vfd predictive and preventive...

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VFD Predictive and Preventive

Maintenance

Instructor: Trey Mayfield

[email protected]

www.emainc.net

Predictive Maintenance

Variable Frequency Drive (VFD)

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Device used to vary the speed of a driven load, such as pumps,

blowers, compressors, conveyors, punch presses, etc. to exactly

match the process requirements & achieve energy savings too

Includes built-in overload protection (no heater elements

required). Adjustable to the motor rated

current. Speed & non-temperature

dependent

Adjusts both the frequency

& voltage to the motor

Reduces the inrush current to

150/115% CT/VT (adjustable) of the

motor rated current

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SafetyThe most important thing to keep working is You!

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Familiarity with ElectricityIs NO Protection!

Skilled Electricians can be electrocuted as well as anyone else!

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Safety Rules

Lock it out!Tag it out!And still measure it Prior to touching it!

Per IEEE, the failure rate is 3times higher for electrical systems

that are not subjected to a regular PM program!

IEEE statistic on PM

Preventive Maintenance

Loose Connections 30.3%

Moisture 17.4%

Line Disturbance 10.4%

Defective Insulation 9.9%

Lightening 8.1%

Foreign Objects 7.3%

Collision 3.9%

Overloading 2.4%

Dust, Dirt, Oil 2.2%

All other causes 8.1%

What Causes

Failures?


According to IEEE, electrical systems that are not subjected to Preventive maintenance are

three times more likely to failure than those that are subjected to PM.

What does a PM Program Entail?

Qualified Personnel

Regularly scheduled inspection, testing, and

servicing

Evaluating Results

Work Performance

Record Keeping


Qualified Personnel

Properly trained on

specific equipment

Trained in Safety

procedures

Special training for

Medium voltage


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Regularly scheduled Inspection, Testing, and Servicing

Visual, thermographic, or other non-invasive inspections prior to

shutdown

All circuit breakers/disconnects repeatedly opened and closed

to insure proper operation

Protective Relays and Devices tested and calibrated

Test oil samples from all oil filled equipment (transformers)

Electronic equipment inspected, cleaned, and tuned


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Evaluating Results

The Person doing the evaluation must be thoroughly

familiar with the specific tests/observations. HE/SHE

will decide upon the next actions


EMA performing

Verification

Ground fault

working at Greer

Industry

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Perform the work!

No good to test and inspect if problems aren’t

resolved

Keep it clean

Keep it dry

Keep it tight

Keep it cool


EMA Service Engineer, Charles Smith

Performing start up check on a Toshiba

T300MVi at Greer Industry in WV….May 2012

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Record Keeping

Most overlooked part of PM program

The factor in tracking cost savings

Tracking test results over time help identify failures

before they occur


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Specific Equipment Maintenance Considerations


EMA of NY Service Manager, Jon

Blasklee Performing Pre-PM check on a

Toshiba T300MVi at United

Water…February 2013

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AC Drive PM ConnectionsCabling

ShieldedPowerMotorCapacitorsCoolingCleaningTuning


EMA Service Engineer, Charles Smith and Alfaredo

Performing Pre-Start up checks on a Toshiba T300MVi

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Component Failure

Electrolytic Bus

Caps

5 Years

Cooling Fan 3 Years

Contact Relays 500,000 operations

Connectors 100,000 Operations

Per Toshiba Study / Oil filled Caps and Electrolytic


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Type of Capacitor

• Oil filled and aluminum electrolytic

capacitors used in the Medium

Voltage Drives have specific life

expectancy that will contribute to the

life time cost of the Drive. Oil filled

capacitors have a 20-30 year life

expectancy compared to a 7-9 years

of an electrolytic capacitor.

Replacement of these aluminum

electrolytic capacitors is a very

significant expense and usually

requires at least one week of

downtime.

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Oil filled Caps Vs Electrolytic

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Bus Caps are Usually secured withClampsClamps help prevent swellingBe sure to tighten when replacing capsInspect buss capacitor for leakage and bulging


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Capacitor Life is affected by:TemperatureOvervoltageMounting/ClampingShelf Life


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Overvoltage ShortensCapacitor Life


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Increase in Temperature

Causes increased Electrolytic Loss


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Overcurrent conditions plusHigh Temperature rapidly accelerates

Capacitor failure


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Reform Bus capacitors on Spare Cells before

rotating cells…Applies to Voltage Source Drives


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Therefore… for Cap Life…Keep the Drive CoolCheck your line voltageDon’t overload your DrivesTighten your clamps

Electrolytic Bus capacitors life span


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Drive Cooling fans are easily checked,

But often overlooked.Apply 480V three phase to the fans

Listen for them running

Rotate them by hand and listen to bearing noise

Feel the air flow

Verify redundant fans are working if applicable

VFD Cooling fans


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Connections Matter!

Power and Control Wiring in

Separate conduit

Shields properly connected

Grounding connections tight

And properly made

Conduit connections tight

Power and control terminals

Checked for tightness


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Diodes, IGBTs, the

Power Device of Choice

Use on Voltage Source

Drives

They usually fail by shorting

Check connections

Should be mounted securelyFor cooling


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Check gate resistance

Check anode/Cathode for low reading

Check for tightness of power and gate leads

Check mounting tightness, which allows for cooling

Current Source Drives use Thyristors

IGCTs, SGCT, SCRs


Integrated Gate-Commutated Thyristor, Symmetrical Gate Commutated Thyristor and Silicon Control Rectifier

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Dust absorbs moisture resulting in failure

Use compressed dry air….Moisture free


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Moisture resulting in corrosion on the

board, resulting in damage of traces


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Other AC Drive PM Considerations


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Transformer PM

Sound Level Variations

Voltage Levels +/- 5%

Heating

Colorization of windings (dry type)

Liquid Levels (oil filled)

Oil replenishment

Insulation

Connections


EMA of GA Service Manager, Trey Mayfield Performing Transformer check

on WEG MV01 MV transformer at American Cement 2011

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Transformer PM


Damaged phase shifting transformer from Siemens Harmony VFD

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Meg the motor

Predictive Maintenance

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SwitchGear, Disconnects and Contactors


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Switchgear PM

Failures are often

catastrophic

Use qualified people ONLY

Follow Manufacturer’s

procedures and safety rules

Items of concern are

sequencing, Auxillary contacts,

fault current interruption,

connection integrity


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VFD Power Supplies

Most VFDs including MV VFDs use

DC to DC conversion to produce the

low DC power supplies like 5V, 24V,

12V and -12V.

Power resistors and transformers

around the capacitors can cause

over heating


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Power On Testing

All Checks Perform in Low Voltage

Compartment

Discoloration on power supplies filtering

capacitors and transformer

Check Switching Power Supplies for

tolerance (24V, 15V, -15V, 5V) and also for

ripples

Check output waveform on the low

voltage compartment with scope and also

input waveform

Check your current feedback on low

voltage compartment

Check the buss ripple


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Voltage Ripple


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Good DC Bus Voltage

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Switching noise on DC Bus Voltage

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Snubber board

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Bad bus capacitors due to switching noise

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DC Bus Ripple on PQube3

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Programming/TuningVolt/Hz PatternTorque/LimitAccel/Decel

Save your parameters!


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Shop Repairs on VFDs, Multilins and HMI

Field Service on VFDs and PLCs

Turn Key System Retrofits on VFD/PLCs

PM (Predictive and Preventive Maintenance)

MV VFD, MVSS and Low Voltage VFD sales

Training (Two day VFD hands on training)

EMA Services

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Questions?

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