Results of a systematic survey of Power Line Harmonic Radiation (PLHR) observed by a recently (June 2004) launched French spacecraft DEMETER are presented. In order to obtain a statistically significant number of events, an automatic identification procedure has been developed and all the available high-resolution data have been processed. Altogether, 58 events have been found in 865 hours of data recorded during the first year of operation. These events form three different classes: with frequency spacing of spectral lines of 50/100 Hz (10 events), with frequency spacing of 60/120 Hz (13 events), with other spacings/not clear cases (35 events). The first two classes of events are discussed in detail, showing that their origin is most probably connected with the radiation from the electric power systems which are magnetically conjugated with the place of observation. Additionally, in more than one half of the cases, the frequencies of PLHR lines well corresponded to the multiples of the power system frequency. The frequency drift of all the observed events was very slow, if observable. The events occurred without any significant preference for low or high geomagnetic activity, although more intense events were observed during disturbed times. Simultaneous observations of electric and magnetic components of PLHR suggest that the waves propagate in the electromagnetic right-hand polarized whistler mode.