What term describes a condition where small undamped oscillations start without apparent cause?

The term that describes a condition where small undamped oscillations begin without an apparent cause is dynamic instability. This phenomenon is often observed in systems where feedback mechanisms exist, and it can occur when there is an imbalance or when system parameters change such that the system does not stabilize over time.

Dynamic instability typically indicates that the oscillations are not being effectively damped, which can lead to growing deviations from the intended operational state. This is particularly relevant in power systems and control engineering, where maintaining stability is crucial for reliability and safety.

The other terms provided refer to different concepts. Voltage fluctuation pertains to variations in voltage levels, phase shift describes a change in the phase of a waveform, and current surge refers to a sudden increase in electrical current. Each of these terms pertains to specific behaviors in electrical systems but does not specifically describe the phenomenon of small undamped oscillations occurring spontaneously as dynamic instability does.