Toshiba GR200 Series Instruction Manual page 240

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From Equation (2.9-1), (2.9-2), and (2.9-3), the following equations are derived:

The magnitude of the fault current depends on the impedance across the system, the

difference in phase angle, and the magnitude between the power source voltages behind both

As noted earlier, the BCD element detects the presence of a fault by measuring the ratio

between the negative sequence current and the positive sequence current (I

obtained from the negative sequence impedance (Z

hence, the equation of the ratio is expressed as follows:

A ratio value of 0.5 or higher is obtained when the zero sequence impedance is larger

than the negative sequence impedance. The ratio, thus, is close to 1.0 if the system is high-

impedance earthed or a single-end earthed system.

) and the zero sequence impedance (Z

6F2S1915 (0.46)

). The ratio is

GRZ200 (Soft 031 & 032)