VA metering in polyphase systems

1. An arrangement, comprising:

a) an A/D converter configured to generate digital samples of voltage and current waveforms in a polyphase electrical system;

b) a processing circuit operably coupled to receive the digital samples from the A/D converter, the processing circuit configured to:

i) generate a VA calculation using the following relationship

VA

Source

=

1

3

⁡

[



I

→

A

+

2

⁢

I

→

C



·



V

→

CB



+



2

⁢

I

→

A

+

I

→

C



·



V

→

AB



+



I

→

A

-

I

→

C



·



V

→

AB

-

V

→

CB



]

where {right arrow over (I)} A is the current vector on phase A, {right arrow over (I)} C is the current vector on phase C, {right arrow over (V)} CB is the voltage vector across phase C and phase B, and {right arrow over (V)} AB is the voltage vector across phase A and phase B;

ii) provide information representative of the VA calculation to one of a group consisting of a display, a communication circuit, and a billing calculation unit.

2. The arrangement of claim 1 , wherein the processing circuit is further configured to generate a first value representative of {right arrow over (I)} A +2{right arrow over (I)} C at least in part by combining a value substantially equal to two times the magnitude of a phase C current sample with a phase A current sample.

3. The arrangement of claim 2 , wherein the processing circuit is further configured to generate a second value representative of {right arrow over (V)} CB based at least in part on phase C voltage samples.

4. The arrangement of claim 3 , wherein the processing circuit is further configured to generate a value representative of a product of the first value and the second value.

5. The arrangement of claim 1 , wherein the processing circuit is further configured to generate a first value representative of 2{right arrow over (I)} A +{right arrow over (I)} C by combining two phase A current samples with a phase C current sample.

6. The arrangement of claim 1 , further comprising the display, and wherein the display is configured to display the information representative of the VA calculation.

7. An arrangement, comprising:

a) an A/D converter configured to generate digital samples of voltage and current waveforms in a polyphase electrical system;

b) a processing circuit operably coupled to receive the digital samples from the A/D converter, the processing circuit configured to:

i) generate a first value at least in part by combining a value substantially equal to two times the magnitude of a phase C current sample with a phase A current sample;

ii) generate a VA calculation using the first value and at least one other value;

iii) provide information representative of the VA calculation to one of a group consisting of a display, a communication circuit, and a billing calculation unit.

8. The arrangement of claim 7 , wherein the processing circuit is further configured to combine two phase A current samples with the phase C current sample to generate one of the at least one other values.

9. The arrangement of claim 7 , wherein the processing circuit is further configured to generate a second value representative of a voltage difference between phase C and phase B based at least in part on phase C voltage samples.

10. The arrangement of claim 9 , wherein the processing circuit is further configured to generate a value representative of a product of the first value and the second value.

11. The arrangement of claim 7 , further comprising the display, and wherein the display is configured to display the information representative of the VA calculation.

12. The arrangement of claim 7 , further comprising the communication circuit.