Infrared scanning procedures

The purpose of an infrared inspection is to identify and document problems in an electrical or mechanical system. The information provided by an inspection is presented in an easily and understandable form.
A high percentage of problems occur in termination and connections, especially in copper-to-aluminum connections. A splice or a lug connector should not look warmer than its conductors if it has been sized properly. All problem connections should be dismantled, cleaned, reassembled, or replaced as necessary.

Types of infrared problems

There are three basic types of thermal problems:

(1)Mechanical looseness
Mechanical looseness occurs most often. A loose connection will result in thermal stress fatigue from overuse. Fuse clips are a good example because the constant heatup and cooldown creates a poor connection.
An accurate temperature measurement, or use of an isotherm, will identify a loose condition. When the isotherm is brought down to a single pixel, or temperature, it will identify the source of the loose condition.

(2)Load problems


(3)Component failure
Understanding the nomenclature of the problem can identify component failure. Specifically, the actual component will be the heat source. For example, a heat-stressed fuse in a three-phase assembly will appear hotter than the other two fusses.

Common problems found and what to scan

(1)Motor control and distribution centers
Have the switchgear panel covers opened or removed by qualified personnel before inspection. Scan cable, cable connections, fuse holders, fuse circuit breakers,and bus.

(2)Main secondary switchgear
The same to Motor control and distribution centers.

(3)Circuit breaker distriution panels
Covers on small circuit breaker panels do not have to be removed for scanning. Circuit breakers and conductors are very close to the metal covers. Defective components are usually detectable by the heating of the cover in the area of the problem.
If a problem exists, remove the panel cover to locate the problem. Only remove panel covers that can safely be removed.

(4)Bus Duct
Electrical conductors are very close to the metal "skin" of the duct. Defective joints are usually detectable by the heating of the cover in the vicinity of the problem.

(5)Motor
Do not scan motors less than 25 horsepower unless they are critical to production. Bearing problems can be found by comparing the surface temperature of like motors. Overheating conditions are documented as hot spots on teh CRT and are usually found in comparing equipment, end bell and end bell, and stator to edn bell.

(6)Transformer-oil Filled
Scan transformer, transformer fins, cable connections, bushings, and tap changer. On all transformers, the oil level should be inspected during the survey. During the infrared survey, if a transformer appears exceptianally warm, the cooling radiators are near ambient temperature, and the transformer is above 50 percent of full load, the oil level is too low to circulate the oil and cooling is not taking place.
Oil in the transformers is cooled by convection; as the load increases, the oil expands and the level increase until it then circulates in the cooling radiators.
As a result of repeated oil samples and oil leaks, the reduced volume of oil causes the winding to overheat, thus reducing the life of the transformer. Plugged cooling heaters, isolated radiators, and plugged individual cooling fins can also be detected.

(7)Transformers-Dry-Type
The iron in these transformers is hot. It will heat the bus work and cause substantial infrared reflection. By increasing the temperature scale and adjusting the level control on the imager, you will be able to get uniform images, Which will show hot spots in the secondary bus or the iron.
Compare all windings. If temperatures are over a winding, but there is a difference in temperature of two windings, there may be an unbalanced load. A hot spot on a winding may point to s shorted trun.

(8)Capacitors
A capacitors has two conductive surfaces, which are separated by a dielectric barrier. Capacitors usually function as power factor correctors. When energized ,all units should have the same temperature if the size is the same.
A high uniform temperature is normal. A cold capacitor usually indicates a blown fuse or bad cell. Isolated spots showing a high temperature on a surface of the capacitor may indicate a bad capacitor.

(9)High-Voltage Switchgear
Scan lighting arresters, insulators, cables, cables connections, bussing, circuit breakers, and disconnect switches.

(10)Load Break Switches
In the switch, two metal surfaces act as conductors when they are brought into contact. Usually, problems are restricted to the contact surface. Poor contacts usually show up as hot spots.

(11)Fuses
A fuse is a metal conductor, which is deliberately melted when an overload of current is forced on it.

(12)Circuit Breakers
Circuit breakers serve the same function as a fuse. It is a switching device that breaks an electrical circuit automatically.

(13)Conductors
The melting points and current-carrying capacity of conductors are determined by the size and base material of the conductors. During a survey, compare between phases and between conductors and connections.