Same THDi, Different Neutral Current
Why two 3-phase, 4-wire systems with the same THDi can produce very different neutral currents. A visual explanation of 3rd, 5th and 7th harmonics and triplen-harmonic accumulation.
Technical library
Engineering Notes
Practical investigations, calculations and design observations organized for reference.
How Can a 500A Active Harmonic Filter Draw Only ~15A from the Grid?
A worked 480 V example explaining how a 500 A active harmonic filter can inject about 496 A of harmonic compensation while drawing only about 15 A of real input current for assumed internal losses.
Single-Phase Input, Same Motor: Do You Need a Bigger VFD?
Can a three-phase-input VFD run a 10.5 A motor from 240 V single-phase power? Follow the rectifier, DC link and inverter, then separate line current from manufacturer-approved drive derating.
Can Passive Harmonic Filters Be Paralleled?
Can passive harmonic filters be connected in parallel for large VFD applications? This example explains MTE Matrix AP parallel-filter sizing, derating, and practical design considerations.
How an Active Harmonic Filter Cancels VFD Harmonics
A practical waveform-level explanation of how a parallel active harmonic filter senses and injects selected harmonic currents so the upstream source sees the residual.
Long Motor Cables: What Happens to VFD Motor-Terminal Voltage?
Learn how VFD motor cable length affects reflected-wave voltage, rise time, ringing, and motor-terminal voltage, and see how a dV/dt filter reduces motor voltage stress.
Can You Connect a VFD to a Standard Motor the Same Way as to a VFD-Rated Motor?
Can a standard motor run from a VFD? Often yes. Check PWM insulation stress, low-speed cooling, bearing currents and manufacturer limits for the complete system.
PHF vs AHF vs Hybrid — Which Harmonic Filter Strategy Fits a Multi-VFD System?
A practical engineering comparison of all-passive, all-active and hybrid harmonic-filter architectures for a four-VFD 480 V system with changing load diversity.
VFD Motor Cable-Length Rules: When Do You Need an Output Reactor, dV/dt Filter, or Sine-Wave Filter?
A manufacturer-aware guide to selecting VFD motor-side mitigation using voltage class, PWM behavior, cable topology, motor insulation, and exact filter limits—not cable length alone.
Same VFD. Same Motor. Why Does Cable Length Change the Voltage Stress?
A technical explanation of how motor-cable length changes reflected-wave behavior and insulation stress in a 600 V VFD system, with a practical comparison of output reactors, dv/dt filters and sine-wave filters.
Passive Harmonic Filters at Partial Load
A practical investigation of how changing VFD load affects the operating point of a passive harmonic filter.