Cables:

Infraspection Institute

Infrared Inspection of Load Break Elbows

Load break elbows are a common feature in shielded cables.  Thermography may be used to provide evidence of loose or deteriorated connections associated with these connectors.

Load break elbows are insulated plug-type terminals typically used to terminate shielded, underground cables.  Load break elbows act as large power plugs for connecting cables to transformers, switching cabinets and bushings equipped with load break receptacle bushings.

Internal to load break elbows are several mechanical connections each of which is subject to deterioration over time.  A typical elbow contains a crimp connection and a pin electrode that screws into the elbow.  During normal operation, this pin electrode mates with a receptacle which also contains mechanical connections.  Elbows and receptacles that have loose or deteriorated connections will operate at elevated temperatures and are readily detectable with a thermal imager.

 Hot Elbow Loose Internal Connection

Normally, all electrical connections within an elbow are hidden from view due to the elbow's molded rubber insulating body.  Due to their high emittance, load break elbows are excellent candidates for infrared inspections.  In fact, thermal imaging is one of the best ways to inspect these components for the integrity of their connections.

Since line-of-sight access to the electrical connections within load break elbows is not possible, temperatures at the point of origin are likely to be much hotter than observed temperature values on the exterior surface.  Small Delta T's observed on the surface of elbows can be indicative of a serious problem.  Because of this, hot load break elbows should be investigated for cause as soon as possible and appropriate corrective measures taken.

Infrared inspection of power distribution systems is one of the many topics covered in all Infraspection Institiute Level I training courses.  For information on course locations and dates or Distance Learning Courses, visit Infraspection Institute online or call 609-239-4788.

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Infraspection Institute

Detecting Electrical System Overloads

Statistically, overlooked circuits are the second most common causes of exceptions found during infrared inspections of electrical systems.  Although overloads are quite common, they can be tricky to diagnose.

As electrical current flows through a conductor, heat is generated.  As circuit load increases, so does the amount of heat.  Electrical circuits are designed so that loads will not exceed the circuit's ability to safely carry a sustained load and the amount of heat associated with such load.

Typically, overcurrent protection devices such as fuses or circuit breakers are designed to protect circuits from overload conditions.  These devices will interrupt the circuit when the current reaches a predetermined level for a specified period of time.

Serious problems such as fires can be caused by sustained overloads.  Such overloads may be caused by: improperly sized wiring, and improperly sized or defective overcurrent protection.  Fortunately, a thermal imager can be used to detect the thermal patterns associated with sustained overloads.

 Overloaded Cables at a terminal block

When using a thermal imager to detect potential overloads, one should keep the following in mind:

    • Overloaded conductor(s) will be uniformly warm throughout entire length
    • For polyphase circuits, all conductors may be uniformly warm
    • Depending upon ambient conditions and imager settings, overloaded circuits may not appear remarkably warmer than adjacent circuits.

Because an infrared imager cannot measure electrical current, suspected overloads must be confirmed with an ammeter while observing all requisite safety precautions.  For greatest accuracy, a true RMS sensing ammeter is recommended.  Circuits found to be overloaded should be immediately investigated for cause and corrected.

Infrared inspection of power distribution systems is one of the many topics covered in all Infraspection Institiute Level I training courses.  For information on course locations and dates or Distance Learning Courses, visit Infraspection Institute online or call 609-239-4788.

 

Click below to download: Detecting Electrical System Overloads

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