The tests are conducted at Končar – Electrical Engineering Institute (Zagreb, Croatia).
Nonlinear ferro-resonance may overheat windings and damage the earthed Voltage Transformers. Normally, it occurs during single-phase arcing earth.
The tests are carried out in accordance with GOST / IEC 61869-3-2012. Several preliminary tests have been completed with various capacities of the grind and earth currents (1.5A to 11A) in order to determine the most critical mode.
The principal test took an hour: thrice simulation of earth currents per minute, each approximately 3 seconds. It should be noted that each ferro-resonance phenomenon occurred during the tests has a damping nature and poses no harm to the transformer, which confirms reliability and ferro-resonance resistant design of the transformer. As a result, the temperature values of the windings remain within the established limits.
Voltage Transformers are used in AC Switchgears, voltage class up to 35 kV, both indoor and outdoor configuration intended to: transmit signals to measuring instruments and protection devices, gauge, alarm and control; for commercial accounting of electricity; and isolate secondary circuits from high voltage.
