Sharing of Inter-State Transmission
Losses
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Introduction
 Losses are physical phenomenon while transportation
of electric energy from generation to load
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Fixed losses
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Variable losses (I2R)
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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
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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.
Thus generally losses proportional to load and distance of
transportation
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Introduction
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Development of ISTS system
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Treatment of losses
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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
Individual line losses
Associated Transmission losses with individual generator
Pooled losses
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Introduction
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Sharing of Transmission losses
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Inter-regional Transactions:
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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
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.
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Introduction
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Other changes
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Sharing of losses for some state networks
 In schedules….. SR
 In actuals… NR
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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.
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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
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International Practices Prevalent
 Losses settled
 Paid
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Settled
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Fixed and variable(based on location, season, time of the day)
Paid based
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Only drawee
Both injector and drawee
 In some adhoc ratio 50:50 or 45:55
Loss allocation factors may have two component
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For each balancing period
on daily, weekly or yearly
Paid by
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In kind
In Money
on after the fact
on figures declared upfront
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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)
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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
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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
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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.
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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.
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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.
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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
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Some further References
 IEEE Trans Power System pp631-637 May 2000 A Physical flow
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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.
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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.
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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
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PoC Loss Computation (1)
 Computation of changes in losses in the system due
to incremental injection / withdrawal at each node.
 Loss Allocation Factor
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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
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NRLDC
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Loss Sharing Mechanism
Calculation of
Previous week
Losses from
SEM Data
Total Losses
based on PoC
Software
Provided by
CERC
Zonal Losses
as Computed
from Hybrid
Method
Moderation Of PoC Losses
Total Losses
(50% PoC+50%UC)
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NRLDC
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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 %)
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 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 +∑Interregional 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.
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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
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Collective Transactions
Bilateral Transactions
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Case I : Intra-Regional Long Term Transactions
Zone
Moderated
Loss (%)
A
3
B
5
B
A
92.15 MW
100 MW
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Case II : Inter Regional Long Term Transactions
Zone
A
B
Moderated
Loss (%)
3
5
B
92.15 MW
A
97 MW
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100 MW
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Case III : Long Term Transactions Involving
Wheeling Region
Moderated
Loss (%)
Zone
B
A
3
B
5
92.15 MW
97 MW
A
97 MW
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100 MW
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Case IV : Intra-Regional Medium / Short Term
Transactions
Zone
100 MW Contract
Moderated
Loss (%)
A
3
B
5
B
95 MW
A
103.09 MW
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Case V : Inter Regional Medium/Short Term
Transactions
Zone
100 MW Contract
A
B
Moderated
Loss (%)
3
5
B
95 MW
A
100 MW
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103.09 MW
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Case VI : Medium/Short Term Transactions
Involving Wheeling Region
100 MW Contract
B
95 MW
100 MW
A
100 MW
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103.09 MW
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Thank You!