In order to solve the problem of voltage fluctuation and bidirectional power flow due to distributed power generation systems connected to distribution network, a new voltage regulation technology based on series transformer is proposed. By using vacuum contactor and thyristor to control the series transformer tap and star-triangle transformation, the voltage can be regulated quickly and effectively. The voltage regulation principle based on series transformer and the voltage regulation technology based on vacuum contactor and thyristor are analyzed. A winding insulation fault detection technology based on leakage flux is also presented, and its principle, the concrete realization method and experiment verification principle are described too. The analysis shows that the proposed technology can effectively solve the distribution network voltage fluctuation, improve the lifetime of distribution transformer, reduce the loss of distribution transformer, and at the same time, improve the intelligence and reliability of distribution transformer. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2014AA052005).