Ensuring that service is interrupted as little as possible and only during scheduled downtime is the goal of any utility maintenance program. Including inspections and scheduled, regular cleaning in a preventative maintenance program is often overlooked in many fields. Power distribution and transmission is no exception to this with costly repairs, outages, and unscheduled labor overtime easily eclipsing the cost of proactive maintenance practices.
Many of the programs in use by the electrical generation and distribution industry have become outdated due to age, leading to several deficiencies. High voltage insulator cleaning will prevent failure in instances caused by contamination. Cleaning and inspection of insulators easily prevents these incidents. With most transformers currently in operation at the distribution level having an age of multiple decades, transformer painting to replace their external coatings to protect them from damage by corrosion should be implemented. Repainting prevents further damage and extends their operation lifespan for a minimal investment. Substation painting is an effective method for protecting other equipment, such as supporting structures for buswork, line termination, and cooling equipment that are also subject to mechanical failure by corrosion of their steel casings. Instituting an updated preventative maintenance program that includes inspection for contamination, cleaning, and painting of substation and transmission equipment is the most cost effective and viable method of addressing these overlooked equipment damage vectors.
Outdated Maintenance Methods
Large portions of the national grid are over 50 years old and the maintenance programs for many parts are just as old. These programs mistakenly assumed that modern steel structures were not subject to failures caused by corrosion. This has proven to be false. They also did not include sufficient high voltage insulator cleaning and inspection frequencies. Inspection of transformers for rust, especially on the top and around the seals was neglected since it was assumed that they would be taken out of service and given full refurbishment on a regular basis. Transformer painting was left to be a part of refurbishment. The frequency of taking a transformer out of service dropped as technology progressed and knowledge of failure modes increased, leading to a need for paint replacement well before the transformer needs any major work.
High Voltage Insulator Contamination
Pollution has multiple issues it can cause with high voltage insulators. Acid rain, engine exhaust, smog, soot, and ash all float through the air and will settle on insulators. Many of them will wash away with the rain, but some, like the oil droplets in engine exhaust, remain or cause other problems when water is added. Blown soil and dust not only physically erode the insulator, but also contain mineral salts that mix with moisture to create a conductive layer on the surface of the insulator. This layer will not run off of surfaces that have been abraded by wind. The only way to remove these is through the process of high voltage insulator cleaning.
There is also the problem of contaminates hiding damage to the insulators, so high voltage insulator cleaning will also assist with that. This includes damage from corona effects happening to non-ceramic insulators, also known as NCI insulators. Corona arrest systems can fail or be installed incorrectly. Nitric acid is then formed on the surface of the insulator as the corona ionizes the nitrogen in the atmosphere, creating a soup of chemicals that leads to further damage and contamination on the surface. Carbon trails then form in this mix of chemicals, creating areas of lower resistance, leading to arcing, and a flashover. High voltage insulator cleaning carried out regularly will remove the nitric acid layer, slowing and even preventing damage.
Inspection and Cleaning of High Voltage Insulators
Any material that settles on the surface of a high voltage insulator is going to reduce its insulating properties. This is a very complex problem to model and predict, but two inevitable results will happen if an insulator is never cleaned: it will form arcs or a flashover will occur. This will result in service interruption, unscheduled labor costs, and potential equipment damage. Regular high voltage insulator cleaning will minimize these risks and extend the lifespan of the insulators.
High voltage insulator cleaning paired with regular inspections will prevent buildup of contaminates. These practices will also spot damage from other sources, such as corona effects and manufacturing defects. There are methods available to do inspections and high voltage insulator cleaning without interrupting service, with several contractors available across the nation that offer these services.
In the long years that a transformer will be in operation, its exterior is subject to the full force of weather. Thermal cycling, blown dust abrasion, pollution, precipitation, and ultraviolet light all take their toll on the paint that protects the steel from oxidation. No coating is going to last forever, especially when left exposed to the elements for decades. Transformer painting is going to be required at some point.
The ultraviolet light from the sun and the focusing effect on light caused by water droplets sitting on the top of transformers will destroy the paint here first. Rust will then form a thin coat over the exposed metal and lift paint off as it progresses underneath. Sun exposed sides, especially the south facing side, and any side that is unprotected from the prevailing winds will follow the top, but by the time you see the start of rust on the sides the top of the transformer will be heavily rusted.
It is not possible to determine the extent of damage steel has suffered from corrosion without close inspection and removal of the layers of iron oxide first. A problematic process on an transformer in service. They can appear to have only slight rust and still have pin holes that have oxidized all the way through to the other side. This means that moisture and water can gain entry to the internal area of the transformer and contaminate the dielectric oil or the oil can leak out. Both of these scenarios will cause additional maintenance on compromised transformers or even repairs after catastrophic failures.
Repaint Transformers as Soon as Rust Appears
Regular transformer painting, cleaning and inspection will extend lifespan and spot corrosion as early as possible. As soon as rust noticed on a transformer it is time to schedule transformer painting into your currently planned maintenance. The fact that the coating has failed in one location means that it is close to failing on the rest of the surfaces. Other transformers at that location are most likely the same age and have the same amount of wear and tear on their paint as well, so you will not typically be setting up transformer painting for just one transformer at a time.
This will prevent deep corrosion from having the chance to form and compromise the transformer mechanically. Transformer painting can prevent moisture and water intrusion, leading to longer dielectric oil lifespan and a longer required interval before an overhaul or refurbishment is required. It will also lower the likelihood of an unscheduled service interruption, even though moisture related failures of transformers are under 5% of total transformer failures. A more in depth article on transformer painting specifically can be found here.
Transformer painting and rust removal will also increase the efficiency of cooling systems on both actively and passively cooled transformers since rust is a thermal insulator. This will reduce operating temperatures, loads on pumps, and electrical losses in the transformer. Transformer painting will also prevent mechanical failures from corrosion to the pipes and cooling fins in the cooling system, preventing leaks from forming in those parts and leading to the most common failure mode of a transformer cooling system.
Mechanical Failures in Other Substation Equipment
Most of the structures and equipment in a substation are made of steel. Without a coating in good condition, they will be subject to mechanical failure due to corrosion. Inspection, cleaning, and painting of all equipment in a substation should be part of the regular maintenance schedule to prevent premature failure of these structures and equipment.
Large, load bearing structures, such as pylons and line originating or terminating supports, are particularly vulnerable to mechanical failure caused by corrosion. The loads on these structures are dynamic, with weather shifting the loads constantly across the entire structure. Just like a bridge, this causes rust to penetrate deeper into vital components faster. Also, like a bridge, they are difficult and expensive to repair, so they should be regularly cleaned, inspected, and painted to prevent rust from damaging them.
Other equipment in substations should also be cleaned, inspected for rust, and repainted. Instrumentation transformers suffer from many of the same problems with corrosion that power transformers do and will drain completely or suffer from moisture contamination of their dielectric oil from a small leak due to rust far faster than power transformer, leading to thermal failure, service outage, and damage to its circuit and adjacent ones. Substation painting will also protect switching gear and circuit breakers since both have internal components that are protected from weather by steel enclosures, as do fuse panels and other equipment found in substations. The sheet metal used to make these enclosures is typically thin, mild steel and will rust though much faster and easily than metal on heavier equipment.
Regular Inspection, Cleaning, and Repainting
Compared to the potential risk of service interruption and equipment failure, adding in regular inspection for paint wear and corrosion into your maintenance program for substation equipment and transformers is minimal in cost. Some areas may be more difficult to inspect than others, but most of it can be done visually since rain will wash rust stains down the sides of equipment. Particular attention to the tops of equipment with large, flat tops that will catch water after rain, such as transformers, should be taken.
High voltage insulator cleaning, both in substations and along transmission lines, should be regularly done and an inspection of the insulators included as well. This will extend their service life and will allow visual inspections to catch potential failures and flaws before they become larger problems. There are several methods to clean them, along with other substation equipment, without interrupting service.
Substation painting to prevent damaging corrosion should be done at the first signs of rust, especially for transformers. The most vital step in substation painting is getting the surfaces ready. Since paint needs solid, clean surface to adhere to, all surfaces that need substation painting must be cleaned of any dirt, rust, and loose paint. Preparation for substation painting is a significant portion of the cost of substation painting because it is very time intensive and requires specialized equipment. If you only have to clean the surface and remove some slight rust the process of painting is much faster and simpler. Adding a planned time for substation painting after equipment has been in service long enough that the corrosion preventing coating on it has reached the end of its lifespan according to the manufacturer (or applicator in the case of equipment you have already repainted) to your maintenance program will not only prevent corrosion from taking place, but it will minimize the cost of substation painting since the equipment will only need minimal cleaning.
Moving Forward from Here
Updating maintenance practices to the current standard is a regular part of keeping equipment in service and current practices should be regularly reviewed. Insulators have a limited lifespan and extending it to the safest possible amount will save money. This requires regular inspection and high voltage insulator cleaning, especially of NCI insulators. The paint on transformers will not last as long as the rest of the transformer. Transformer painting is more cost effective than to keep them in service until they require refurbishment. Equipment and structures made of steel that are part of substations and power transmission systems require protection from corrosion, so planned substation painting should be implemented. Only preventative maintenance that includes inspection, cleaning, and repainting will stop damage to equipment from corrosion.
Customers demand reliable electrical service. Minimized service interruption requires an aggressive and up to date maintenance program. Inspection, cleaning, and repainting of substation and transmission equipment is a cost effective method to prevent other more expensive repairs to equipment replacement.