Question1: Whether section 51 of CGST regarding TDS is effective. If yes date of its operation.

Answer Notification No. 40/2017-Central Tax, dated the 13.10.17, where a person having turnover < 1.5 crore was exempted from payment of tax on advance received in case of supply of goods has been superseded vide Notification No. 66/2017-Central Tax, dt. 15-11-17 and now all taxpayers irrespective of turnover exempted from payment of tax on advances received in case of supply of goods.

So you are not required to pay tax on advance received even if turnover exceeds 1.5 Crore. .(REPLY dt. 29/1/2018)