Analysis of unsymmetrical faults using the bus impedance matrix, Faults through impedance, Computer calculations of fault currents

1. 10/4/2017
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Analysis of unsymmetrical faults using the bus impedance matrix, Faults
through impedance, Computer calculations of fault currents
Presented by:
Name Roll No. Enrollment No.
Nakum Dharemsh M. 46 150863109005
Nayakwade Ragini b. 47 150863109006
Parmar Ashish kumar 48 150863109007
Patel Bhavin S. 49 150863109008
(2160908 EPS II)
Laxmi Institute of Technology, Sarigam, Gujarat

2. Outline
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 Symmetrical faults : That fault which gives rise to symmetrical fault currents
(i.e. equal faults currents with 120o displacement) is called a symmetrical
fault.
Example: when all the three conductors of a 3-phase line are brought
together simultaneously into a short-circuit condition.
 Unsymmetrical faults: Those faults which give rise to unsymmetrical
currents (i.e. unequal line currents with unequal displacement) are called
unsymmetrical faults.
 Single line-to-ground fault
 Line-to-line fault
 Double line-to-ground fault
Common: a short-circuit from one line to ground
INTRODUCTION

3. INTRODUCTION OF UNSYMMETRICAL
FAULTS
 Most Of the faults that occur on power systems are unsymmetrical faults, which
may consist of unsymmetrical short circuits, unsymmetrical faults through
impedances, or open conductors.
 Unsymmetrical Faults occur as single line--‐to--‐ground faults, line--‐to--‐line
faults, or double line--‐to--‐ground faults. The Path of the fault current from line to
line or line to ground may or may not contain impedance. One Or two open
conductors result in unsymmetrical faults, through either the breaking of one or
two conductors or the achon of fuses and other devices that may not open the three
phases simultaneously

4. Analysis of unsymmetrical faults using bus impedance matrix

10. Sequence Impedances
Slide 10 of 11
Each element of power system will offer impedance to different
phase sequence components of current which may not be the
same. Therefore, in unsymmetrical fault calculations, each piece of
equipment will have three values of impedance—one
corresponding to each sequence current viz.
(i) Positive sequence impedance (Z1)
(ii) Negative sequence impedance (Z2)
(iii) Zero sequence impedance (Z0)