Motor Health KPI’s to Help Improve - Xcelerate...Most industrial motor drive systems operate in CAT III environment as defined by IEC 61010. (Fixed installed 3 phase loads or distribution

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Hilton HammondFluke Corporation

KPI’s to Help Improve Motor Health

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At the conclusion if this session you will be able to:

● Assess the complex drive system in its individual parts, identify key measurements and tests in order to;

○ Uncover hidden problems or investigate root cause of symptoms before they lead to downtime

○ Identify leading indicator measurement variables to gauge the performance and health of the motor drive system

Objective: KPI’s to help improve motor health

Prevent failures, increase reliability and maximize motor lifespan


Most industrial motor drive systems operate in CAT III environment as defined by IEC 61010. (Fixed installed 3 phase loads or distribution equipment)

Safety First: Before we begin - a note on safety

● Test equipment must meet the category rating, area and working voltage, for e.g. 600V CAT IV or 1000 V CAT III

● Ensure the meter used is independently verified and not just “designed to meet?”


● Confirm the test equipment is rated for the use.

○ Installation Environment and working voltage

● Use proper PPE

Three phase systems in Cat III environments

● Mixing CAT III instruments with lower rated accessories

● Short circuiting floating differential test points with a common ground or device with non-isolated inputs

● Holding the meter during testing


Best practices for maintaining health of motor drives


Motor Drive System Failure Modes


Complex System Electrical Tests & Metrics


Uncover hidden problems before they impact the drive

Validate power quality and power capacity

● Under voltage due to overloaded circuits ● Over voltages as result loads dropping

offline and/or efficiency improvements● Voltage events (Dips, Swells or Rapid

Voltage Changes from switching loads or PF correction equipment

● Voltage Unbalance● Harmonic Distortion

● Loss of power to motor● Excess heat and eventual motor winding

insulation failure● Random drive shutdowns● Excess heat dissipation in drive and other

inductive components


Measurement KPI’s using Fluke-438-II Power Quality and Motor Analyzer1. PQ Monitor (According to EN50160) – Log state and resolve

out of tolerance deviations● Frequency● Voltage Variations● Harmonics● Unbalance

● Events

2. Energy Study – Trend Over Operating Cycle● Max, Min and Average Power● Max, Min and Average Voltage, Current, Frequency, THD% and

Unbalance%● RMS Power Trend Graphs. Identify peak point during operating cycle

Validate power quality and power capactiy

Tip: Power consumption is never static – log data over entire process operating cycle – repeat periodically


Compare input power to drive rated specification

Verify input power is within drive operating specification

● Voltage deviation >10%● Frequency drift > 0.5 Hz● Voltage drop due to undersized circuit or

feed conductors● Current exceed max drive rating or motor

rated current (+ Service Factor)● Voltage unbalance >2% and Current

Unbalance >6%● Excessive total harmonic distortion (THD

>6%)

● Drive errors and potential resets● Overloaded input circuit and potential

rectifier failures● Loss of power● Elevated operating temperatures


Measurement KPI’s using Fluke MDA-550 Motor Drive Analyzer

1. RMS Measurements● Voltage● Current● Frequency● % Unbalance

2. Waveform Qualitative Analysis● Signs of “flat topping”● Distortion● Abnormal Fluctuations

Verify input power is within drive operating specification



3. Input Harmonics● Overall % THD● Harmonic Number Amplitudes

4. Check for Supra Harmonics● Validate performance of regenerative drives with

active front ends● Identify higher order frequencies that may be

disruptive to nearby communication equipment

Verify input power is within drive operating specifications

Tip: Compare current harmonics to voltage harmonics – if there are no current harmonics but voltage harmonics is excessive, investigate other loads on same circuit


Verify the operation of the inverter AC to DC to AC (pulse width modulation)

Check drive performance

● Low DC Bus Voltage● Excessive DC bus ripple voltage● Out of range output voltage, current and

frequency● V/Hz Ratio deviation from nominal● Current exceed motor rated current (+ Service

Factor)● Excessive voltage and current unbalance

● Drive errors and potential resets● Loss of power● Increased motor winding harmonic

distortion dissipate in form of heat● Elevated operating temperatures● Loss of operating performance● Motor decreased operating lifespan● Increased mechanical vibration and

component wear and tear



1. DC Bus Measurements● DC Voltage equal to ~1.414 x V rms input● DC Ripple under load: (base line when in known

good working condition)

2. Waveform Qualitative Analysis● Unstable DC Voltage● Ripple voltage amplitude and pattern changes

over time caused by failing capacitor or rectifier impedance change.

● Abnormal Fluctuations


Tip: DC Bus voltage issues can be as result of input power, rectifier or capacitor bank problems. Eliminate input power by checking for flat topping and voltage events (dips, swells etc)



3. Output Nominal Voltage Current & Freq● Check measured parameters to motor name

plate for any out of range parameters● Check if V/Hz ratio is within specified limits for

the applications (Variable or constant torque)


Tip: Use the Fluke Motor Drive Analyzer recording function to plot the V/Hz ratio over the equipment operating cycle


Check output PWM waveform for any abnormalities that lead to winding and/or bearing failure

Check drive pulse width modulated waveform

● Excessive peak voltage reflections ● PWM, pulse dv/dt ratio (Change in voltage

over change in time) exceeds motor winding rating

● Motor winding insulation degradation and eventual failure

● Stray earth leakage currents causing random ground fault interrupts

● Voltage discharges across bearing surfaces leading to premature wear



1. Overall PWM Characteristics● Effective voltage delivered to windings (Vpwm)

compared to programmed voltage● Output Frequency● V/Hz Ratio


Tip: Capture and compare the PWM waveforms (Zoom 1, 2 & 3) at the drive output and motor input to verify cable installation



2. Peak voltages exceed winding insulation breakdown voltage rating

● V pk < winding insulation breakdown voltage rating

● NEMA MG1 Part 31, 2006 calculation for peak voltage = 1.1 * 2 * √2 * V rated

3. Trend PWM Pulse overshoot over time● % Overshoot




4. Insulation stress as a function of pulse rise time and peak amplitude

● dv/dt ratio or the pulse edge amplitude increase in volts per second

● The dv/dt ratio should be within the manufacturers specification or motors manufactured in accordance with

○ NEMA MG1 Part 31 2006 or○ IEC 600034-25




1. Fast voltage discharges across bearing surfaces

● Check for excessive counts/s of fast discharge events

● Industry experts suggest >6 Volts may be problematic

Check for shaft voltage discharges

Tip: Check periodically as bearing lubrication, load and other factors can influence the rate and occurrence of discharge events


Check motor load given the condition of the electrical power quality and mechanical installation

Assess motor load under operating conditions

● Poor power quality like unbalance, harmonic distortion and load conditions impact power transferred to motor shaft

● Operational changes exceed motor load rating

● Driven component wear or obstructions overload motor

● Loss of power and operating performance● Shortened motor lifespan● Potential shutdown● Excess operating cost or waste (kW/hr to

run motor)


Measurement KPI’s using Fluke 438-II Power Quality Motor Analyzer

1. Electrical characteristics compared to motor rating

● kW electrical power● Power Factor● % Unbalance● Harmonics

2. Mechanical characteristics compared to motor rating

● HP, mechanical power● Torque● Speed● % Efficiency



Measurement KPI’s using Fluke 438-II Power Quality Motor Analyzer

3. Directly coupled motor’s derating factor according to NEMA guidelines

● Total derating factor

4. Trend derating factor over the complete operation cycle

● Load vs. Derating Factor historic cross hair marker plot should not traverse into red overload zone


Tip: Take action to reduce cost or increase reliability by periodically checking % load and NEMA Derating factor (Under or over loaded)


Capture, Trend & Document Measurement Metrics


Available resources to learn moreVisit us at the Fluke Booth

www.fluke.com/mda500series

Thank you!


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Documents

Motor Health KPI’s to Help Improve - Xcelerate...Most industrial motor drive systems operate in CAT III environment as defined by IEC 61010. (Fixed installed 3 phase loads or distribution