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Considerations for Selecting VFD’s

Considerations for Selecting VFD’s. Quentin Nesbitt, PE Agricultural Engineer Idaho Power Company . Introduction . What is a VFD Applications of VFD Technical Considerations. Variable Frequency Drives. Other common terms – VSD - ASD - Variable Frequency Panel

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Considerations for Selecting VFD’s

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  1. Considerations for Selecting VFD’s Quentin Nesbitt, PE Agricultural Engineer Idaho Power Company

  2. Introduction • What is a VFD • Applications of VFD • Technical Considerations

  3. Variable Frequency Drives • Other common terms – VSD - ASD - Variable Frequency Panel • Solid state electronic device • Normal utility 60 Hz power no longer just 60 Hz • What does it look like?

  4. What I want you to Know After This Presentation • Cost of Pressure (psi) • Higher awareness of energy wasting practices • Good applications for VFD’s

  5. Formulas • HP = Flow X Head /3960 X Efficiency • Cost $=BHP/Motor Eff.*.746*hrs*$/kWh

  6. Considerations • Hp and pump curve shape with time at different conditions determine energy operating cost • Ask specific questions on system characteristics • Where is the power, is it only single phase - Line extension costs - Single phase options-Utility running current and starting current limits • Consider other options – multiple pumps,valves

  7. Potentially Ideal Applications • Widely varied flow Requirements • Less total head needed as flow requirements are dropped (Extreme friction loss or major draw-down changes in a well) • Single Well serving a very large acreage • Long operating hours at less than full flow – Varied crops, multiple systems on one pump • Steep pump curves

  8. Alternatives • Multiple Pumps • Valveing – automatic, manual, Pressure regulating • Utilize more than is needed – more flow or more pressure or both

  9. Advantages /Disadvantages • Ease of daily management (+) • Energy savings (+) – sometimes less than expected • Initial cost $ (-) • High Tech device where service is harder to come by (-) • Power quality considerations – Harmonics (IEEE 519 standard) – Filtering usually required & adds to cost (-) • Usually the drive is 97-98% Eff.(heat loss in panel all the time) (-)

  10. Energy Savings • Normally no Demand Savings – Sometime during the month probably going to run at maximum • Energy Savings Calculations are not hard, but they do require the Pump Curve and some knowledge of the specific System • Design head is usually constant (although multiple set points are advantageous) • Pump efficiency does not stay constant

  11. Application example • 450 Hp Well • 490 acres • 3 Pivots, 2@130 ac, 1@100 ac, • 150 ac of handlines and wheelines including some corners • Analysis with: 450 Hp w/VSD, 450 Hp alone, 300 Hp &125 Hp Booster w/VSD on Booster

  12. Cost estimates • Cost per horsepower seems to range between $90 and $200 per Horsepower • Medium voltage drives are considered to be 2300 volts - seem to be on higher end even though large horsepower • Low voltage is 480 volts and lower. • Single phase drives that convert to three phase maybe a option for single phase customers • 200 Hp 6 pulse filter $8000, LR-$500 • Check with Idaho Power and know and understand harmonic standards-(IEEE519)

  13. Cost (cont.) • Hp $ • 40 $4,500 • 100 $20,000 • 200 $32,000 • 300 $38,000 • 600 $52,000

  14. Summary • Check with Utility know or understand your risk get information to determine IEEE 519 requirements • Owner’s that I know are very pleased • There are applications where there are cheaper alternatives

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