MASSEY TECHNICAL SERVICE LLC 10-Millbrook Rd. Bridgeport WV. 26330 Phone:304-842-6948

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Trolley Wire Insulator

The inspection of Coal Mine Underground Trolley Systems with Thermography is very important to mine safety. Loose or improper connections of the DC trolley system can cause electrical outages, fires, or even roof falls.

The example below shows a trolley insulator that has shorted causing current leakage through the support bolt into the roof. The trolley wire is the positive side of the power supply that is insulated from the roof by using insulators. The rail is the negative side that equipment operates on, similar to a train.

The roof is also a return path for the positive (300 volts DC) current to the negative. From the information we have gathered from the mining industry we have found that if an insulator is bad it can cause leakage current to go into the roof causing a heating of the general rock structure in that area. The concentrated heat in the roof area may cause a roof fall in the area which can result in fatalities.

The two pictures below show the trolley hanger where it goes into the roof. You can see the temperature change and heat at the point where the hanger metal rod goes into the roof rock structure. There was an ambient temperature of 46 degrees F in the area, and the roof temperature changing from 63 to 58 degrees F. With the 63 degrees F located where the hanger entered the roof. You can also see the migrating temperature change in the roof. The first picture is an IR picture taken in a color palette of Rain 900, and second picture has a color palette of Iron.


The digital picture below shows the insulator hanger marked with a paper cup so the insulator could be immediately replaced.


The picture below shows the inside of the insulator which is completely destroyed allowing for leakage current to flow through the bad insulator to the roof bolt.


By the use of Infrared testing we helped eliminate a potential safety hazard.

There are many areas that IR inspections can be used in the underground coal industry from the DC trolley system (trolley insulators, Rectifier connections, ITE breaker connections, return and ground terminations, battery equipment inspections) to the AC distribution system. Examples of other possible inspection sights are belt starters, power centers, high voltage terminations, equipment plugs and breakers.

This newsletter reinforces that infrared thermography is a vital part of any predictive and proactive maintenance program.

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Last modified: May 19, 2015