Variable Frequency Drives

Transcription

1 Variable Frequency Drives Presented by: Chris Caldwell, Sulzer-ABS Sean Fitzpatrick, Schneider Electric/Square D Industry Webinar 9-14

2 Pumping Systems & Controls 2011 Participants are in a listen-only mode. To ask a question during the event, use the chat feature at the bottom left of your screen. Technical questions will be answered by ReadyTalk. Questions for our speakers can be asked at any time and will be answered during the Q&A at the end of the session. Visit pump-zone.com in the coming days to access the recording of the webinar or download the presentation. Copyright Submersible Wastewater Pump Association (SWPA)

3 Variable Frequency Drives Presented by: Chris Caldwell, Sulzer-ABS Sean Fitzpatrick, Schneider Electric/Square D Industry Webinar 9-14

4 Pumps & VFDs Energy Savings and MORE! Protection, Prevention, Communication

5 Energy Savings with VFD Pump Systems Energy represents 40% or more of Total Life Costs of many pump systems The majority of pump applications offer Energy savings potential Most all states have utility driven incentive programs to install/upgrade VFDs in pump applications Typical pump life-cycle cost profile (Courtesy of Hydraulic Institute and Pump Systems Matter)

6 Other Savings with VFD Pump Systems What if these same VFDs could reduce operating costs in areas such as Pump maintenance Pump operations Downtime Represents an additional 38% of pump life-cycle costs Typical pump life-cycle cost profile (Courtesy of Hydraulic Institute and Pump Systems Matter)

7 Intelligent Pumping Energy Efficiency Urbanization Water Crisis/Efficiency Environmental Impact/Operating Costs Intelligent Pumping

8 Application and Pump Selection for VFD Systems While many pumping applications will benefit from VFDs, not all applications are appropriate. To maximize energy savings it s important to understand where VFDs are of benefit, and where other starting methods are more appropriate. In a properly selected VFD application, where does the energy savings come from?

9 Application and Pump Selection for VFD Systems The Affinity Laws predict the performance of a centrifugal pump at differing speeds. The change in flow is proportional to the change in speed. The change in head is proportional to the square of the change in speed. The change in power is proportional to the cube of the change in speed. Q = flow H = head pressure P = power Q Q H H P P = = = n n n n 1 2 n n

10 Application and Pump Selection for VFD Systems Reducing the frequency (and rotational speed) from 60Hz to 50 Hz, or about 16.7% results in: A flow reduction of 16.7% to 1667 gpm A head reduction of 30.6% to 69.4 feet A power reduction of 42.1% to 38.8 hp Of course the pump will not necessarily run at this new flow and head. The actual new operating point depends on where the system head curve intersects with the reduced speed pump curve.

11 Application and Pump Selection for VFD Systems Slowing the pump down with a VFD helps reduce the power consumed overcoming the dynamic losses in the system (friction in the pipes and fittings). Slowing the pump down does not help with overcoming the static head in a system. Static head is the enemy, and pretty much all pump applications have it. Systems with a low percentage of static head in the total head make good VFD applications and systems with a high percentage of static head do not make good VFD applications. Let s look at some curves to see why.

12 Application and Pump Selection for VFD Systems H / ft Typical six inch, 140 hp submersible pump curve Head Q / US g.p.m.

13 Application and Pump Selection for VFD Systems H / ft Add reduced speed curves at 5 Hz intervals, down to 35 Hz H z H z H z 40 H z 45 H z 20 Head Q / US g.p.m.

14 Application and Pump Selection for VFD Systems H / ft Add lines of constant efficiency % % % 69 % % 68 % % H z H z H z 40 H z 45 H z 20 Head Q / US g.p.m.

15 Application and Pump Selection for VFD Systems H / ft Add duty point A1, 1,800 gpm at 160 feet of head % 65 % 68 % 69 % Add system head curve with a static head of 60 feet A1 69 % 68 % 65 % H z H z H z 40 H z 45 H z 20 Head Q / US g.p.m.

16 Application and Pump Selection for VFD Systems H / ft Same duty point except the static head is now 145 feet % 65 % 68 % 69 % Very flat system curve forces the reduced speed operating point to move left very quickly A1 69 % 68 % 65 % 55 H z H z H z 40 H z 45 H z 20 Head Q / US g.p.m.

17 Application and Pump Selection for VFD Systems First rule of thumb: Applications where the static head is greater than 50% of the total head are not usually good applications for VFD variable speed pumping. This is because: Since the system curve is very flat, the pump efficiency at the reduced speed operating point falls off rapidly. The opportunity for energy savings at reduced speed is minimal. Since the system curve is very flat, there is very little useable speed reduction range. Pump rotational speed at reduced speed, lower flow conditions remains very high, resulting in high energy recirculation cavitation, which can damage the pump.

18 Application and Pump Selection for VFD Systems H / ft Alternate pump selection with best efficiency point further to the left Previous pump had the full speed BEP at about 1,950 gpm. With this pump, it s about 1,480 gpm % 64 % 66 % 68 % 35 H z 40 H z 68 % 45 H z 66 % 50 H z 64 % 55 H z 60 % 363.8* H z Head Q / US g.p.m.

19 Application and Pump Selection for VFD Systems H / ft The same 1800 at 160 duty point, and 60 feet of static head % 64 % 66 % 68 % 68 % % A1 64 % % 363.8* H z H z H z 45 H z H z 30 Head Q / US g.p.m.

20 Application and Pump Selection for VFD Systems H / ft The same 1,800 at 160 duty point, and 145 feet of static head % 64 % 66 % 68 % 68 % % A1 64 % % 363.8* H z H z H z 40 H z 45 H z H z Head Q / US g.p.m.

21 Application and Pump Selection for VFD Systems Second rule of thumb: For variable speed applications, select pumps with the full speed operating point to the right of BEP whenever possible, especially with systems having a high percentage of static head. Selecting to the right of BEP improves efficiency at reduced speed since the intersection point with the system curve moves toward BEP when slowing down. Variable speed applications often allow the use of smaller, less expensive pumps. Smaller pumps and selections right of BEP provide the best opportunity for energy savings at reduced speed (where the pumps run most of the time). Check NPSH margin for all selections, especially when selecting to the right of BEP!

22 Assuming a proper application, what else will a VFD do for you Soft starting/stopping capability Reduction of mechanical stress, extending the life of both pump & motor, reducing maintenance expenses Reduction and/or elimination of water hammer caused by an abrupt change of flow Elimination of starting inrush currents (6-8X motor FLA) reduce likelihood of peak demand charge penalties Some utilities require that motors over a certain horsepower undergo a soft start Inherent Power Factor correction, increasing efficiency

23 VFD functions Typical VFD built in functionality includes: Motor thermal overload protection Phase loss/reversal detection Built-in equipment efficiency monitoring to optimize systems Sleep/wake function - to stop the motor in standstill situations. Results in energy savings and prevents premature aging of equipment

24 VFD functions Pump specific VFD functionality may include: Loss of prime detection Low/no flow detection prevent the pump from being damaged or destroyed under these conditions Low/high pressure level detection sensor-based solution to prevent pump damage Broken pipe detection Pump over cycle protection Advanced sleep/wake function POWER TREND Alarm

25 VFD functions Pump Specific VFD functionality may include: Pump cycle start protection provides an alarm signal to prevent excessive starting Cavitation protection Impeller wear indication and alarming Drift detection with userdefined allowable limits Dry run protection sensorless and sensor-based solutions to prevent pump damage

26 VFD functions Pump Specific VFD functionality may include: Sensorless flow estimates flow based on input of specific pump curves Jockey pump control increases system efficiency in low demand situations Anti-jam protection allows for manual or automatic forward and reverse pump rotation Pipe fill function reduce or eliminate waterhammer Friction loss compensation offset pressure drop over the pipeline system

27 Maintenance Reduction Corrective Maintenance: The pump seal has failed we need to fix it now! Preventive Maintenance: The pump seals fail after 2.5 years on average, so we ll replace them during shutdown every two years. Predictive Maintenance: We can see the pump performance is drifting looks like the seal is starting to go, we need to replace it at the next opportunity.

28 Diagnostic Logs Time stamping of events Current and historical error conditions Current and historical warning conditions Configurable customer warnings Submersible Wastewater Pump Association

29 Dynamic QR codes The display can create a QR code which can be used to: Access online documentation Automatically create a support ticket Report diagnostic information Dynamic QR codes for diagnostics information and online manuals and information Submersible Wastewater Pump Association

30 Maintenance Reduction Corrective Maintenance: The pump seal has failed we need to fix it now! Preventive Maintenance: The pump seals fail after 2.5 years on average, so we ll replace them during shutdown every two years. Predictive Maintenance: We can see the pump performance is drifting looks like the seal is starting to go, we need to replace it at the next opportunity.

31 Pump Operations Data A VFD may track and record pump operation history: Run time Number of starts Custom warnings set a date and time for an alarm to occur Submersible Wastewater Pump Association

32 Maintenance Reduction Corrective Maintenance: The pump seal has failed we need to fix it now! Preventive Maintenance: The pump seals fail after 2.5 years on average, so we ll replace them during shutdown every two years. Predictive Maintenance: We can see the pump performance is drifting looks like the seal is starting to go, we need to replace it at the next opportunity.

33 Pump Curves Pump curves can be entered into the drive to monitor pump performance: Application efficiency Predictive maintenance Submersible Wastewater Pump Association

34 Pump Curves Analysis of pump performance can provide information on application problems and maintenance problems Submersible Wastewater Pump Association

35 VFD functions Embedded web server access information any time, anywhere

36 VFD functions Integrated PID Control Eliminating the need for an external PID controller Costs less Simpler to configure Reduces of the integration need of multiple-control components Reduce wiring costs and possibility of loose connections Requires less panel space Reduces maintenance

37 VFD functions Phase Conversion The VFD converts incoming AC power to DC whether the source is single or three phase. Regardless of the input power, the output will always be three phase. As a rule of thumb, for a drive supplied by single phase input most manufacturers recommend using a drive that is double the motor size to handle the increase in current. Must always select three-phase pump motor. Low harmonic systems available for placement of relatively high loads onto these power grids.

38 Pumping Systems & Controls 2011 Don t miss SWPA s two-day Pumping Systems and Controls all based on the systems approach. November 5-6 Chicago, Ill. Register by calling or visiting swpa.org. Today s webinar attendees may receive ½ off their registration.* *offer available to first-time SWPA attendees only

39 Q & A Pumping Systems & Controls 2011 To contact today s presenters, Chris Caldwell Chris.Caldwell@sulzer.com Sean Fitzpatrick- sean.fitzpatrick@schneider-electric.com Visit pump-zone.com in the coming days to access the recording of the webinar or download the presentation. The next webinar in the SWPA series will be on December 11, More details coming soon.