A protection relay is provided for protection of an electric network. The protection relay measures an electric signal in the network, converts the measured signal to a frequency domain representation of the measured signal, and generates a measuring phasor based on the frequency domain representation, where the phase rotation of the measuring phasor is dependent on one or more frequency components present in the measured electric signal. The protection relay compares the measuring phasor to the reference phasor, where the phase rotation of the reference phasor is based on either a nominal or a measured frequency of the electric network, and launches protection if the comparison of the of the measuring phasor and the reference phasor fulfils a predetermined criterion.