Six tips for testing motor insulation systems

Insulation resistance (IR) tests are useful for motor insulation systems and users should take steps such as recording conditions and watching for factors that may have an impact on the test to ensure maximum accuracy.

05/03/2017


Although there are many ways to assess motor insulation systems, the insulation resistance (IR) test remains a useful tool for determining if a motor should be removed from or placed into service. When conducting the test and evaluating the results, consider these six tips.

Table 1: Guidelines for dc voltages to be applied during insulation resistance tests. Courtesy: EASA, IEEE

1. Discharge for safety and accuracy. Discharge the winding to ground before and after IR testing. A good rule of thumb is to ground the winding for 15 minutes or four times the test time, whichever is greater.

2. Winding configuration for testing. If possible, isolate and test each phase separately and ground the two phases not under test. This allows for testing of the phase-to-phase insulation as well as the ground insulation.

3. Record important test conditions. Document the ambient temperature, relative humidity, dew point, winding temperature, time since service, test voltage and connection arrangement.

4. Simple test procedure. Energize the winding for one minute at an appropriate voltage (see Table 1) and correct the measured IR value to 40°C by multiplying by a KT from Table 2. Most modern insulation falls under the "Thermosetting" category. Use the "Thermoplastic" values if you know it is a much older winding with an asphaltic or shellac mica system.

Table 2: Kt versus temperature for thermoplastic and thermosetting insulation stator winding systems. Courtesy: EASA, IEEE

5. Watch for factors that can affect the IR test. During the test, watch out for these four factors that can have an impact on the test and its results:

  • Surface contamination such as oil, dust and salts may be conductive, causing lower IR. Cleaning and drying the winding will usually improve the IR.
  • If the winding temperature is at or below the dew point, moisture may accumulate on the surface, causing low IR values. When the winding is otherwise in good condition, drying will resolve this issue.
  • Winding IR decreases when winding temperature increases, which is why correction to a baseline temperature is recommended.
  • Voltage magnitude and existing charge also can affect IR, but selecting the voltage from Table 1 and following proper grounding practices before testing should eliminate this issue.

Table 3: Recommended minimum insulation resistance values at 40 °C (all values in MΩ). Courtesy: EASA, IEEE

6. Evaluate the test results. Table 3 shows the recommended values for the corrected IR. Lower values warrant further investigation before the unit is placed into service. Some machines do operate below these values. Having historical data on-hand is valuable.

Mike Howell is a technical support specialist at the Electrical Apparatus Service Association (EASA), a CFE Media content partner. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.

MORE ADVICE

Key Concepts

  • Insulation resistance (IR) tests are useful for determining whether a motor should be removed.
  • During the test, the user should discharge for safety and accuracy and record important test conditions.
  • Users should also be aware of factors that might affect the IR test.

Consider this

What other aspects should users watch for while performing an IR test on a motor?



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
Prescriptive maintenance; Hannover Messe 2017 recap; Reduce welding errors
Safety standards and electrical test instruments; Product of the Year winners; Easy and safe electrical design
Safer human-robot collaboration; 2017 Maintenance Survey; Digital Training; Converting your lighting system
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
Automation modernization; Predictive analytics enable open connectivity; System integration success; Automation turns home brewer into brew house
Commissioning electrical systems; Designing emergency and standby generator systems; Paralleling switchgear generator systems
Natural gas for tomorrow's fleets; Colleges and universities moving to CHP; Power and steam and frozen foods

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
Compressed air plays a vital role in most manufacturing plants, and availability of compressed air is crucial to a wide variety of operations.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me