What measures the quality of voltage, frequency, and resulting current in the grid or user system?

The measure of voltage quality, frequency, and the resulting current in a power grid or user system is referred to as Power Quality. This concept encompasses various factors that define the stability and reliability of the electrical supply.

Power quality is critical because it affects the performance of electrical devices and the overall efficiency of the power system. It involves maintaining the voltage levels within specified limits, ensuring that frequency is stable, and managing the current characteristics to prevent issues like harmonics, sags, swells, or transients. As such, monitoring and improving power quality is essential for avoiding interruptions, enhancing the efficiency of electrical appliances, and reducing wear and tear on equipment.

The other options relate to different aspects of the power industry but do not specifically address the measurement or assessment of voltage, frequency, and current quality. Power Line Carrier refers to a method of transmitting communication signals over power lines; Power Development Program relates to plans and strategies for enhancing the overall power infrastructure; and Primary Response generally pertains to the immediate actions taken during grid disturbances rather than ongoing measurements of power quality.