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Rockwell Automation’s Allen-Bradley softstarter suits in centrifugal pumping applications [Oct 2011]

Rockwell Automation, one of the leaders in the market, thanks to the flexible, stepless, cost-effective and user-friendly softstarter that suits most applications. Exceptions being those with constant or square torque control requirements, such as in lifting/hoisting type applications.
“Although the Allen-Bradley SMC Flex has been on the market for a number of years now, its proven reliability, fully featured control, protection, diagnostic and metering features and ease of application as a high-end starter have earned it a solid reputation in the market since its release. Subsequently, it has brought about a new dimension to motor control in this highly competitive space,” says Rockwell Automation business manager, Adrian van Wyk.
On-board integrated bypass circuitry that automatically closes when the motor reaches speed is offered as standard. This provides cooler operating temperature, lower heat dissipation requirements and hence a much reduced enclosure size and starter cooling requirements. It is generally 50 per cent smaller than traditional designs with heat losses being 80 per cent lower, notwithstanding the fact that the unit is rated to operate to an ambient temperature of 50° C without derating.
“The SMC Flex is ideal for almost any softstarting requirement application and is especially well suited when used in centrifugal pumping applications. It offers a unique approach to reducing fluid ‘surges’ or ‘hammering’ by utilising its pump control algorithm to bring unrivalled closed loop starting and stopping performance without the use of additional external devices. Almost 85 per cent of starters sold feature pump control,” says Van Wyk.
Available in varied power ranges, for voltages from 200 to 690 V AC for motor currents ranging from 5 to 1,600 A, the softstarter can run connected in line or inside the delta-loop configuration, making it even more attractive to utilize when upgrading or retrofitting traditional 3 or 6-wire electro-mechanical and star-delta type starters.
With its relatively small dimensions, the unit is ideal for retrofit, as it typically fits comfortably in a third of the usual space when compared to traditional electro-mechanical and star-delta type starters. This space saving is achieved by eliminating the need for at least two contactors and the overload device.
From a temperature and altitude perspectives device performance excels: “For the most part in southern African conditions, there would be no need to derate this starter as a result of high ambient temperatures or high altitudes. It is designed to perform to its full stated rating current to an ambient temperature of 50° C, up to an altitude of 2,000 m without derating, instead of the usual 40° C and 1,000 m as is the industry norm,” explains Van Wyk.
The SMC Flex softstarter fits perfectly into the Rockwell Automation Integrated Architecture environment when connected to Open Networks EtherNet IP, ControlNet or DeviceNet. “It shares the same DPI communication module platform with the PowerFlex 7 Class AC and PowerFlex DC drives. All levels of warning and trip set points are adjustable, additionally, all set points allow delay and inhibit per warning and trip set point to suit application and site variability,” explains van Wyk.
Diagnostic and troubleshooting feedback is enabled by the use of alpha-numerical text, instead of codes. As a result, the operator or technician is guided to identify problems faster, more accurately and can leverage from the diagnostic data to call out the correct technician to rectify the problem.
With the SMC Flex, all regular metering devices that would traditionally be required on the door of the motor control centre are onboard to be viewed on the integrated backlit LCD screen. This translates into space and cost savings.
The starter contains a full three-phase controller with current transformer measurement in each phase and offers under/over voltage, over/under-current (jam/underload), unbalance, stall and phase rotation protection. It also features an input for an external ground fault CT and an input for the positive temperature coefficient sensors imbedded in most high power electric motors.
“Even with its compact design, the SMC Flex’s smart control firmware allows the starter to be intelligent enough to protect the load and itself from high running currents, thus extending the life of the bypass circuitry. It will always switch the bypass circuitry in a closed transition (arc less) pattern on transition to bypass, transition from bypass and in the event of trip from bypass. Additionally, it switches back to thryristor control when it detects that the running current has exceeded the rating of the bypass circuitry and then switches back to bypass once the current has normalised,” concludes Van Wyk.
Rockwell Automation provides training as well as maintenance and service support for the SMC Flex softstarter.
 

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