Fairford synergy, User Manual

Page: 192 / 233

Synergy Series Soft Start User Manual
MAN-SGY-017. Version 01. 27/06/2016
192
8.3.6 Running Induction Motors (continued)
All Synergy soft-starters are microprocessor controlled, and this gives them a number of advantages. Firstly,
there are no adjustments to be made for the energy saving function: all calculations necessary to find the
best degree of phase-back of the thyristors for any load condition is made by the microprocessor. Secondly,
the start always synchronises with the supply voltage and a special structure of turn-on pulses virtually
eliminates the inrush currents normally associated with motor start-up; this happens every time. Lastly,
there is the absolutely stepless starting process, found only with the primary resistance or reactance
electromechanical starters - but without the wasted energy, and with the opportunity to control the
maximum current allowed to flow during the starting process. Other features such as soft stopping are
included to give considerable control over all modes of induction motor operation.
8.3.7 Reliability Considerations
An aspect of electronic controllers for induction motors which is of increasing concern is that of reliability.
There is little point in installing an expensive item of electronic equipment to save potentially considerable
amounts of money if the device is unreliable to the point that vital processes are constantly interrupted.
There are electronic products in the market place which appear to offer soft starting cheaply. They almost
always rely on less advantageous technologies such as analogue control, or half-control, where one of the
two thyristors in each phase is replaced with a diode. There are systems which only control the energy flow
in one phase while the other two are directly connected. Owing to the variable quality and performance of
many so-called inverters and soft-starters available to the unsuspecting purchaser, international standards
for these products have been developed.
So far, IEC 60947-4-2 - ‘AC Semiconductor Motor Controllers and Starters’ defines the softstarter in every
important respect, including thermal and overload performance as well as electromagnetic compatibility.
By ensuring that any motor controller equipment purchased conforms to IEC 60947-4-2, a user should be
reasonably safeguarded from shoddy or inadequate products when specifying equipment for future
installations. A particular advantage of the use of the optimising soft starter is its impact on the
maintenance requirements of associated electro-mechanical equipment. Optimising lowers the surface
temperature of the motor by reducing the losses within the motor. This prolongs the motor life - and
reduces heating of the surrounding atmosphere in the process. If the atmosphere is subject to air
conditioning, reducing the heat input will reduce the air conditioning costs. Reduced starting and running
currents reduces cable losses and, contactor switching operations are carried out under the most
advantageous conditions. No current flows on switch-on since all switching is carried out by the thyristors -
virtually eliminating the need for contact replacement.
Indeed, there are a growing number of installations where contactors are no longer employed,
being replaced by controllable circuit breakers or isolators instead.
In summary, electronic controllers for most fixed-speed applications are opening new ways of increasing
the efficient operation of induction motors, as well as offering significant benefits in control. Intending
users need to ensure themselves of the quality and performance of any products they expect to fit and this
can be reasonably expected if compliance with the appropriate IEC standards is demanded.
8. Applications (continued)