Investigating timing reliability in relation to control of a power transmission system

The invention is related to a method, power control device and computer program product for evaluating the accuracy of timing provided by time generating equipment (12, 14, 16, 20, 22, 24, 26, 28, 32) in relation to wide area control in a power transmission system, where the wide area control is performed based on time stamped measurements (P1, P2, Pn) of system data. The power control device (10) includes a timing deviation handling unit (30) that investigates the timing (TS, TI, GCT) used in relation to measurements, determines if the timing is reliable or not based on the investigation and aborts wide area control if the timing is deemed unreliable.