Component failure results in a wide variety of problems within the HV network, but identifying the actual components at risk in advance of failure continues to be a real challenge to preventative maintenance managers.
There can be many causes of component failure, but one problem which causes much debate is that of UV emissions, also referred to as corona discharge or partial discharge (PD). UV emissions from man-made sources are invisible to the human eye as they occur outside the visual spectrum. PD is believed to be responsible for contributing to a high proportion of the component failures which cause major downtimes.
Now there is real hope of a major breakthrough in HV preventative maintenance due to the relatively new technology of UV corona cameras, which detect ultra violet light emissions from components carrying medium and high voltage (HV).
The ability to detect and locate UV emissions, could lead to reductions in component failure and subsequent downtime by preventing the sort of problems which arise from aging and degradation within a high voltage environment.
These problems occur where a voltage of, typically 6kV and above is present, so includes the power generation, transmission and distribution activities, electrified rail systems, HV laboratories and motors and induction devices.
These are problems which then can lead to intermittent, interruptive or catastrophic failure of systems.
Preventative maintenance managers will be mindful of the following situations:
Where a low-grade emission occurs but at a slow rate of deterioration (e.g. dust or contamination from the environment builds up but is washed away by rainfall in a cyclical pattern). The component may well be damaged, despite the lack of physical evidence noticeable without specialist equipment.
Where an affected component left in place, is likely to cause an interruption to the system and so needs to be replaced at a time of convenience to the maintenance schedule. For example, a disconnector with a partial breakdown.
Where a component has actually failed and as a result, the system requires an immediate shutdown and access for repair. For example, a fractured component, such as an insulator, could potentially result in such a system failure.
The key point is that whilst the problem remains invisible, without specialist equipment it also remains undetected. Therefore any deterioration will continue until eventually there is a failure, either due to the electrical failure, the weakening of the mechanical structure or a combination of both.
So what causes UV emission? It is a result of a high electrical charge on a component that exceeds a certain value, causing the air at that micro millimeter point to become ionised and emit a UV light of a very narrow bandwidth.
Typically at risk are components which are contaminated by dirt particles, or perhaps have a stress crack, or share an interface of two materials, or possess a sharp edge along with other causes. These situations can create an ionising effect that, in turn, will cause further deterioration.
In the field of HV preventative maintenance, there is more familiarity with the more established infra-red technology more than the more recent developments in UV. As there can be some confusion between the two, here is a good time to explain the key difference. UV is a point source due to a concentration of the electric field that causes an emission and is due entirely to the voltage being present, whereas Infra-Red (IR) emission however, is caused by the heating effect of current flowing through a component and not the presence of voltage.
When attempting to identify UV, corona cameras provide maintenance staff with the ability to view the UV emission by creating a visual light where the emission occurs and superimposing this onto an image of the standard camera.
The technique to achieve this is a combination of the fields of chemistry, optics and electronics to create the means to view only the phenomenon that could lead to component failure.
UV problems can of course occur in a wide variety of environments, some of which are more accessible than others. The opportunity to detect UV and corona discharge which could affect important components in remote or relatively difficult to access locations has been increased with the design of the cameras themselves.
Essentially there are two main categories of camera. Firstly there is the fixed version, which can be mounted to vehicles, trains and even helicopters. Secondly there are the handheld portable types. Both types include recording and comparative intensity measurement features.
As more preventative maintenance managers become aware of the contribution of the damaging impact to industry of UV corona discharge, then the demand for solutions to the problem will increase.
Solutions which provide high quality data, insight and new information will enable preventative maintenance managers to make new informed decisions.
Predicting component failure will continue to be a complex and debated area within the fields of science and preventative maintenance. However, new forms of technology which seek to provide key evidence in the form of images and data which can then be mapped against other data will surely form a key role in the future.