Sharing of Inter-State Transmission Losses

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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

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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

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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.

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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.

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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 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

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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)

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  

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 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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Loss Sharing Mechanism

04/21/23 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 %)

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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 +∑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.

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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

Collective Transactions Bilateral Transactions

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Case I : Intra-Regional Long Term Transactions

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A

B

100 MW

92.15 MW

Zone Moderated Loss (%)

A 3

B 5

Case II : Inter Regional Long Term Transactions

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B

A

Zone Moderated Loss (%)

A 3

B 5

100 MW97 MW

92.15 MW

Case III : Long Term Transactions Involving Wheeling Region

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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

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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

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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

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B

A

103.09 MW

95 MW

100 MW

100 MW

100 MW Contract100 MW Contract

Thank You!