VA metering in delta-wired electrical service

1. An arrangement for measuring VA loading on a transformer in a delta-wired electrical service, comprising:

a) a meter housing;

b) a sensor circuit disposed within the meter housing, the sensor circuit configured to be electrically connected to receive voltage and current provided to a load from a secondary side of one or more source transformers arranged in a delta-wired electrical service having phase A, phase B and phase C lines, the one or more source transformers including at least one center-tap secondary winding, the sensor circuit configured to generate voltage measurement signals and current measurement signals representative of the received voltage and current;

c) an A/D converter disposed within the meter housing, the A/D converter configured to receive the voltage measurement signals and generate therefrom contemporaneous samples of V A , V B , V C , and to receive the current measurement signals and generate therefrom at least three of I A , I B , I C , and I N , where I A is a current measurement signal of phase A, I B is a current measurement signal of phase B, I C is a current measurement signal of phase C, I N is a current measurement signal of a neutral connection, V A is a voltage measurement signal from phase A to neutral, V B is a voltage measurement signal from phase B to neutral, and V C is a voltage measurement signal from phase C to neutral;

d) a processing circuit operably coupled to the A/D converter, the processing circuit configured to:

i) obtain a value indicative of a ratio K of a first impedance of one leg of the at least one center-tap secondary winding to a second impedance of a different secondary winding;

ii) determine at least one of an I BC sample value, an I CA sample value, an I NB sample value, and an I AN sample value, based on K and contemporaneous samples of at least three of I A , I B , I C , and I N ,

iii) determine a VA value corresponding to at least one secondary winding of the at least one source transformer based at least in part on the at least one sample value determined in ii); and

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

2. The arrangement of claim 1 , wherein the processing circuit is further configured to:

a) generate a plurality of at least one of the I BC , I CA , I NB and I AN sample values; and

b) generate a magnitude value for the plurality of the at least one of the I BC , I CA , I NB and I AN sample values.

3. The arrangement of claim 2 , wherein the processing circuit is further configured to determine the VA value further based at least in part on the generated magnitude value.

4. The arrangement of claim 3 , wherein the processing circuit is further configured to determine the VA value further based in part on a magnitude of a voltage from phase A to neutral and a magnitude of a voltage from phase B to neutral.

5. The arrangement of claim 4 , wherein the processing circuit is further configured to determine the magnitude of the voltage from phase A to neutral and determine the magnitude of the voltage from phase B to neutral using a root-mean-square calculation.

6. The arrangement of claim 4 , wherein the processing circuit is further configured to generate the VA value based on the equation:

VA=|{right arrow over ( V B )}|*|{right arrow over ( I NB )}|+|{right arrow over ( V A )}|*|{right arrow over ( I AN )}|

wherein |{right arrow over (V B )}| is a magnitude of the voltage from phase B to neutral, |{right arrow over (I BN )}| is the I NB magnitude value representative of the current from phase A to neutral, |{right arrow over (V A )}| is a magnitude of the voltage from phase A to neutral, and |{right arrow over (I AN )}| is a magnitude value representative of the current from phase A to neutral.

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

8. The arrangement of claim 1 , wherein the at least one transformer is disposed external to the meter housing.

9. An electricity meter arrangement for measuring VA loading on a transformer in a delta-wired electrical service, comprising:

a) a meter housing;

b) a sensor circuit disposed within the meter housing, the sensor circuit configured to be electrically connected to receive voltage and current provided to a load from a secondary side of one or more source transformers arranged in a delta-wired electrical service having phase A, phase B and phase C lines, the one or more source transformers including at least one center-tap secondary winding, the sensor circuit configured to generate voltage measurement signals and current measurement signals representative of the received voltage and current;

c) an A/D converter disposed within the meter housing, the A/D converter configured to receive the voltage measurement signals and generate therefrom samples of V A , V B , V C , and to receive the current measurement signals and generate therefrom at least three samples of I A , I B , I C , and I N , where I A is a current measurement signal of phase A, I B is a current measurement signal of phase B, I C is a current measurement signal of phase C, I N is a current measurement signal of a neutral connection, V A is a voltage measurement signal from phase A to neutral, V B is a voltage measurement signal from phase B to neutral, and V C is a voltage measurement signal from phase C to neutral;

d) a processing circuit within the meter housing, the processing circuit operably coupled to the A/D converter, the processing circuit configured to:

i) obtain a value indicative of a ratio K of a first impedance of one leg of the at least one center-tap secondary winding to a second impedance of a different secondary winding;

ii) determine an I BC sample value based on K and contemporaneous samples of at least three of I A , I B , I C , and I N ;

iii) determine an I CA sample value based on K and contemporaneous samples of at least three of I A , I B , I C , and I N ;

iv) determine an I NB sample value based on K and contemporaneous samples of at least three of I A , I B , I C , and I N ;

v) determine an I AN sample value based on K and contemporaneous samples of at least three of I A , I B , I C , and I N ;

vi) determine a VA value corresponding to the secondary windings of the at least one transformer based at least in part on the I BC , I CA , I NB and I AN sample values;

vii) provide information representative of the VA value to one of a group consisting of a display, a communication circuit, a memory and a billing calculation unit;

viii) determine a real energy consumption value by a load based at least in part on samples of V A , V B , V C , and samples of I A , I B , I C .

vi) provide information representative of the real energy consumption value to one of a group consisting of a display, a communication circuit, a memory and a billing calculation unit.

10. The electricity meter arrangement of claim 9 , further comprising the communication circuit, and wherein; the communication circuit is supported by the meter housing; and the processing circuit is further configured to cause the communication circuit to transmit the information representative of the VA value to a computing device external to the meter housing.

11. The electricity meter arrangement of claim 10 , further comprising the computing device, and wherein the computing device is configured to communicate with the communication circuit via an optical connector.

12. The electricity meter arrangement of claim 10 , wherein the computing device is disposed remote from the meter housing, and wherein the communication circuit is configured to transmit the VA value using a communication network.

13. The electricity meter arrangement of claim 10 , wherein the at least one transformer is disposed external to the meter housing.

14. The arrangement of claim 9 , wherein the processing circuit is further configured to:

a) generate a plurality of each of the I BC , I CA , I NB and I AN sample values; and

b) generate a magnitude value for each of the plurality of the I BC , I CA , I NB and I AN sample values.

15. The arrangement of claim 14 , wherein the processing circuit is further configured to determine the VA value further based at least in part on the I BC magnitude value, the I CA magnitude value, the I NB magnitude value, and the I AN magnitude value.

16. The arrangement of claim 15 , wherein the processing circuit is further configured to determine the VA value further based in part on a magnitude of a voltage difference from phase C to phase B and a magnitude of a voltage difference from phase C to phase A.

17. The arrangement of claim 16 , wherein the processing circuit is further configured to determine the magnitude of the voltage from phase C to phase B and determine the magnitude of the voltage from phase C to phase A by:

a) generating a plurality of the V BC sample values, each V BC sample value comprising a difference between a phase C sample and a contemporaneous phase B sample; and

b) generating a V BC magnitude value using the plurality of the V BC sample values;

c) generating a plurality of the V CA sample values, each V CA sample value comprising a difference between a phase C sample and a contemporaneous phase A sample;

d) generating a V CA magnitude value using the plurality of the V CA sample values.

18. The arrangement of claim 16 , wherein the processing circuit is further configured to generate the VA value based on the equation:

VA=|{right arrow over ( V CB )}|*|{right arrow over ( I CB )}|+|{right arrow over ( V CA )}|*|{right arrow over (I CA )}|+|{right arrow over (V B )}|*|{right arrow over (I BN )}|+|{right arrow over ( V A )}|*|{right arrow over ( I AN )}|

wherein |{right arrow over (V CB )}| is the V BC magnitude value, |{right arrow over (I CB )}| is the I BC magnitude value, |{right arrow over (V CA )}| is the V CA magnitude value, |{right arrow over (I CA )}| is the I CA magnitude value, |{right arrow over (V B )}| is a magnitude of the voltage from phase B to neutral, |{right arrow over (I BN )}| is the I NB magnitude value, |{right arrow over (V A )}| is a magnitude of the voltage from phase A to neutral, and |{right arrow over (I AN )}| is a vector value representative of the current from phase A to neutral.