Archives for 2017

The Five Whys of Equipment Failure

The five whys refers to the practice of asking five times why a motor failure occurred in order to get closer to the root cause of the problem. Failure to determine the root cause can result in treating the symptoms of the problem instead of its cause, in which case you will continue to have the same problems over and over again.

Why did the motor fail? It shorted to ground.
Why did it short to ground? The ground wall insulation failed.
Why did the ground wall insulation fail? The insulation overheated.
Why did the insulation overheat? Excessive ambient temperature.
Why was the ambient temperature so high? The cooling fan motor was not operating correctly.

Just replacing the motor would not solve the cooling fan problem and the new motor would be in the same high risk environment.

Dry Ice Blasting Prolongs Life of Motor at Paper Mill

Dry Ice

Decatur Industrial Electric performs DC and synchronous motor PMs on a routine basis for an industry leading paper mill. Our tracking and trending of electrical testing revealed that a 2,000 HP synchronous motor had degrading insulation and resistance to ground readings over time. Our reliability specialists, during a scheduled plant outage, inspected and dry ice blasted the motor onsite. The resistance had huge improvement.

Dry ice blasting is an effective and quick way to clean electric motors. It also allows the equipment to be cleaned in place and in an environmentally friendly manner. And, because dry ice converts to gas, there is no fluid or water residue. As a result, there is no disassembling of electrical components or equipment.

Through this method, we were able to clean the motor on-site to the point where it was able to stay in service and a spare didn’t have to be installed. The PM testing saved over $250,000 because the motor did not run-to-failure causing unplanned downtime. The on-site cleaning altogether saved downtime, equipment change out costs, and repair costs.

Commutator Wear? D.I.E. can Help with the CL-Profiler

CL Profiler

The CL-Profiler is the perfect solution for profiling slip ring assemblies and commutators.

This tool can be used during the repair process and also in the field during DC motor PM’s in order to have a baseline; or, as a troubleshooting tool for aggravated commutator and brush wear. It can also be used annually in order to check for trending for commutator looseness, wear, vibration, and contamination influences.

Don’t Forget the 5th

In an AC Induction motor the rotor turns slower than the rotating magnetic field in the stator. This differential rotation loosely referred to as slip can be easily seen in a current spectrum by an elevated pole pass frequency (Fp) peak equal to the number of poles times the slip. The basic analysis concept is to use the amplitude variations of this peak to identify and trend defects in the rotor condition. The higher the amplitude of the Fp, the higher the severity of a possible rotor defect. However, it is important to remember that rotor condition is not the only thing that can affect the Fp amplitude. Machine train load fluctuations can often match the Fp creating a false indication of a rotor anomaly through an elevated Fp. An easy way to isolate the elevated Fp to either a mechanical or electrical source is to evaluate the 5th harmonic frequency peak in the same current spectrum. The 5th harmonic is not fooled by a mechanical load fluctuation and can greatly increase the confidence of the analyst in making the right call on a possible rotor anomaly.

To see more details on the 5th harmonic and other rotor analysis techniques visit the PdMA YouTube channel at:
https://www.youtube.com/watch?v=P4XIYg-695A&list=PLjgXwy4LaY3rMI2MNKer7SxDA50n9LMSa&index=6

Motor Management Plan at a Metals Mills Saves Customer from Unplanned Downtime

Decatur Industrial Electric is regularly scheduled at a customer site to inspect and maintain their equipment to ensure optimal performance. Our routine inspections help reduce unexpected downtime and extend equipment life.

This particular inspection included an air flow measurement of a large DC motor forced air cooling system. Our reliability specialists determined the air flow was not within normal value and further investigation was needed to determine the cause. Upon disassembly, we could readily see an excessive buildup of oily dirt in the impeller and the housing.

A D.I.E. technician cleaned both the impeller and the housing on-site and restored the cooling fan to its optimal performance levels. When cleaning these components it is very critical that all the contamination be removed from the impeller. The blower was returned to service in just a short period of time.

Through routine maintenance, this issue was discovered before it became a larger more costly problem or caused downtime.

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