disconnecting resistive load from transformer
Let's break this down step by step:
When you're talking about the transformer, it's important to note that the primary and secondary windings have their respective self-inductances. An abrupt change in current (di/dt) in an inductor results in a voltage spike due to the relationship (V = L \times \frac{di}{dt}). This spike, however, is mitigated in transformers designed for AC operation because the core is made from laminations that help reduce the effects of changing currents.
If you disconnect a purely resistive load suddenly, you're causing a rapid change in the current (especially if it's as large as 100A or 1000A). For the transformer's secondary winding, this sudden change in current won't directly produce a significant voltage spike because it's resistive. However, the sudden change in current does affect the primary due to mutual inductance. This change in current is seen as a change in the magnetic field, which will induce a voltage in the primary. Because of the transformer action, this will cause a voltage disturbance on the primary side.
If the transformer has a 10:1 step-down ratio, a change of 100A in the secondary would correspond to a change of 10A in the primary. Although this ratio reduces the current change on the primary side, as you rightly pointed out, the primary winding often has a higher inductance. The net effect on the spike magnitude can't be universally stated without more specifics because it's contingent on the actual inductance values and the rate of change of the current.
Do I need an RC snubber?
An RC snubber can be used across switches or contacts to dampen the voltage spikes caused by the circuit's inductive nature. Depending on the scenario, you might also consider other solutions like transient voltage suppressors (TVS) or metal-oxide varistors (MOVs).
Does that in anyway decrease the voltage spike?
The magnitude of the voltage spike is related to the rate of change of the current (di/dt). A larger change in current would result in a larger spike, provided all else remains constant. So, if you disconnect 1000A instead of 100A suddenly, the potential spike could be much more significant.
Let's return to 200A peak. If you had a 50A load and you add a 100A load, the combined current would be 150A. If you disconnect the 100A load, the current would return to 50A (not 200A).
Lastly, in real-world scenarios, components like transformers are usually designed with some safety margins, and other elements in the circuit (like wires and contacts) also have resistive and inductive properties that could further influence the outcomes. Always consider these factors when analyzing or designing circuits. Hope this helps.
