Calculation For Dyn1 Tranformer Stability And Sensitivity.

Trasformer Details:

TAP:N (11) (Nominal TAP)

MVA= 67MVA

HV=115.0kV

LV=13.8kV

HV CT RATIO=600/1

LV CT RATIO=4000/1

CALCULATION OF SECONDARY CURRENT:

CURRENT IN HV: TAP:NI= 67X10^6/(1.732X115000X10^3)FULL LOAD CURRENT = 336.37

CURRENT IN LV: TAP:NI= 67X10^6/(1.732X13.8X10^3)FULL LOAD CURRENT = 2803.15

SHORT CIRCUIT CURRENT:

%IMP=29.71

Ish=F.LOAD CURRENT/%IMP= 2803.15/0.2971 = 9435.03A

AT 380V SHORT CIRCUIT CURRENT WILL BE:

=(9435.03*380)/13800

=259.89 A(LV)

=31.21 A (HV)

CALCULATION FOR DIFFERENTIAL CURRENT:

SENSITIVITY:TAP: N

HV PRI =31.24A,

FOR LV PRI=260.32 A,

DURING SENSITIVITY THIS HV AND LV CURRENT ADD TOGETHER AND THE DIFFERENTIAL CURRENT IS

IDiff=(W1-W2)*K1*HV CT PRI.CURRENT

HV SEC CURRENT=52.0mA, LV SEC CURRENT=65.0mA

K1=0.418

K2=0.523

W1= 52.0mA/0.418=0.124

W2=65.0mA/0.523=0.124

IDiff=(0.124+0.124)*0.418*600

=62.19A

If we short one CT the Diff Current will be Half of the above Current i.e 31.099A

TAP:1 (MIN TAP)

MVA= 67MVA

HV=129.375kV

LV=13.8kV

HV CT RATIO=600/1

LV CT RATIO=4000/1

CALCULATION OF SECONDARY CURRENT:

CURRENT IN HV: TAP:1I= 67X10^6/(1.732X129.375X10^3)FULL LOAD CURRENT = 299.0

CURRENT IN LV: TAP:1I= 67X10^6/(1.732X13.8X10^3)FULL LOAD CURRENT = 2803.15

SHORT CIRCUIT CURRENT:

%IMP=32.39

Ish=F.LOAD CURRENT/%IMP= 2803.15/0.3239 = 8654.36 A

AT 380V SHORT CIRCUIT CURRENT WILL BE:

=(8654.36*380)/13800

=238.30 A (LV)

=25.41 A(HV)

CALCULATION FOR DIFFERENTIAL CURRENT:

SENSITIVITY:TAP: 1

HV PRI =25.41A,

FOR LV PRI=238A,

DURING SENSITIVITY THIS HV AND LV CURRENT ADD TOGETHER AND THE DIFFERENTIAL CURRENT IS

IDiff=(W1-W2)*K1*HV CT PRI.CURRENT

HV SEC CURRENT=42.3mA, LV SEC CURRENT=59.5mA

K1=0.371

K2=0.523

W1= 42.3mA/0.371=0.114

W2=59.5mA/0.523=0.1137

IDiff=(0.114+0.113)*0.371*600

=50.68A

If we short one CT the Diff Current will be Half of the above Current i.e 25.37A

TAP:27 (MAX TAP)

MVA= 67MVA

HV=92000kV

LV=13.8kV

HV CT RATIO=600/1

LV CT RATIO=4000/1

CALCULATION OF SECONDARY CURRENT:

CURRENT IN HV: TAP:27I= 67X10^6/(1.732X92000X10^3)FULL LOAD CURRENT = 420.89

CURRENT IN LV: TAP:27I= 67X10^6/(1.732X13.8X10^3)FULL LOAD CURRENT = 2803.15

SHORT CIRCUIT CURRENT:

%IMP=26.2

Ish=F.LOAD CURRENT/%IMP= 2803.15/0.262 = 10699.046A

AT 380V SHORT CIRCUIT CURRENT WILL BE:

=(10,699.046*380)/13800

=294.611 A(LV)

=44.23 A (HV)

CALCULATION FOR DIFFERENTIAL CURRENT:

SENSITIVITY:TAP:27

HV PRI = 44.02 A,

FOR LV PRI= 293.5A,

DURING SENSITIVITY THIS HV AND LV CURRENT ADD TOGETHER AND THE DIFFERENTIAL CURRENT IS

IDiff=(W1-W2)*K1*HV CT PRI.CURRENT

HV SEC CURRENT=73.3mA, LV SEC CURRENT=73.3mA

K1=0.522

K2=0.523

W1=73.3mA/0.522=0.140

W2=73.3mA/0.523=0.140

IDiff=(0.140+0.140)*0.522*600

=87.696 A

If we short one CT the Diff Current will be Half of the above Current i.e 43.84 A