Re-ignition and restrike in vacuum breakers switching capacitor banks — the difference and why it matters

Switching capacitor banks (for reactive power compensation or harmonic filtering) is electrically more demanding on a breaker than switching an ordinary load: on opening, the capacitor remains charged at the peak value of the voltage, while the system voltage on the other side of the breaker has already reversed half a cycle later. This produces a voltage across the open contacts that can rise to roughly twice the peak voltage — and it is precisely under this stress that the distinction between re-ignition and restrike, as defined in IEC 62271-100, becomes of direct practical importance.

The definitions: the current-zero interval as dividing line

IEC 62271-100 defines both phenomena based on how long the current between the contacts remains zero after the breaker has interrupted, expressed as a fraction of a power-frequency cycle:

Re-ignition: resumption of current between the contacts with a current-zero interval of less than a quarter cycle after the initial current interruption.
Restrike: resumption of current between the contacts with a current-zero interval of a quarter cycle or more after the initial current interruption.

Both involve a breakdown across the contact gap after the breaker has already "interrupted" — the distinction lies purely in the time that elapses before that breakdown occurs, not in the physical cause (which in both cases is the combination of an excessive recovery voltage against a still-insufficiently-strong dielectric medium between the contacts).

Note: the exact quarter-cycle threshold and the precise test conditions under which this distinction is established in type tests are laid down in IEC 62271-100 itself and must be checked against the current text of the standard; this guide article presents the core logic of the distinction, not the full test procedure.

Restrike as a rejection criterion for capacitor-bank switching duties

For breakers specifically intended for switching capacitor banks (designated switching class C1, or the stricter C2, in IEC 62271-100), the occurrence of a restrike during type testing is considered a failure of the breaker for that application. A restrike indicates that the dielectric medium between the contacts has not recovered quickly enough to withstand the build-up of the recovery voltage, resulting in a renewed current surge that places additional mechanical and electrical stress on the switched circuit — and the breaker itself — and can also produce a significant overvoltage transient on the network.

A re-ignition, with its shorter current-zero interval, is not necessarily judged in the same way as a restrike, but remains an equally significant indication of insufficient dielectric recovery of the switching medium immediately after interruption.

Why vacuum breakers specifically warrant attention here

Vacuum breakers typically recover their dielectric strength between the contacts very quickly after current interruption, which in most applications makes them highly suitable. When switching capacitive currents (capacitor banks, but also long, lightly loaded cables), however, the problem is not the speed of dielectric recovery as such, but the combination of that fast current interruption with the high recovery voltage specifically arising in capacitive switching duties. For this reason, a vacuum breaker deployed for capacitor-bank switching duties is explicitly specified with a C1 or C2 classification per IEC 62271-100, rather than being assumed suitable purely on the basis of its general circuit-breaker rating.

NSDD as a separate, distinguishable phenomenon

Alongside re-ignition and restrike, IEC 62271-100 defines a third, separate phenomenon: the non-sustained disruptive discharge (NSDD). An NSDD is a breakdown across the contact gap that occurs after the breaker has already interrupted a current (typically a fault current), but that does not result in the recovery of power-frequency current — the discharge self-extinguishes. An NSDD is therefore not equated with a restrike or re-ignition, and is typically judged differently in type tests: a limited number of NSDDs are considered acceptable in certain tests, while a restrike during capacitor-bank switching duty constitutes a failure.

Practical relevance

When selecting or assessing a vacuum breaker for a capacitor-bank installation (see also the [guide on power-factor correction](/guides/nen-1010/vermogensfactorcorrectie) and the guide on detuned reactors and resonance in capacitor banks), it is important to explicitly verify that the breaker is classified per its rating plate and type-test certificate for capacitive switching duties (C1/C2) under IEC 62271-100, rather than assuming that any vacuum breaker suitable for ordinary load switching is automatically suitable for switching capacitor banks as well.

Common mistakes

Deploying a vacuum breaker without a C1/C2 classification for capacitor-bank switching duties, on the assumption that the fast dielectric recovery time of vacuum technology alone provides sufficient protection against restrike.
Treating restrike and re-ignition as the same phenomenon, while IEC 62271-100 explicitly distinguishes them based on the duration of the current-zero interval, with different assessment criteria in type tests.
Confusing NSDD with restrike, while an NSDD does not cause recovery of power-frequency current and is therefore an essentially different, generally less critical phenomenon.
Underestimating the recovery voltage in capacitor-bank switching, without recognising that the phase shift between capacitor voltage and system voltage can raise it to roughly twice the normal peak voltage.