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Best Practices for VFD Cabling
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  1. Best Practices for VFD Cabling Peter Cox P.Eng. Project Manager Belden Industrial Cable

  2. Peter Cox Bio Licensed Professional Engineer Worked in or as a consultant to Industry for 28yrs – mostly in a Drives and Industrials Controls Participated in the testing of the first VFD cables developed with a major drive manufacturer in 1995 Did Beta testing of the 1336 Impact drive at Belden

  3. Learning Objectives Understand Belden’s VFD Product Line Belden Premium VFD Belden CTC Construction Grade VFD Understand the 4 Reasons to Specify VFD Cable Common Mode Current Capacitive Coupling/Cable Charging Reflected Wave Voltage Safety and Reliability Discussion of Paralleling

  4. One thing you need to Remember….. There is no standard for VFD cables Performance is all about Copper

  5. VFD Cable • Connects Motor and Drive Power Circuit • Provides Reliable and Robust Connection • Protects against harmful noise

  6. Belden VFD Cable Product OfferingClassic Foil/Braid Design VFD Classic Cables • Four Conductor Foil / Braid Shield Design VFD Cables (Three stranded TC Conductors + 1 Insulated Ground – green with a yellow stripe) 29500: 16 AWG VFD 29501: 14 AWG VFD 29502: 12 AWG VFD 29503: 10 AWG VFD 29504: 8 AWG VFD 29505: 6 AWG VFD 29506: 4 AWG VFD 29507: 2 AWG VFD Advantages – This construction offers thicker insulation for better performance and extended transmission distance Other Designs – Interlocked Aluminum and Steel armored VFD products (part numbers available in NP316) Much More Copper than 3C designs – Compared to Construction Grade these cables have as much as 3 times the copper at ground potential. Nearly as much as is in the circuit conductors When comparing, look at product weights. More Info in NP 235

  7. Belden VFD Cable Product OfferingSymmetrical Design VFD Classic Cables • Symmetrical Design VFD Cables (Three stranded TC Conductors + 3 Symmetrical BC Grounds + 2 Spiral Copper Tape Shields) 29528: 1 AWG VFD 29529: 1/0 AWG VFD 29530: 2/0 AWG VFD 29531: 3/0 AWG VFD 29532: 4/0 AWG VFD • 29533: 250 AWG VFD (2KV) • 29534: 350 AWG VFD (2KV) • 29535: 500 AWG VFD (2KV) Advantages – The symmetrical ground design provides a balanced grounding system that is preferred in the industry on larger HP drives Other Designs – Interlocked Aluminum and Steel armored VFD products (part numbers available in NP316) More Info in NP 235 We use 2 copper tapes with twice the surface area for better high frequency conduction. Contra helically applied where possible for lower inductance and higher performance. Much more effective and more expensive than a single tape used on all other products.

  8. Application Issues • Customer Drivers • Energy Savings • Low Total Cost of Ownership • High Availability • Safety: People & Processes • Challenges • Common Mode Current • Capacitive Coupling and Cable Charging • Reflected Wave Voltage – Motor and Cable Life • Application Reliability and Safety • Requirements • Reliability - high MTBF • Manufacture recommendations • Resistance to harsh environment • NEC • There it NO STANDARD FOR VFD cables • Belden • Quality and higher MTBF components in the industry. • The only product in the market that was co-designed in conjunction with a major drives manufacturer • Global availability • 17 years as a leading supplier of VFD cable

  9. Application Issues Common Mode Current AKA Current Noise • Effects • Network Errors - Encoder Faults • Loss of signal reliability analog and digital signal error • Ground plan noise pollution • Motor bearing failures • False stops and safety circuit trips and alarms • EMI and RFI • Definition • Current that flows between the drive and motor by any path other than the 3 primary motor leads • Kirchhoff’s Law – The sum of current at any point is zero - All current must return to the drive somehow • Mitigation • Lowest Impedance ground path and ShieldingMake the cable the most attractive path for HF currents • High Surface area (4-8x) Conductors reduce HF cable heating and reject less CMC • Why Belden • We put up to 3 times more copper at ground potential than competitors “VFD” cables – with flexible stranding we contain CMC 300% better on our premium VFD • Combination of foil braid, or 2 layers of CU enhances performance

  10. What Does Common Mode Noise Look Like?

  11. Motor Bearing Currents High Voltage can also discharge through the bearings causing etching in the races and premature motor failure

  12. Application Issues Capacitive - Coupling Cable Charging • Effects • Loss of motor torque or stalling • False trips of drive overcurrent • reduced system efficiency • Charging of DE energized adjacent circuits • Human safety issues • Definition • Current that leaves the drive but is lost due to capacitive interaction with other cables. (Cable Charging) • Mitigation • Lowest Capacitance 150ma/kft /conductor for THHN vs. 50ma/kft/conductor for Belden VFD cable • Shielding to prevent interaction between systems • Why Belden • Superior shielding • Lowest capacitance

  13. Application Issues Reflected Wave Voltage • Effects • Motor failure and downtime • Cable failure (wet THHN) • Definition • A voltage spike originating at the motor, caused by the impedance miss match between the motor and cable • Mitigation • Lowest Capacitance cable • Output reactor (an immediate 3-8% efficiency loss) • Why Belden • Our 600V cables have a minimum 5500V Corona inception voltage (CIV) wet THHN can be 1600V or less • Lowest capacitance increases distance before harmful voltages are created by up to 3x compared to THHN

  14. Application Issues Reflected Wave Voltage

  15. Application Issues Installation reliability and safety • Issues • Cable/motor failure and degradation with PVC/Nylon • Reference manufacturers cable selection instructions • System noise issues • Downtime • Liability

  16. The 2kv Myth • Issues • In the 90’s VFDs lead to high failure rate on 600V THHN installations • The engineering community began to specify 2000V THHN as a result • 600V VFD cable, even the weaker construction grade, has higher dielectric strength than 2Kv THHN • Belden has never had a claim for dielectric failure in 16 years making 600V VFD Cable • Code requirements are satisfied by 600V cable

  17. Belden Features • Feature • Foil Braid – Drain and full sized ground • Benefits • 50% more copper than most 3C symmetric • -300% better common mode current protection • Enhanced flexibility

  18. Belden Features • Feature • Flexible Stranding • Benefits • 4-8 times higher surface are means reduced High Frequency Losses • Cooler operation • Enhanced flexibility • Flexible motor supply rating

  19. Belden Features • Feature • Oversized wall thickness for lower capacitance (0.045 vs 0.030) • Benefits • Reduced cable charging current • Longer critical distances for reflected wave buildup • Longer cable life

  20. Belden Features • Feature • Dual copper tapes • Benefits • Better HF shielding than a single 5mil • Reduced noise • Enhanced flexibility

  21. Belden Features • Feature • Tinned stranding • Benefits • Corrosion resistance • Thermal stability • Connection reliability

  22. Belden Features • Feature • ER rating • Benefits • Reduced installation costs • Enhanced mechanical performance

  23. A Comparison of Mitigation Strategies • Input Line Reactor • Output Line Reactor • Common Mode Choke • Motor terminator/snubber • VFD Cable

  24. Input Line Reactor • Feature • Adds impedance on the Line side of the drive • Benefits • Protect the drive from line transient damage • Reduces Overvoltage faults • Reduces Harmonic currents

  25. Output Line Reactor • Feature • Adds impedance on the load side of the drive • Effects • Can be protective of non inverter motors • Reduces Dv/Dt rise time downstream of the reactor thus increases critical distance • Can have harmonic interaction with Motor • Has high associated efficiency losses (3-8%) • Reduces motor voltage and torque

  26. Common Mode Choke • Feature • Reduces common mode current • Effects • Reduction of common mode current • Reduces noise emissions • Does no reduce EMI or RFI at all

  27. Motor Terminator/Snubber • Feature • Burns of reflected wave energy as heat at the motor • Effects • Reduction of reflected wave voltage • Protection of motor and cable systems • Great for vulnerable motors on very long leads

  28. Pete Comber Competitive landscape Best: • Fine strand, tinned copper • XLPE Insulation • 3 power conductors and 1 full size ground • Foil and braid shields • Manufacturers are in the on machine world There is no standard for VFD cables, but we can categorize the product available: Better: • Stranded copper (some have tinned) • XLP or THHN insulation • 3 power conductors and 3 reduced size grounds • Copper tape shield • Manufacturers are in the power cable market Good: • Bare copper (think tray cable stranding) • THHN insulation • 3 power conductors and 3 reduced size grounds • Copper tape shied • Manufacturers are from any background

  29. Placeholder for Pete Comber Competitive landscape • Upgraded THHN • Construction Grade VFD XHHW • 4C vs 3C Symmetric designs optimized for high frequency There is no standard for VFD cables

  30. Compared to THHN in Conduit • No Common Mode Current Containment or Shielding Do you want to put the noisiest signals in the plant in unshielded cable? • Cost does not include conduit and labor, with ER or Tray, these costs are dramatically reduced • Faster “Ring Up” of Reflected Wave Voltages • Higher cable charging current – Significant for small drives • Short cable life on long runs - 10yr MTBF estimates-Not rated for 1600V • No protection from capacitive coupling - Shielding • Conduit transitions have high HF impedance-Reduced surface area • Faults in THHN may not be catastrophic but periodic due to pin holes

  31. When to use Belden C Series (Construction Grade) • When we are comparing to Service Wire/General etc. And there is no spec or performance standard • IF No Flexible Motor supply rating is required and flexibility is not desired • The environment is not noise sensitive • Cable Charging, and EMI, and RFI are the only issues There is no standard for VFD cables

  32. Advice for Proper Instalation • Directly connect the Shield at the Motor and Drive Only • Do not introduce jumping off points for CMC through shield termination- Use Insulated glands • Do not cut the shield between the motor and drive • Do not use intermediate termination for the conductors if safely avoidable • Maintain maximum spacing from sensitive circuits and route cables away from instrumentation and networks • Reference the Belden VFD Termination guide The following are best practices for VFD Cable installation and Termination:

  33. Advice for Proper Instalation • Run a separate ground to the safety disconnect • Avoid contact between the VFD cable grounds and shield with the ground in the disconnect • If you must cut the grounds, terminate through an isolating terminal block or connection Using VFD Cables with Safety Disconnects

  34. Termination videos • Run the Videos

  35. Scenario Based Q&A • You may have issues you don’t know • Process measurement error • Overcurrent or ground fault trips • Loss of efficiency • Network errors • Remember that ground plane pollution is additive, one bad install may not cause a problem, but the accumulation of many bad installs may cause problems in the future A customer resiest VFD Cable because he always uses THHN without issue

  36. Scenario Based Q&A • What Questions should you ask • How long are the motor leads • Is the motor wet • What type of failures • How large is the motor • What are the likely causes of failure • Reflected wave voltage • Bearing Currents A customer has contacted you because he experiences frequent motor failures on pumps driven by VFD’s

  37. Scenario Based Q&A • How is the drive cable run • How long are the motor leads • What type of cable has been used? • Does it correlate with drive starts stops enables A customer experiences network drops on the mixer ever since the line was upgraded Could it be drive related?

  38. Scenario Based Q&A • What issue do you think is the likely cause • How long are the motor leads • What type of cable has been used? A contractor has installed a large drive system for airport baggage handling. On commissioning many of the drives trip on overcurrent or will not run

  39. Paralleling and TC-ER Rating • Installations savings • Material • No metal conduit • No metal clad cable • Labor • Less time • Maintenance • Simplifies equipment moves, no conduit to re-route / install

  40. Parallel Conductors Sizing Parallel VFD Cable: Per NEC 310.15(16) When installed in Cable tray with air spacing, or in separate conduits When parallel in Single conduit additional derate is required

  41. Belden VFD Resources & Tools • Industrial Cable VFD Page on Belden Website • Unarmored VFD cable Termination Guide • VFD Cable solutions guide • Belden VFD Product Bulletin • Belden VFD Cable Selection guide (based on Motor HP) • Choosing the Right Cable for your Variable Frequency Drive (VFD) System White Paper • Building a Reliable VFD System White Paper • Control Engineering • 1-800-Belden1