Protecting large machines from arcing faults

Conventional methods of protection are not certain due to the intermittent nature of an arcing fault since any single arc may not last long enough to operate time-delayed neutral protection. Arcing faults can occur due to dirty insulators or broken strands in the stator windings. Such faults, if undetected, can lead to overheating along with catastrophic electrical failure. These events typically require extensive repairs with an extended shutdown of the machine. It is highly desirable to detect such faults at an early or incipient stage so that remedial action can be taken before a complete failure occurs. This paper presents a new protection method to detect arcing faults along the entire winding and trip the unit before extensive damage can occur. This paper shows the protection engineer how to properly identify the faulted phase. Faulted phase identification is important since it will greatly aid in locating the source of an intermittent arcing fault.