WEG S Series - Starting with Reduced Current; Starting with Reactor; Starting with Autotransformer; Starting with Frequency Inverter

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32 l Installation, Operation and Maintenance Manual – Synchronous Motors – S Line – Brushless – Horizontal 11866576
5.2 STARTING WITH REDUCED
CURRENT
If direct online start is not possible, the following starting
systems can be used in order to reduce the starting
current:
 With reactor
 With autotransformer
 With frequency inverter
 With soft-starter.
A
TTENTION
T
he selection of the starting method depends
on a previous evaluation of the motor
performance to validate the procedure.
5.2.1 Starting with reactor
In the starting with reactor, an impedance in the form of a
reactor is connected in series to the main terminals of the
motor, reducing the voltage at the motor terminals,
resulting in a reduction of the starting current. For being a
function of the current that passes through the reactor, the
impedance gradually reduces the motor acceleration, and
when the motor reaches 95% of the rated speed, the
reactor is short-circuited, the motor is synchronized and
starts operating at full voltage.
A
TTENTION
It is necessary assure an acceleration torque
that is sufficient to start the motor, because
with this starting method there is a
substantial reduction in the starting torque.
5.2.2 Starting with autotransformer
The effect of starting with autotransformer is similar to that
of starting with reactor. The use of a transformer to limit
the voltage reduces the starting current and the torque.
The starting torque is reduced proportionally to the line
current.
The start of the motor with autotransformer consists of a
voltage transformer with taps that allow the operation with
reduced voltage until reaching the full voltage. The taps
may be modified during starting until reaching the
synchronization torque and speed.
5.2.3 Starting with frequency inverter
For the starting and operation of the motor with frequency
inverter, refer to the equipment manual.
5.2.4 Starting with soft-starter
The starting procedure with soft-starter is similar to direct
start, except for the time to accelerate the load up to the
synchronization speed, which is longer.
During the starting process, the soft-starter progressively
increases the motor voltage from zero, allowing the motor
to accelerate the load up to the rated speed without
causing current or torque peaks.
The soft-starter can also be used to control the motor
stopping.