Helm of Might and Magic

When you defend with a card it remains on the combat chain until the chain closes, therefore you cannot defend with an equipment multiple times on the same combat chain.

When this card is destroyed, it is sent to your graveyard.

The ability becomes a layer on the chain when the combat chain closes.

The Blade Break ability becomes a layer on the chain when the combat chain closes.

The ability goes on the stack when the combat chain closes.

Spellvoid does not go on the chain as it is not a trigger. It is a replacement effect. There is no time to respond after the decision to destroy the card and prevent that damage.

Spellvoid is optional. You choose whether to use spellvoid or not at the time the arcane damage resolves.

If a card has Spellvoid 2 but only prevents 1 arcane damage, there will not be a leftover prevention shield. Note: It can only defend arcane damage from a single source, Spellvoid 2 cannot prevent one arcane damage each from two different sources.

Spellvoid does not go on the chain as it is not a trigger. It is a replacement effect. There is no opportunity to respond after the decision to destroy the card and prevent that damage.

If a card dealing arcane damage is fully prevented by spellvoid (Or in conjunction with other preventions) it would not be considered to have dealt arcane damage and would not trigger effects that rely on arcane damage being dealt.