What type of transformer is being described with a 100 KVA rating and a 1.8% impedance designed for a 240-volt panel?

The transformer described is most appropriately categorized as a 3-phase, 3-wire unit when considering its characteristics. A 100 KVA rating indicates a substantial capacity, commonly associated with three-phase systems that are used in industrial or commercial applications. The mention of a 1.8% impedance is typical for transformers functioning in a three-phase configuration, where impedance is distributed across three separate windings.

The reference to a 240-volt panel also supports the three-phase arrangement because three-phase systems commonly distribute power at lower voltage levels effectively. In a 3-phase, 3-wire configuration, you can deliver power using three phase conductors, making it ideal for balanced loads and reducing the neutral requirement.

In contrast, the other options don't align well with the implications of a 100 KVA rating and operational design for a 240-volt panel in this context. Single-phase options would generally have lower capacities than what is indicated in this scenario. Additionally, the two-wire configuration wouldn’t be suitable for 240 volts in a three-phase system, which generally requires at least three wires for proper operation and load balance. Thus, a 3-phase, 3-wire transformer is the most fitting classification for the specifications given.