Electrical engineering department university of santo

Electrical Engineering Department
University of Santo Tomas
Transformer Angular Displacement
EE 523 – Power System Analysis and
Design
A
B
C
a
b
c
1
2
3
4
5
6
V
A
V
B
V
C
V
ab
1
2
3
4
V
bc
5
6
V
ca
Vector Group: Yd1
a
b
c

Electrical Engineering Department
University of Santo Tomas
Transformer Angular Displacement
EE 523 – Power System Analysis and
Design
A
B
C
a
c
b
1
2
3
4
5
6
V
A
V
B
V
C
V
ab
1
2
5
6
3
4
V
bc
V
ca
Vector Group: Yd11
a
c

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
INTRODUCTION TO FAULT STUDIES
Rotating machineries will contribute
fault current to the system.
Alternators will continue to contribute
at the duration of the fault.
Motors (induction and synchronous)
will have a decaying fault current at the
duration of the fault

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
SHORT CIRCUIT CURRENT CHARACTERISTIC

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
SHORT CIRCUIT CURRENT CHARACTERISTIC
Short Circuit Network Cycle
½ Cycle Network
Used to calculate momentary SC current and
protective devices at the ½ cycle after the fault
Also referred as Sub-Transient Network
1. 5 to 4 Cycle Network
Used to calculate the interrupting SC current and
protective device duties 1.5-4 Cycle after the fault
Also referred as Transient Network
30 Cycle Network
Used to calculate the steady-state SC current

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
TYPES OF FAULTS
 Shunt Fault: Unintentional Connection between phases or between phase
to ground.
 Balanced/ Symmetrical Fault
• Three – phase fault
 Unbalanced/ Unsymmetrical Fault
• Singe Line – to – ground fault
• Double Line –to – ground fault
• Line – to – line fault
 Series Fault: Unintentional Opening of phase conductors
 Simultaneous Fault

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design

Electrical Engineering Department
University of Santo Tomas
Fault Point
EE 523 – Power System Analysis and
Design

Electrical Engineering Department
University of Santo Tomas
Fault Point
EE 523 – Power System Analysis and
Design

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
FAULT CALCULATION USING
NETWORK REDUCTION
(EQUIVALENT THEVENIN CIRCUIT AT
FAULT POINT)

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
Consider the three bus system shown below. Reduce the system into its
equivalent sequence network when fault occurs at (a) bus 1, (b) bus 2, and
(c) bus 3.

Electrical Engineering Department
University of Santo Tomas
EE 523 – Power System Analysis and
Design
Seatwork
15 MVA
13.8 kV
x'' = 0.15
x
0
= 0.05
20MVA
13.8 kV - 115 kV
x = 0.10
Z
1
= j500 ohms
Z
0
= j800 ohms
15 MVA
115 kV - 13.2 kV
x = 0.12
10 MVA
13.2 kV