When it Comes to AC Drives, Smaller is Better

Those who rely on AC drives in complex food manufacturing applications have come to realize that smaller is indeed better. Thanks to advances in electronics and materials, the latest generation of AC drives is more reliable, simpler to use and program, and delivers more functionality in a smaller footprint than ever before. And since drives play such an integral role in the food manufacturing industry – by giving processors the ability to optimize their yield, quality and throughput to achieve maximum efficiency – size has become a key factor.

How processors can optimize yield, quality and throughput


Those who rely on AC drives in complex food manufacturing applications have come to realize that smaller is indeed better. Thanks to advances in electronics and materials, the latest generation of AC drives is more reliable, simpler to use and program, and delivers more functionality in a smaller footprint than ever before. And since drives play such an integral role in the food manufacturing industry – by giving processors the ability to optimize their yield, quality and throughput to achieve maximum efficiency – size has become a key factor.
       

Stand-Alone Drives versus Multi-Drives: Basic Differences in Application

Single industrial drives

Adjustable Speed Drives are used in any application in which there is mechanical equipment powered by motors; the drives provide extremely precise electrical motor control, so that motor speeds can be ramped up and down, and maintained, at speeds required; doing so utilizes only the energy required, rather than having a motor run at constant (fixed) speed and utilizing an excess of energy. Since motors consume a majority of the energy produced, the control of motors, based on demands of loads, increases in importance, as energy supplies become ever more strained. Additionally, end users of motors can realize 25-70 percent energy savings via use of motor controllers. (Despite these benefits, the majority of motors continue to be operated without drives.)
Industrial drives convert AC power to DC, and then invert the DC back to an AC output to a motor. These drives cover a wide, full range of powers and voltages. Single industrial drives also feature a wide range of built-in options as standard equipment.

Multidrives

A multidrive is built from industrial drive modules that are connected to a common DC bus bar. The common bus bar is used to supply the drive modules with DC power, and each module then inverts the DC to AC and powers an individual motor. The DC power is derived from a single supply unit that is built into the front end of the same multidrive configuration.
This construction simplifies the total installation and results in many benefits: savings in cabling; reduced line currents and simpler braking arrangements; energy distribution over the common DC bus bar, which can be used for motor-to-motor braking without the need for a braking chopper or a regenerative supply unit; reduced component counts; increased reliability; and space savings; and there is no need for a separate Motor Control Center (MCC).

Where can multidrives be used?

In general terms, multidrives can be used whenever several drives/motors form part of a single or integrated mechanical process. The common supply of the multidrive enables the implementation of overall safety and control functions, and permits the close coordination of individual drive motors. For example, a paper machine has many motors that must be individually controlled as a complete system. Multidrives offer fast communication of torque and speed signals between the drives, to control the tension in the paper web. Multidrives also can be used where the shafts of the individual drive motors are not tightly coupled; for example, in processes where each drive module can be programmed with a speed profile so that the overall use of energy is minimized.
-- ABB Inc.

One of the most valuable assets in a food processing facility is space. Smaller components, such as drives, reduce the space requirements of control cabinets, allowing for more room for food processing machinery on the plant floor. In addition, by improving the reliability of the drives, food manufacturing operations can avoid failures due to heat or failed mechanical components that can bring the process to a standstill. Unscheduled stops to a process result in lost production while the drive is being replaced and lost time as the process ramps up again. Also, food manufactured during the ramp-up time will not meet quality standards and must be thrown away, resulting in yet another loss. The impact can be devastating to a food manufacturer.
       
Reliable drives, therefore, greatly minimize downtime and increase the operational efficiency of food manufacturing operations. This is one of the key factors driving the overall productivity of the processing application.
       
How do engineers create variable-speed drives that deliver consistent quality and take up less space? The formula is simple – replace electro-mechanical components with smaller and efficient electronic technology. Engineers have successfully developed new drives with components that generate significantly less heat than previous generations of drives, helping to eliminate a major cause of drive failures. In addition, they have worked to reduce the amount of wiring needed and the number of wiring connection points, saving space and eliminating a potential failure and major source of electromagnetic noise.
       
Here are some innovations that have advanced drive performance and improved reliability in food manufacturing applications.    

Reducing heat

Heat is one of the worst enemies of electronic performance, particularly in a small-footprint, high-use component such as an AC drive. To combat excess heat, design engineers have taken advantage of a wide range of new technologies:
       

AC drives play an important role in keeping processing equipment, such as conveyors, operating at optimum capacity. Today's more efficient and reliable drives help to keep systems up and running.

Improved IGBTs The new generation of insulated gate bipolar transistors (IGBTs) offers attributes such as high switching speed, low conduction voltage drop and high current carrying capability – thanks to “trench technology” – that helps to lower the cost of systems while allowing the same drives to be effective over a broader range of food processing applications. Trench technology improves the resistance of IGBTs, reducing the heat generated as a byproduct of IGBT operation. Less heat generation in the transistor means better thermal efficiencies, which translates into a more reliable drive. When there is less heat to dissipate the drive can be engineered in a smaller package. This gives engineers a cost-effective alternative to use the same drive for numerous food manufacturing applications: mixing, heater/blowers in confection ovens, to simple material handling.
       
Nanocrystalline core technology Like IGBTs, improvements in the core material used in a drive’s electromagnetic compatibility (EMC) filter offer another key advancement in reducing heat. The latest generation of EMC filters uses nanocrystalline material, an amorphous structure that is highly permeable compared to the ferrous materials traditionally used in EMC cores. Nanocrystalline material provides higher inductance and, consequently, generates less heat because it is permeable. This allows designers to use a filter that is 20 percent smaller than those found in previous generations of drives, freeing up valuable space.
       

The new Telemecanique® Altivar® 71 variable speed AC drive from Schneider Electric offers best-in-class motor control for up to 700 HP motors, making it the most advanced AC drive on the market for applications such as mixers and heater/blowers in food processing facilities.

Improved heat sinksVirtually all power electronic devices feature a heat sink that is designed to radiate heat away from the components inside. A well-designed heat sink is essential to drive reliability because it dissipates unwanted heat that can lead to component failure. Engineers have developed a heat sink fabricated of a unique aluminum alloy that transfers heat better, allowing a smaller heat sink to dissipate heat more efficiently. On average, the heat sink size can be reduced by 10 percent when using this new alloy. Again, this frees up manufacturing space for critical processing equipment.    

Eliminating potential failure points

Heat isn’t the only enemy of drive performance in food manufacturing, however. Failed mechanical components and electrical connections also contribute to drive failure. New AC drive designs eliminate these components, greatly increasing reliability.
       
A controlled input bridge is a combination of diodes and silicon controlled rectifiers (SCRs) that convert incoming AC power to DC power. Replacing mechanical components with an input bridge controlled by a microprocessor reduces its size and also makes it more reliable because it is a solid state package.
       
Replacing traditional wiring and wiring connections with laminated bus technology, which is used for carrying high-power current within an AC drive, is another significant innovation in food processing applications. Bus technology greatly reduces drive size while also eliminating electrical noise.
       
Modern drive technology advancements continue to make new and better solutions available to component designers in food processing applications. Understanding and taking advantage of these advances can help manufacturers optimize their processes, prevent drive failures and reduce their overall downtime.

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