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Power stations generate electricity at relatively low voltages, around 10-15kV, but it must be transmitted over long distances through transmission lines to reach consumers. Transmitting at higher voltages reduces line losses that occur as heat, but it is not economical to solely decrease conductor resistance. Therefore, step-up transformers raise the voltage at the beginning of transmission lines, and step-down transformers lower it back down through a series of stages until it reaches usable voltages of 400V or less for consumers. Power transformers play a key role in modern power systems by facilitating the high-voltage transmission of electric power over great distances through the grid to numerous consumers.