Measurement system for electrical variables in a high EMI environment

This paper introduces a system for measurement of electrical signals under very aggressive EMI conditions at a high power testing laboratory. Basically, the measuring process includes sensing voltage and current signals, in the order of tens of kV and kA, with the appropriate shunts or dividers, signal conditioning, analog modulation and transmission from the testing zone. The transmission media is optical fiber to ensure signal integrity, avoiding distortion due to EMI caused by the large currents and voltages during tests. At the other end, in the control room, the data acquisition system converts the optical signals back to electrical signals to be demodulated, amplified and digitized for further processing. The electronics take care of other potentially harmful influences such as temperature variation, which may cause DC-shifting and gain variations. The measurement system is currently under factory and on-site acceptance tests with excellent results so far. This system was conceived and developed in the Department of Instrumentation and Control of the Electrical Research Institute (IIE), under specific request from the National Electricity Company (CFE) in Mexico.