Smart Load to Reduce Ferroresonance
The AFR 31 Smart Load is an instrument designed to protect metering voltage transformers against adverse effects of ferroresonance in medium voltage power distribution systems with ungrounded or indirectly grounded neutral wire. Ferroresonance comes up between transformer inductance and conductors’ or switching elements’ capacitance. Connecting, disconnecting, ground faults or other transitional effects may be the trigger events. Ferroresonance oscillations cause significant overvoltage and current surges as a result of transformer magnetic circuit saturation. This most often leads to metering transformer destruction.
AFR 31 Smart Load acts as metering voltage transformer protection against such effects. Unlike other methods, it is targetedly enabled only when ferroresonance occurs, being passive in common operation or with asymmetric loads.
Magnitude of trigger voltage can be adjusted to 20, 25 or 30 volts. For selectivity with ground connection protection devices an activation time delay circuit (4 seconds as default) is used. This is suitable at installations where a voltage transformer is used not only for measuring but as power supply for protection devices too (ground connection detection, automatic reconnection circuits etc.).