Professional Answer: The use of voltages in multiples of 11 kV (e.g., 11 kV, 22 kV, 33 kV) in electrical distribution and transmission systems is a result of historical engineering practices and the need to manage voltage drop over long distances. While it's not a universal rule in modern grids, the principle has its roots in early AC power systems.

Originally, power was transmitted at a nominal voltage, such as 10 kV. To compensate for the inevitable voltage drop and power losses that occur along the length of the transmission line, engineers would add an extra 10% to the sending-end voltage. This means a system designed to deliver 10 kV at the receiving end would be transmitted at 11 kV (10 kV + 10%). This practice created a standardized series of voltages: 11 kV, 22 kV, 33 kV, and so on.

In modern distribution networks, 11 kV is a widely used medium voltage for local distribution. It offers a good balance between cost, safety, and efficiency for distributing power from substations to smaller, pole-mounted transformers that then step down the voltage for final customer use.