What causes of voltage runaway in series LC resonant circuit?

In summary, in a series LC resonant circuit, the voltage rises exponentially due to the distributed capacitance of the inductor acting as a voltage multiplier and the voltage wave reflecting from an imperfectly matched impedance. However, this only occurs in simulators with no resistance present, as real series tuned circuits have some resistance. The voltage magnification is equal to the ratio of XL / R, where XL is the reactance of the inductor, and this value is reached almost instantly. This phenomenon can also occur in a tuned LC circuit with external excitation and has been known to cause damage to components, as seen in an incident at a high voltage electrical substation.
  • #1
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I'm trying to understand why the voltage in a series LC resonant circuit exponentially rises?

Can anyone explain exactly what happens that creates the effect?

I've been wonding if it the distributed capacitance of L becomes a voltage multiplier, or if it is a voltage wave reflection from a imperfectly matched impedance?
 
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  • #2
This only happens in simulators and only if you specify a circuit with no resistance in it.

Real series tuned circuits have some resistance.

The voltage magnification is equal to the ratio of XL / R (where XL is the reactance of the inductor) and this value is reached almost instantly.
 
  • #3
Death to all uncontrolled simulators!
They have a lot to answer for.
 
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  • #4
I wouldn't exactly say this can only happen in simulators - a tuned LC Ckt with external excitation ( like a radio signal) can easily generate enough V to damage the components. Had this happen once in a High Voltage Electrical substation where a parallel feed (not electrically connected) was able to excite an isolated portion of the substation - to Overvoltage condition.

When the isolated section ( now damaged by overvoltage) was re energized the result was - well - interesting...
 

1. What is a series LC resonant circuit?

A series LC resonant circuit is an electrical circuit composed of a inductor (L) and a capacitor (C) connected in series. It is used to produce a resonant frequency, where the reactive components cancel each other out and the circuit behaves as if it has a purely resistive component.

2. What is voltage runaway in a series LC resonant circuit?

Voltage runaway, also known as voltage magnification, is a phenomenon in a series LC resonant circuit where the voltage across the capacitor continuously increases without limit. This occurs when the resonant frequency is close to the natural frequency of the circuit, causing the reactive components to amplify each other's effects instead of canceling them out.

3. What causes voltage runaway in a series LC resonant circuit?

Voltage runaway is caused by a lack of damping in the circuit. This can be due to a low resistance in the circuit, which prevents the dissipation of energy, or a high-Q (quality factor) value, which indicates a high amount of energy stored in the circuit. In either case, the reactive components continue to reinforce each other, leading to voltage magnification.

4. What are the consequences of voltage runaway in a series LC resonant circuit?

Voltage runaway can have damaging consequences in a series LC resonant circuit. The continuously increasing voltage can cause components to overheat and fail, leading to circuit malfunction or even fire. It can also cause interference with other circuits nearby and disrupt the overall operation of a system.

5. How can voltage runaway in a series LC resonant circuit be prevented?

There are several methods to prevent voltage runaway in a series LC resonant circuit. One approach is to decrease the Q value of the circuit by increasing the resistance or adding a damping element. Another option is to design the circuit with a wider separation between the resonant frequency and the natural frequency. Additionally, implementing a protection circuit to detect and interrupt voltage runaway can also be effective.

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