Thursday, March 29, 2012

Incorrect kW load results from corrupted TLC three phase TOU meter data

[Updated - see end of post for details]

In the last few days I have informed TLC's CEO (John Anderson) of the details of a serious data error that appears likely to affect a large number of customers with three phase supplies and who also have Time of Use meters. These would typically be larger consumers but will include some domestic homes also.

In essence the problem is that the half hour data from certain types of time of use meters used at three phase installations (including at least the EM5100, EM5200, EM5300 models) has been corrupted and when that corrupted data has been processed incorrect kW load values have been produced. Often, perhaps in the majority of cases, I would expect the incorrect results to be higher than they should, hence causing higher payments for the customer.

TLC have not disclosed details of how the new Accommodation/Holiday Home formula has been derived but if this was done using some data from installations with this problem then the formula may well be similarly affected, especially as I expect a higher than average proportion of 3 phase installations within that group. It may affect the dairy shed formula also.

There is no direct evidence that the meters themselves are faulty. Instead it seems likely that the data has been corrupted either during the data download from the meter (a manual procedure carried out after each winter) or possibly in some subsequent processing by TLC or its agents. (Please note carefully at this point that I am no longer contracting to TLC - they informed me that my services were no longer needed last December!)

The reason for suspecting that the problem is not directly within the meter itself is that the LCD display has shown the (approximately) correct time over the last year or two, so the meter clock itself has not obviously been wrong.

I provided John Anderson with a detailed analysis of the fundamental nature of the corruption within the data files. The essence of that is as follows:

1. Some meters (including the models listed above) have sufficient memory to store roughly two years worth of half hour data.

2. If they have been installed for a sufficiently long period of time, this means that the data downloaded after the 2011 winter period also included much or all of the 2010 data, often including dates when daylight saving officially ended in April

3. If the above conditions are true (but perhaps others also) then the half hour data that TLC processed (and also supplied to those customers who requested it) in order to produce the kW load figures that determine the monthly charges from 1 April 2012 was incorrect, as the April 2010 daylight saving transition did not appear in the data (for some reason not yet determined).

4. Later daylight saving transitions did appear. The net result is that the data (from the point where the April 2010 daylight saving transition should have appeared) is one hour advanced from the "correct time".

5. As the process of determining a kW load figure from the data requires reconciling the half hour data from the meter (with its own dates and times derived from the meter clock) against TLC's separately determined records of when load controlling was occurring on the appropriate channel, this means that consumption during the hour before load controlling started will be incorrectly included in those calculations, and similarly, the last hour of each qualifying period of load controlling will be treated as if it was outside of the controlled period and therefore ignored.

6. If there are any situations during the winter period where inclusion of the lead-in hour could result in significantly higher kW load (e.g. from controllable load such as hot water and so on), then the overall result from the average of the top 6 such periods (and charges to the customer for the following year) will also most likely be inflated.

The story of how this problem came to be uncovered is interesting and goes back a long way but I will leave that for later. Suffice to say that the first set of half hour data showing this problem led to a pricing letter from TLC that had the (incorrect!) kW load value at roughly 3 times what it should have been, and for this (large power user) that would have meant roughly $700 extra per month, coincidentally with payments starting on April Fool's Day...

I recommend any customer with an EM5100, EM5200, or EM5300 time of use meter installed (look at the top left on the front for the model number) who has any concerns that they could be affected negatively by this to immediately request a full copy of the raw data used to generate their kW load results from TLC, including the load control timing information that was also used, plus any other relevant information to allow full verification of the kW load calculation. The EM1000 meters like the one at my home only store about 9 months of data and don't seem to be affected but you could ask for your data anyway, just to be sure. There are many other situations in which similar problems could crop up.

If a few other customers hadn't asked for their data then this problem would probably not have been uncovered.

TLC's Elizabeth Anglesey kindly pointed out in a letter to the Ruapehu Press on 25 Jan 2012 that any customer was entitled to ask for their information. See the extract below for what she said:

I'd be very interested to hear from anybody who has asked for and received their data. Clive at xnet dot co dot nz will reach me or else try 07 8954556. At the very least I should be able to help you determine if you are affected by the problem I've described above.

Update: On 2 April I received an email from TLC about this issue. After thanking me for my help the email went on to say:
We have discovered that one of the hand held readers used by the TOU meter readers was found to have faulty/incorrect software.  Fortunately it was not the reader used for the majority of the customers.  We found around 40 customers who kW load needs to be reduced.  All these customers will be notified directly and will have their load level reduced for 2012.
Note that I currently do not know the full number of meters affected. I also do not know if any of the affected installations were included in the data sources used to generate the various formulae. I have asked TLC for further information on both points.

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