Buchholz relay is gas operated relay. It will operate when internal fault occurs in transformer. It is placed between tank to main conservator. It has two contacts trip and alarm. Use of Buchholz relay in distribution transformer is not economical.
Simple logic of reactance diagram is that simplified equivalent circuit of power system in which the various components of power system are represented by their reactances. The reactance diagram can be obtained from impedance diagram if all the resistive components are neglected.