Kindly guide me about earthing system and what power required for satellite modem and BUC and if the proper earthing not available at site what would be the alternate.

More info required. Start with equipment make and model, indoor and outdoor.

//greg//

I have Linkstar DVB-S2 modem and BUC

Ah, I see your problem. LinkStar installation instructions seem to generally be rather devoid of earthing guidance. So I'll provide to you what I consider to be minimum earthing steps. This assumes you're using a metal pole mount;
1. use a short piece of stranded wire (1.5-2.5mm) to bond the BUC to the antenna bracket. Many manufacturers anticipate this, and pre-drill a bonding point. If not, under any bolt head is acceptable.
2. use a short piece of 2.5mm stranded wire to bond the antenna bracket to the pole. Metal poles however, are not likely to be pre-drilled to accept the bonding wire. In that case, I drill my own and use a self-tapping metal screw.
3. then use 4mm stranded wire to bond the pole with whatever serves as the earthing point for the structure that contains the modem.
4. Indoors: ensure that the modem power adapter receives AC power via a 3-wire supply, one of which is earthed back to the common point mentioned in #3 above

Additional grounds cannot hurt. Those I listed only represent what I consider to be minimum requirements.

//greg//