marketrelations@nyiso.com writes to the NYISO_TECH_EXCHANGE Discussion List:

Dear Market Participants

Many Market Participants recognized the mismatch in prices which were posted 
on
the NYISO website versus those which were used for billing in the settlement
statements.

The NYISO has identified the various differences and has modified software
necessary to update and / or correct the prices associated with the categories
listed below;

Upon completion of all the Historical LBMP updates noted below, the NYISO will
recompute and post new real time weighted files.  Information on what 
intervals
have been changed, as a result of a specific issue noted below, will be
provided.

Issue #1:  Prices and Postings During Reserve Pickup Intervals:
During instances where the dispatch interval is in response to a  Reserve 
Pickup
request, the price which will be used to bill a Reserve Pickup (RPU)  period 
is
the price associated with the most recent normal SCD execution interval
preceding the reserve pickup interval. There were limited instances during the
first 11 months of operation where an LBMP was incorrectly calculated and 
posted
for the reserve pickup intervals.

Solution Issue #1:  For the period 11/99 until the present, all RPU intervals
that were inadvertently posted with price calculations based on the reserve
pickup intervals will be replaced with the price from the dispatch cycle
immediately preceding the reserve pickup.  Any modifications made which result
in changes to the billing data will be corrected through the re-bill and 
true-up
process in future months.


Issue #2:  Posted Price Discrepancies Between Proxy Bus and Load Bus Prices:
During the process of correcting and reposting prices, the Generator or proxy
bus prices were updated, but not the Zonal or load prices.

Solution Issue #2: ALL proxy gen prices which are different from their
corresponding zonal prices, will be copied into the zonal bus prices to
overwrite any possible discrepancies between these two files, as these should 
be
identical. NOTE: The Billing & Accounting System (BAS) was coded to use the
generator proxy bus price.  Therefore the BAS calculations have been 
consistent
with the generator proxy price and should not affect any bills.


Issue #3:  Missing SCD Intervals In Pass of Data Between SCD and PTS- Due to
Loss of Communications:
At times there periods exist when communication links between operating 
systems,
namely SCD and Performance Tracking (PTS) in this case, have failed and have 
to
be manually reactivated.  During these sub-system failure periods, SCD 
intervals
are being saved and when communications are restored or through the price
correction process the SCD intervals are restored.  During these failure 
periods
the SCD Start/Stop signals are not being transferred to the PTS. Six-second
actual data continues to be received by PTS during these failure periods.  PTS
develops an average actual value over the SCD interval periods. During the
failure periods the PTS observations do not match the number of SCD interval
observations. The BAS is coded to ignore any intervals where there is not a
match between the price file and the metered MW files. For example, if SCD had
intervals for :05, :10 and :15 and the PTS integrated actuals covered the 
period
:05 - :15 then the BAS would calculate the billing based on the consistent 
sets
of data, The interval then becomes a 10 minute interval.

Solution Issue #3 The system will be programmed such that it will recognize 
when
an interval is missing in PTS and the PTS interval will be generated by
splitting the large interval,  with the assumption that the energy was 
delivered
uniformly over the entire interval.   Retroactive to Nov'99, the missing
intervals will be created.  Through the monthly rebill and true-up process,
these intervals will be used and billing results may change as a result.

Issue #4:  Dispatch Interval Type "R"
When SCD is in a reserve pickup, and the pick-up is unsuccessful after 10
minutes, an extra PTS interval is generated for performance tracking of units.
This interval is not an actual interval where basepoints are calculated and 
sent
to generators.  At the time the PTS intervals are sent to the MIS, an LBMP
interval is also sent.    These intervals were posted on the OASIS and then
ignored in BAS.

Solution Issue #4 Retroactively to Nov'99, all LBMP intervals generated as 
part
of the reserve pickup performance tracking process will be deleted.  In the
future, the intervals will not be sent to MIS for posting.

Issue #5:  Consistent Updated Price Postings
Prior to January 2000, intervals updated as part of price corrections were
posted to a different spot on the OASIS in a different format,  thus making it
difficult for market participants to locate the correct data.

Solution Issue #5 Retroactively to Nov'99, an update of the current LBMP 
posting
files will be accomplished to include the price corrections not originally
posted.


The intent of the NYISO is to have all corrections for retroactive price 
posting
discrepancies, and software enhancements completed by the end of Nov 2000.