This is called high speed reclosing Transformer failures can be due to

# This is called high speed reclosing transformer

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deionized is the solution to this problem. This is called high speed reclosing. Transformer failures can be due to deterioration caused by aging or over-voltages as a result of lightening or switching transients. Faults may be external to transformer but the can still cause large mechanical forces internal to transformer. These forces can cause windings or other parts to move or damage insulation or actually cause structural failures. These types of faults may be in generators also. Two parallel conductors carrying current can subject a force of attraction or repulsion, depending on the direction of current. Magnitude of this force is given as F Where I = current in each conductor D = separation between conductors Currents in same direction cause attraction whereas currents in opposite direction cause repulsion. In EHV this force can be enough to cause the movement of conductors if circuit breaker does not operate in reasonable time. Other effects include corona, corona losses, radio noise and radio interference (RI). 1.3 FAULT ANALYSIS AND ITS IMPORTANCE The Power System analysis may be classified as: Power flow --- evaluate normal operating conditions Fault analysis --- evaluate abnormal operating conditions 3
The purpose of fault analysis is to have the maximum and minimum fault currents and voltages at different locations of power system for various types of faults so that a proper protection scheme can be designed. Fault analysis results are used for specifying ratings for circuit breakers and fuses protective relay settings specifying the impedance of transformers and generators Magnitude of fault currents depend on: the impedance of the network the internal impedances of the generators the resistance of the fault (arc resistance) Network impedances are governed by transmission line impedances transformer connections and impedances grounding connections and resistances Generator behavior is divided into three periods sub-transient period, lasting for the first few cycles transient period, covering a relatively longer time steady state period Fault Studies Sub-transient period, X G = X d " determine the interrupting capacity of HV circuit breakers determine the operation timing of the protective relay system for high-voltage networks Transient period, X G = X d determine the interrupting capacity of MV circuit breakers determine the operation timing of the protective relay system for medium-voltage networks transient stability studies 1.4 TRANSIENT ON A TRANSMISSION LINE Let us consider the short circuit transient on a transmission line. Certain simplifying assumptions are made at this stage. The line is fed from a constant voltage source Short circuit takes place when the line is unloaded Line capacitance is negligible and the line can be represented by II lumped RL series circuit.