One idea that we incorporated into the design of the ELITEpro™ and ULTRAlite™ is derived from Blondel's Theorem. It enables you to save a CT, or use one less CT, thus reducing costs..
Blondel's Theorem
The theory of polyphase metering was first set forth on a scientific basis in 1893 by Andre E. Blondel, engineer and mathematician. His theorem applies to the measurement of power in a polyphase system of any number of wires. The theorem is as follows:
If energy be supplied to any system of conductors through N wires, the total power in the system is given by the algebraic sum of the readings of N wattmeters, so arranged that each of the N wires contains one current coil, the corresponding voltage coil being connected between that wire and some common point. If this common point is on one of the N wires, the measurement may be made by use of N-1 wattmeters.
The bottom line is that you can save a CT if you are creative in how you reference your voltages. Please be careful though. This method is not always the best choice and can only be used on a 3-phase, 3-wire system. Review the following wiring diagrams for examples of the theorem in use:
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