Abstract
The time derivative (d H/dt) of the geomagnetic field horizontal component (H) for seven intervals of high geomagnetic activity in 2003–2005 has been calculated, based on the data of Alma-Ata, Novosibirsk, and Irkutsk observatories, in order to estimate the probability of appearance of geomagnetically induced current (GIC), the value of which is linearly dependent on d H/dt, in power lines on the territory of Kazakhstan. The distributions of the H and d H/dt directions have been constructed; in this case it was most interesting that these distributions were narrow and extended along the magnetic meridian for Alma-Ata and were wider angular for Novosibirsk and Irkutsk. It has been indicated that large H values, determining significant GIC values, took place at a sudden commencement of strong storms, which had a character of a pulsed disturbance of the geomagnetic field, and during large-amplitude geomagnetic field pulsations. The duration of the periods of large |d H/dt| values exceeding the threshold (30 nT/min), when GIC could cause unwanted consequences in power circuits, has been determined.