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IEEE C57.12.91-2020 pdf free download

IEEE C57.12.91-2020 pdf free download.IEEE Standard Test Code for Dry-Type Distribution and Power Transformers.
8.5 Frequency conversion of excitation losses and current
In the event that the load loss and impedance test cannot he done at the rated power frequency, see Annex 13
for 50/60 Hz frequency conversions.
9. Load losses and impedance voltage
9.1 General
The load losses of a transformer are the losses due to the load current earned by the transformer. Load losses include !2R loss in the windings due to load current. 12R loss in the leads or bus bar due to load current, and stray losses due to eddy currents induced by leakage flux in the windings. leads or bus bar, core clamps. magnetic shields, tank walls, and other conducting parts. Stray losses may also be caused by circulating currents in parallel windings or strands. Load losses arc measured by applying a short circuit across either the high-voltage terminals or the low-voltage terminals and applying sufficient voltage across the other terminals to cause a specified current to flow in the windings. The power loss within the transformer under these conditions is the load losses of the transformer at the ambient temperature and load current of the test.
The impedance voltage of a transformer is the exciting voltage required to circulate rated current through one winding and its associated leads or bus bar when the other winding(s) and associated leads or bus bar are short-circuited, with the windings connected for rated voltage operation. Impedance voltage is usually expressed in per unit, or percent, of the rated voltage of the winding across which the voltage is applied and measured. The impedance voltage comprises a resistive component and a reactive component. The resistive component of the impedance voltage, called the resistance drop. is in phase with the current and corresponds to the load losses. The reactive component of the impedance voltage, called the reactciiice drop, is in quadrature with the current and corresponds to the reactance caused by leakage-flux linkages between the windings. The impedance voltage is the phasor sum of the two components. The impedance voltage is measured during the load loss test by measuring the voltage required to circulate rated current in the windings and associated leads or bus bar. The measured voltage is the impedance voltage at the temperature of test, and the power loss dissipated within the transformer is equal to the load losses at the temperature of test and at rated load current. The impedance voltage and the load losses are corrected to a reference temperature using the formulas specified in 9.4.IEEE C57.12.91-2020 pdf free download.

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