If a 480 x 120/208 volt transformer is connected to a line with a voltage of 518 volts and compensating taps are not used, what will the secondary line voltage be?

To determine the secondary line voltage of a transformer when given an input voltage of 518 volts, we need to understand how transformer ratios work. The transformer in question is specified to accept a primary voltage of 480 volts.

In this case, first, we note that the transformer’s primary voltage is expected to be 480 volts to take full advantage of its designed circuitry. The secondary winding is rated for 120/208 volts, which tells us it's designed to deliver a secondary output voltage based on this primary rating.

When the primary voltage exceeds the rated voltage, as it does here with 518 volts, we'll calculate the secondary voltage using the turns ratio of the transformer. The turns ratio can be found by comparing the primary to secondary voltage ratings. Since we have a transformer designed with a primary voltage of 480 volts to an expected secondary voltage of 208 volts (for the three-phase configuration):

1. The turns ratio calculates as 480/208, which simplifies to approximately 2.3077.

2. When the voltage on the primary side is adjusted for the 518 volts, we apply the turns ratio to find the equivalent secondary voltage:

[ \text{Secondary Voltage} = \frac{\text{Primary Voltage}}