This document summarizes the results of a fault study lab report submitted by 6 students. The study examined: 1) the severity of different fault types, finding 3-phase faults to be most severe and SLG faults least; 2) the effect of transformer connections, with delta connections producing highest fault currents; and 3) the effect of network changes, with fault currents increasing when lines are removed. Neutral grounding increased fault currents only when both the high and low voltage transformer sides were grounded.

1. EEP303 LAB REPORT
FAULT STUDIES
SUBMITTED BY:
Vivek Mangal (2010EE50566)
Umang Gupta (2010EE50564)
Mehul Mittal (2010EE50553)
Indra Bhushan (2010EE50548)
Srishti Mahajan (2010EE50561)
Ciddhi Jain (2010EE50011)

2. Aim: To carry out the following fault studies:
 To compare the severity of different types of faults.
 To observe the effect of transformer connection in fault studies
 To observe the effect of network changes on fault level (only 3 phase fault)
 To observe the effect of neutral connections in fault studies
Introduction:
Observation:
1. Comparison between severity of different types of faults
a) 3- Phase fault, Bus -5 :
Fault current = - 5.05245 j
Line 5 – 4 flow = 1.30946 j
Line 2 – 5 flow = - 3.74299 j
Zero Sequence Positive Sequence Negative Sequence Phase currents

3. b) SLG fault A to Gnd, Bus -5 :
Fault currents
I0 = - 1.217 j I1 = - 1.217 j I2 = - 1.217 j
Zero Sequence Positive Sequence Negative Sequence Phase currents
Line 5 – 4 flow:
Ia = 0.916 j
Ib = Ic = - 0.03 j
c) LL fault B to C, Bus -5 :
Fault current
I0 = 0 I1 = - 2.526 j I2 = 2.526 j Ic = -Ib = 4.3752
Zero Sequence Positive Sequence Negative Sequence Phase currents
Line 5 – 4 flow:
Ia = 0
Ib = 1.134
Ic = -1.134
d) LLG fault, Bus -5 :
Fault current:
I0 = 0.953 j I1 = - 3.003 j I2 = 2.050 j

4. Zero Sequence Positive Sequence Negative Sequence Phase currents
Ib = -4.373+1.43i
Ic = 4.373+1.43i
Line 5 – 4 flow:
Ia = 0.778 j
Ib = - 0.531 j
Ic = - 0.223 j
Observation : Severity of fault
Fault Type
Fault
Current
3- Phase 5.05245 j
SLG 0.916 j
LL 4.3752
LLG 4.373+1.43i
The order of severity of fault:
3-phase > LLG > LL > SLG
2. Effect of changes in Transformer in fault studies
All changes in Transformer 2-7
The High voltage side is kept Star-connected.
Star Grounded: 0
Star Ungrounded: 1
Delta: 2
a) 3 – phase fault on bus 5
HV LV Fault Current i(1-6) i(2-7)
0 0 -5.03245 j 2.29824 j 2.75421 j
0 1 -5.03245 j 2.29824 j 2.75421 j
0 2 -5.03245 j 2.29824 j 2.75421 j
Any change in Transformer doesn’t affect the fault current in a 3-phase fault.

5. b) SLG fault
HV LV Sequence
Fault
Current i(1-6) i(2-7)
0 1 Positive -1.059 j 0.482 j 0.557 j
Negative -1.059 j 0.482 j 0.557 j
Zero -1.059 j 1.059 j 0
0 0 Positive -1.314 j 0.598 j 0.716 j
Negative -1.314 j 0.598 j 0.716 j
Zero -1.314 j 0.479 j 0.835 j
0 2 Positive -1.354 j 0.616 j 0.738 j
Negative -1.354 j 0.616 j 0.738 j
Zero -1.354 j 0.388 j 0.967 j
Zero Sequence Positive Sequence Negative Sequence Phase currents
Note: The sequence diagrams for all configurations are the same.
The fault current order for connections at low voltage side:
Delta > Star-Grounded > Star-Ungrounded
HV LV
Fault
Current
Star - Grnd Star - Ungrnd 1.059 j
Star - Grnd Star - Grnd 1.314 j
Star - Grnd Delta 1.354 j
c) LLG fault
Zero Sequence Positive Sequence Negative Sequence Phase currents

6. HV LV Sequence
Fault
Current i(1-6) i(2-7)
0 2 Positive -3.092 j 0.191 j -0.191 j
Negative 1.960 j 1.99-0.58j 2.387-1.11j
Zero 1.132 j -1.99-0.58j -2.387-1.11j
0 1 Positive -2.912 j 1.325 j 1.588 j
Negative 2.14 j -0.974 j -1.167 j
Zero 0.772 j -0.772 j 0
0 0 Positive -3.065 j 1.394 j 1.671 j
Negative 1.988 j -0.904 j -1.084 j
Zero 1.077 j -0.393 j -0.684 j
HV LV
Fault
Current
(Ib) Phase
Star - Grnd Star – Ungrnd 4.526 165.18
Star - Grnd Star – Grnd 4.665 159.74
Star - Grnd Delta 4.693 148.79
The fault current order for connections at low voltage side:
Delta > Star-Grounded > Star-Ungrounded
Observation : Transformer connection changes
Transformer connection changes don’t affect the 3-phase fault currents.
For SLG and LLG faults, the fault current order for connections at low voltage side comes out to
be:
Delta > Star-Grounded > Star-Ungrounded
3. Effect of network changes on fault studies
3 – phase fault at bus 5
Normally fault current at bus 5 (Single phase) = - 5.05245 j
a) When Line 2-5 removed
If = -2.11375 j
I(5-4) = 2.11375 j
b) When Line 5-4 removed
If = -4.31755 j
I(2-5) = -4.31755 j

7. 4. Effect of neutral connection
a) 3 – phase fault on bus 5
As observed in part 2 of the experiment, the fault current come out to be the same for Y-
connected LV side of the transformer with Neutral grounded / ungrounded.
b) SLG fault
HV LV
Fault
Current
Star - Ungrnd Star - Ungrnd 1.059 j
Star - Grnd Star - Ungrnd 1.059 j
Star - Grnd Star - Grnd 1.314 j
The fault current is more when the LV and HV side are both neutral-grounded as compared to
other cases.
c) LLG Fault
HV LV
Fault
Current
(Ib) Phase
Star – Ungrnd Star – Ungrnd 4.526 165.18
Star - Grnd Star – Ungrnd 4.526 165.18
Star - Grnd Star – Grnd 4.665 159.74
Observation : Effect of neutral connection
Neutral connection on one side doesn’t affect the current. The fault current increases only when both the
HV and the LV side of the transformer has their neutral grounded.