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agility
TM
Series Soft Start User Manual
MAN-AGY-001. Version 04. 21/09/2018
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.
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 soft starter
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
Applications (continued)
Motor Efficiency/Loss Characteristic