The present invention relates to apparatus 30 for determining a condition of a network section 34 comprised in an electrical power network 32. The network section 34 is configured such that electrical power flows to or from each of plural locations in the network section. The apparatus 30 is configured to receive a first quantity in respect of a first location in the network section 34 and to receive a second quantity in respect of a second location in the network section, each of the first and second quantities corresponding to a signal amplitude and a signal phase angle at its respective location. The apparatus 30 comprises a processor 42 which is operative to determine a condition quantity corresponding to a loading condition of the network section 34 between the first and second locations in dependence on the first and second quantities.