FinalCalculation Size of Neutral Earthing Transformer (NET)Generator Details::Calculate Size of Neutral Earthing Transformer:Generator Voltage (VL) (L-L)31.5KVPhase to Neutral Voltage (Vp1)18.19KVVL/1.732Maximum Over Voltage40.95KV% of Force field condition for Neutral Earthing Transformer30%1.3Frequency50HzPhase to Neutral Voltage under Force Field Condition (Vf)23.64KVVf=Vp1x 1.3Generator Transformer Details:Capacitive charging current/phase (Ic)3.54AmpIc=Vf / XcTransformer Primary Voltage31.5KVTotal Capacitive charging current (It)10.63AmpIt=3xIcTransformer Secondary Voltage11KVRating of Neutral Earthing Transformer (Pr)334.86KVAPr=VpxItCapacitance Per Phase:Neutral Earthing Transformer overloading factor2.6Generator Winding Capacitance / Phase0.22 FaradSize of Neutral Earthing Transformer (P)129KVAP=Pr/ 2.6Generator Connection Capacitance / Phase0.001 FaradResidual Capacitive reactance (Xct)2224.12Xct=Xc / 3Generator Transformer Capacitance / Phase0.006 FaradRequired Resistance value at secondary side (Rsec)0.119Rsec=Xct / (NxN)Generator Transformer Connection Capacitance / Phase0 FaradRequired Grounding Resistor value at primary side (Rp)2224.12Rp=XctTransformer Cabale Capacitance / Phase0.0003 FaradNeutral Earthing Transformer Secondary Current559.96AmpSurge Arrestor Capacitance / Phase0.25 FaradNeutral Earthing Transformer Secondary Resistor Current (for 30 Seconds)1892.67AmpOther Capacitance / Phase FaradNeutral Earthing Transformer Reactance Base(Base X):0.45Total Zero Sequence Capacitance (C):0.47730 FaradNeutral Earthing Transformer Reactance (X)0.01X=Xpu x Base XTotal Zero Sequence Capacitance Reactance to Ground (Xc):6672.35/PhaseNeutral Earthing Transformer X/R Ratio0.11Neutral Earthing Transformer Size:Fault current through Neutral (single line to ground fault) (If)8.18AmpIf=Vp1/RpPrimary Voltage of the Grounding Transformer (Vp)31.5KV:Results:Secondary Voltage of the Grounding Transformer (Vs)230VoltRating of Neutral Earthing Transformer (P)129KVATurns Ratio of the Grounding Transformer (N)136.96Short time Rating of Neutral Earthing Transformer335KVANeutral Earthing Transformer % Reactance (X%)3%0.03Ratio of Neutral Earthing Transformer31500 /230VoltNeutral Earthing Transformer Reactance in PU (Xpu)0.03PUNeutral Earthing Transformer Secondary Current559.96AmpNeutral Earthing Transformer Base KV (Bv)0.24KVRequired Grounding Resistor value at primary side (Rp)2224.12Required Resistance at secondary side (Rsec)0.12Jignesh.Parmar, www.electricalnotes.wordpress.com, jiguparmar@yahoo.comNeutral Earthing Transformer Secondary Resistor Current (for 30 Seconds)1892.67Amp

&C&"Arial,Bold"&12&PJignesh.Parmar, www.electricalnotes.wordpress.com, jiguparmar@yahoo.com