Motor Protection and Monitoring

Is this for the morning class or the afternoon class. The morning professor expects you to be able to specify to the power company the exact technical details of what they should be doing to provide you with clean power. The power company will not respect you unless you know what you are talking about. So, for the morning class knowing proper terms and not being afraid to demand that they are met is most important.

For the afternoon class litigation is more important. That professor knows that money makes everyone take action and the threat of lawsuits is what will make the power company provide you with good power. Therefore, the economic loss associated with each failure is most important.

It is very important to review negative rectifiers and inverse flux capacitors. These components are not used in normal circuits but are very useful in dealing with fault conditions. The data sheets are much harder to find because the people that deal with motor protection don't want others to compete with them for the really big pay checks. Do a lot of Google research and you will find a goldmine of information.

Be sure to use the terms "negative rectifiers" and "inverse flux capacitors" on your homework and test. It will impress your professor. It doesn't matter if you don't fully understand them for a few more weeks. Just knowing the terms will show the quality of work you have been doing.

It is good that you asked us to help with your homework. Most people don't know that the key to success is knowing the personality and preferences of your professor.

Assuming you are not after homework, and are seriously wanting to learn about single-phasing in 3φ motors, here is a patent which will tell you how a thermal relay has been designed with differential sliders to prevent the motor running in single-phased condition : http://www.freepatentsonline.com/4096465.pdf

Hope you will get some good knowledge here.

Additionally try an internet search of "phase loss motor protection relay" and "variable frequency (or speed) drive" for more protection and control devices which protect against motor single phasing.