Surge arrester on the earthed neutral point of HV transformer

[essamalbanna]

I'm searching for a logical explanation or practical purpose for installing a lightning arrester at both neutral points of the transformer 220/66 KV, YNynd11, Although both neutral points are connected directly to earth through a disconnector!.
View attachment 2014

 

[waross]

That provides some protection when the disconnector is opened.