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The open-circuit test, or no-load test, is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer. The no load is represented by the open circuit, which is represented on the right side of the figure as the "hole" or incomplete part of the circuit.
Recently time-consuming testing procedures in test labs have been replaced by on-site oil testing procedures. There are various manufacturers of portable oil testers. With low weight devices in the range of 20 to 40 kg, tests up to 100 kV rms can be performed and reported on-site automatically.
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An initial SFRA test is carried out to obtain the signature of the transformer frequency response by injecting various discreet frequencies. This reference is then used for future comparisons. A change in winding position, degradation in the insulation, etc. will result in change in capacitance or inductance thereby affecting the measured curves.
A different form of short-circuit testing is done to assess the mechanical strength of the transformer windings, and their ability to withstand the high forces produced if an energized transformer experiences a short-circuit fault. Currents during such events can be several times the normal rated current.
IEC 61007 Transformers and inductors for use in electronic and telecommunication equipment – Measuring methods and test procedures; IEC 61008 Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs)
A high-voltage current transformer may contain several cores, each with a secondary winding, for different purposes (such as metering circuits, control, or protection). [7] A neutral current transformer is used as earth fault protection to measure any fault current flowing through the neutral line from the wye neutral point of a transformer.
Eddy Current Testing at Level 2, International Atomic Energy Agency, Vienna, 2011 (pdf 5.6 MB). ASTM E3052 Standard Practice for Examination of Carbon Steel Welds Using Eddy Current Array Official web page of Lorentz Force Velocimetry and Lorentz Force Eddy Current Testing Group Archived 2013-11-17 at the Wayback Machine