Which term refers to communication equipment that transmits data signals through power transmission lines?

The correct term for communication equipment that transmits data signals through power transmission lines is Power Line Carrier (PLC). This technology utilizes the existing power lines to transmit both voice and data signals, making it an efficient way to leverage the electrical infrastructure for communication purposes.

PLC operates by modulating data signals onto the higher frequency overlay on the electrical power transmission, which allows for two-way communication without the need for additional wiring. This is particularly advantageous for monitoring and managing power systems, as it enables real-time data transfer with minimal additional investment in communication infrastructure.

The other options do not pertain to this specific function of transmitting data signals. Power Quality Management relates to ensuring that the power quality benefits the reliability of electrical systems, whereas Preliminary Project Planning involves the initial stages of project setup and organization in various contexts, and Active Power Control deals primarily with managing and regulating the actual flow of electricity rather than communication.