The most common failures in a transformer can occur in different parts or components due to mechanical and electrical problems or thermal stress caused by different conditions. Here are the most common transformer failures along with their causes:
Winding fault
A winding is a very important part of the transformer. In distribution there are two of these: one on the primary side and one on the secondary side.
High voltage and low electric current run in the primary winding, and it is through the electromagnetic induction voltage that it goes down to the secondary. Windings can withstand dielectric, thermal, and mechanical stress during this process, but sometimes it is so much that it results in failure and subsequent breakdown. These are the types of problems that can arise:
Dielectric failure
Dielectric failure occurs when insulation breakdown arises, which is caused by electrical stress and voltage above average levels. This triggers a short circuit.
The reasons for the high levels can be:
- Lightning strike without arresters.
- Voltage faults.
Thermal fault
The windings are usually made of copper. Due to the resistance, thermal losses occur, which affect it if there has not been a proper maintenance. Over time, these deteriorate and physical strength is lost.
Mechanical failure
Mechanical faults are distortions, loosening or displacement of the windings. This is the result of decreased transformer performance, improper repairs, corrosion, poor maintenance, manufacturing defects, and movements and vibrations within the transformer.
Bearing failure
Bearings are devices that isolate a high voltage electrical conductor so that it passes through a ground conductor. In a transformer, these provide a path for current through the tank wall. Inside the transformer you can find insulating paper surrounded by oil, which provides greater insulation. A bearing failure occurs due to wear and for these reasons:
- Loosening of conductors caused by vibrations in the transformer, resulting in overheating. This damages the insulation paper and the oil.
- A sudden surge in voltage, which generates a partial discharge that damages the bearing and causes a breakdown in a matter of hours.
- Bearing seal breakage caused by water, wear, or excessive dielectric losses.
- Do not replace oil or oil leakage.
Tap changer fault
The function of a tap changer in the transformer is to regulate the voltage level. This is done by adding or removing turns of the secondary winding. It is the most complex part and one of the most important. Even a small fault can affect the power. Some causes of problems in this are:
- In a run-through fault, the tap changer lags after a relay changes the ratio of the turns. This is because the relay has debris. Another cause is spring wear.
- Lack of maintenance that results in a desynchronization of the shaft connection between the changer and the motor.
- Old and worn capacitors in the motor, causing the shifter to fail to control the direction of movement.
- Regular use that wears out the spring and makes it more brittle to the point of breaking. Therefore, the changer cannot change the ratio of the winding turns.
- Engine breakdown in shifter due to excessive voltage.
Core failure
A transformer has a laminated steel core in the middle surrounded by the windings. Its function is to concentrate the magnetic flux. If it fails, the windings are affected. Laminate is there to prevent this, but poor maintenance, not replacing oil, or corrosion can be the cause of the problem. Minimal breakdown in the sheets results in an increase in thermal energy. The effects of overheating are:
- The windings are damaged because the superheat reaches the surface of the core.
- Damage to the transformer oil, which generates a gas that can affect other components.
Tank failure
The function of the tank is to contain the oil, which is used for insulation and cooling. It can also be used to support other transformer equipment.
A tank failure occurs when there is some type of environmental stress, high humidity or solar radiation. All of the above can cause cracks or leaks in the tank walls, so soon the oil will start to run out. These are the consequences:
- Reduced insulation in the transformer and damage to the windings.
- Overheating and damage to other parts of the transformer.
Protection system failure
The main function of the protection system is to protect the transformer from any fault by detecting it and solving it as quickly as possible. Transformer testing is very important. If that is not possible, then isolate it to avoid further damage. Its components are the Buchholz relay, the pressure relief valve, overload protection and the sudden pressure relay. This is what happens when any of these parts fail:
The Buchholz relay is a protection device sensitive to dielectric faults in the transformer. Overheating occurs when gases accumulate, affecting its functions. A low oil level causes the relay to go into action even if there is no fault. This is a waste of energy.
The pressure relief valve prevents the transformer from exploding due to gas pressure build-up, which is caused by overheating of the oil. If the spring fails, the valve will not be able to release pressure properly, which could be dangerous. In the same way, we would have a problem if the pressure builds up quickly, since the release process is slow.
Overload protection allows a specific magnitude of voltage to go to the transformer, preventing excessive surge. A fault means the input of a large voltage load to the windings and subsequent damage. Moisture, heat, and corrosion are the main reasons for a breakdown.
The surge pressure relay protects the transformer from exploding due to a possible exponential increase in gas pressure. Moisture can affect your internal circuitry.
