The AFR 31 Smart Load is an instrument designed to protect metering (PT) voltage 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.