Transcript Document

MATING VFD’S
TO EXISTING
MOTORS
Jack Gibbs – Instructor
Cincinnati State College
The “Existing” Motor
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Motors Connected to VFD’s
Receive Power That Includes A
Changeable Fundamental
Frequency, a Carrier
Frequency, and a Rapid
Voltage Buildup.
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These Factors Have a
Negative Impact When
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High Carrier Frequency
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Side Effects are: HEAT, Audible
Noise, and Vibration.
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Extremely High and Rapid Voltage
Rise.
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Carrier Frequency is a By-Product of
Obtaining Current at a VARIABLE
FUNDAMENTAL Frequency!
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With Frequencies Other Than
the Fundamental the Motor
Runs With Excessively HIGH
Slippage.
The Fact that Many More Lines
of Flux are Being Cut
Contributes to Additional
HEAT, and Additional WATTS
in the Motor.
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The SYNCHRONOUS SPEED of
This CARRIER Frequency is
120,000 rpms in a Four Pole
Motor!
Carrier Frequencies are Typically
2 to 15 KHz.
This ADDITIONAL Current is
Transmitted to the Rotor Bars
and Dissipated as “Rotor
Losses” in the Form of Heat.
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This ADDITIONAL HEAT
Represents another 5% to
10% Thermal Buildup in the
Motor.
• Because of These and Other
Conditions One May Need To
DERATE the Motor.
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Other Side Effects~
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NOISE~Component Resonating
VIBRATION~Skip Frequency
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Bearing Problems
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(Disintegration)
Pitting Due to
Bearing Currents.
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Air Flow Problems ~
COOLING!!!
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Conductor Insulation
Breakdown
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In PWM Circuitry, with HIGH
Voltage Buildup at HIGH
Frequencies Insulation WILL
Break Down!!!
• Turn to Turn Shorts.
• Skin Insulation Breakdown.
• Stator Shorting and
Meltdown.
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Motor Application
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A Motor is a CONSTANT TORQUE
Machine ~ at RATED Torque and
RATED Speed it, it will Produce a
CERTAIN HP!!
When Speed is REDUCED by Voltage
and Frequency Reduction, the Motor,
by Consuming MORE Current, will TRY
to Maintain Constant Horse Power.
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• THE MOTOR MUST
THEREFORE BE SIZED TO
MOVE THE LARGEST
LOAD AT THE SLOWEST
DESIRED SPEED!
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At Times, This May Make the Motor
Appear Too Large.
How Much HP is Required at the LOW
END of the Speed Range?
Voltage is Also Reduced in a VFD
meaning That at 50% Speed We’re
at 230 VAC or ½ Rated HP at Full
Speed.!!
The Motor Will Have to have
Sufficient Thermal Capacity to
Handle the Load.
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Troubleshooting Your
Drive
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The Problem is Fourfold~
Simply by Design.
Nobody PLANNED on Non-Linear
Drives or Variable Frequency
Anything.
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Measurements
All.
ARE the Key to It
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The Facility Power
Supply
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“Over and Under” Voltages
Greater Than 10%+/- WILL
TRIP MOST DRIVES!!!
• A Voltage Unbalance of
3% to
5% Can Cause Tripping of a
Drive’s Overload Device.
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What To Do~
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Measure the INCOMING
Line Voltage at the INPUT
Side of the Drive Itself.
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Measure ALL Three Phase to
Phase.
Look for Over and Under
Conditions.
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Measure at PEAK and NONPEAK Times. Look For
Unbalances, Too!
Is the Facility, Itself, Causing
These Problems?
Take a Current Reading of ALL
Three of these Phases on the
Line Side of the Drive.
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Take VFD Readings
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Measure DC BUSS Voltage.
Actual DC BUSS Voltage (Line
plus x 1.414).
DC BUSS Under Load ~ At The
Drive Capacitor Connections `
Take = and – Readings (Line +
1,414).
Now Take the SAME Reading on
“AC”. NOTHING Above 5 VAC!!!
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Volts Per Hertz Meas.
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Maintaining a 7.67: 1 Ratio???
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Leakage Current ~ A Transistor
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Does not Actually “Open Up” like a
Mechanical Switch ~ it Just
Reduces the Amount of Current it
Lets Through.
It Should be < 40V While Energized
In RUN w/ Speed @ Zero (Meas
Between Phases).
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The LOAD!!!
Rotational Direction Correct???
• Why FAST Acceleration
Speed???
• What Type of Load???
• Harmonics and Overvoltage
Reflections.
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METERS TO USE
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DON’T Throw Out That Old
Simpson 260 Rev. D ANALOG!!!
• Use it on the Inverter!!
(Smoothing Effect of the IGBT
Switch.)
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The MOTOR
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Measure Voltage at the Drive
AND at the Motor!!!
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Look For Voltage
DROP AND
Volts Buildup!!!
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Take Temperature
Readings!!
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Introduction
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State the purpose of the
discussion
Identify yourself
Topics of Discussion
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State the main ideas you’ll be
talking about
Topic One
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Details about this topic
Supporting information and
examples
How it relates to your audience
Topic Two
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examples
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Topic Three
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examples
How it relates to your audience
Real Life
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Give an example or real life
anecdote
Sympathize with the audience’s
situation if appropriate
What This Means
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Add a strong statement that
summarizes how you feel or
think about this topic
Summarize key points you want
your audience to remember
Next Steps
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