Margins are imposed by Exchanges as Financial safeguards to ensure that Brokers and Traders fulfill the obligations on their open futures and options contracts. Both buyers and sellers of futures and options contracts are required to deposit Margin money with brokers, who in turn maintain Margin money deposits with exchanges.

Margins are determined on the basis of market risk and contract value. Internationally also referred to as performance-bond margin. The exchanges impose extra margin to curb volatility, called as Cash Margin etc. The margin can change from day to day.

Applicable margin by exchanges
http://www.ncdex.com/Market_Data/hist_Margin.aspx