The number one application for infrared thermography globally is electrical applications. The reason is obvious; virtually every industry, process, building or facility in the industrialized world requires electrical energy to operate.
The principle behind an electrical fault is very simple. When electrical energy flows in an electrical circuit there is a conversion from electrical energy to thermal energy. This is a naturally occurring phenomenon. As the resistance to the flow of electrical energy increases, the surface temperature of the component increases as well. Additional infrared energy is emitted from the surface of the object and the infrared camera detects this deviation.
No Electrical system is 100% efficient. Universally, the electric industry understands that temperature is an excellent indicator of the operating condition and hence the reliability of an electrical component. Associations like IEEE, ANSI, IEC, and manufacturers all publish standards and temperature ratings for electrical components and materials are drastically reduced as temperature is increased. Again this is to emphasize that temperature is an unavoidable aspect of almost every industry’s safety
Typical Infrared Electrical Applications & Anomalies Detected
|Application||Bad Condition Detected by Thermograhpy|
|√ Power Distribution|
√ Lightning Arrestors
√ Circuit Breakers
|√ Loose/corroded/improper connections and splices|
√ Railed lightning arrestors
√ Poor breaker connections
√ Conductor strands are broken
|√ Miscellaneous Electrical Apparatus|
√ Load Centers
√ Motor Control Centers
|√ Loose/corroded connections|
√ Poor contacts
√ Unbalanced loads
|√ Transformers||√ Loose/deteriorated connections|
√ Overheated bushings
√ Poor contacts (tap changer) overloading
√ Unbalanced 3-phase loads
√ Blocked/restricted cooling tubes
√ Fluid levels
|√ Motors/Generators||√ Overheated bearings|
√ Unbalanced load
√ Shorted/open windings
√ Heating of brushes
√ Slip rings and commutators
√ Blocked cooling passages
|√ Emergency Power|
√ Stand-by Generators
√ Terminal Connections
√ Automatic Stand-by Switches
|√ Poor battery terminal connection|
√ Dead cells in batteries
√ Defective/inoperative contactors/stand-by switches
The electrical component will usually show signs that originate from heating from a current passing through a conductor with a certain resistance, i.e. Joule’s Law. Sometimes the current can be induced by a magnetic field, but the heating takes place according to the same mechanisms.
Typical Failure Modes
A failing connection will have an increased resistance for a number of possible reasons. Corrosion is a frequent cause of failure as well as dirt, dust and faulty installation.
Breakers and contactors can develop internal faults in the contacts themselves, and also in the internal connections that may exist.
An overheated component may also cause arcing. If a highly loaded circuit suddenly opens up by fusing a part of it, there may be an arc as a result. Remember that an arc will start easier at higher voltages, but the energy of an arc is depending on the current. With a high current, a lower voltage circuit may cause disaster as well.
There is also a risk of fire caused by electrical faults. In Insurance statistics of industrial fires worldwide electrically induced fires are always represented, typically to a degree of perhaps 20% or so. Even a small fire may very well prove to be the end of the life of a production facility it may never produce again.
SCIENTIFIC BACKGROUND FOR USING THERMOGRAPHY
A correctly working termination will have low resistance. When the resistance goes up, the termination becomes hotter. The heating power follows Joules’s Law (P= R x I2). As the heating power goes up, the temperature goes up as well, but not in direct proportion to the power.
It is recommended that the load should be 50% or higher when the survey is done. At lower loads, the target signatures can become very weak and difficult to see.
Power (P) is the rate of doing work or the rate at which heat is produced and equates to the thermal energy generated from an electrical component. It is directly in proportion to the square of the current (I2) passing through it multiplied by the resistance of the component (R). As the condition of the component deteriorates, its resistance will increase and generate more heat. As the component temperature rises, the resistance will increase further. This self-propagating process continues until the melting point of the weakest component is reached. By utilizing thermography to inspect electrical systems and components under load, the faulty components can be identified and classified by severity of the problem or fault.