South African industries facing rising energy costs, constrained capital budgets, and increasing pressure to improve uptime can now rethink how large motors are started, controlled and protected. A new medium-voltage motor control approach allows multiple high-power motors to be managed using a single medium-voltage variable speed drive, delivering significant reductions in capital expenditure, footprint and system complexity, without compromising reliability.
Referro Systems, Rockwell Automation’s trusted local distributor, is introducing the PowerFlex 6000 medium-voltage AC drive with synchronous transfer bypass (STB) to mining, water, utilities, and heavy-processing operations across South Africa. The solution represents a step change in medium-voltage motor control design, particularly for sites with numerous large motors operating in unison.
Rethinking traditional motor control architectures
Conventional medium-voltage motor control systems typically rely on individual drives or starters for each motor. While effective, this approach can be capital intensive, space consuming and complex to maintain, especially in applications such as pumps and fans, where motors are often started one at a time rather than simultaneously.
The PowerFlex 6000T with STB addresses this challenge by enabling up to 10 motors to be started and synchronised across the supply line utilising a single medium-voltage drive. The system supports combined currents of up to 3000 A, with a maximum of 680 A per motor, across voltage ranges from 2,3 to 11 kV.
Once any motor in the system reaches operating speed, it is synchronised to the fixed-frequency bus and the drive is automatically freed to start the next motor in sequence should the process require this. This architecture dramatically reduces the number of variable speed drives required across a site, while still delivering all the benefits of variable-speed control during continuous speed requirements, smooth start up acceleration and deceleration control delivered by the variable speed drive.
Smoother starts, longer equipment life
At the heart of the solution is STB, which ensures that voltage, frequency and phase are precisely matched during the transfer from variable-frequency operation to fixed-speed operation and vice versa. This synchronous transfer enables a smooth, bumpless handover. It eliminates the inrush current spikes, voltage dips and mechanical stress that typically plague traditional motor starting methods.
In practical terms, the benefits are substantial. Softer acceleration reduces torsional stress on shafts, couplings and driven equipment, extending asset life and reducing maintenance costs. Continuous processes such as pipeline compression avoid pressure surges, while fans and pumps experience fewer process upsets and less unplanned downtime. This results in significant energy savings for equipment driven by the variable speed drive.
Fewer assets, lower lifecycle costs
By consolidating motor starts into a single drive system, organisations can significantly reduce both capital and operating expenditure. In some applications, customers have reported up to 80% fewer drives required compared to traditional architectures. Reducing the number of drives not only lowers upfront costs, but also simplifies maintenance and spares management, and creates a cleaner, more manageable automation environment with intelligence built in.
The PowerFlex 6000T with STB also integrates seamlessly into a variety of modern digital architectures through networked connectivity, enabling direct communication with control systems. This connectivity supports predictive maintenance strategies, enhanced diagnostics and improved visibility into motor and process performance.
Designed for resilience and operational flexibility
The architecture of the PowerFlex 6000T with STB features dedicated variable-frequency drive input and output cabinets, individual per-motor bypass sections, line reactors and controls, all coordinated through a centralised control system.
This design enables secure, seamless handover between variable-speed and fixed-frequency operation via dedicated buses. The practical outcome is a highly resilient motor control system that protects both the process and the equipment.
Under normal operating conditions, the variable frequency drive (VFD) provides precise speed control for energy efficiency, soft starting and optimised performance under partial-load conditions. However, if the VFD needs to be taken offline for maintenance or experiences a fault, the system can automatically or manually transfer the motor to run directly at full fixed speed. Crucially, this can be done without interrupting production. In essence, the motors always have a reliable backup pathway. Integrated protection mechanisms, along with mechanical and electrical interlocks, are incorporated throughout the system to enhance operational safety and overall reliability.
Supporting national infrastructure and efficiency goals
Well suited to mining, water and wastewater, oil and gas, concentrated solar plants and utility infrastructure industries, the PowerFlex 6000T with STB is designed to perform in the most demanding industrial environments. By combining advanced Rockwell Automation technology with strong local expertise, Referro Systems is helping South African industry modernise motor control strategies, improve resilience and build more sustainable, efficient operations for the future.
For more information contact Referro Systems,
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