To better understand the reliability of an electrical substation, it is first necessary to identify the origin of possible damage. Here are the main causes of failures in electrical substations:
underground wires
One of the big concerns about underground cables is the penetration of moisture in the presence of an electric field, which reduces the dielectric strength of the cable insulation. When it degrades enough, transients caused by lightning or switching can result in dielectric breakdown. This is known in English as electrochemical treeing.
The phenomenon usually affects extruded dielectric cables such as cross-linked polyethylene (XLPE) and ethylene propylene (EPR) cables, and is primarily attributed to imperfections in the insulation and faulty manufacturing.
To reduce failures in electrical substations, you can install surge protection on vertical poles (transitions from above to below ground), purchase retardant cable, or test reels before purchase.
Another test method is to inject a small signal at one end and check if any kind of reflection occurs at the partial discharge points.
You can also apply spectroscopy, analyze physical samples of insulation for polymeric breakdown, or use indenters on wires to test insulation toughness.
Not all underground cable system failures are due to insulation. An important percentage occurs in the terminations, joints and joints. The main causes have to do with contact with water and human error. Heat shrink covers can be used in these areas to make them waterproof and improve reliability.
Another big concern is excavations. Heavy machinery often breaks buried cables, so routes need to be identified before work begins.
transformer failures
Transformers are very important links in electrical substations, and it can take a long time to replace them if there is a fault. Extreme physical stress on the windings is often the main cause of breakdowns.
When a transformer heats up, the insulation in the windings slowly breaks down and becomes more brittle. The rate of thermal breakdown doubles with every 10°C.
Due to this exponential relationship, transformer overloads can result in rapid aging. When the insulation is already very brittle, the next fault current that passes mechanically shocks the windings, causing cracks in the insulation and eventual internal failure.
This is because hot spots can generate bubbles that reduce the dielectric strength of the liquid. And even if this does not happen, high temperatures will increase the pressure in the tank causing an overflow or rupture.
Ray
A lightning strike occurs when the voltage generated between the cloud and the ground exceeds the dielectric strength of the air. This results in a massive current that usually exceeds 30,000 amps. Also, the drops consist of multiple downloads in a fraction of a second.
Lightning can affect power systems through direct strikes (when there is contact) or indirect strikes (when a nearby voltage surge travels to make contact).
Ways to protect structures against lightning:
· A BIL (Basic Insulation Level) system.
· Cable protection.
· Lightning rod.
· Low grounding impedance.
contact with trees
The continuous growth of the trees endangers the drivers, since the branches can fall on them, bring them closer to each other and can even serve as an entrance for different animals. For this reason, constant pruning is considered a preventative maintenance activity.
It should be clarified that a fallen branch that joins two conductors does not cause an immediate failure. This is because a wet one has substantial strength. But after a few minutes, the cellulose chars and the resistance drop, which shortly leads to a short circuit.
Branches touching phase conductors do not generally result in system failures.
This problem can be largely avoided by using special aerial cables, which have superior insulation.
Birds
Among animals, birds are the ones that most cause failures in electrical substations. Different species cause different problems.
Those that commonly nest do so in high voltage towers or substations. This material can cause failure, while the excrement can contaminate the insulators.
Similarly, their presence can attract all kinds of predators, which means more animals to worry about.
Some birds prefer to just perch on wires to rest or search for prey. As long as they are on one of them, there is no risk, but if they touch another, they generate a circuit that electrocutes them. There are several devices to prevent these animals from perching on the equipment.
Woodpeckers also represent a big problem, as their constant pecking can cause significant damage to high-voltage poles. One way to avoid it is by using repellents or making the bird believe that another already lives on the pole; This has to do with the fact that they are highly territorial.
Failures in electrical substations caused by birds are a challenge for technicians who deal with maintenance.
Land animals
squirrels
These animals are a concern in wooded areas, and although they do not usually climb power poles, they can jump onto them from nearby trees. Squirrels can cause faults by bridging grounding equipment and conductors. The problem can be mitigated by cutting access branches or installing obstacles.
snakes
Because of their size, snakes are of concern for failures in electrical substations and underground systems. Since they are almost always in search of prey, removing the presence of rats may be the solution. There are also some special fences to prevent them from entering the premises.
insects
It is very common for ants to build their colonies on computers. The material can cause a short circuit, plus they can eat away at the insulation of the conductors.
bears or cattle
These large animals often damage power poles by tearing them with their claws or horns. Bears even climb on these. It is best to install fences or some type of protection to avoid it.
rats and mice
These rodents can eat away at the insulation of underground cables, plus they attract snakes to the site. They are the animals that most cause electrical failures in electrical substations and underground equipment.
Types of electrical cogeneration plants
