= 0.30I/InO and 87-2 I DIFF>> =12I/InO. It also details the restricted earth fault protection scheme, which compares the current flowing in the star point connection 3I0' with the sum of the phase currents 3I0" to detect internal earth faults. Settings are selected to provide full sensitivity for internal faults while allowing through faults to pass without tripping."> = 0.30I/InO and 87-2 I DIFF>> =12I/InO. It also details the restricted earth fault protection scheme, which compares the current flowing in the star point connection 3I0' with the sum of the phase currents 3I0" to detect internal earth faults. Settings are selected to provide full sensitivity for internal faults while allowing through faults to pass without tripping.">
7ut613 Setting Calculation
7ut613 Setting Calculation
7ut613 Setting Calculation
CALCULATION
DIFFERENTIAL PROTECTION
87-1 I DIFF> = 0.30I/InO
CONSIDERING THE CT ERRORS, OLTC REGULATION ERROR CURRENTS(10%) & MARGIN,
THE VALUE OF 0.30I OF THE PROTECTED TRAFO IS SELECTED.
87-2 I DIFF>> =12I/InO
(1/0.165) * (136000/(1.732*132))= 3605.23
CONSIDERING THE MAXIMUM THROUGH FAULT CURRENT OF THE TRAFO AT 136MVA OF3605A
THE VALUE OF 12I OF THE PROTECTED TRAFO IS SELECTED WHICH IS
ABOVE THE THROUGH FAULT VALUE.
Primary Full load Current at Generator 7138.36 7140 A Nominal Currents of
Transformer FLCat132kV side 594.86 595 A Gen,transformer
AuxiliaryTransformer FLCon 11kV side 656.1 656 A Aux Transf.
Calculation of differential and Restraining Current Generator
87-2 I DIFF> FLC/fault Current 0.17 Sum of the Current
Allowing Ctratio error 87-2 I DIFF> 0.3
87-2 I DIFF>> '=12I/InO 6.06 6
Add on Stabilization Current(Gen and GT) 1.53 2 ( The sum of the currents flowing to the device)
Instant Restraint Ratio(2nd Hormonic) 0.2
Stabilizing Ratio for 5th Hormonics 0.3
GENERATOR TRANSFORMER
VECTOR YNd1 HV side is STAR with grounded neutral
RESTRICTED E/F SIEMENS
PROTN.
The restricted earth fault protection compares the fundamental wave of the Current flowing in the star point
connection 3I0' with the fundamental wave of the sum of the phase currents, 3I 0"
3I0' = Isp
3I0" = IL1+IL2 +IL3
86 of 126
SIEMENS 400/220/33kV CHHABRA SS
3I0' acts as the tripping effect quantity, during the fault with in the protected zone
2.Internal earth fault, fed only from star point 3I0 " = 0
3.Internal earth fault fed from the star point and from the system 3I0" = 3I0'
The tripping effect current is equals to starpoint current, the restraining quantity is negative
For internal fault no stabilization is effective since the restraint quantity is eaither zero or
negative. Small earth current will cause tripping, strong restraint becomes effective for external
fault.
87 of 126
SIEMENS 400/220/33kV CHHABRA SS
0.74375
0.0656
0.714
1.52335
pares the fundamental wave of the Current flowing in the star point
88 of 126
SIEMENS 400/220/33kV CHHABRA SS
the tripping effect quantity, during the fault with in the protected zone
89 of 126