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Skyler MacDougall

Homework 6: due 2/26/2020

  1. A single-phase transformer has a rating of 100kVA, 7200V-600V, 60Hz. If it is reconnected as an autotransformer having a ratio of 7800V-7200V, calculate the load it can carry.

100kVA= S;\ 7200V = V_1;\ 600V=V_2\ 100kW=P_1

  1. In the above problem, How should the transformer terminals (H_1, H_2, X_1, X_2) be connected?

  1. Many airports use series lighting systems in which the primary windings of a large number of current transformers are connected in series across a constant current, 60Hz source. In one installation, the primary current is kept at 20A. The secondary windings are individually connected to a 100W, 6.6A incandescent lamp.

    1. Calculate the voltage across each lamp.

    2. The resistance of the secondary winding is 0.07\Omega while that of the primary is 0.008\Omega. Knowing that the magetizing current and the leakage reactance are both negligible, calculate the voltage across the primary winding of each transformer.

    3. If 140 lamps, spaced at 50m intervals, are connected in series using No. 14 wire, calculate the minimum voltage of the power source. Assume the wire operates at a temperature of 105^\circ C.