Preventing a Transformer Fireworks Display
Infrared inspections of oil filled transformers can help to increase reliability and extend transformer life. Detecting hotspots on the bushings of these transformers may also help to prevent a catastrophic explosion.
Hot spots on transformer bushings are usually due to a loose or deteriorated electrical connection. Frequently, the source of a hot bushing connection is external to the transformer and can be corrected by repairing the defective connection. However, loose connections which originate within the transformer case can represent an extremely dangerous condition.
Loose electrical connections within an oil-filled transformer can lead to a condition known as arcing. When arcing occurs in oil, the molecular structure of the transformer oil breaks down forming several combustible gases. The most significant gases produced are acetylene, hydrogen, methane, ethane, and ethylene.
The amount of gas produced will depend upon the temperature of the arc and length of time; however, even small amounts of gas can lead to a potentially explosive condition. In a sealed, oil-filled transformer these gases can build to a potentially explosive level within a very short time. In short, combustible gases combined with an arcing condition within a transformer are a recipe for potential disaster.
When inspecting oil filled transformers, any inexplicable temperature rise on bushings should be investigated and corrected immediately. Performing a dissolved gas analysis of the transformer oil is recommended if the cause of the problem is suspected to originate within the transformer.
Infrared inspections of electrical distribution systems is a topic covered in all Infraspection Institute Level I training courses. For course locations and dates or information on our Distance Learning courses, visit infraspection.com or call us at 609-239-4788.
IR Inspections for Sewer Systems
In regions with older infrastructure, sewer system integrity is often a primary concern. Under the right conditions, thermography can often detect sewer leaks or voids surrounding the system that can lead to sinkholes.
In the case of sewer systems, thermal imaging is usually employed during evening hours after a sunny day. During the inspection, the thermal imager is maneuvered over the pathway of the subject sewer system looking for unusual thermal patterns. The imager may be operated on foot, from a motor vehicle or an aircraft.
Sewer system defects which may be detectable include leaks to surrounding soil and voids around sewer piping. The detectability of these defects will be largely dependent upon:
- Depth of sewer system
- Amount of loss
- Pipe construction
- Soil type and ground cover
One should be aware that a negative finding does not necessarily mean defects are not present; they simply may not be detectable by thermal imaging. Conversely, positive findings can be caused by conditions other than leaks. Therefore, it will be necessary to verify all thermal data by visual inspection.
The topic of infrared inspections of buried piping systems is covered in depth in our Level I Certified Infrared Thermographer® training course. For more information on class locations or our Distance Learning program, visit www.infraspection.com or call 609-239-4788.
Heat Stress & the Human Body
Tip written by: Infraspection Institute
For many, the peak of Summer brings high temperatures to the workplace. For others, high temperatures in the workplace are an everyday occurrence. Understanding heat stress and its attendant safety challenges is crucial for those working in hot environments.
What is heat stress?
Heat stress is a physical hazard. It is caused by environmental conditions and results in the breakdown of the human thermal regulating system.
What are the symptoms of heat stress?
There are various degrees of heat stress. Each has its own unique symptoms. The most common form of heat stress is heat exhaustion. Symptoms of heat exhaustion include dizziness, confusion, headaches, upset stomach, weakness, decreased urine output, dark-colored urine, fainting, and pale clammy skin.
What do I do if I think I am experiencing some form of heat stress?
Act immediately –
- Advise a co-worker that you do not feel well
- Move to an area away from the hot environment
- Seek shade and cooler temperatures
- Drink water (1 – 8 oz. cup every 15 minutes) unless sick to the stomach
- Have someone stay with you until you feel better
What should I think about before working in a hot environment?
Before working in a hot environment, consider the type of work to be performed, duration of time to be spent in hot areas, level of physical activity, and other nearby hazards. Always use appropriate PPE and work together as a team.
Inspecting Service Entrance Cables
When performing infrared inspections of electrical systems, many thermographers tend to focus their attention on outdoor substations and overhead electric lines. Unexpected failures can occur when service entrance cables are overlooked.
Service entrance cables provide a critical link between outdoor electric supply and a building’s indoor electrical equipment. Like other parts of the electrical system, these conductors are subject to loose or deteriorated connections which can cause unexpected interruptions in electrical power. Fortunately, such loose connections can often be detected with a thermal imager.
When inspecting service entrance cables, one should bear the following in mind:
- Prior to inspection, ascertain that service cables are under adequate load
- When possible, inspect cable connections at both ends. Emissivity issues aside, in most cases connections should be the same temperature as cable conductors
- On long cable runs, be certain to inspect any inline splices for hotspots
- To avoid the effects of solar loading, inspect cable assemblies early in the morning, on a cloudy day or at night
Because it is impossible to predict time to failure based upon temperature, inexplicable temperature rises should be investigated for cause as soon as possible. Doing so can help to avoid unexpected downtime and improve the reliability of a facility’s electrical distribution system.
Infrared inspection of electrical systems is one of the many topics covered in the Level I Infraspection Institute Certified Infrared Thermographer® training course. For information on thermographer training or to obtain a copy of the Standard for Infrared Inspection of Electrical Systems & Rotating Equipment, visit us online at www.infraspection.com or call us at 609-239-4788.
IR Inspections of Smooth Surfaced Roofs
Tip written by: Infraspection Institute
Having the right tool for the job is often essential for success. When performing infrared inspections of smooth-surfaced roofs, a short wave thermal imager can significantly outperform a long wave imager.
Smooth-surfaced roofs, both single-ply and built-up, can present significant challenges during an infrared inspection due to reflectivity of the roof membrane. Should reflectance be sufficiently high, areas of latent moisture may be undetectable to a thermal imager.
Most infrared inspections of flat or low slope roofing systems are conducted at night by walking across the roof surface using a handheld thermal imager. This technique often results in a relatively shallow viewing angle thereby lowering the emittance of the subject roof membrane.
Depending upon site conditions and roof materials, roof membranes can appear to be as reflective as polished metal surfaces. Membrane reflectivity will be especially noticeable on cool, clear nights that permit the cold night sky to be reflected from the roof surface. It will also be significant on roofs that have been coated with aluminum paint.
To this day, the most practical way to deal with the reflectivity of smooth roof membranes is to utilize a thermal imager with short wave (2 to 5.6 micron) spectral response. This will help to eliminate reflections from the roof and can significantly increase inspection accuracy. Although long wave imagers can be used for smooth membranes, they can significantly understate the size of moisture-damaged areas or miss them entirely.
Infrared inspections of low slope roofs is one of the many topics covered in the Level I Infraspection Institute Certified Infrared Thermographer® training course. For information on thermographer training and certification, visit us online at www.infraspection.com or call us at 609-239-4788.