Diagnostic Insulation Testing Rotating Machines

Medium and High Voltage rotating machinery, be it a motor or generator, is expensive capital equipment which is usually critical to the smooth running of a system or process. It is generally very reliable and is often designed for a working life of 50 years or more. This design life only allows for normal levels of ageing and degradation. In its lifetime, the machine will be subjected to electrical, mechanical, thermal and environmental stresses which all cause a gradual deterioration of the electrical insulation. This degradation will, if left unchecked, eventually lead to failure of the machine. If these stresses exceed the levels allowed for in the design, the result will be premature failure. The consequences of an unexpected failure can be extremely expensive and cause untold disruption to processes that may be critical to your company. What can you do about it?

Well, fortunately the condition of the electrical insulation of the stator is a pretty good measure of the overall condition of the machine and today's sophisticated insulation testers are capable of carrying a variety of tests automatically. Instruments such as the MEGGER S1--5010 insulation tester can perform automatically timed insulation resistance, polarization index, step voltage tests during a charging cycle, and dielectric discharge tests during the discharge cycle. Test results are stored in memory for later download to a PC or can be downloaded real time.

Of course, you can carry out most of these tests with a non-automatic instrument. This involves close monitoring of data using a stop watch, great care in manually recording results, and care in processing data to get indicators required to predict the condition of the machine. Not an easy task!

However, a single test can only give a partial window into the condition of the machine and each different type of test looks at a different window. To get an accurate picture, we may need to carry out hundreds of measurements over a period of time and process a lot of data to get easily understood indicators of the machinery condition. Fortunately help is at hand in the form of the MEGGER EDA Electronic Dielectric Analyzer.

The MEGGER EDA Electronic Dielectric Analyzer is a PC controlled test instrument that can be easily taken on site. It carries out condition based diagnostic testing on off-line rotating machines. All of the tests can be carried out using individual test instruments, but this takes a long time, involves complicated calculations, and there is difficulty in being able to repeat the test conditions the next time you want to carry them out. There are companies out there who use one machine that takes all day to test, record data and process the results. Fortunately, the EDA achieves this testing in only 1½ hours.

The EDA performs nearly thirty tests automatically. Each test gives an insight into the machine condition and, when combined, provide an extremely powerful diagnostic sequence. The EDA saves the user and extraordinary amount of time and money.

AVO International, 4651 S. Westmoreland Rd., Dallas, TX 75237. Tel: 800-723-2861; Fax: 214-333-3533.