IEEE Std C57.13.1 pdf free download

IEEE Std C57.13.1 pdf free download.Field Testing of Relaying Current Transformers.
5.1 Demagnetizing CTs If there is any reason to suspect that a CT has been recently subjected to heavy currents, possibly involving a large dc component, or has been magnetized by any application of dc voltage, it should be demagnetized before conducting any tests that require accurate measurements of current. It is also prudent to demagnetize the CT after the tests are completed. One method used for demagnetizing the CT is to apply a suitable, variable alternating voltage to the CT’s secondary winding, with an initial magnitude sufficient to force its flux density above its saturation point, and then decrease the applied voltage slowly and continuously to zero. The test connections used for this method of demagnetizing are identical to those required for the excitation test as shown in Figure 10. Another method used by transformer analyzers to demagnetize a CT, is to vary the secondary loop resistance gradually from low to high to low at a consistent rate. The amount of variable secondary loop resistance will be determined by what resistance is required to drive the CT beyond the knee of its B-H excitation curve and demagnetize its core. This is typically a resistance that will cause a 65% to 75% reduction in secondary loop current. As an example, provided the CT under test produces at least 2.5 A secondary loop current, a series resistance is varied gradually from0.1 Q to 8 h and back to0.1 Q at a consistent rate. This operation effectively overburdens the CT and demagnetizes the core. When demagnetizing a CT with less than 2.5 A secondary current, a larger resistance of up to 50 Q may be required. See IEEE Std C57.13 for further information on demagnetizing CTs and IEEE Std C37.110 for examples of waveforms showing magnetized CTs.
6.3 Insulation resistance test The CT should be tested to prove that the windingto-winding and winding-to-ground insulation is satisfactory. 6.4 Resistance measurement This test confirms that the dc resistance of the CT secondary winding is within specification and that there is no high resistance connection in the CT or the wiring connected to it (see Clause 11). 6.5 Excitation test This test confirms that the CT, as supplied, is of the correct accuracy rating, has no shorted turns in the CT, and that no wiring or physical short circuits have developed in the primary or secondary windings of the CT after installation. The manufacturer ‘s design curves for the CT should be available so that the actual results can be compared with those curves (see Clause 12). 6.6 Admittance test This test confirms the installed condition of the CT’s internal burden and external burden connected to the CT (admittance is the reciprocal of impedance). The admittance of a CT secondary loop can be measured with or without current flow in the secondary winding (CT in or out of service). The instrument used for conducting admittance tests injects an audio signal into the secondary winding of a CT and measures the reflected waveform to determine the admittance. The circuit admittance of a CT is nearly constant throughout its normal operating range unless a fault develops (see Clause 13).
IEEE Std C57.13.1 pdf download.