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    VFD Presentation

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    juhi993
    This document discusses whether variable frequency drives (VFDs) are worth it for pump applications or have been oversold. It provides an overview of different pump speed control solutions, including mechanical and electrical options. It also discusses various process solutions as alternatives to VFDs. Key considerations for pump selection, system design, and the electrical and commercial factors of VFD installations are reviewed. The document concludes that while VFDs provide a suitable solution in some cases, they do not always save energy and engineers need a strong understanding of both mechanical and electrical aspects of pump and motor operation.

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    Attribution Non-Commercial (BY-NC)
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    VFD Presentation

    Uploaded by

    juhi993
    282 views29 pages
    This document discusses whether variable frequency drives (VFDs) are worth it for pump applications or have been oversold. It provides an overview of different pump speed control solutions, including mechanical and electrical options. It also discusses various process solutions as alternatives to VFDs. Key considerations for pump selection, system design, and the electrical and commercial factors of VFD installations are reviewed. The document concludes that while VFDs provide a suitable solution in some cases, they do not always save energy and engineers need a strong understanding of both mechanical and electrical aspects of pump and motor operation.

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    This document discusses whether variable frequency drives (VFDs) are worth it for pump applications or have been oversold. It provides an overview of different pump speed control solutions, including mechanical and electrical options. It also discusses various process solutions as alternatives to VFDs. Key considerations for pump selection, system design, and the electrical and commercial factors of VFD installations are reviewed. The document concludes that while VFDs provide a suitable solution in some cases, they do not always save energy and engineers need a strong understanding of both mechanical and electrical aspects of pump and motor operation.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    282 views29 pages

    VFD Presentation

    Uploaded by

    juhi993
    This document discusses whether variable frequency drives (VFDs) are worth it for pump applications or have been oversold. It provides an overview of different pump speed control solutions, including mechanical and electrical options. It also discusses various process solutions as alternatives to VFDs. Key considerations for pump selection, system design, and the electrical and commercial factors of VFD installations are reviewed. The document concludes that while VFDs provide a suitable solution in some cases, they do not always save energy and engineers need a strong understanding of both mechanical and electrical aspects of pump and motor operation.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    of 29

    Pump Applications Using VFDs

    Are VFDs worth it for pump applications? Have they been oversold to the market? Presented by Geoffrey D Stone C.Eng FIMechE; CP Eng FIEAust RPEQ Design Detail & Development
    http://waterhammer.hopout.com.au/ Skype address geoffrey.d.stone

    Why Are VFDs Specified for Pumps


    Process conditions Electrical supply

    are not fully developed Variable process conditions Poor pump selection Future process upgrades Energy efficiencyReduced operating cost Prior art-Industry

    restraint-Soft starting Braking- Dynamic or hold Unlimited number of starts and stops Waterhammer mitigation-Fatigue Ignorance -Engineer having no understanding of other process control

    Pump Speed Control Solutions


    Mechanical Cone & disc variator Cyclic variator Vee belt & pulleys Gearbox Internal combustion engine Scoop control fluid couplings Hydraulic drive Electrical Variable Frequency Drive Eddy current drive Two speed motor Direct Current drives Slip ring motors Multiple pole motors Relay pulsed motors

    Process Solutions-Alternatives
    Pressure, Change pump

    temperature or flow control valves Bypass valves Larger suction tanks or sumps Holding tank Pump for longer periods Stop/start controls

    impeller diameter Alternate pump type Multiple pumps Different sized pumps

    Pump Considerations

    Pump Selection-The Issues


    Duty point(s) Casing pressure

    Static head (Hs)


    Friction loss (Hf) Dead head Transients Design factors

    - head - flow - NPSHa

    rating Efficiency Specific speed Moment of inertia Curve shape Stability over range Best efficiency point 1st Critical speed

    System Design-Issues
    Software allows the Motor/VFD

    analysis of systems Excessive design factors used Pump suppliers design factors New vs. Old pipe friction losses Pipe wall /lining tolerances

    Efficiency Wire to Water kW The original Affinity Laws are based on systems with no static head Affinity Laws overstate energy savings Revise the 2nd Affinity Law for

    Pump Curve #1-VFD Viable

    Pump Curve #2-VFD Not Viable

    Existing Pump Oversize?


    This is a common pump dilemma that VFDs are used to solve but the VFD does NOT save the energy! The credit goes to the reduced head/flow requirements. VFD suppliers offer the retro-fit of a VFD to change pump speed to meet reduced process conditions Change of pump or impeller reduced diameter achieves the necessary reduced flow, hence power A flow control valve achieves the necessary reduced flow and maintain the best efficiency point (BEP)

    Pump Curve #3-VFD, control valve or


    reduced impeller viable

    Pumps using VFDsConsiderations


    Energy savings with a VFD occurs for duties

    reduced to between 60% to 85% of the BEP. Where duty is reduced to only 85% of BEP, a control valve or reduced impeller energy demand is less than that for the combined VFD installation inefficiencies Wire to water energy kW-hr per m3 delivered should be the criteria used in assessing a VFD application VFDs offer little benefit for systems with more than 50% static head VFDs are ideal for closed systems with varying process duties-no static head

    Electrical Design Considerations

    What is a Variable Frequency Drive?


    Legacy- < 600Hz
    BJTs (Bipolar Junction

    Today >20kHz
    IGBT (Insulated Gate

    Transistor) SCRs (Silicon Controlled Rectifier) GTO (Gate Turn Off Thyristor)

    Bipolar Transistor)these offer the benefits of higher frequencies and increased efficiencies

    Electrical Factors to be Considered


    Voltage (LV, MV or Overspeed capability

    HV) Braking requirements Power Power loss Line & load side Ride through time harmonics Audible noise Load torque Length/type of cable Speed range Power factor Speed regulation correction Failure mode Altitude Acceleration/decelerat Motor, insulation and ion times VFD life Mechanical engineers are required to Efficiency

    understand the electrical issues

    Cable
    Voltage peaks at motor terminals can be

    increased to 2 times the peaks of the VFD output for a long cable 25m is the recommended cable length Cables longer than 25m have an inductive load that affects a motors life Cables need to be screened to avoid EMI

    Motor Considerations

    Bearing Damage Induced Shaft Voltage


    Induced Shaft Current Types 1. Conductive mode bearing current-low speed , good conductivity. 2. Discharge mode bearing current-higher inverter output frequencies-The capacitive voltage builds up until it is able to break down the dielectric resistance of the grease.

    Motor Cooling
    Below 25hz motor fan speed will not cool

    motor Supplementary fan required Added cost of drive, cable, SCA, controls, access and maintenance Reduced reliability

    Efficiency
    Published motor efficiency

    data is based on a pure sinusoidal voltage The high frequency harmonics created by VFDs increase copper and core losses decreasing the efficiency of the motor Materials behave differently under these operating conditions resulting in a higher efficiency drop when fed by VFDs.

    Current
    A higher r.m.s. current to supply the same

    output (about 10% higher) Increase in motor operating temperature On average, VFD fed motors will have a temperature increase of about 15C, at rated speed and load

    Noise Level
    Due to the harmonics, the motor noise level

    will increase when it is operated using a VFD Experience shows that the sound pressure level at A scale at motor rated speed is increased by anything between 2 and 15dBA with a VFD This extra noise level depends mainly on the inverter switching frequency and harmonic content. Noise mitigation costs increase

    Motor Design Life


    Standards VFD voltage peaks (Vp) < 1,000V and dV/dT <500 V/s but VFD motors are subjected to 5000V/s and 1,500V Voltage peaks depend on carrier frequency dV/dT affects the insulation between turns, the high voltage spikes affect the insulation between phases Damage peaks breakdown dieelectric strength of insulation Die electric strength reduced by humidity & temperature Corona & partial discharge destroy motors Standard motors design life reduced by up to
    IEC 34-17 and DIN VDE 530 Repeated voltage

    Commercial Considerations

    Costs of a Pump/VFD Installation


    Capex
    VFD components with

    Opex
    VFD inefficiency

    a design life < 10years Larger switchroom Increased air conditioning Screened cable Harmonic protection Special motors Supplementary fans Increase in noise

    95% Inefficiency of motor Supplementary fans Special motor spares Air conditioning energy Reduced life of motor Spares for VFD Spares costs oversize pump

    Commercial-Other
    Engineers who use suppliers to select pumps or

    process solutions lose engineering control of the procurement process Pump suppliers do not necessarily know, or care, about the process vs. electrical requirements of the VFD/motor interface-divided responsibility String testing motor/pump/VFD is difficult during the contract period for larger motors because of :-time -manufacture location of components -responsibility of the other parties equipment -packing/unpacking/re-packing

    Conclusions
    Engineers need to specify all operating & electrical

    conditions to pump, motor & VFD supplier Invest in the mechanical engineering and specify correctly Future operating conditions may not occur. If they do they can be met with alternate solutions VFDs do not always save energy, Capex or Opex VFDs do not avoid transients from power loss VFDs provide a suitable solution to some pump operating conditions but should not be considered a panacea You just can't ever beat the energy efficiency of running a properly sized pump at 100% BEP rated flow. Mechanical engineers have a poor understanding of electric motors & VFDs and fail to communicate with process or electrical engineers

    Questions

    Please ask questions remembering I am a mechanical engineer!

    Useful links
    This presentation was by Geoff Stone
    geoffrey.stone@yahoo.c o.uk

    sulzerpumps.com mcnallyinstitute.com

    eng-tips.com
    nidi.org pumpsystemsmatter.org

    Tel 0402 35 2313


    Or 02 8850 2313

    aft.com
    toshont.com/vfdapp.htm virtualpipeline.spaces.live.com

    canterburyengineeringassociat

    es.com

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