Substations and Switchgear
Substations call for a predictive approach to maintenance because a failure can be costly for end users in terms of lost production and revenues and lead to lower revenues for the utility from lost sales due to unreliable service. Since overheating as well as abnormally cool operating temperatures may signal the degradation of an electrical component, thermal imagers provide the predictive capabilities required for substation and switchgear maintenance.
In the power generation and distribution industries, the term substation is used in many ways. Various outdoor facilities ranging from switchyards at generating stations to equipment at utilities or at industrial facilities that switches or modifies voltage, frequency or other characteristics of primary power are called substations. Predictive maintenance (PdM) helps ensure the quality of an end user’s electricity by enhancing the reliability of substations. PdM accomplishes this increased reliability by monitoring equipment over time in order to isolate conditions that indicate impending failure. Our goal is to determine whether corrective action is required and, if so, to recommend that action before equipment fails.
One set of tools for monitoring equipment in substations a Thermal imager with the capability to capture two-dimensional representations of the apparent surface temperatures of electrical components and other objects. Our cameras now include a technology that fuses a visual, or visible light, image with an infrared image for better identification, analysis and image management. The dual images are accurately aligned at any distance heightening details so problems are easier to spot.
What to check and whenOur Thermal imaging engineers typically inspect transformers, regulators, switches, circuit breakers and capacitors among other components. The time of day is an important factor in collecting thermal images of substation components. Readings in the stillness of early morning may avoid the effects of solar reflections and wind, which can skew temperature readings. However, in pre-dawn hours loads are generally lighter and problems less detectable. The training and experience of the thermographer may also affect when outdoor IR scans should be performed.
What to look for
Following a thorough inventory of the equipment in a substation, we scan the entire substation yard, saving images of any known or possible anomalies. We look especially for similar pieces of equipment under similar loading that are clearly operating at different temperatures.
A good thermographic approach to substation maintenance is to create inspection routes that include all the substations owned by your utility or facility. Thermal images of each substation component are then stored on our computer and temperature measurements tracked over time. This way, we will have baseline images with which to compare later images. Doing this will help us determine if temperature levels are unusual and, following corrective action, help us determine if maintenance was successful.
What represents a “red alert?”
Equipment conditions that pose a safety risk should receive the highest repair priority. Regulatory guidelines say that when the temperature difference (T) between similar components under similar loading exceeds 15 °C (27 °F) immediate repairs should be performed. It is also recommended the same action when the T between a component and ambient air exceeds 40 °C (72 °F). Following this line of thinking, one way to categorize maintenance tasks and flag equipment urgently needing repairs is to monitor substation equipment for specific degrees of temperature rise above established reference points. Knowledgeable technical, safety and maintenance personnel might establish these limits to range from “continue to monitor” to “correct immediately,” with other levels of action such as “schedule maintenance” or “repair as soon as possible” in-between. This approach has been successful when reference points take into account the differences between line-of-sight scans (e.g., metal-to-metal contacts in switchgear) and non-line of sight situations (e.g., the internal components of transformers), where heat is dissipated or obscured from the direct view of the thermographer and the IR camera. In a non-line-of-sight scan, the actual operating temperature will be much higher than the IR camera registers, so the reference points that signal what corrective action to take must be much lower. Also, abnormally cool as well as abnormally hot components should be included in the mix.
What’s the potential cost of failure?
The costs associated with a failed electrical substation depend upon many factors including the number and types of customers affected. One source*, estimates the average hourly cost of downtime across all industries at nearly £850,000.
Follow-up actions
Whenever we discover a problem during a thermography survey, we use our associated software to document our findings in a report that includes a digital, visual-light image of the equipment and a corresponding thermal image. This is the best way to communicate any problems we find and to make any suggestions for correcting them. Following corrective action, a new thermal image can be used to assess the effectiveness of repairs and evaluate the materials and techniques used.
With this information, we can continuously improve your maintenance program for substations.
Our Recommendation
IR scans of substations during the winter and early spring months are recommended rather than during the summer when loading is the highest. In the summer, it is more difficult for maintenance personnel to get authorization for shutdowns for repairs. However, during peak loading in the summer is when equipment is most likely to fail. Repairs made in winter and spring will put equipment in tiptop condition to meet the demands of summer.