Energy Measurement in High Voltage Power Networks at Low Currents

With the advance of renewable generation in power systems, a new measurement problem arises. Wind and solar plants inject energy to the power network most of the time, but during some periods, as in the night or during low wind, they consume. The meters record separately the consumption from the supply with different commercial regulations and rates. However, the energy measuring system (watthour meters, instrument transformers) is the same and it is designed for the maximum power, as generators. When consuming, the power is much lower, and the measuring system must operate in some cases between 0.1% and 1% of its nominal current, out of precision specification. The regulating bodies generally do not take into account this problem, and even states the application of fines for exceeding consuming power over the contract. In this paper a survey on the response of watthour meters and current transformers at very low currents, not covered by standards or manufacturer specifications, is presented.