Running a motor continuously at full speed and then throttling its flow with a valve or damper is like driving with the accelerator floored while applying the brakes to slow down: it wastes energy and accelerates mechanical wear. A variable speed drive (or variable frequency drive, VFD) solves this problem by matching motor speed to the actual process demand. However, it is not always justified. For a maintenance manager or technical director in Burkina Faso, the real question is not “what is a drive?” but “on which machines is it profitable, and from what point?”. This article addresses these questions by focusing on concrete applications and total cost of ownership.
What a Variable Frequency Drive Actually Does
A variable frequency drive is an electronic device installed between the power supply and the motor. It converts the input frequency and voltage to precisely control rotational speed, unlike direct-on-line (DOL) starting, which only provides two states: stopped or full speed. Beyond speed adjustment, it delivers soft starting that eliminates inrush current peaks (which can reach 6 to 8 times the nominal current in direct starting), precise acceleration and torque control, and integrated motor protection (overload, phase imbalance, overheating). This versatility explains why its value extends far beyond energy savings alone.
When Is a Variable Frequency Drive Truly Worth It?
The value of a drive depends primarily on the type of load driven by the motor and how demand fluctuates over time. Below are the applications where it is most justified—and those where the return is tangible, yet different.
Pumps and Fans: Maximum Savings (Variable Torque Loads)
This is where a drive offers the highest return on investment. On a centrifugal pump or fan, power consumption varies approximately with the cube of the speed: reducing speed by 20% does not reduce consumption by 20%, but by roughly half. Whenever flow rate or pressure is currently regulated by a valve, damper, or bypass, a drive delivers the same output while consuming significantly less power. Energy savings typically observed in these applications range from 20% to 50%. On pumping, ventilation, or compressed air systems that operate for a substantial part of the day, payback is often achieved in months rather than years.
Conveyors, Mixers, Compressors: Control and Flexibility (Constant Torque Loads)
On constant torque loads, pure energy savings are more modest, but the drive delivers other decisive advantages. On a conveyor belt in mining or cement plants, it allows for smooth starting under load, matches throughput to material flow, and reduces mechanical wear on pulleys and splices. On a mixer or crusher, it regulates speed according to the recipe or material characteristics. The drive thus becomes a key asset for process quality and mechanical longevity as much as for energy efficiency.
Processes Requiring Fine Regulation and Synchronisation
Whenever a process demands precise speed control, synchronisation across multiple motors, or closed-loop feedback based on a process variable (flow, pressure, level, temperature), a drive is virtually indispensable. Paired with measurement instrumentation and a PLC, it continuously modulates speed to maintain a setpoint—something impossible to achieve with on/off starting.
Benefits Beyond the Electricity Bill
Reducing kilowatt-hours is the most prominent argument, but rarely the only one that justifies the investment. By eliminating starting shocks, the drive extends the lifespan of the motor and transmission components (belts, couplings, bearings) while reducing stress on the electrical grid. It prevents abrupt restarts that, on an unstable network, can burn out windings—and ultimately lead to the dilemma of motor rewinding versus replacement. Finally, certain models provide a ride-through function during brief voltage dips, which is invaluable when dealing with grid disturbances.
When a Drive Is NOT the Best Solution
A drive is not a universal solution. On a motor operating continuously at constant speed and load, with no requirement for regulation, energy savings are negligible, making the investment difficult to justify. If the sole objective is to soften starting without ever varying the speed afterwards, a simple, more cost-effective soft starter is often sufficient. Furthermore, a drive introduces sensitive electronics into the control panel: in environments with extreme heat, dust, or humidity, appropriate cooling and ingress protection must be provided to avoid creating new operational issues. The right approach is to size equipment according to actual operating conditions rather than retrofitting drives systematically.
Thinking in Terms of Total Cost of Ownership
Procurement decisions should not be based solely on initial purchase price, but over the asset’s entire lifecycle. Over a ten-year period, energy accounts for approximately 95% of the total cost of an induction motor; acquisition and maintenance represent only a small percentage. A drive that cuts power consumption by 25% on a continuously operating pump pays for itself comfortably, often within 2 to 3 years, and subsequently yields net savings throughout the remainder of its service life. A sound evaluation balances the upfront cost of the drive against cumulative energy savings, reduced downtime, and extended mechanical lifespan.
| Load Type / Application | Energy Savings | Is a Drive Worth It? |
|---|---|---|
| Variable flow pump / fan | High (20–50%) | Yes — High priority |
| Conveyor, mixer, compressor | Low to moderate | Yes — For control and longevity |
| Process requiring regulation / synchronisation | Variable | Yes — Virtually indispensable |
| Constant speed and load motor | Low | Rarely — Consider a soft starter |
The West African Context Factors into the Decision
In Burkina Faso and across the subregion, two operational realities heighten the value of variable frequency drives—provided they are installed correctly. On one hand, elevated energy costs and the growing share of on-site power generation (generator sets, solar) make every saved kilowatt-hour critical: cutting consumption on pumps and fans directly lowers utility bills and relieves capacity constraints on generators. On the other hand, on grids subject to frequent outages, soft starting mitigates current spikes during restarts following load shedding. Conversely, ambient heat and dust demand well-ventilated and filtered enclosures: a properly protected drive is a drive that lasts. This underscores the importance of sizing equipment for local field conditions rather than simply copying a European catalogue.
FAQ
Does a variable frequency drive genuinely save energy?
Yes, particularly on variable-flow pumps and fans, where energy consumption typically decreases by 20% to 50%. On these loads, power demand varies with the cube of the speed: a modest reduction in motor speed yields substantial power savings. Conversely, on a constant-speed motor, energy gains are minimal.
What is the difference between a variable frequency drive and a soft starter?
A soft starter serves solely to smooth out the starting phase, after which the motor runs at full speed. In contrast, a variable frequency drive continuously modulates speed throughout operation, enabling sustained energy savings. If your process does not require speed variation, a more economical soft starter is sufficient.
Which Machines Should Be Prioritised for Drive Installation?
Priority should be given to centrifugal pumps, fans, and compressors that operate for long hours under variable flow, as they deliver the fastest return on investment. Next are conveyors and industrial processes that require precise speed control or gentle starting under load.
Does a Drive Protect the Motor from Power Outages?
It mitigates electrical stress by eliminating inrush current peaks during startup and, on certain models, can maintain motor operation through brief voltage dips. However, it does not replace a comprehensive uninterruptible power solution; on an unstable grid, it must be combined with suitable surge and power protection equipment.
Select and Size the Right Drive with GEMCO
A properly selected and installed drive represents one of the most effective energy performance investments for an industrial facility—provided it is engineered around the actual operating parameters of each machine rather than a generic rule. GEMCO assists industrial operators across Burkina Faso and West Africa with requirements analysis, selection, procurement, and commissioning of variable frequency drives, partnering with leading manufacturers such as WEG (for whom GEMCO is the exclusive representative in Burkina Faso for motors, drives, and transformers), Schneider Electric, and ABB.
Contact GEMCO engineers for a technical assessment of your installations and a quotation for drives tailored to your process and site conditions.
