Motor protection delivers reliable, efficient operation

04/15/2013


Benefits of using a VFD

  • Energy savings
  • Reduces peak energy demand
  • Reduces power when not required
  • Fully adjustable speed (pumps, conveyors, and fans)
  • Controlled starting, stopping, and acceleration
  • Dynamic torque control
  • Provides smooth motion for applications such as elevators and escalators
  • Maintains speed of equipment, making drives ideal for manufacturing equipment and industrial equipment such as mixers, grinders, and crushers
  • Versatility
  • Self-diagnostics and communications
  • Advanced overload protection
  • PLC-like functionality and software programming
  • Digital inputs/outputs (DI/DO)
  • Analog inputs/outputs (AI/AO)
  • Relay outputs  

VFDs offer the greatest energy savings for fans and pumps. The adjustable flow method changes the flow curve and drastically reduces power requirements. Centrifugal equipment (fans, pumps, and compressors) follow a general set of speed affinity laws. The affinity laws define the relationship between speed and a set of variables:

  • Flow
  • Pressure
  • Power

Based on the affinity laws, flow changes linearly with speed while pressure is proportional to the square of speed. The power required is proportional to the cube of the speed. The latter is most important, because if the motor speed drops, the power drops by the cube. 

Figure 4. Affinity Laws – Flow/Speed. Courtesy: Eaton

Figure 4. Affinity Laws – Flow/Speed 

Figure 5. Affinity Laws – Pressure/Speed. Courtesy: Eaton

Figure 5. Affinity Laws – Pressure/Speed 

Figure 6. Affinity Laws – Power/Speed. Courtesy: Eaton

Figure 6. Affinity Laws – Power/Speed

In this example, the motor is operated at 80% of the rated speed. This value can be inserted into the affinity laws formula to calculate the power at this new speed:

Therefore, the power required to operate the fan at 80% speed is half the rated power.

Selecting the correct equipment

Choosing a soft starter or a variable frequency drive often depends on your application. Soft starters are smaller and less expensive when compared with VFDs in larger horsepower applications. Larger VFDs take up more space and are usually more expensive than soft starters.

Figure 7: Flow/pressure relationship. Courtesy: Eaton

That being said, while a VFD is often more expensive up front, it can provide energy savings of up to 50%, thereby producing more cost savings over the life of the equipment.

Speed control is another advantage of a VFD, because it offers consistent acceleration time throughout the entire operating cycle of the motor, not just during start-up. VFDs can also provide more robust functionality than soft starters offer, including digital diagnostic information.

It is important to note that a VFD can initially cost two to three times more than a soft starter. Therefore, if constant acceleration and torque control is not necessary, and your application requires current limiting only during start-up, a soft starter may be a better solution from a cost standpoint. 

Robert Fenton is a product line manager at Eaton. 


<< First < Previous 1 2 Next > Last >>

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
The true cost of lubrication: Three keys to consider when evaluating oils; Plant Engineering Lubrication Guide; 11 ways to protect bearing assets; Is lubrication part of your KPIs?
Contract maintenance: 5 ways to keep things humming while keeping an eye on costs; Pneumatic systems; Energy monitoring; The sixth 'S' is safety
Transport your data: Supply chain information critical to operational excellence; High-voltage faults; Portable cooling; Safety automation isn't automatic
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Maintaining low data center PUE; Using eco mode in UPS systems; Commissioning electrical and power systems; Exploring dc power distribution alternatives
Synchronizing industrial Ethernet networks; Selecting protocol conversion gateways; Integrating HMIs with PLCs and PACs
Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.