# Skyler MacDougall

## Homework 6: due 2/26/2020

7. 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.

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

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

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14. 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.
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    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.
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    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 $105^\circ C$.
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