Low-cost soft starter replaces star/delta units

Low cost soft starter has simplified wiring that fits in the same space as a conventional Star/Delta Starter and provides motor protection by offering soft starting/stopping.

Fairford is making it quick, easy and cost effective for companies to overcome the problem of transients associated with Star/Delta starting.

The company has developed the low cost SDF Soft Starter; a unit with simplified wiring that fits in the same space as a conventional Star/Delta Starter, and provides motor protection by offering the key benefits of both Soft Starting and Soft Stopping.

Launched at the recent Hanover Fair, the SDF offers a new form of soft starting which overcomes the problems of Star Delta current surges by ramping up to an initial voltage, holding the voltage, and then ramping up to full volts without disconnecting the motor from the mains supply.

This eliminates the high current that can occur at the transition from Star to Delta The introduction of the SDF unit is important because Star/Delta starter arrangements for AC induction motors are still used widely across all UK industry.

The traditional advantage they provide is that 58% of the line voltage is applied to the motor at start-up.

However, the system has several drawbacks.

First, the arrangement is complicated and costly, using three contactors and a timing mechanism to switch between them.

Second, installation costs are high because of the need for six connections between the motor and starter.

Third, if the transfer from Star to Delta occurs at less than 80% of normal speed, large current and torque surges can arise.

Fourth and final, Star/Delta arrangements cannot provide soft stopping.

In the past the arguments against replacing Star Delta arrangements with soft starters have centered on the costs and lost production time involved.

Today these costs can be avoided by employing Fairford's SDF soft starter.

Designed with the same footprint as that for Star/Delta starters, the SDF unit offers the convenience of fitting in the same installation space.

Furthermore, the SDF does not require all six wires to be brought back to the starter.

As a retrofit unit, the Delta connection can be made at the Soft Starter using the existing six wires from the motor; while in new installations, the Delta can be configured at the motor with only three wires being brought back to the starter.

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