Every infrared image tells a story. These images and accompanying information are presented as brief snapshots to show examples of thermography in action in the real world. This is an Industrial Eye regular feature on infrared images from members of the Australian Professional Thermography Association Inc. (AUSPTA).
Solar pitfalls for thermographers and installers
Author: Liam Mitchell Secretary, AUSPTA
Figure 1. 100amp 3ph circuit breaker for solar input; load at 75amps/ phase however conductor temperature still exceeds the 90deg rating. Terminations are tight; likely due to harmonic effects from switchmode inverters. The circuit breaker casing is also starting to deform and discolour from overtemperature (at 110deg).
With seemingly never-ending government stimulus being poured into the industry via the STC, LGC and REC schemes, even quite large private solar generation systems have become highly affordable and almost ubiquitous. And, of course, where significant government spending exists then that demand will create jobs, businesses and opportunities that would not otherwise have existed. But what are the downsides? Where demand booms, quality can suffer.
Commercial and industrial solar generation essentially represents a heavy-current capacitive load (or input). Historically it has been standard installation practice with heavy-current capacitive loads, like power factor correction systems, to require that cabling and protective devices are oversised by a factor of 33%. This provides additional headroom for the inevitable effects of harmonics, and drastically reduces the likelihood of electrical faults related to overtemperature when operating for extended periods of time at close to 100% of the rated current of the installation. This practice does not appear to have carried over into solar generation, either by lack of a regulator mandate or the lack of adoption of an industry de-facto standard.
Electrical infrastructure associated with solar power generation is, by definition, designed to operate under high load conditions for long durations (ie. while the sun is shining). It’s common sense that operating an engine, or any other complex system, at ‘redline’ all the time is going to have negative long-term effects. Electrical installations are no different in this regard. To ensure reliability and minimise the risk of costly and inconvenient down-time and equipment failure, it is necessary to ensure that solar installers adhere to only the highest standards of workmanship. Unfortunately, it is self-evident that this is not always the case. Solar installation infrastructure often operates at close to 95% of it’s rated capacity, solar installation workmanship is often of low quality, and solar electrical enclosures are often not ‘fit for purpose’ (commonly over-crowded with little or no passive/active airflow).
So, all this begs the question, what role do we have to play in addressing these issues as condition monitoring professionals? Like any other electrical installation, thermographers should always endeavour, where practical, to inspect solar input connections, circuit
Figure 2. 40amp 3ph solar AC input isolator; operating at 15amps/phase
breakers, contactors, and grid protection relays under periods of maximum load. It is important to establish, and document, the load conditions (and ratings) at the time of inspection. This information can usually be obtained via the inverter or grid protection relay, or failing that, using a simple clamp-on ammeter (safely of course). Not only does this ensure we are inspecting equipment under the appropriate conditions, but it also provides both the thermographer and their client with recourse in the event that it was not practical or possible to inspect the installation under full operating load conditions and a undetected issues surface in the future.
When preparing repair recommendations or assisting clients with programming repair work on solar infrastructure, electrical thermographers must be aware that our ‘usual suspects’ (poor terminations, poor internal contacts, or faulty components) may not always apply. Where the thermal profile is also influenced by harmonic effects introduced by switch mode inverters, then simply replacing and reterminating components will not necessarily result in a successful repair. It may be necessary to increase the current capacity of conductors and protective devices. Alternatively, in some instances a repair may be as simple as providing additional airflow through the solar equipment enclosure or introducing a small air gap between adjacent components.
Figure 3. 55amp 3ph AC1 rated solar input contactor, operating at 34amps/phase
Thermographers also need to ensure that we work with solar installers to improve their understanding of the thermal effects of electricity generally. Simple additional steps at the time of installation, such as slightly oversising conductors and introducing air gaps between components, can dramatically reduce the likelihood of headaches and costly remedial work down the track.Practices that are common and acceptable on a 5kW domestic installation will not necessarily fly on a 30kW or 100kW commercial installation where the current, and heat generated, is orders of magnitude higher.
And, of course, we can all live in hope that at some point in the not-too-distant future the regulators catch up and the relevant standards are amended to require some of these common-sense mitigation strategies.