Current detection device
The current detection device includes a plurality of air-cored coils respectively attached to conductors for a plurality of phases, which are supported by an insulator and housed in a ferromagnetic tank a plurality of output-voltage detection circuits that detect output voltages of the air-cored coils for respective phases; and a correction processing circuit that obtains, by dividing the output voltages of the air-cored coils for respective phases by transformation ratios of the air-cored coils, current value levels, which are temporary values of currents flowing in the conductors for respective phases, calculates the output-voltage correction values for respective phases according to the current value levels of respective phases, and calculates and outputs current flowing in the conductors for respective phases on the basis of the output-voltage correction values.
1. A current detection device comprising:
a plurality of air-cored coils that are attached to conductors for a plurality of phases, respectively, the conductors being supported by an insulator and housed in a tank made of a ferromagnetic material;
a plurality of output-voltage detection circuits that detect an output voltage of the air-cored coil for each phase; and
a correction processing circuit that calculates an output-voltage correction value for each phase on a basis of an output voltage of the air-cored coil for each phase, and calculates and outputs current flowing in the conductor for each phase on a basis of the output-voltage correction value, wherein
the correction processing circuit obtains, by dividing an output voltage of the air-cored coil for each phase by a transformation ratio of the air-cored coil, a current value level, which is a temporary value of current flowing in the conductor for the phase, and calculates the output-voltage correction value for each phase in accordance with the current value level of each phase.
2. The current detection device according to claim 1 , wherein the correction processing circuit stores, for the output-voltage correction value for another phase when an output voltage of the air-cored coil for a given phase among a plurality of phases is a correction processing target, a voltage correction factor in accordance with a magnitude of current flowing in the conductor for the another phase, and calculates the output-voltage correction value for each phase by using a simultaneous equation including a plurality of equations with each of which the output-voltage correction value for the given phase is obtained by, when the output voltage of the air-cored coil for the given phase is a correction processing target, subtracting, from the output voltage of the air-cored coil for the given phase, a value that is obtained by multiplying the output-voltage correction value for the another phase by the voltage correction factor in accordance with the current value level of the another phase.
3. The current detection device according to claim 2 , wherein the correction processing circuit stores a plurality of the voltage correction factors in accordance with a magnitude of current flowing in the conductors in a table format and derives the voltage correction factor by referring to and interpolating the table in accordance with the current value level.
4. The current detection device according to claim 2 , wherein, before a normal operation is started, the correction processing circuit stores, as the voltage correction factor for the output-voltage correction value for an energized phase when an output voltage of the air-cored coil for another phase is a correction processing target, a value that is obtained by dividing the output voltage of the air-cored coil for the another phase, which is different from the energized phase, by an output voltage of the air-cored coil for the energized phase when current is individually caused to flow in the conductor for each phase.
5. The current detection device according to claim 1 , wherein, before a normal operation is started, the correction processing circuit stores, as the transformation ratio of the air-cored coil for an energized phase, a value that is obtained by dividing an output voltage of the air-cored coil for the energized phase by energizing current when current is individually caused to flow in the conductor for each phase.
6. The current detection device according to claim 1 , wherein the conductors for a plurality of phases are conductors for three phases in which phase currents respectively flows from a three-phase power source.