IEEE Std C57.123:2002 pdf free download

IEEE Std C57.123:2002 pdf free download.IEEE Guide for Transformer Loss Measurement.
3.2.7 Workmanship
The quality of workmanship in slitting, cutting. annealing, and handling of the individual core laminations and the quality of the assembly of the core have a direct effect on the magnitude of core losses. Quality of joints in the core also affects the value of core loss to a certain extent but usually has a greater effect on the magnitude of the exciting current. These factors can partially explain why loss measurements on essentially duplicate units can differ by a few percent.
3.2.8 Core temperature
Core losses are affected to some degree by the temperature of the core at the time that losses are measured. Generally, core losses decrease with an increase in core temperature. This is due to a reduction of the eddy loss component of the core material iron loss caused by the higher resistivity of the material at higher temperatures. The calculation method to correct the measured values of core losses of distribution transformers to the reference temperature is given in 8.4 of IEEE SW C57.l2.X)’ 1999 and IEEE Std C57.l2.9l-200l. The mainitudc of this effect is in reality a function of core design and core material. However, the effect is sufficiently small (about 1% for every IS °C). In this case, using an average value of the correction factor would be satisfactory. The factor was chosen to be 0.065% per °C (0.(XX)65 p.u. per °C). Its value was arrived at through consensus of the transformer industry and is based on typical values. Due to uncertainly in the actual value of the core temperature during operation, the reference temperature was chosen to he 20 °C for liquid-immersed transformers (per IEEE Std C57.l2.0O-2000). According to these standards, since core loss measurements on power transformers are typically made at, or near. room temperature. there is little need for applying temperature correction in his case.
3.2.9 Impulse tests
No-load toss ineusurements taken directly after impulce tests are usually slightly higher (typically 1 % to 3%) than those taken beforehand. Higher magnitudes of increased no-load loss have been experienced in some cases. This phenomenon is not fully understood at the present time. Existing data, however, shows that this increase is seldom permanent arid usually diminishes with time (several hours).