The detection and location of partial discharge (PD) in cast-resin dry-type transformers using the acoustic emission (AE) method is very difficult: the sound in filled epoxy is highly attenuated and is easily interfered with external sound sources. In addition, there is no operating procedure for the detection, identification and location of PD in cast-resin dry-type transformers up to present. In this paper, we used a waveguide and a specially designed AE-sensor pair to overcome the shortcomings of the AE method. Test results indicate that the two techniques used not only greatly improve the sensitivity but also increase the reliability of the AE measurement system. In a practical case using the proposed techniques, the winding with PD was found in a high-voltage transformer, and further analysis was carried out to restrict the scope of PD to two points which are bilaterally symmetrical about the waveguide. An operating procedure for detection, identification and localization of PD is developed based upon the techniques described.