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Transcript

True-False Questions A magnetic core material may exhibit hysteresis or saturation but not both A magnetic core material may exhibit hysteresis or saturation but not both False Core losses in a transformer may be calculated by knowing only the volume of material, thickness of laminations, resistivity of the iron, and using the B-H plot. Core losses in a transformer may be calculated by knowing only the volume of material, thickness of laminations, resistivity of the iron, and using the B-H plot. False Given a fixed core dimension, the maximum flux density may decreased by decreasing the number of primary winding turns Given a fixed core dimension, the maximum flux density may decreased by decreasing the number of primary winding turns True Leakage reactance is a function of core material and is unaffected by winding geometry. Leakage reactance is a function of core material and is unaffected by winding geometry. False In transformer design, the area product defines an envelope of values for B and J, but does not fix either one. In transformer design, the area product defines an envelope of values for B and J, but does not fix either one. True Problems Given the system below, calculate the required VA rating for the transformer. (Remember the dot convention) The transformer in the figure below can be assumed to be ideal. If I connected a hand-held Ohm-meter to the primary coil (left) what would the reading be? N1=100 Turns N2=10 Turns R=1k Ω The transformer in the figure below can be assumed to be ideal. If I connected an AC voltage source to the primary coil (left) what would the equivalent impedance of the primary be? N1=100 Turns N2=10 Turns R=1k Ω Assume a magnetic core material with infinite resistivity and the following B_H characteristic: We have designed an inductor with a total volume of 10-4 cubic meters of material, and wound it with a suitable number of turns such that the core just reaches saturation with 120V excitation at 60 HZ. What is the real power loss in the core? If you are given a transformer primary and secondary voltages, VA rating and frequency, the open circuit voltage, current and power, and the short circuit voltage, current, and power: How do you find the transformer model impedance values? How do you find the expected voltage regulation? If you are given the primary and secondary voltages, VA rating, frequency, number of primary turns, lamination specifications, number of laminations, voltage regulation, and efficiency: How do you find the peak flux density? How do you calculate the core losses? How do you find the full load primary & secondary currents?