Power Quality and Drives LLC

Variable Frequency Drives Seminar:
Problems Encountered and Basic Mitigation Techniques

Problems encountered with variable frequency drives may often be
either avoided before or quickly remedied after installation. The
presentation will be open for attendees to ask questions and discuss
problems that have been encountered in the past.

Estimated time is four hours which will consist of three 1 1/4 hour
segments with ten minute breaks between segments. Additional time
beyond four hours will be available for any technology or application
questions that you may have.

Frank Martino, who has thirty years experience in electric motor control
as well as degrees in Electrical Engineering and Electronics Engineering
Technology, will be presenting the seminar.

The seminar may be presented in your facility to your company personnel
in the Connecticut area. Cost of the seminar will be $400.00 plus tax.

Variable Frequency Drives Seminar:
Problems Encountered and Basic Mitigation Techniques

Motor Characteristics:

Operational differences of Inverter Duty, Premium Efficient and Standard designs,
Original frame, U frame and T frame motors, operation on vector control.

Effects of VFD Generated Harmonic Currents, dv/dt, and EMI/RFI:

Derating of motors and transformers, torsional stress from harmonic motor current,
winding burnout caused by reflected waves, cable length and rise times, bearing fluting
from dv/dt, ground to neutral voltages, capacitor resonance.


Generation of harmonics, three phase and single phase systems, derating of
upstream general purpose transformers, K Factor transformers, interharmonics,
harmonic analyzers vs. spectrum analyzers, THD and TDD at Point of Common Coupling
per IEEE Std 519-1992.

Mitigation of Harmonic Currents on Single and Three Phase Systems, dv/dt, EMI/RFI:

Reactors (input, output, DC bus chokes), passive and active harmonic filters, 6, 12 and 18
pulse drives, dv/dt output filters, carrier frequency, motor cable, bonding and grounding,
drive isolation transformers, common and differential mode ferrite cores, true earth
ground, high resistance grounding and GFI noise problems, EMI filters, signal conditioning
(0-10 VDC and potentiometer signal conversion to 4-20 mA), fiber optic cables,
bearing currents, shaft brushes.

Separation of Input and Output Cables:

Minimizing EMI/RFI and harmonic interaction, preventing torsional stress on the motor
shaft and driven equipment.


Effects on voltage regulators caused by UPSs and VFDs.

Safety Considerations:

Electrostatic coupling between motor cables - locked out, tagged out and still deadly.

Short-circuit Capacity:

Transformer sizing, voltage sag on start-up, large motor contribution, bus duct vs. wire,
current limiting fuses and breakers, need for reactors on VFDs, flicker.


Utility capacitor switching, lightning strike, suppression technology and issues
(Peak Let-Through Voltage, fusing).

Torque characteristics of an induction motor in the “constant horsepower” range above 60 Hz.

Solid-state Reduced Voltage Starters:

Starting torque capabilities compared to variable frequency drives, replacement of
Wye-Delta starters, inside the delta.

Horsepower requirements when increasing blower speed by belt and pulley changes.

Centrifugal pumps and energy savings, payback calculations, programming for constant torque
vs. variable torque.

Blower Application:

Air Density - size motor for run speed, start motor at low speed, then increase speed as
temperature increases.

Overload Protection for Motors:

NEMA Class 1, 5, 10, 20, 30 protection, single phasing.

Power Quality and Drives LLC

Power Quality and Drives LLC
P.O. Box 83
Middlebury, CT  06762
Phone: (203) 217-2353
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