Electrical power quality (PQ) data is one of the prevalent types of engineering data. Its measurement at relevant sampling rates leads to large volumes of PQ data to be managed and analyzed. In this paper, an extensible database architecture is presented based on a novel generic data model for PQ data. The proposed architecture is operated on the nationwide PQ data of the Turkish Electricity Transmission System measured in the field by mobile PQ monitoring systems. The architecture is extensible in the sense that it can be used to store and manage PQ data collected by any means with little or no customization. The architecture has three modules: a PQ database corresponding to the implementation of the generic data model, a visual user query interface to enable its users to specify queries to the PQ database and a query processor acting as a bridge between the query interface and the database. The operation of the architecture is illustrated on the field PQ data with several query examples through the visual query interface. The execution of the architecture on this data of considerable volume supports its applicability and convenience for PQ data. (C) 2009 Elsevier Ltd. All rights reserved.