Find faults where they begin, not where they end. When the highest reliability is demanded of your motors, high voltage testing is not just an option - it's a necessity. This webinar will focus on the theory and application of electric motor insulation testing techniques.

1. 1
Blind Spots of Low Voltage Testing
Finding faults where they begin,
Not where they end
Leslie Reed, Application Engineer

2. 2
The BIG 5: Critical Motor Tests

3. 3
The Big 5: Critical Motor Tests
1. Kelvin Resistance Testing
2. Nominal DC Testing
3. High Voltage DC Testing
4. Surge Testing
5. Dynamic Testing

4. 4
Kelvin Resistance Testing
 Test Configuration
• 4-Wire Configuration
• Calculated Resistance
 Evaluation of Balance in the Circuit
• Deviation from Average/ Average
• Max-Min / Average
 No established standard for imbalance %
 Temperature Corrected (to 25°C Typical)

5. 5
Nominal DC Voltage Testing
 Evaluation of the ground wall insulation resistance value
 Insulation Resistance Test or “Megger Test”
 DA/PI – Extended Megger Test

6. 6
High Voltage DC Testing
High Voltage DC Testing evaluates the ground wall insulation
and determines if it is approaching the end of life criteria.
 Ground Wall Stress Test
 Conventional “HiPot”
 Step Voltage “HiPot”

7. 7
Surge Testing
 Copper to Copper insulation testing
 Reveals weak interturn insulation that will eventually lead to
phase to phase or ground wall insulation failure.
Turn-to-
Ground
Turn-to-
Turn
Coil-to-Coil Phase-to-
Phase

8. 8
Surge Testing

9. 9
Dynamic Testing
 Dynamic testing is performed while the motor is in operation
to determine the system operating environment.
 The power quality, motor and load are each evaluated for heat
producing conditions.
 Excessive heating leads to insulation degradation.
 Excessive loading can also accelerate mechanical failure.

10. 10
Dynamic Testing

11. 11
Insulation Life Curve
BREAKDOWN
VOLTAGE
TIME (Years)
Cu-Cu 16,800VDC
Cu-Ground 28,400VDC
Bus Voltage
FACTORS

12. 12
High Voltage Testing

13. 13
Insulation Design
 Nameplate Voltage
 Operational Voltage Stress
 Insulation Design

14. 14
Nameplate Voltage Rating
 Nameplate Voltage: The voltage at which the motor is
designed to operate.
• High Voltage: >110% could lead to saturation of the stator iron
core and lead to excessive external insulation heating
• Low Voltage: < 95% will lead to over current and excessive
heating internal to the windings as a function of I2R.

15. 15
Operational Voltage Stress
 High breakdown rating necessary to withstand switching
surges which can be as high as 4x nameplate voltage.
 460V motor has a beginning of life breakdown voltage of
28kV.

16. 16
Single slot in a random wound 3 Phase Motor
Slot liner is 20,000 VDC
Nomex-Mylar-Nomex
8,400
+ 20,000
28,400
Magnet Wire Dielectric Strength
Slot liner Dielectric Strength
VDC Combined Insulation to Ground

17. 17
Breakdown Voltage Design Rating
 Insulation breakdown voltage design rating is by design far
higher than nameplate.

18. 18
Modern Test Equipment
Vintage test equipment relied heavily upon the experience and
technical ability of the testing technician or engineer.
Today modern test equipment like the Megger Baker AWA takes
the guess work out of testing.
 Arc detection circuit trip
𝜕𝑉
𝜕𝑡
 Rate of change of current trip
𝜕𝑖
𝜕𝑡
 Instantaneous overcurrent trip (1/10/100/1000 µAmps)
 Surge wave instability trip (PP EAR)

19. 19
Common Analysis Finds

20. 20
Resistive Imbalance
Common Finding:
 High Resistance Connections
• Contactor surfaces
• Fuse connectors
• Termination crimps
• Loose or overtightened connections
 Improper Motor Circuit Connections
• Improper Connections(External / Internal)
• Error in Labeling

21. 21
Resistive Imbalance
Results Summary Test Date/Time 9/14/2010 1:24:12 PM
Test ID: GP 480's Repair/Job #
Tested By Tested For
Room # MCC
Area ESCO LC Location 121-076.20
Temp Status Tested PI Status PASS
Temp 32.2°C 90.0°F Volts (V) 510
Resist Status DELTA R DA Ratio 2.3
L1-L2 (Ohms) 0.0566 Corr: 0.0551 PI Ratio DA Only
L2-L3 (Ohms) 0.0593 Corr: 0.0577 Step-Voltage PASS
L3-L1 (Ohms) 0.0580 Corr: 0.0564 Volts (V) 2000
Max Delta R % 4.707% Current(µA) 0.37
Coil 1 (Ohms) 0.0276 Corr: 0.0269 Resist (Mohm) 5341 At 40°C 3115
Coil 2 (Ohms) 0.0290 Corr: 0.0282 Surge Status PASS
Coil 3 (Ohms) 0.0303 Corr: 0.0295 Peak Volt(V) L1 2020
Megohm Status PASS Peak Volt(V) L2 2020
Volts (V) 510 Peak Volt(V) L3 2020
Current(µA) 0.07 Max P-P EAR% 6.4%,6.4%,5.9%
Resist (Mohm) 7293 At 40°C 4253 EAR 1-2,2-3,3-1 No Test

22. 22
Contamination / Moisture
 Grounding paths
• Low megger readings
• Low PI / DA <1.5
 Surface Contamination Build
• Increased PI
• Increased capacitance to ground

23. 23
Contamination / Moisture
Moisture Contamination (Flatten PI)

24. 24
Aging Insulation
Contamination and age will be indicated by low PI and DA
readings where the insulation resistance values are not
necessarily low.

25. 25
Ground Wall: End of Life
At the end of insulation life a non-linear current response will be
exhibited in the leakage current.
High potential testing doesn’t have to fail to demonstrate that the
insulation is reaching its end of life

26. 26
Test results from two identical motors
Step Voltage HiPot Motor
2
Step Voltage HiPot Motor
1
Linear Not Linear

27. 27
Surge Instability: PP EAR
 Copper to copper insulation weakness
• Turn to Turn
• Coil to Coil
• Phase to Phase
 Copper to Ground insulation weakness

28. 28
Surge Instability

29. 29
Dynamic Testing
 Power Quality
• Voltage Imbalance
• High / Low Voltage
• Voltage Distortion (Harmonic/Non-Harmonic)
 Motor Related
• Broken Rotor Bars
• Efficiency
• Severe Bearing Defects

30. 30
Dynamic Testing
 Load Related
• Process Related Overloading
• Improper Applications Design
• Cavitation
• Gearbox related issues
• Belt Related Issues

31. 31
Questions or Comments?
Email Nicole VanWert-Quinzi nvanwert@Transcat.com
Transcat: 800-828-1470
www.Transcat.com
For related product information, go to:
www.transcat.com/brand/megger-store