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A system for temporary measurement of voltage and current simultaneously in high-voltage distribution lines was developed. The sensing heads use a resistive divider and a magnetic pickup for sampling voltage and current, respectively. A self-powered transmitter converts both signals into a pulse-frequency-modulated optical signal for transmission in multimode optical fiber. At ground potential, the optical signal is received and demodulated back into voltage and current signals. Then, a microcontroller calculates V and I for the three phases as well as VA, power factor, and watt-hour, storing these in memory. The system exhibits all data in instantaneous mode and stores 5-min mean values of a period of up to ten days. Optionally, the data can be collected by a personal computer through a standard RS-232C serial port. The system linearity for both current and voltage is better than 2% in the range of 0 to 800 A and 0 to 15 kV, respectively. It can be installed by live-line techniques in less than 10 min, without de-energizing the line.