EEP303: Fault studies
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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.
EEP303: Fault studies
- 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.