MOV Burning issue in SMPA

[prakash12346]

We have a problem in our SMPS with battery charger. Problem is the MOV (275V) connected between Earth & Phase is getting burnt'd off. Its happening when we install in site. Can anybody help us

Line voltage 230 to 260 V. Generator also been used in that building. Three MOV's are connected between as follows one from Earth & Phase next Neutral & Phase and other b/w Earth & Neutral.