The Hanover Insurance Group of Worcester is set to acquire Windsor, Conn.-based  property and casualty insurer AIX Holdings.

The planned acquisition of AIX Holdings follows the purchase of two other companies by The Hanover in recent months. Last September, The Hanover acquired professional liability insurance company Professionals Direct. Earlier this year, the company purchased Verlan Holdings, a manufacturing insurance company.

The AIX transaction is subject to regulatory reviews and approvals. It is expected to close during the fourth quarter of this year. The company had gross written premiums of $85 million in 2007.