| 摘要 |
PURPOSE:To measure insulation resistance accurately with respect to earth in the system, by outputting the current signal which lags by 90 deg. in the phase from the zero-phase voltage of a bus while the magnitude thereof is equal to the zero-phase current from a control section to be added to the detection zero-phase current with respect to the zero-phase current of the bus. CONSTITUTION:In a current vector chart which indicates the relationship among zero-phase current I1 flowing through the bus, current signal IH outputted from the control section and added value IB, when the IH and I1 are the same in the magnitude, the current IC1 flowing through the capacitance out of the zero- phase current I1 is cancelled to convert I1 as shown by IB. The phase difference phiB is determined with respect to the zero-phase voltage of the addition signal to calculate ¦I'B¦cosphiB, based on which insulation resistance can be obtained. When the phase of the output signal shifts, for example, by theta' in the direction of advance from the phase of the actual signal due to the temperature characteristic of a band-pass filter, currents are represented by I<+>1, IC1<+>, IH<+> and IB<+>. As the phase angle phiB of the addition signal IB is very close to 0 deg. with respect to real axis, the addition signal IR without phase deviation and the addition signal IR<+> therewith are roughly equal.
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