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45mm-wide module replaces star-delta starters

01 January, 2002

45mm-wide module replaces star-delta starters

Rockwell has developed a 45mm-wide motor starter module that replaces conventional start-delta starters, but takes up a third of the panel space. The Allen-Bradley SMC-Delta module combines the functions of contactors, overload relays, timers, and internal power and control wiring in a single device that is said to be quick and easy to install.

The true three-phase controller includes six motor winding terminals allowing contractors to wire it as they would a conventional installation. It incorporates an electronic overload relay and an SCR bypass contactor on all three phases, thus avoiding the need for parallel contactors and helping to dissipate heat.

The module uses a current-limiting starting technique that eliminates the current transition point usually found in star-delta applications, thus reducing electrical and mechanical shock to the system. The maximum starting current is limited to 150-350% of full load, and start times are selectable from 2-15s. The starters are available in ratings from 3-64A (30kW at 415V).

Settings are chosen using miniature DIP switches. According to Rockwell`s product manager Jeff Stewart, the module requires "no more setting up than a star-delta starter". He says that price of the module will be similar to that of a conventional star-delta installation.

Rockwell has also developed a companion soft-start in a similar modular format but offering more sophisticated functions. For example, the SMC-3 incorporates a selectable kick-start that can provide a current pulse up to 450% of full load current for up to 1.5s. This allows the motor to develop additional torque for loads that are hard to start.

The SMC-3 incorporates programmable overload protection with an adjustable trip class, as well as advanced diagnostics and configurable auxiliary contacts. At present, the soft-start is available in ratings from 3-37A, but it will eventually be extended to upwards to "hundreds of amps" according to Stewart.

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