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Question:

What happens when you open a switch when it is connected in parallel with an inductor?

What happens when you open a switch when it is connected in parallel with an inductor?

Answer:

Inductors store energy when they are first energized so they release that energy when the circuit is turned off. The result is that the amperage stays high for many milliseconds after the switch starts to open. NOTE: when you are dealing with electrical systems like this, there is no such thing as instantly. This increased amount of energy means the arc has more energy to dissipate before it extinguishes. That does not, necessarily, incinerate the switch. Switches are (or should be) designed to survive the arcing that they will encounter in service. The design life of a swtich can, of course, be controlled by the design (which also influences the cost). Almost every switch arcs. The only ones which don't operate at, like, less than 20 millivolts. An arc is a high temperature plasma. The plasma temperature is on the order of 10000 C, more than hot enough to melt any substance we know of. So temperature is part of it but it is really the arc energy that is most important. The material science (metallurgy) of arcing contacts is a rather specialized field. The details of what happens depend on many things including opening vs closing, AC vs DC, frequency, voltage, current, the circuit (resistive vs inductive), opening speed, atmosphere (or lack thereof), the number of cycles the switch has seen, the temperature of environment, among others. Electrical engineering deals with the electrical behavior during steady state and during transients (when the circuit is turned on or turned off). If you want to see the equations that describe some of the physics involved, check out Wikipedia for inductance or induction.
The voltage across an inductor is given by EL di/dt. So when you open the switch, the voltage will become very large, because di/dt is very large. In reality, the voltage will increase until the swith breaks down and then an arc forms. This is where the energy that was stored in the inductor is dissipated. Some switches cannot handle this and will fail, but some can.

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