METHODOLOGY FOR THE EVALUATION OF
THE NTC VALUES AT THE GREEK
INTERCONNECTIONS
(This methodology is not binding for the north neighboring TSOs)
ADMIE
INTRODUCTION
The calculation of the NTC values at the Greek north interconnections (at the borders
Greece-FYROM, Greece-Albania, Greece-Bulgaria, Greece-Turkey) is based on
common transmission models which at all times take into account the actual topology
and conditions of the South East European (SEE) region.
The calculation forms the basis of the allocation of capacity rights on each
interconnection.
This document refers to the calculation of transfer capacity for imports and exports at
the north borders of Greece. For the Greece-Italy connection, due to the fact that this
is a DC cable, the NTC value is always 500 MW on both directions (same with the
maximum capacity of the cable).
1. EVALUATION OF THE TOTAL NTC VALUE FOR IMPORTS
AND EXPORTS FOR THE NORTH GREEK INTERCONNECTIONS
1.1 NTC DEFINITION AND DETERMINATION
ADMIE is responsible for the operation of the Greek electric power system and its
interconnections with other systems in order to guarantee the security of supply and
provide the maximum available transfer capacities to the market.
The Net Transfer Capacity (NTC) values are evaluated using always a complete
network of the South East European (SEE) region and an agreed maintenance plan.
For the evaluation of the NTC values the papers taken into account are listed in the
references [1-5].
The NTC calculation is performed in different timeframes, on yearly, monthly and
daily basis.
As a general rule the evaluation of the NTC values takes into account the ENTSO-E
rules and definitions as well as the recommendations from the EU CM 1228/2003
guidelines in order to establish a transparent congestion management methodology
that will cope efficiently with the interdependency of the loop flows.
At first the Base Case Exchange (BCE) among ADMIE and its neighbouring TSOs is
established. The set of cross-border transactions considered in the base case relates to
the best forecast for exchanges at the time frame considered. To be realistic the base
cases have to rely on historical recorded data, adapted in order to take into account the
foreseeable electric system changes. The same procedure follows for the entire
countries of the South East European region. After the complete BCE for the entire
SEE region is established among TSOs (harmonized) the individual TSOs send the
forecasted models that correspond to the previously defined BCE programs.
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After merging the forecasted models, the base case exchange (BCE) model for the
entire South East European region is established.
In order to calculate the maximum total TTC/ NTC values for imports/exports for the
Greek system by taking into account the interdependency of the loop flows, ADMIE
performs combined NTC calculation where one area is considered by the north Greek
neighbouring countries, Albania, FYROM, Bulgaria and Turkey and the other area is
Greece. Similar procedure is followed by other TSOs for the calculation of the total
TTC/NTC values [5].
For the calculations, production is increased in one area by (ΔΕ), proportional to its
remaining capacity while production in the other area is decreased by the same
amount (according to generation remaining capacity again). When under the N-1
criteria the security limit is reached for the entire South East European region, the
Total Transfer Capacity between the two areas is established, taken as
TTC=BCE+ΔΕ. In case the generation limit is reached in one area before violation of
the N-1 criteria then additional generation will be taken into account though transits
from neighbouring countries (e.g transits from Serbia and Romania for the evaluation
of the Greek imports and transit from Italy for the evaluation of Greek exports).
The above TTC value corresponds to the overall maximum importing/exporting
capacity for the Greek north borders.
In order to calculate the overall maximum importing/exporting capacity for the Greek
north borders that can be offered to the market players under security conditions the
TTC is reduced by a margin for security purposes (TRM). The Net Transfer Capacity
can then be taken as NTC= TTC-TRM.
The following graph illustrates the procedure that is followed between ADMIE
(system A) and the neighbouring TSOs, OST, MEPSO,,ESO EAD and TEIAS
(system B)
NTC = BCE + ΔΕ – TRM (1) where:
BCE: Base Case Exchange
ΔE: Maximum Shift of generation that can be assigned preventing any violation from
appearing with (n-1) criterion.
TRM: Transmission Reliability Margin
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1.2 GENERATION SHIFT DEFINITION
The NTC determination depends on the power plant profile (location and power), and
therefore an important issue is the method to shift generation for the determination of
the NTC values.
The Increase/decrease proportional to the power reserve of the modelled power-plants
is done at the following way:
The power plants are simultaneously increased/decreased in proportion to the
remaining reserve Pmax – Pbase case (for increase), i.e. Pbase case – Pmin (for decrease).
All chosen injections are modified proportionally to the remaining available capacity.
(2)
Pi
: Actual active power generation (MW)
inc
Pnew
: New increased injection
dec
Pnew
: New decreased injection
E
: Shift generation, negative for increasing and positive for decreasing
Pimax
: Maximum permissible generation (MW)
Pimin
: Minimum permissible generation (MW)
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2.
EVALUATION
OF
THE
NTC
VALUES
FOR
IMPORTS/EXPORTS PER INTERCONNECTION FOR THE GREEK
NORTH BORDERS
Being active in providing efficient competition on the Internal European electricity
market, ADMIE follows Regulation No 1228/2003 and its ANNEX as amended by
Commision´s Decision 2006/7707EC, referred to as ``The Guidelines``.
According to the above congestion management guidelines, coordination of electrical
borders shall include:
(a) Use of a common transmission model dealing efficiently with
Interdependent physical loop-flows,
(b) Allocation and nomination of capacity to deal efficiently with
Interdependent physical loop-flows
As mentioned previously, the starting point for the NTC evaluation is the
establishment of the Base Case Exchange model. The physical flow over the Greek
interconnections in the base case prior to any generation shift represents the Notified
Transmission Flow (NTF) in each interconnection [1].
A PTDF (power transfer distribution factor) is the share of a power transfer that flows
on a considered border. Multiplied by the amount of the power transfer we get the
power flow on the considered border. The physical flow Fi , X is the physical flow
over an interconnector i that was induced by a generation shift  X , (from the base
case exchange up to an amount X) can be given from
Fi , X  PTDFi *  X
(3)
N
It is obvious that
 PTDF  1 and
i 1
N
 F
i 1
i, X
   where N is the number of
interconnectors.
For the maximum generation shift from the base case exchange up to the total TTC
limit, the total transfer flow can be established for each interconnector as:
Fi  NTFi  Fi ,TTC
(4)
For each interconnector the additional exchange program that can be offered due to
the maximum generation shift (TTC condition) can be taken from the formula:
 i ,TTC  Fi ,TTC
(5)
For each interconnector i the final TTC value can be given from
TCi  CEi   i ,TTC
(6)
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For all interconnectors the total TTC value can be found as
N
TTC ALL   TTC
(7)
i 1
The calculation of the TRM according to ETSO is based on empirical figures of the
TSOs, or on statistical methods. ADMIE among other TSOs [5] uses the following
formula to calculate the total TRM value:
TRM ALL  100 N
(8)
where N is the number of interconnectors in operation between the control areas of
ADMIE and the Greek north borders (the countries, Albania, FYROM, Bulgaria and
Turkey). The above formula has proven its worth in practice the last few years and is
appropriate for the evaluation of the NTC values at the Greek interconnectors since it
can be applied for coordinated NTC calculation (NTC calculation which takes into
account the interdependency of the loop flows).
The above total TRM value is split to each interconnector according to the PTDF
factors calculated in (3), so
TRM   PTDFi * TRM ALL
(9)
From the above formula it is obvious that the more the transfer capacity at an
interconnector the more the safety limit in this interconnector.
For each interconnector the additional exchange program that can be offered due to
the maximum generation shift under secure operating conditions (NTC conditions)
can be taken from the formula:
Ci  TTCi  TRM i
(10)
For all interconnectors the total NTC value can be found as
N
NTC ALL   NTC
(11)
i 1
3. NTC CALCULATION FOR IMPORTS AND EXPORTS AT
YEARLY LEVEL
The yearly transfer capacity between the transmission network of Greece and the
transmission network of each neighbouring TSO in both directions is calculated for
the period from the 1st of January (00:00 h CET) to the 31st of December (24:00 h
CET) of the year of reference.
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In determining the guaranteed Yearly transfer capacity between the transmission
network of Greece and each neighbouring country`s transmission network, ADMIE
takes into account the agreed maintenance plan among the South East European
region TSOs. Calculations of the guaranteed yearly values of the transfer capacities
between the transmission network of Greece and each neighbouring transmission
network are based on winter (January) and summer (July) forecast models of the
entire ENTSO-E region. From the two forecasted models, ADMIE considers a ratio
(approximately 50%) of the minimum of the two calculated NTC values as yearly
right, in order to cope with uncertainties at the transmission network.
ADMIE and each neighboring TSO perform security analysis and calculates the NTC
values. After all calculations, NTCs are exchanged and finally harmonized. If no
agreement is taken then the lower value sets the NTC.
ADMIE and the TSO of each neighbouring transmission network harmonize the
guaranteed yearly transfer capacity values (corresponding to the agreed coordinated
maintenance program and the N-1 security criterion) by November 15th of the
previous year.
4. NTC CALCULATION FOR IMPORTS AND EXPORTS AT
MONTHLY LEVEL
Monthly transfer capacity values are evaluated by ADMIE and the TSOs of each
neighbouring transmission network, agreed in written by the 9th calendar day of the
previous month, and shall apply as from the first calendar day (00:00 h CET) until the
last calendar day (24:00 h CET) of the month. If the 9th calendar day is not a working
day, then it will be the first working day following the 9th calendar day.
TSOs agree for monthly reference network models, which are used for the monthly
NTC calculation. A general monthly time schedule for making the network model for
the 3rd Wednesday 10h30 CET of month M:
- till 15th of month M-2: sending of the Base Case Exchanges (table)
- till 17th of month M-2: harmonization of Base Case Exchanges (table)
- till 20th of month M-2: exchange of the network models with agreed totals
- till 25th of month M-2: checking and merging of the regional model
- till 1st of month M-1: NTC calculation for month M
- till 5th of month M-1: harmonization of NTC values for month M
The countries which models are exchanged and merged into a common regional
model within this procedure are: Albania, BiH, Bulgaria, Croatia, Greece, Hungary,
Austria, FYROM, Romania, Slovenia, Serbia, Montenegro and Ukraine. If any of the
above models is not available the last available model/information is used (e.g DACFDay-Ahead Congestion Forecast files obtained from the EH).
The calculation of the NTC values is performed in a monthly basis with the complete
network for 1030 CET (high tariff) as well as an additional monthly NTC calculation
and evaluation is performed when one of the critical lines is expected to be out of
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operation (for example for maintenance purposes) as well as in cases when there is
something unexpected in the region.
The parties inform each other for any unplanned disconnection of transmission
components in their own grid, provided that these disconnections have an essential
impact on the grid security of other party.
Each TSO performs security analysis and calculates the NTC values. After all
calculations, NTCs are exchanged and finally harmonized. If no agreement is taken
then the lower value sets the NTC.
After all monthly NTC calculations for imports/exports will be completed, then the
monthly Available Transfer Capacity for imports/exports (assuming no netting) that
will be offered to the market will be taken from the following formula:
ATC MONTHLY = NTCMONTHLY-AACYEARLY RIGHT
(12)
where ATCMONTHLY is the Available Trasfer Capacity for monthly auction,
NTCMONTHLY is the Net Transfer Capacity for mothly auction and AACYEARLY RIGHT
is the Already Allocated Capacity from the yearly auction.
The following graph illustrates the procedure that is followed where area A is Greece
and area B is the Greek north countries. (Albania, FYROM, Bulgaria, Turkey).
5. NTC CALCULATION FOR IMPORTS AND EXPORTS AT DAILY
LEVEL
Calculation of the daily transfer capacity values is based on day-ahead congestion
forecast (DACF) models, with the models of the Greek and its neighbouring TSOs
transmission systems being planned using the latest data available (generation, load
and system data for the auctioning day).
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After all daily NTC calculations for imports/exports will be completed, then the daily
Available Transfer Capacity for imports/exports is taken from the following formula
(assuming that no netting is applied):
ATC DAILY = NTCDAILY-AACNOTIFIED YEARLY RIGHT -AACNOTIFIED MONTHLY RIGHT
(13)
Where as ATC DAILY is the Available Trasfer Capacity for daily auction, NTCDAILY
is the Net Transfer Capacity for daily auction and AACNOTIFIED YEARLY RIGHT is the
Already Allocated Capacity from the yearly auction that has been notified and
AACNOTIFIED MONTHLY RIGHT is the Already Allocated Capacity from the monthly
auction that has been notified.
6. OTHER ASPECTS
ADMIE and the neighbouring TSOs have agreed to inform each other immediately,
i.e on short notice in case of an unplanned disconnection and not later than the fifth
working day of the previous month in case of a planned disconnection, of any
disconnection of transmission elements in their own grid, provided that such
disconnection has an essential impact on other country´s grid (according to the
Annual Maintenance program for the SEE region).
If such necessity should arise , ADMIE upon agreement with the neighbouring TSO`s
or in its own discretion yet on a short notice, may introduce amendments in the
initially evaluated ATC values depending on the specific combination of
circumstances that compromise the system operation security.
REFERENCES
[1]
Definitions of Transfer Capacities in liberalised Electricity Markets, ETSO,
April 2001
[2]
Net Transfer Capacities (NTC) and Available Transfer Capacities (ATC) in the
Internal Market of Electricity in Europe (IEM). ETSO, March 2000
[3]
Procedures for Cross-Border Transmission Capacity Assessments, ETSO,
October 2001
[4 ]
Technical guidelines for NTC determination, UCTE, March 2004
[5]
General model used by Vattenfall Europe Transmission GmbH for calculating
the TTC and the safety margin, www.vattenfall.de
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