Considerations for Selecting VFD

1
Considerations for Selecting VFDs

• 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 VFDs

5
Formulas

• HP Flow X Head /3960 X Efficiency
• Cost BHP/Motor Eff..746hrs/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_at_130 ac, 1_at_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
• Owners that I know are very pleased
• There are applications where there are cheaper
  alternatives