A transformer is given a 90-kilovolt impulse test. What is the voltage applied?

The applied voltage for a transformer undergoing a 90-kilovolt impulse test is 90,000 volts. This is derived from the fact that "kilovolt" (kV) is a unit of voltage equivalent to 1,000 volts. Therefore, when a transformer is subjected to a 90-kilovolt impulse test, it means that the test involves a voltage of 90,000 volts being briefly applied to assess the transformer’s insulation and performance under high voltage conditions.

Understanding the concept of impulse testing is crucial, as it is a standard method used to ensure that electrical equipment, like transformers, can withstand momentary voltage surges that can occur due to lightning strikes or switching operations in the electrical grid. This test helps identify weaknesses in insulation that might not be apparent under normal operating conditions.

The other options reflect much lower voltage levels that would not be suitable for an impulse test on a transformer, which is built to handle high voltages in its operational conditions. Therefore, the correct interpretation of the test requirement leads directly to the conclusion that 90 kilovolts translates to 90,000 volts.