Chapter 3: Applications
3.1.11 – Efficiency
Although the use of the soft starter introduces a power loss, the system still retains an overall
efficiency of approximately 99.5%. If the optimizing function is selected, then the gain in motor
efficiency at partial loads is far greater than the loss of efficiency arising from thyristor heat losses.
If prolonged operation at full load is expected, the thyristor loss can be eliminated (as in some
matched motor/pump drives) by closing a bypass contactor around the soft starter. (This contactor
is readily controlled by the programmable relay set as
‘top-of-ramp
’ contacts as the circuit in
section 2.4.1 shows.)
3.1.12 – High-Efficiency Motors
Due to an inherently steep front to the speed/torque curve, high-efficiency motors can exhibit
instability when lightly loaded, and the optimizing rate parameter P19 may need to be adjusted to
compensate.
3.1.13 – EU Compliance with the EMC Directive
When considering the use or fitting of any Soft Starter, users and installers in European countries
must comply with the EMC Directive 89/336/EEC. The manufacturer of the soft starter has a
statutory obligation to provide a guide for compliance with this directive.
For the SR44, this guidance is given in the EMC guide which is chapter 4 of this manual. It is
essential that users and installers understand and comply with the requirements described in these
sections.
3.1.14 – Fuses
Circuit protection fuses should be rated to allow for the extended start times associated with the
use of a Soft Starter. Traditional HRC motor fuses may need to be rated higher than the motor
rated current for normal low-inertia applications, but modern “extended start” fuses will generally
give full motor protection. (See also section 3.2.2 relating to high inertia loads.)
Semiconductor fuses are available for the short-circuit protection of the thyristors in the SR44. See
the “Fuse and Current Ratings” section in chapter 2 (“Electrical Installation”) of this manual for
semiconductor fuse recommendations and details of the Overload incorporated into the SR44.
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019
3–4
Содержание Stellar SR44
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