Appendix E—Motor/Application Considerations
S811+ Soft Starter MN03900001E—November 2012 63
Appendix E—Motor/Application Considerations
Squirrel Cage Motor
This is the most common application.
The motor is configured with three motor leads available.
In this case, wire the motor to the soft starter with one lead
per phase, observing proper phase rotation. An in-sight
disconnect means should be installed, per code
requirements.
Wye-Delta Motor
The wye-delta motor is a traditional way of achieving a
reduced voltage start using regular contactors and starters.
In this method, the motor is constructed with all six leads
brought out to connect the unit in a wye configuration. This
allows about 58% of the current (33% starting torque) to be
applied during start-up. A timer is used to control the circuit
and switch to the delta configuration as the unit approaches
full speed.
In this case, wire the six-lead motor in a standard delta
configuration. The soft starter is then used to control the
voltage and motor torque without the need for additional
circuitry. An insight disconnect means should be installed,
per local code. The S811+ Soft Starter must be wired into
the three-phase line feeding the three main motor input leads
as would be done for normal across-the-line starting. It must
not be wired internally between motor windings in an
inside-the-delta configuration.
Part Winding Motor
The part winding motor is another design created to help
achieve a soft start to the load. A part winding motor is
constructed of two separate (but parallel) windings. When
using a traditional starter, the first winding would receive full
voltage. This winding supplies as much as 400% of the
motors FLA; about 45% starting torque in a delta
configuration for motor startup. After a timed delay, full
voltage is applied to the second winding. The second
winding acts in parallel with the first to provide for normal
running current. Part winding motors are available in both a
wye and delta configuration, dependent upon the
manufacturer. Refer to the motor nameplate for the correct
wiring information. In this case, wire the two windings in
parallel. The soft starter is then used to control the current
applied to the motor. An in-sight disconnect means should
be installed, per code requirements.
Dual Voltage Motor
A dual voltage motor should be wired into the appropriate
configuration for the line voltage it is being applied to. Refer
to the motor nameplate for the correct wiring information.
The soft starter must be selected for the appropriate line
voltage.
Multi-Speed Motor
Some motors have multiple windings to allow operation at
different base speeds. The multiple speeds are sometimes
utilized for soft starting and other times for a process
requirement of the machine to which it is attached. If only
one speed is required, the motor should be wired for that
speed. If multiple speeds are required, the appropriate
contactors will need to be connected to the output of the
Soft Starter. The contactors must be in the selected speed
position before the soft starter is started. The motor must be
stopped and the soft starter turned off before the speed
selection contactors are changed.
Other Winding Configurations
Motors with other winding configurations, designed for
specific characteristics, should be wired in a fashion
consistent with their intended use. The motor nameplate
contains information on the available configurations. The
motor winding configuration chosen must be appropriate for
the available line voltage. The soft starter must also be
selected on the basis of the configuration chosen.
Power Factor Correction Capacitors
Power factor correction capacitors should be installed on the
line side of the soft starter. It is recommended that at least
10 feet of cable be between the capacitor and the soft
starter. The power factor correction capacitors can be
switched with a separate contactor. NEMA ICS2-1988 Part
2-210.81.01 provides recommendations for when a separate
contactor should be used to switch the power factor
correction capacitor including high inertia loads, reversing
motors, frequently jogged motors and multi-speed motors.
It is not recommended that the power factor correction
capacitors be used on the load side of the soft starter. If used
on the load side, the overload relay will measure the
combination of capacitor and motor current causing the
overload relay to not function correctly.
To Next Page
Loading...
