lecture6 - EE 740 Professor Ali Keyhani Lecture #6...

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EE 740 Professor Ali Keyhani Lecture #6 Load-Tap-Change Transformer (LTC)
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Load-Tap-Changing Transformers (LTC): Np Np Ns Ns V L-N Tap Tap Np Ns Tap HV LV LTC: In LTC transformers the taps are changed when the loads are not connected. TCUL: The taps are changed when the loads are connected. In LTC transformers the number of turns on the primary side and secondary side can be changed. Nominal Turns Ratio: When all turns of both the primary and secondary are carrying currents. V HV / N HV = V LV / N LV or V HV / V LV = N HV / N LV = a Off-Nominal Turns Ratio: When parts of the turns of one or both windings are not carrying currents Note: When nominal turns ratio is used the base voltages are selected as: Vb HV = (V HV / V LV )xVb LV or Vb LV = (V LV / V HV )xVb HV
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Problem 1: A single tap-changing transformer has 2000 turns on the primary side, and a variable number of turns on the secondary side (Nsec max = 7300, Nsec min = 5300). Compute the minimum and maximum voltage that can be maintained on the secondary side. Assume the maximum primary voltage is equal to 36.4 kV. Primary 1 36.4 kV 2 3 Secondary Nsec max = 7300 Np = 2000 4 5 Nsec min = 5300 6 7 8 9 10 11 12 13 14 Vp/2000 = 36.4x10 3 /2000 = 18.2 V/T Vp/2000 = Vsec/Nsec max = 18.2 = Vsec/7300 Vsec = 132.86 kV Vp/2000 = Vsec/Nsec min = 18.2 = Vsec/5300 Vsec = 96.46 kV The secondary voltage can be changed between 132.86 and 96.46 kV
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lecture6 - EE 740 Professor Ali Keyhani Lecture #6...

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