during motor operation is simply that of the contactor only, which is much less than when the SCRs are connected. This condition consents to reduce the size of electric panels. During the stopping, the SCRs can be reactivated for eventual deceleration. In addition, during the by-pass operation, the soft starter maintains all of the motor protections (e.g. phase loss, motor thermal status, locked rotor, motor current too low) active. |
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Can the restarting of a motor be controlled by a soft starter whenever it is locked in load conditions? |
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Using the torque-control soft starters, ADX series, it is possible to also control the restarting of a motor in load conditions, for example a mill, stopped for an emergency. This type of operation can be obtained in two different ways. The first is to increase the parameter related to the torque step during the starting phase; this allows the soft starter to deliver more torque during the initial motor acceleration and then linearly increase it up to the maximum value. Instead, the second consents to enable a voltage boost during the starting phase. This function sets up a very high torque for the motor during the first 100ms of starting. The boost can be used when the initial torque step, mentioned above, is insufficient to overcome the force of static friction. |
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During the final testing of an electric panel which includes a soft starter for a high-rated motor, can the testing of the soft starter be done with a low-rated motor? |
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During
the phases of acceleration and deceleration or when the bypass
contactor is closed, the soft starter continuously monitors the
current absorption of the motor at the internal current
transformer terminals. In the event the current value results to
be very low compared to the set nameplate motor current value,
the soft starter trips the relative alarms such as single phase
or current too low , and stops the motor. To avoid such circumstances during the final testing of an electric panel with a large-rated soft starter, the ADX series of LOVATO Electric has been equipped with a special parameter, which momentarily disables current control and consents to simulate the motor starting. |
