Třífázová zemní ochrana, ochrana proti přetížení a nevyváženosti IM30-C (Microelettrica Scientifica).
Three-phase overload Earth Fault and unbalance relay with programmable inverse and definite time characteristics suitable for protection, of ungrounded double-wye capacitor banks.
The overload is measured as image of phase currents detected by the three main CTs. The phase elements compute the contribution of the current harmonics as inversely proportional to their order.
The unbalance current input circuit includes a third harmonic active filter.