Transformer evaluation

1. A method of evaluating a condition of a plurality of transformers that are located remotely from each other, the method comprising the steps of:

obtaining an ambient temperature for respective sites of the transformers at a plurality of times during a period;

determining the ambient temperatures based on an estimated ambient temperature for the respective sites of the transformers including estimating the ambient temperature by

clustering the sites into a plurality of clusters,

determining a centroid for each cluster,

associating each centroid with a measurement station, and

estimating the ambient temperature at each of the sites based on a temperature at the measurement station associated with the centroid of the cluster including the transformer site;

determining respective loading at the transformers at the plurality of times; and

determining respective aging rates of the transformers during the period based on the respective ambient temperatures and loadings.

2. The method of claim 1 , wherein determining the respective aging rates comprises determining respective hottest spot temperatures of the transformers at the plurality of times.

3. A method of evaluating a condition of a plurality of transformers that are located remotely from each other, said method further comprising the steps of:

performing said method of claim 1 for a plurality of periods; and

determining respective cumulative aging of the transformers over a time including the plurality of periods.

4. The method of claim 1 , wherein the plurality of times are spaced at intervals of an hour or less.

5. The method of claim 4 , wherein the plurality of times are spaced at intervals of approximately five minutes.

6. The method of claim 1 , wherein

the transformers are associated with respective meters;

the meters provide respective indications of loading based on power consumption at respective customer locations;

the loading at each transformer comprises a total loading at each of the plurality of times; and

the total loading is based on the indications of loading of the associated respective meters.

7. The method of claim 1 , wherein there are more transformers than measurement stations.

8. A transformer evaluation device, comprising:

a data storage; and

a processor configured to

obtain an ambient temperature for respective sites of the transformers at a plurality of times during a period;

determine respective loading at the transformers at the plurality of times; and

determine respective aging rates of the transformers during the period based on the respective ambient temperatures and loadings;

wherein the processor is configured to determine the ambient temperature based on an estimated ambient temperature for the respective sites of the transformers; and wherein the processor is configured to estimate the ambient temperatures by

clustering the sites into a plurality of clusters;

determining a centroid for each cluster;

associating each centoid with a measurement station; and

estimating the ambient temperature at each of the sites based on a temperature at the measurement station associated with the centroid of the cluster including the transformer site.

9. The transformer evaluation device of claim 8 , wherein the processor is configured to determine the respective aging rates including determining respective hottest spot temperatures of the transformers at the plurality of times.

10. The transformer evaluation device of claim 8 , wherein the processor is configured to

determining respective cumulative aging of the transformers over a time including a plurality of periods.

11. The transformer evaluation device of claim 8 , wherein the plurality of times are spaced at intervals of an hour or less.

12. The transformer evaluation device of claim 11 , wherein the plurality of times are spaced at intervals of approximately five minutes.

13. The transformer evaluation device of claim 8 , wherein

the transformers are associated with respective meters;

the meters provide respective indications of loading based on power consumption at respective customer locations;

the loading at each transformer comprises a total loading at each of the plurality of times; and

the total loading is based on the indications of loading of the associated respective meters.

14. The transformer evaluation device of claim 8 , wherein there are more transformers than measurement stations.