If the transformer is repeatedly overloaded, the system will deteriorate faster. A compromised insulating system is the net outcome of minor, incremental improvements in loading capacity over time. For example, if a certain section of a transformer's insulation fails each time it goes through an overload cycle, then soon nothing would be able to stop more than its current load from destroying it. When that happens, the transformer loses its ability to pass on excess voltage to other parts of the circuit.
Other factors such as temperature and material quality also play a role in determining how long a transformer can withstand an overload. For example, if a transformer operates at high temperatures, the insulation materials may change color or become brittle and break down more quickly. The amount of voltage a transformer can handle before failing depends on how it is constructed. If it passes too much voltage into a small area of core material, the iron inside the transformer may melt or burn away entirely. This could cause the windings to short out and expose them to dangerous levels of voltage if they are not properly protected from the environment.
Transformer failures can be caused by many different factors.
The magnitude of the voltage stress is influenced by the polarity of the transformer and the direction of current flow in the two windings. Engineers observed that when voltage stress grows, the transformer's life is reduced. The higher voltage stress was primarily responsible for winding insulation failures. They also noticed that if current flows in the same direction in both windings, then the voltage stress is lower than if it flows in the opposite direction.
The voltage stress in a transformer can be divided into two parts: magnetizing and leakage. Magnetizing voltage is the voltage that is required to magnetize the core and primary coil of the transformer. This voltage is present even if no power is being transmitted because some circuit elements (such as resistors) require energy to switch on their connections. Leakage voltage is the actual voltage drop across the secondary coil caused by the presence of resistance and other parasitic effects. If more current flows through the secondary coil, then this results in higher voltage stresses because more heat is generated due to greater current flow. Transformers usually have voltage limits specified by their manufacturer to prevent damage from occurring.
When voltage stress increases beyond what is safe for winding insulation, the transformer will eventually fail. Winding insulation degradation is typically seen as white or brown powder on the exposed surface of the wire after removal from the transformer. This is evidence that the insulation has broken down and allows electricity to leak into or out of the winding.
Because of the internal resistance of the battery, the terminal voltage lowers as the load increases. Now, here's a transformer: Draw an analogous transformer schematic to get series winding resistance and leakage inductance of both primary and secondary windings. What is the effect of load on transformer voltage?"/>
The voltage across the primary will drop due to the input resistance of the source, just as it would with a diode or other linear device. The voltage across the secondary will drop because of the internal resistance of the coil, just as it would with a resistor. Thus, the total voltage drop across the transformer will be the sum of these two contributions, rather than just the primary voltage as with a diode.
Here's what happens if we connect a 1K resistor between the positive terminal and ground of the 9V battery:
First, note that there's no longer any voltage across the primary when the circuit is closed. This means that the primary current must be coming from the secondary, through the load. Since the secondary voltage is now zero, its resistance must also be zero - which implies that the only way for current to flow into the resistor is through the primary!
This means that the input resistance of the battery has completely shut off the circuit, leaving only the leakage inductance of the transformer as a factor in reducing the voltage across it.
The following are the impacts of stress on potential transformer performance: When we raise the burden, both the secondary and primary currents rise; however, because the primary voltage remains constant (because the primary of a PT is linked to the line), the secondary voltage decreases. This is because more current requires less voltage. Thus, more burden means that there is more current flowing through the secondary, so it takes more energy out of the system. As well, more burden means that the magnetic field around the core gets weaker, which reduces the efficiency of the transformer.
When we lift the burden, both the secondary and primary currents drop; however, because the primary voltage remains constant (because the primary of a PT is linked to the line), the secondary voltage increases. As well, less burden means that the magnetic field around the core gets stronger, which improves the efficiency of the transformer.
These are the only two ways in which raising or lowering the burden affects the performance of a potential transformer. Any other change would be due to mechanical loading on the transformer, such as when it is mounted on top of an engine block.