Utility Infrared Inspection

Utility Infrared Inspection

Utility systems are probably one of the most important systems to monitor on a regular basis with a utility infrared surveys. A small failure can lead to significant losses not only to the utility but to its customers. Thermal surveys seem to be common in substations and substation equipment but what about the distribution and transmission systems?

An infrared inspection of utility systems cannot only help prevent a failure but also improve efficiency. Lost energy is in the form of heat so when you look at the thermal pattern across an electrical device, component or system you can evaluate whether it is consistent with normal operation or if there is a problem. Locating a potential problem during an infrared inspection of a utility (infrared survey) may prevent a failure later if appropriate action is taken. Any abnormal pattern or temperature should be documented for further investigation. Usually, when problems are found in the early stages they can be corrected at a minimal cost and prevent unnecessary down time. Infrared inspections can help increase reliability and reduce maintenance costs.

When you look at these systems and the numbers of components needed to operate these systems you realize the opportunities for failure. Each component is subject to failure and when that happens you have an unhappy customer. 

However, using a thermal survey can detect many possible failures before they happen allowing the opportunity to schedule an outage. In most cases, a scheduled outage will be much shorter and less expensive for all involved. This is particularly true now that materials and labor costs have increased significantly along with some regulations further pushing up the costs.

There are other reasons to do an inspection. On new construction an inspection should be done to verify the installation was properly done, no loose connection, properly sized, and to create a baseline for future inspections. After a repair is completed the equipment repaired should be inspected to verify the repairs were properly done and to establish a new baseline. 

To do a thermal inspection or survey of any electrical system the system must be under a load. There are two schools of thought on what type of load should be on the system. Some inspectors feel there should be at least 40% of the maximum load present during the inspection. The other belief is the most accurate inspection is when the system is under normal loaded conditions. 

As previously mentioned, utility systems have almost an unlimited number of components to survey and too numerous to list. Even metal components near electrical conducts can heat up due to the magnetic fields of conductors. 

Starting at the supply moving towards the load, the connectors of the service conductor to the switch is looked at and the contacts of the switch itself. A loose or corroded connection will appear hot. The components of a circuit should be compared to other components of the circuit and the temperatures should be equal. Also, comparing like or similar components under the similar load will help determine if there is a problem or the beginning of one.

Once the system connecting the substation to the incoming power is surveyed the equipment to adjust the incoming voltage to the proper outgoing circuit voltage should be surveyed which would be the transformers. Depending on the function of the substation these may be step down transformer or step up transformer. The survey will check the condition of the bushing that connects incoming line to the internal windings of the transformer. The oil level of a transformer can quickly be checked along the radiators. If the oil is below the radiator manifold the radiator tubes will appear cool. Surveying the radiator will also indicate any plugged tubs. Finally, if the radiator fans are running, they will be inspected.

Other equipment to be surveyed with the infrared camera in the substation are the circuit breaker connecting the power from the substation to the individual outgoing circuits. The thermal survey in the substation should include all control boxes and control panels. Loose or corroded connections may be located or shorted current transformer windings may be discovered to name a couple issues.

The utility should then do a thermal inspection of the distribution or transmission systems. Select a circuit to perform a thermal inspection on and survey the entire circuit. This will include

• cables
• insulators
• fuses
• arresters
• transformers
• switches
• capacitors
• switchgear enclosures
• and others

Surveying cables can indicate cables that have broken strands. This will be indicated by a spiral heating pattern of the cable due to some strands carrying current and others not. 

Another problem that will show up in a thermal inspection are cables that not sized properly. These cables will appear hotter than other cables carrying the same load. Loose or corroded cable splices will be indicated by a hot spot on the cable. 

Insulators and lighting arresters will show warm areas when the components age and the cores start leaking current. 

Fuses and switches will show hot components when there are loose or corroded contact points, 

Faulty or damaged transformers can be located if they are not operating at similar temperatures of other transformers of the same size and load. 

Finally, failed capacitors can be located due to lack of temperature.

As part of the utility inspection, inclusion of the utility customer’s connections should be done. Regardless how large or small a customer may be, they will all suffer some type of consequence if that connection fails.

Regardless of what system a thermal inspection is being performed on, it is important that the person doing the inspection is properly trained, is using the proper equipment, and has the experience to perform the inspection accurately and safely. 

Especially with an outdoor inspection, there are numerous variables that will affect the survey. Sun shining on or reflecting onto the component being surveyed will indicate a higher than actual heat pattern or hide a heated component. 

Likewise, a breeze or wind will cool a component and mask a possible problem. There are other conditions that affect an outdoor thermal survey. The distance from the object being surveyed and how much moisture is in the air, or if there is steam or dust in the air.