Smart Load to Reduce Ferroresonance - KMB Systems - #1

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KMB systems, s.r.o. Dr. M. Horákové 559, 460 06 Liberec 7, Czech Republic tel. +420 485 130 314, fax +420 482 736 896 email : kmb@kmb.cz, url : www.kmb.cz AFR 31 Smart Load to Reduce Ferroresonance Description The AFR 31 Smart Load is an instrument designed to protect metering voltage transformers against adverse effects of ferroresonance in high 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 connection 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 nonsymmetrical 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.). The AFR 31 is designed to be installed on a 35-millimeter DIN strip (DIN EN 50 022). The AFR 31 works in conjunction with a metering voltage transformer while open delta is connected to auxiliary windings (terminals da, dn). One of pole must be grounded. Before connection. The open delta configured auxiliary windings may be, together with the AFR 31 Smart Load, used for ground connection protection relay, which is to be connected in parallel to AFR 31 using the protection relay manufacturer’s recommendations. AFR 31 parallel connection does not affect protection relay operation. 6/2009