Frequently Asked Questions
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The line currents in a delta are shifted 30° compared to the line-line voltage. One line current will be shifted +30° and the other line current shifted -30° when compared to the line-line voltage. Since power factor is COS(theta), then COS 30° = .866. This will be true for the hardware channels. If the power sum channel (5 or 6) is used, the power factor for the whole load should be as expected.
The line currents in a delta are shifted 30° compared to the line-line voltage. When connected to a load that has a PF of <.5 (>60°) (e.g. a motor not fully loaded) one line current becomes shifted >90° (30° +>60°) when compared to the line-line voltage. The other phase is shifted >30° (-30° + >60°). The COS of an angle >90° is negative, therefore WATTs = COS(theta)VA is negative for that phase. However, as with the power factor the sum of the watts in a delta should be positive. If not, check the CT orientation, one or both may be reversed. Also check to make sure the CT’s are referenced to the correct line voltages.
Metering Project Guide
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