Protections; Motor Overload Protection - Emerson CS Serie Guia Del Usuario

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6.4

Protections

The Digistart CS includes the following types of protection for the motor and starter:
6.4.1 Excess start time protection
The Digistart CS will trip on excess start time if the motor does not successfully start within the time selected
in the Excess Start Time setting. This may indicate that the load has stalled.
If the soft starter frequently trips on excess start time:

check that the Current Limit setting is high enough for the application

check that the Excess Start Time setting is long enough for the application

check that the load has not stalled or increased since the soft starter was installed

6.4.2 Motor overload protection

The Digistart CS will trip on motor overload if it calculates that the motor has been running above its
operating range for longer than the time selected in the Motor Trip Class setting. Motor Trip Class should be
set to match the motor's locked rotor time. If this information is not available from the motor datasheet, use
the default setting (Motor Trip Class = 10). Using a higher setting can damage the motor.
NOTE Motor overload protection does not protect the soft starter, and does not protect the motor from
short circuit.
6.4.3 Current imbalance protection
The Digistart CS will trip on current imbalance if the highest and lowest currents on the three phases vary by
an average of 30% for more than 3 seconds. Current imbalance protection is not adjustable, and is only
active when the average motor current is 50% or more of the programmed motor FLC.
If the soft starter frequently trips on current imbalance:

check that there is no imbalance on the mains voltage (on the input side of the soft starter)

insulation test the motor

move all input cables over one position (move L1 cable to L2, move L2 cable to L3, move L3 cable to
L1) to rule out a cabling fault
6.4.4 Supply frequency protection
The soft starter will trip on supply frequency if the frequency rises above 72 Hz or falls below 40 Hz for more
than five seconds while the soft starter is running. These trip points are not adjustable.
In pre-start, starting and stopping modes the high and low frequency limits both apply with no time delay.
A supply frequency trip will also occur if:

all three input phases are lost while the soft starter is running

all three input phases fall below 120 Vac at start or while the soft starter is running

the line contactor opens while running
6.4.5 Bypass overload protection
Bypass overload protection protects the soft starter from severe operating overloads while running. The
protection is not adjustable and has two components:

The soft starter will trip if it detects overcurrent at 600% of the programmed motor full load current.

The soft starter models the temperature of the internal bypass relays and will trip if the temperature
exceeds the safe operating level.
If the trip occurs frequently, this indicates that the soft starter has not been selected correctly for the
application.
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