A sound stator core is the foundation of a good motor winding. As we discussed in the previous post on Core Loss Testing, this test is essential to determining the viability of a stator core prior to motor rewind. In this video, we explore how to properly conduct core loss testing, the warning signs of a bad stator and some best practices that your motor shop should observe when performing this test.
Core loss defined
Look closely at a stator core and you see that the core consists of laminations of metal plates. These plates are separated by a thin insulating material that can fail over time as a result of friction and other stresses. The video shows what happens when stator insulation fails, resulting in hot spots in the core. The result is increased heat and current imbalances that can be measured as increased power losses.
Be sure you are getting proper core loss testing
During a typical induction motor rewind. a high level of current is passed through the core using one of the testing machines made for this purpose. Learn what a good rule of thumb is regarding lost wattage/pound of stator weight. Any core with an average wattage loss inside that range would be deemed acceptable and would be rewound. Unfortunately, many motor repair shops perform this test without answering some key questions that can spell the difference between a good stator core and a bad one. Learn what questions to ask before performing the test.
Core loss testing standards
We refer to two standards for core loss testing – the EASA AR-100 and the IEEE 432. It is suggested that your motor repairs conform to one or the other standard. If they don’t it might be worth your time to shop around for a motor repair facility that adheres to these standards. EASA also commissioned studies on this topic, EASA/AEMT Rewind Study, 2003.
Protecting your investment
It’s a good practice to visit your repair shops personally to inspect their repair facilities. We offer a useful and easy shop audit guideline to help you. We also provide an electrical testing summary, which you will find handy when discussing electrical testing with vendors. The core loss testing video will help you formulate some best practices when evaluating your core loss testing procedures and vendors who perform them
To discuss your motor repair needs, call 800.993.3326, or email our motor services team EECOMotorTeam@eeco-net.com