What is the result of applying voltage below the rated primary voltage to a transformer?

Applying voltage below the rated primary voltage to a transformer results in the transformer operating at lower efficiency. This is because transformers are designed to operate optimally at their specified voltage levels. When the voltage is below the rated level, the magnetic flux in the core does not reach the ideal level required for effective energy transfer.

As a consequence, the transformer may not deliver the expected output voltage or power levels, leading to increased losses in the form of heat and reduced performance. Additionally, lower input voltage can cause issues like insufficient magnetizing current, which might result in a decrease in the overall efficiency of the transformer.

This situation does not inherently cause malfunction, nor does it guarantee that the transformer will not work at all, as it may still produce some output. It also does not directly damage the transformer unless other factors come into play, such as prolonged operation under these conditions, which could lead to overheating or other operational issues over time. Therefore, the efficiency drop is the most relevant consequence of applying a lower than rated primary voltage.