The accuracy of state estimation determines the usefulness of real-time power system operation and control applications. To have an accurate state estimation it is essential to have the capability of detecting bad measurement data and topology errors in the model. While analogue measurement errors have received considerable attention, relatively little effort has been given to detection of topology errors. A procedure that combines numerical computation and various consistency checks is proposed to detect topology errors in the state estimation model. Tests based on real-time measurement data collected in an energy control centre have indicated that the proposed method can be used to detect branch inclusion, exclusion and bus configuration errors.