In power system, operation in the leading mode (drawing Vars into the generator from the power system) can be required during periods of light load. High-voltage transmission lines are highly capacitive when lightly loaded. The Vars produced by these lines can raise system voltage to unacceptable levels. Under such conditions, generators are operated in the leading mode to absorb excess reactive power, thus controlling system voltage. When a relatively large generator is connected to a weak system, the unit may be required to operate in the leading mode to prevent overvoltage caused by the transmission of real power across the system. The most obvious limit to leading Var operation is the bottom portion of the generator