Questions practice unit iv
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1) A symmetrical short circuit occurs on a 22kV bus bar. The fault apparent power is 73MVA and the fault current is 1.91kA. 2) Fault current measurements for a 50MVA alternator allow calculation of its per unit sequence reactances as 1.403, 0.351, and 0.151. 3) For a 100MVA generator with given reactances, the sustained short circuit current is 2467A, initial breaker current is 16882A, and maximum DC current is not provided.
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![Unit IV Practice Questions
Q1. A symmetrical short circuit occurs on the 22KV load bus bar. Find the fault apparent power and the
fault current. Choose a base of 150MVA. Also draw the reactance diagram
[1.91KA, 73MVA]
Q2. A 50 MVA, 11KV, 3 phase alternator was subjected to different types of faults. The fault currents
were: 3 phase fault 1870A,LL fault 2590A and SLG fault 4130A. The alternator is solidly grounded. Find
the per unit values of the 3 phase sequence reactances. [1.403, 0.351, 0.151]
Q3. A generator connected through a 5 cycle circuit breaker to a transformer, is rated 100MVA, 18KV
with 19%, 26% and 130% as sub- transient, transient and steady state reactances respectively. It is
operating under no load and rated voltage when a three phase short circuit occurs between the breaker
and transformer. Find:
(i) The sustained short circuit current [2467]
(ii) The initial rms current in the breaker [16882]
(iii) The maximum possible DC component of the short circuit current in the breaker
Q4.
A 3 phase fault occurs at
point F. The reactances
are marked in per unit
values based on 100MVA.
Neglecting the pre fault
power and losses,
calculate the fault MVA at
F. Allow a multiplying
factor of 1.4.
[1430, 2000]](https://image.slidesharecdn.com/questionspracticeunitiv-130507003022-phpapp02/85/Questions-practice-unit-iv-1-320.jpg)
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POWER SYSTEM ANALYSIS_254ppt.pdfMillionAlemayehu2
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This document contains details about the Power System Analysis course offered at Muthayammal Engineering College. It includes 5 units that cover topics like power flow analysis, fault analysis of balanced and unbalanced faults, and power system stability. The course aims to impart knowledge of power system modeling and numerical methods for solving power flow and stability problems. It also covers analysis of faults using methods like symmetrical components. The document lists the course faculty, objectives, outcomes, textbooks, and topics to be covered in each unit.Power system safety and protection
Power system safety and protectionHakim Futra
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This document contains 10 problems related to power system protection and safety calculations. The problems involve calculating short circuit currents, fault currents, impedances, and voltages for various power system configurations involving transformers and generators. The solutions show the step-by-step working to arrive at the values of various requested parameters such as short circuit MVA, fault current, impedance, and voltage. Diagrams are provided with the problems to illustrate the system configurations.Computer Application in Power system: Chapter three - fault studies
Computer Application in Power system: Chapter three - fault studiesAdama Science and Technology University
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The document discusses fault studies in power systems, specifically focusing on fault analysis methods and calculations for three-phase faults, admittance and impedance matrix equations. It outlines the process of collection and processing of data to form a nodal equivalent network, and how fault currents and voltages can be determined. The document emphasizes the importance of accurate fault analysis for circuit breaker capacity and protective relay performance.Section 7 Fault Analysis.pdf
Section 7 Fault Analysis.pdfALIFEVIOUSCHRISTIANX
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This document section discusses fault analysis in power systems. It begins by defining different types of faults like line-to-ground and line-to-line faults that can result in excessive current. It then discusses fault current calculations for a symmetrical three-phase fault on a simple system using superposition and per-unit calculations. As an example, it calculates the subtransient fault current, generator current, and motor current for a bolted three-phase fault at a bus.Fault Level Calculation
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This document discusses fault level calculations in electric power systems. It explains that fault level calculations are necessary to select protective devices, circuit breakers, and equipment that can withstand short circuit currents. The document outlines the procedure for calculating fault levels, which involves representing the system with a single line diagram, choosing a base MVA, calculating per unit reactances, determining the equivalent reactance to the fault point, and using formulas to calculate fault MVA and current. It also discusses how current limiting reactors can be used to insert additional reactance and reduce short circuit currents to match circuit breaker ratings.ELECTRICAL POWER SYSTEM - II. symmetrical three phase faults. PREPARED BY : J...
ELECTRICAL POWER SYSTEM - II. symmetrical three phase faults. PREPARED BY : J...Jobin Abraham
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This document discusses symmetrical three-phase faults in electrical power systems. It defines a symmetrical fault as one where equal fault currents are produced in each line with 120 degree phase displacement. This is the most severe type of fault. The document covers transient currents on transmission lines during a fault, selection of circuit breakers based on maximum fault currents, fault currents and induced emfs for synchronous machines under no-load and loaded conditions, and provides an algorithm for short circuit studies.Fault Analysis using Z Bus..pdf
Fault Analysis using Z Bus..pdfSaravanan A
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(1) A symmetrical fault occurs on bus 3 of a 3-bus system.
(2) The Thevenin equivalent impedance is calculated to be j0.21 p.u.
(3) For a fault impedance of j0.19 p.u., the fault current is calculated to be -j2.5 p.u. and the post-fault bus voltages are determined.
(4) For a bolted fault with zero impedance, the fault current is -j4.76 p.u. and the post-fault bus voltages and line currents are found.Unsymmetrical fault
Unsymmetrical faultSmile Hossain
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This document discusses unsymmetrical faults in power systems. It begins by defining unsymmetrical faults as faults that result in unequal line currents and displacement. It then discusses the causes of unsymmetrical faults such as falling trees, wind, and insulation failures. The document also summarizes the effects of faults such as overcurrent, equipment loss, and electrical fires. It describes the types of unsymmetrical faults and introduces symmetrical components and Fortescue's Theorem for analyzing unsymmetrical faults using positive, negative, and zero sequence networks. Finally, it briefly discusses fault limiting devices like fuses, circuit breakers, and protective relays.283481961-POWER-SYSTEM-FAULTS-ppt.ppt
283481961-POWER-SYSTEM-FAULTS-ppt.pptAshaLatha456489
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- Any abnormal condition that causes excessive current flow through unintended paths in a power system is defined as a fault.
- Faults can be caused by insulation failures, lightning strikes, or accidental operations and must be safely disconnected to prevent equipment damage.
- Short circuit current calculations are required to select properly rated circuit breakers and relay settings for protection schemes.
- Faults are classified by nature, participating phases, and whether they are symmetrical or asymmetrical. Symmetrical faults can be analyzed using positive sequence networks while unsymmetrical faults require symmetrical component analysis.Computer Application in Power system: Chapter three - fault studies
Computer Application in Power system: Chapter three - fault studiesAdama Science and Technology University
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Questions practice unit iv
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