What are Variable / Adjustable Speed Drives?

Blog | August 31st, 2017

In the context of bearing technology, variable speed drives regulate motor shaft velocity. Gearing configurations alter the power transmitting characteristics of a drive system. Alternatively, electronic devices also act as adjustable speed drives, although they use voltage and frequency manipulating circuits, not actual adjustable mechanical components. Do both of these drive speed manipulating configurations perform equally? Here’s a guide to both drive solutions.

Mechanically Configured Variability 

Long before electronic circuits arrived on the scene, gearing trains acted as adjustable speed drives. Today, they’re still fitted between a prime mover and its main drive system as a series of gears. Larger and smaller gears mesh to alter torque, maintain overall transmitted energy, and govern the drive shaft’s radial velocity. Granted, these are entirely reliable speed management systems, but there are a number of parts in play in this operational setup. Belt drives need to be tightened, gear wheels need initial heat treatment work in the form of a case hardening procedure, and there’s also a need for a lubricating film throughout the gearing assembly. Still, it’s hard to imagine an equipment setup that’s more efficient, especially when the gearing parts and their associated bearings are manufactured from high-performance components.

Variable Speed Drives: Electronic Solutions 

Compared to their more established mechanical antecedents, electronic speed control technology is an immature upstart. However, that upstart is backed by decades of finely tuned science. Voltage regulators, power inverters, and frequency regulators control shaft speed this time, with the equipment dismissing gearing packages and lubricating agents in favour of an adjustable power input signal. It’s here that complex equipment lines use electronic feedback modulations to finitely regulate sophisticated motors and their coupled drive trains, but that electronic option does require some site stability. On the other hand, as long as the sealed gearing unit is bathed in a suitable lubricant, mechanically adjustable speed drives operate in incredibly harsh environments, including the mines and quarries that age all other system types.

Fundamentally speaking, gearing units have a reliance factor that can’t be overcome. Their ratio changing armatures and speed altering spur gears operate at peak efficiency and their bearings deliver lossless power. Equipped with ingress protection systems and toughened motors, those adjustable speed drives still surpass their electronically equipped counterparts. Still, away from coarser operational settings, the more compact electronic variable speed drives (VSDs) are cutting out a space of their own. But do remember, that mechanical model has developed as a workhorse shafting solution, one that doesn’t suffer heat losses, not when the underlying bearings are performing at their best.

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