standards / manuals / guidelines for small hydro development - AHEC

ii) Radio interface voltage (r.i.v.) testsiii) Temperature rise testsiv) Measurement of the resistance of the main circuitv) Short-time withstand current and peak withstand current testsvi) Mechanical and environmental testsvii) Miscellaneous provisions for making and breaking testsviii) Short circuit making and breaking testsix) Basic short circuit test dutiesx) Critical current testsxi) Single phase short making and breaking testsxii) Capacitive current switching testsxiii) Magnetizing and small inductive current switching tests7.2 Routine testsi) Power frequency voltage withstand dry tests on the main circuitii) Voltage withstand tests on control and auxiliary circuitsiii) Measurement of the resistance of the main circuitiv) Mechanical operating testsv) Design and visual checks8.0 Fault CalculationIn order to determine interrupting duty of circuit breakers it is necessity to determine faultcurrent at each circuit breaker location. Determination of maximum short circuit currentis the most important requirement of circuit breaker application. Rigorous determinationof short circuit current as a function of time involves complex calculations. Growth ininterconnecting power system as systems expand will increase short circuit duty.Accordingly some approximation and degree of judgment should be used.Different published methods of determining short circuit currents are available.Reference may be made to the following for details and selection.IEEE application guide for AC high voltage circuit breakers rated on a symmetricalcurrent basis IEEE std. C37010-1999.First step in carrying out short circuit studies is to determine system impedances withreference to the point of fault and current distribution for different kind of faults. Forpresent day large interconnected system this becomes time consuming laborious study.AC or DC network analyzer for calculation of fault current was previously frequentlyused for short circuit studies. In the analyzer all the essential elements of the powersystem were represented in a miniature replica and fault currents determined fromcalculation readings. In this method constant voltage behind sub transient/synchronousreactance were used as required. Accordingly real time studies to determine DC4-17