Earthing 336-kV Lightning Arrestor

Hai everybody. Please clarify me whether it is advisable to connect the 336kV lightning arrestors of power station to the stand-alone earth pit. Or is there any advantage if the earth pit is linked to the station earth grid which is common to the several system of voltages. It is observed that the views of authors of different text books when searched in the web are not the same. The statute like BIS is also not very particular about the type of earthing, even though it is indicated in a typical earthing lay out diagram as inter-connected to the earth grid. The doubt is that as the combined resistance of an earth grid is far lesser than the stand alone earth pit, then what is the need of an earth pit. Also what is the effect of travelling waves in the event of discharge of a lightning stroke in to the earth grid which can cause high frequency oscillation. The purpose of the earthing the lightning arrestor is to discharge the surges in to the earth with out causing raise of dangerously high potentials in the vicinity of the lightning arrestors and to dissipate the power in to the soil, it seems that a stand alone earth pit is preferable than connecting to an earth grid.