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Sharing of Inter-State Transmission Losses
04/20/23 1
Introduction
Losses are physical phenomenon while transportation of electric energy from generation to load Fixed losses
core or iron losses in transformers, losses in shunt devices such as shunt reactors, shunt capacitors etc SVC, part of losses in HVDC terminals and other FACTS devices Generally depend on system voltage and thus constant.
Variable losses (I2R) Copper losses in transformers, transmission lines Depend on load current Load current varies with quantum of load and thus variable Resistance of lines and thus on line lengths
In transmission system variable losses >> fixed losses Thus generally losses proportional to load and distance of
transportation
04/20/23 2
Introduction
Development of ISTS system 1960-70: State systems connected with few inter-state lines, 1970-80: Development of Central Generators and their associated
transmission system. 1991: POWER GRID came in existence and transfer of associated
system to new company Post 2k/2003: ISTS licensees
Treatment of losses Individual line losses Associated Transmission losses with individual generator Pooled losses
04/20/23 3
Introduction
Sharing of Transmission losses 1960-70: Based on drawal on individual lines on some
mutual/collective understanding 1970-80: based on drawal or actual energy allocation from concerned
generator. 1990: Regional Pooled losses with some exceptions in proportion to
the energy drawal. Post ABT: Estimated Regional Pooled losses in proportions to
schedules from Grid. In all above drawee utilities used to bear the losses
Inter-regional Transactions: Regional (whether pooled or otherwise) losses and inter-regional link
losses. Inter-regional link losses merged with regional pool Thus regional postage stamp for losses.
04/20/23 4
Introduction
Other changes
Sharing of losses for some state networks In schedules….. SR In actuals… NR
Operation of ‘POWER EXCHANGES’ in 2008 Based on point of connection (connection to which region) Injector /drawee both have to bear losses Wheeling region losses only if studies prove it.
04/20/23 5
New Regulation for sharing of losses
CERC Regulation on sharing of ISTS charges and losses Regulation notified in in June 2010 NLDC has prepared procedure in compliance with
Regulation 6(1) Formation of Implementation committee and various
meetings of Implementation committee Validation Committee Final approval of the commission for implementation To be implemented w.e.f 1st April 2011
04/20/23 6
International Practices Prevalent Losses settled
Paid In kind In Money
Settled For each balancing period on daily, weekly or yearly
Paid by Only drawee Both injector and drawee
In some adhoc ratio 50:50 or 45:55 Loss allocation factors may have two component
Fixed and variable(based on location, season, time of the day) Paid based
on after the fact on figures declared upfront
04/20/23 7
Issues in Recovery of Transmission Losses System Operation Requirement
Losses are physical in nature and thus to be supplied in real time Loss compensation shall be as actual losses in real time so that
proper load generation balance is maintained.
Market Operation Requirement Losses to be known in advance (as longer as possible)
to plan for future scenario to make bid/price strategy
Calculation of individual payout is easy. Whole process is transparent Allocation is fair
Overall requirement Administration of losses is easy
04/20/23 8
Loss sharing Methods…explained in literature
Loss allocation is a complex issue. To date no single loss allocation method has been universally accepted to be the most precise or the best one. Globally, different markets adopt different loss allocation schemes which suit their market structure. Various commonly followed methods are
Pro rata allocation Proportional sharing Marginal / Incremental loss allocation Loss allocation methods using the admittance
matrix Each of the above mentioned method has its
own advantages and limitations.
04/20/23 9
Loss sharing Methods… Pro rata allocation
This is the method presently being followed in India. Under this, the loss is shared among the beneficiaries on pro-rata basis in a pre-defined manner, based on schedules/shares. It is relatively a simple method to use, however this does not take in to account the geographic distribution of the loads and the generators and is not sensitive to distance and direction. Since the losses are socialized, the calculations are simple and clear.
04/20/23 10
Loss sharing Methods… Proportional sharing
In this method it is assumed that the inflow of power in to the bus is to be proportionally shared by all the out going feeders and the tracing of power between the generator and the load is to be achieved. It works on the principle that the loss of each line is to be shared by the loads in proportion to the power flow attributable to them and the respective losses are to be borne by the generators or the load. However the assumption of the proportional sharing of power may not always meet the electrical power flow laws and power tracing may also give erroneous results, particularly in the situations like loop flows and under such situations more assumptions have to be made to trace the power flows.
04/20/23 11
Loss sharing Methods… Marginal / Incremental loss allocation
Under this method losses are determined on the logic that any marginal change in bus injection/drawl leads to marginal change in the losses. Choosing of slack bus and handling of negative loss allocation etc, are some of the issues of this method
04/20/23 12
Some further References
IEEE Trans Power System pp631-637 May 2000 A Physical flow based approach to allocating transmission losses .............
IEEE Trans Power System pp143-150 Feb 2000 Allocation of transmission losses to bilateral contracts.......
IEEE Trans Power System vol16 pp105 110 Feb 2001 Z 'Z' Bus loss allocation
IEEE Trans Power System vol 17 pp 26-33 Feb 2002 Incremental transmission loss allocation under pool dispatch....
IEEE Trans Power System vol 15 pp184-188 Feb 2000 Fair allocation of transmission power losses IEEE Trans Power System vol17 no3 pp571-576 Aug 2002 Transmission loss allocation: A comparison of different practical algorithms.
04/20/23 13
Procedure for sharing of losses based on June 2010 regulation of CERC
Procedure for Sharing of ISTS Losses Prepared by NLDC in compliance with Regulation 6(1)
The procedure aims to keep computation: Simple Non-Recursive
Loss Application on Regional Basis In line with existing practice No Pan caking.
Injection and withdrawal loss would be calculated for each zone.
04/20/23 14
New Methodology
Point of Connection Losses Independent of Contract Path
50% PoC losses + 50% Uniform Losses
Uniform Loss component Based on Regional Losses of last week
Moderation of Losses Based on Actual Regional Losses of last week and Losses based
on studies
04/20/23 15
PoC Loss Computation (1)
Computation of changes in losses in the system due to incremental injection / withdrawal at each node.
Loss Allocation Factor
04/20/23 16
PoC Loss Computation (2)
Output of System Studies Loss Allocation Factor MW Losses of each node Weighted average losses (%) for each region
Zonal Loss : Weighted Average of losses at each node
Moderation of Zonal Losses
One PoC Loss for each entity per week
04/20/23 NRLDC 17
Loss Sharing Mechanism
04/20/23 NRLDC 18
Zonal Losses as Computed from Hybrid
Method
Calculation of Previous week Losses from SEM Data
Total Losses based on PoC
Software Provided by
CERC
Total Losses(50% PoC+50%UC)
Moderation Of PoC Losses
Moderation of Losses (1)
Need of Moderation Difference in actual and study scenarios Correct computation of injection and drawal schedule of various
utilities. Scheduled losses to be closer to actual losses in the system so
that system mismatch is avoided. Minimizing the mismatch between UI payable and receivable
Moderation at regional Level Moderation Factor
= Actual Losses of previous week (Aact) ( In %)
------------------------------------------------------------------
Regional Losses based on Studies (As)(In %)
04/20/23 19
Regional Losses Based on Studies (As) Weighted average Actual losses of a region
Actual Transmission losses (in MWh) in Regional ISTS, L = ∑Injection of Regional Entities G + ∑Interregional injection I) - (∑Regional Entity drawals +∑Inter-regional drawals)
Actual Percentage Regional losses, l = L*100/ (G+I)
This would be computed for each 15 min time block and then averaged for each week.
04/20/23 20
Application of Losses in Scheduling
Net PoC Loss = 50% Moderated PoC Loss + 50% Uniform Loss
Net PoC Loss to be applied on each regional entity
Drawee Entity to bear full losses for : Long Term Transactions
Injecting Entity and Drawee Entity to share losses for: Medium Term Transactions Short Term Transaction
Collective Transactions Bilateral Transactions
04/20/23 21
Case I : Intra-Regional Long Term Transactions
04/20/23 22
A
B
100 MW
92.15 MW
Zone Moderated Loss (%)
A 3
B 5
Case II : Inter Regional Long Term Transactions
04/20/23 23
B
A
Zone Moderated Loss (%)
A 3
B 5
100 MW97 MW
92.15 MW
Case III : Long Term Transactions Involving Wheeling Region
04/20/23 24
B
A
100 MW
92.15 MW
97 MW
97 MW
Zone Moderated Loss (%)
A 3
B 5
Case IV : Intra-Regional Medium / Short Term Transactions
04/20/23 25
A
B
103.09 MW
95 MW
Zone Moderated Loss (%)
A 3
B 5100 MW Contract100 MW Contract
Case V : Inter Regional Medium/Short Term Transactions
04/20/23 26
B
A
Zone Moderated Loss (%)
A 3
B 5
103.09 MW100 MW
95 MW
100 MW Contract100 MW Contract
Case VI : Medium/Short Term Transactions Involving Wheeling Region
04/20/23 27
B
A
103.09 MW
95 MW
100 MW
100 MW
100 MW Contract100 MW Contract
Thank You!