What design features ensure optimal performance and longevity in VFDs?

• Input Isolation Transformer: This component protects the VFD from utility transients caused by lightning or equipment switching. Without it, drive and motor reliability can be compromised, leading to costly motor failures and lost revenue.
• Motor Voltage Selection: Matching the output voltage to the power component and switching frequency needs ensures reliability. Allow the drive manufacturer to determine the optimal motor voltage for compatibility and reliability, and consider buying the VFD and motor from the same manufacturer.
• Low Total Harmonic Distortion (THD): Aim for a Total Harmonic Voltage Distortion of no more than 5% at all operating load levels and speeds to comply with IEEE 519 standards. Minimize noise impact on nearby equipment, avoid legal liability and prevent financial penalties from the utility. In case of  a 3-level inverter , you should opt for minimal 18-pulse (or higher) diode converter or a properly designed active front end to ensure low input harmonic distortion.  A multi-level cascaded H Bridges cells topology  drive will deliver quite clean input power thanks to the cancellation of harmonics by phase displacement (=>multi-pulse input from 18 to 54).
• Avoid outdated VFDs that can cause power problems and financial penalties due to noise injection into the power grid.
• High Power Factor: A  total power factor (including harmonics) of 95% or higher at all speeds and loads above 10% prevents utility penalties, voltage drop problems and heating in other utility system components. This is often achievable with a VSI but not with an LCI or a CSI (without AFE).
• Multi-Level Output Drive Topology: For applications above 250HP, a multi-level drive output (topology M2C/MMC or 2L SC-HBI) can create a near-sinusoidal output waveform, eliminating the risk of reflected voltage stress. This increases the service life of cable and motor insulation systems and reduces the need for costly output filters.
• Conservative Design and Component Application: Choose a drive with a proven track record of reliability. A well-designed drive uses components at much lower levels than their ratings and is applied appropriately to the job, leading to a higher Mean Time Between Failure (MTBF). A good target for your MTBF is a minimum of 100,000 hours which is more than 10 years before a predicted failure appears. The Mean Time to Repair (MTTR) is the amount of time the component is shut down in order to repair or replace a part and influenced by:
  • The ease of replacing defect components without the need to disassemble the drive.
  • The containment of the fault thanks to the inherent protection of the drive (one failure only).
  • The available support (technicansapre parts,7/24,time to get onsite)
• Low Parts Count: A low parts count in the inverter, particularly when using IGBT technology, leads to improved reliability and a smaller footprint, making installation easier, especially for retrofits.
• High-Quality Components: Utilise high-quality, long-lasting components such as oil-filled capacitors with a 20-year life expectancy and cooling fans with a more than 7-year recommended replacement cycle to reduce lifecycle costs and maintenance.

By considering these design features and asking pertinent questions to the vendor, you can select a VFD that offers optimal performance, reliability, and longevity, ultimately contributing to lower operating costs and higher efficiency.

We can support your decision-making process by providing expert, independent advice and assistance on AC or DC-drive applications for the following tasks:

• Develop the project plan presentation.
• Define and manage the requirements for the Power Drive System (PDS).
• Evaluate the composition and components of the Power Drive System.
• Organize and coordinate internal and external pre-bid meetings.
• Prepare and issue invitations to bid in collaboration with Engineering, Procurement, and Contracting compagnies and/or vendors.
• Assess preferred manufacturers for transformers, inverters, and motors.
• Review offers and verify compliance with your PDS specifications.
• Assist in the selection of vendors for transformers, variable frequency drives, and motors.
• Clarify any outstanding issues related to your PDS.
• Define requirements and test plans for both witnessed and non-witnessed Factory Acceptance Tests (FAT).
• Establish requirements for Site Acceptance Tests (SAT).
• Validate the on-site execution of Site Acceptance Tests for the components of your Power Drive System (PDS).