Contents I. INTRUDUCTION
On-line monitoring of the excitation parameters of power generator, such as rotor's voltage and rotor's current signal, has a great significance for the proper operation of power generators. The maximum magnitude of the rotor's voltage signal can reach DC 1000V, the rating current magnitude of rotor's current signal has several kilo-ampere. A shunt is normally installed in the rotor's loop of power generator to measure the rotor's current, its rating output is 5OmV or 75mV. It is needed to transfer the measuring results of the rotor's voltage and current signal to the controlling room, which is normally far from the power generator. The signal transmission media is metallic cable in nowadays. For the high-voltages (HVs) in the rotor loop, the security can't insure when the cable is shorted to ground. In the other hand, the output of shunt for current measurement is so weak that it is munity to electromagnetic interference during long-distance transmission in metallic cable. The measuring accuracy and step response performance may be deteriorated. In addition, the rotor's voltage and current signals are not a stable DC value, they are the superposition of pulse signal (6 pulse, 12 pulse et. al) and DC signal. There are some transient phenomena during voltage step response, the initial excitation and inversion-field suppression process, et al. Traditional DC transducer has poor accuracy (0.5% in ratio, for example) and poor dynamic response time, 400 ms, for example. They are not acceptable during some circumstances needed precision measurement.
