1 - Acta Technica Corviniensis

ACTA TECHNICA CORVINIENSIS – Bulletin of EngineeringZo− Z1KCTwhere, Ko= and KZ= (11)3. ZK1PHASE TO EARTH FAULT CURRENT CALCULATION ONPRESENCE GCSCFigure 4 is shows the equivalent circuit fortransmission line en presence single phase (phase A)to ground fault with fault resistance (R F ) at busbar Bwith GCSC inserted on midline.Figure 4. The equivalent circuit with GCSCThe total transmission line (Z AB‐GCSC ) impedance withGCSC inserted on midline is given by:ZAB GCSC AB [ ( )−= R + j XAB − XGCSC β ] (12)Regarding reference [22], the basic equation for thisfault is:I = I = 0(13)bcV . 0a= V1+ V2+ V0 = RF Ia≠ (14)The coefficients Z AB‐T and Z GCSC‐T are defined forsimplicity is:ZAB− T= ZAB.1 + ZAB.2 + ZAB.0(15)XGCSC− T= XGCSC.1 + XGCSC.2 + XGCSC.0(16)From figure 4, the symmetrical currents componentsare:VS+ VGCSCI1= I2 = I0= (17)⎛ ZAB−T ⎞ ⎛ ZAB−T ⎞⎜ ⎟+ XGCSC −T+ ⎜ ⎟+3. RF⎝ 2 ⎠ ⎝ 2 ⎠I Awhere, I1+ I2+ I0= (18)3From equations (17) and (18), the current in phase A is:3.( VS+ VGCSC)IA= (19)⎛ ZAB−T ⎞ ⎛ ZAB−T ⎞⎜ ⎟+ XGCSC −T+ ⎜ ⎟+3. RF⎝ 2 ⎠ ⎝ 2 ⎠VTThe symmetrical components of voltages are:⎡V0⎤ ⎡1 1 1⎤⎡VA⎤⎢ 1 2V⎥1=⎢ 1 a a⎥⎢ V⎥ (20)⎢ ⎥ B3 ⎢ ⎥⎢ ⎥2⎢⎣V⎥2⎦⎢⎣ 1 a a⎥⎦⎣⎢V⎥C ⎦From equation (14) and matrix (20), the voltage atphase A is:3. RF.( VS + VGCSC)VA= (21)⎛ ZAB−T ⎞ ⎛ ZAB−T ⎞⎜ ⎟+ XGCSC −T+ ⎜ ⎟+3. RF⎝ 2 ⎠ ⎝ 2 ⎠From equations (10), (17), (19) and (21), the measuredimpedance Z seen by distance relay is only related to: Parameters of transmission line : U n , l L , R AB ,and X AB , Current and voltage transformer ratios: K CTand K VT , Parameters of GCSC installed: V GCSC and X GCSC ,Fault conditions: location n F and resistance R F .CASE STUDY AND SIMULATION RESULTSThe electrical network 220 kV, 50 Hz studied in thispaper [23], is the eastern Algerian electricaltransmission networks at Sonelgaz group (Algeriancompany of Electrical and Gas) is shows in figure 5.The MHO distance relay is located on the busbar at AinM’lila in Oum El Bouaghi to protect the singletransmission line between busbar A and busbar B atKhenchela substation HV/MV.Figure. 5. Algerian electrical networks studyThe GCSC system is installed in the midpoint of theprotected line by a MHO distance relay. Theinvestigation were carried out for three case studiesrespectively for 30, 50 and 70 MVar of injectedreactive power as well as for 10, 20 and 30 kV injectedvoltage. The parameters of transmission line and theinstalled GCSC are summarized in the appendix.2012. Fascicule 3 [July–September] 83