Tom Bishop, P.E.
EASA Senior Technical Support Specialist
EASA’s
Getting The Most From Your Electric Motors is a great marketing tool for service centers to provide to customers (end users). As such, this valuable 40-page booklet provides end users with information that will help them obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors with these characteristics:
- Three-phase, squirrel-cage induction motors manufactured to NEMA MG1 standards
- Power ratings from 1 to 500 hp (1 to 375 kW)
- Speeds of 900 to 3600 rpm (8 to 2 poles)
- Voltages up to 1000V, 50/60 Hz
- All standard enclosures (i.e., DP, TEFC, WPI, WPII)
- Rolling element (ball and roller) and sleeve bearings
The following is an overview of the contents of the booklet indicating some of the ways that using it can benefit end users, i.e., your customers — and potential customers.
Installation, startup and baseline information
The first of the two major sections addresses three subtopics: motor installation, startup and baseline information. Early on it recommends making sure to document the motor’s initial condition to establish a baseline for comparison with future results. Among the benefits to the end user by following this practice is that it’s often possible to recognize small or developing problems before they lead to costly motor failures and downtime.
Reference is made to the “Motor and installation baseline data” sheet (see Figure 1) found in Appendix A. Recording the nameplate data and pertinent electrical and mechanical parameters at the time of installation and startup makes that information available for reference in hard copy or, if scanned, electronic format. Review of the motor data, including the nameplate information, can provide insight into the motor’s suitability for the application.
Specific items to check include motor suitability for use with a variable frequency drive (VFD), bearing suitability if the application is a belt drive, lubrication points accessibility, and verifying that the motor control and overload protections are sized properly for the motor rating. The last two points can be critical if the motor is a replacement and of a different power rating than the motor that it replaced.
Installation considerations such as the adequacy of the foundation and base are important for motor reliability. A weak or otherwise inadequate base can result in frame distortion, rapid bearing wear and vibration.
The booklet not only provides details on these topics, it extensively covers shaft alignment, including the issues of soft foot, alignment tolerances, and alignment methods for direct-coupled and for belt-drives. The end user can find a great deal of installation related information in just a few pages of the booklet.
The information in the booklet proceeds from the installation considerations to startup procedures. In many cases the motor being installed had been in storage; details are provided to help assure that the motor functions properly. Among the storage related topics are lubrication and the lubricant, and checking winding insulation resistance (see Table 1).
Next, recommendations are provided for pre-operation startup tests. Measuring and recording vibration levels is recommended. Recommended tests with the motor under load include line to line voltage, line currents, winding temperature (if possible), bearing temperature and ambient temperature. The booklet suggests these baseline values be recorded on the motor data sheet as a basis for future trending measurements. Two examples are provided to show the importance of recording baseline and trending data.
The section on motor installation, startup and baseline information concludes with the topic of total motor management. These programs typically track purchases and spares in a database by nameplate information, facility/location, and application. Usually they also track baseline data, maintenance, storage and repair. The primary benefits for the end users are that such programs lower costs by reducing downtime (spares are readily available) and decreasing inventory (identification of spares used in multiple locations).
A key consideration here is whether the most cost-effective and reliable solution is to store spare motors on site or to outsource storage to a service center or other vendor. Motor management and spare motor (and other equipment) storage is yet another opportunity for a service center to provide a value-added service for their customers. Further, having the customer’s spare motor at your facility provides a better opportunity to receive the replaced motor to perform the needed repairs.
Operational monitoring and maintenance
The second of the two major sections deals with operational monitoring and maintenance. Primary topics include application-specific conditions, preventive and predictive maintenance, inspection and testing, and bearing relubrication. By making use of the advice in this section the end user can extend the useful life of their motors, as well as the mean time between failures requiring repair.
Abnormalities in the electrical supply such as transient voltage can result in transient currents and torques which can damage not only windings but also mechanical components of the motor or driven equipment. To help the end user avoid these abnormalities, a bullet list identifies over a half-dozen potential sources. Another source of transient conditions that is not an abnormality is motor starting. The booklet provides the end user with guidance in dealing with motor starting and emphasizes the need to limit the number of motor starts.
The subsection on preventive maintenance (PM), predictive maintenance (PdM) and reliability-based (RBM) maintenance defines and describes each. Electrical and mechanical test and inspection techniques and physical condition assessments are identified for PM, PdM and RBM [also termed reliability-centered maintenance (RCM)]. Even if an end user already has a PM, PdM or RBM program, they can benefit from review of this subsection as it may identify missing elements in their program. Also, if an end user is not familiar with any of these programs the booklet provides information to get them started on the path to more reliable motor operation. That is, it provides an opportunity for the end user to get the most from their electric motors and probably the connected equipment as well.
Additional information on PM, PdM and RBM is included in the subsequent section on motor inspection and testing. All too often we hear the statement “don’t overlook the obvious.” That describes the importance of physical inspection in detecting missing, broken or damaged parts, blocked airflow paths and contaminants. Any one of these conditions could lead to premature and perhaps rapid motor failure.
Tests that are described in detail include insulation resistance, winding resistance and motor current signature analysis (see Table 2). When available from industry standards, criteria for evaluation are provided so that the end user can determine if their levels are acceptable or warrant corrective action. Cautionary information is provided regarding high-potential and surge testing of installed motors. Information about vibration analysis using a spectrum analyzer is also provided.
This final subsection of the main body of the booklet provides guidance to help assure long and reliable motor operation. Recommendations include not only relubricating bearings, but also monitoring lubricant levels and checking for leaks and contamination. Guidance is provided to help the end user determine the correct relubrication interval and the lubricant type and grade when the motor manufacturer instructions are not available.
The importance of grease compatibility is stressed, and a grease incompatibility chart is provided. Sage relubrication advice is given in the statement: “The best practice is to use the same grease that’s already in the bearings–provided it’s suitable for the application." A formula is provided to determine the precise amount of grease required; a graphic illustrates grease relubrication intervals based on bearing type, size and speed.
Oil-lubricated sleeve and rolling element bearing lubrication is also addressed, including topics such as oil compatibility, viscosity, and relubrication intervals. Specific topics such as dealing with abnormal conditions and how to replace oil are also described.
Appendices
The three appendices provide supplementary information that can help the end user get more from their motors in terms of record-keeping, understanding motor terminology and storage. Appendix A contains a two-page data form (see Figure 1) intended for use in recording motor nameplate data and electrical and mechanical test data. Initially the data form can be used for baseline information, and then updated when maintenance or repairs are made. As such it can provide invaluable historical information for the end user and service firms when it becomes necessary to perform a simple failure analysis or more comprehensive root cause failure analysis.
The information in Appendix B is a compilation of key terms associated with motor nameplate data. (Note: There is also a standalone glossary at the end of the booklet.) However, the real value of this information is in determining the meaning of terms that at times are misunderstood. Knowing the true meaning and importance of these terms can help an end user avoid a costly and time-consuming mistake in purchasing a motor that is not suited for a specific application.
Based on member inquiries, motor storage recommendations, which are the topic of Appendix C, are a common end user request. These storage recommendations alone make the booklet a valuable resource for end users. The last page of this appendix summarizes how often to perform certain storage maintenance routines. It is rare to find this time versus task information all in one place, which is something many end users will appreciate.
Ordering information
Printed copies of Getting The Most From Your Electric Motors booklet can be purchased in EASA’s Online Store or you may download a PDF copy for FREE.
Imprinting available to EASA members
EASA members may also imprint their company name, logo or contact information on the cover of this booklet. This makes for an excellent marketing and educational tool to distribute to you customers. Download the imprinting guidelines and contact customer service to place you order. |
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