Congestion Management

Workshop organized at SRPC28th May 2013

Bengaluru

Outline

• Congestion definitions• Congestion Management in different time horizons

– Long term– Medium term– Operational Planning– Real time

• CERC procedure on congestion charges in real time

Pillars of Market Design

Sally Hunt – ‘ Making Competition Work in Electricity’

Congestion in Power System

“Congestion is a situation where the demand for transmission capacity exceeds the

transmission network capabilities, which might lead to violation of network security limits,

being thermal, voltage stability limits or a (N-1) contingency condition.”

CIGRE_WG_C5.04_TB_3014

Indian Electricity Grid Code 2010

• ‘Congestion’ means a situation where the demand for transmission capacity exceeds the Available Transfer Capability;

First formal definition of congestion in power system in our statute wef 3rd May 2010!!!

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Visibility of congestion

• Visible to the market players– “If for a given interconnection, there is more demand for cross

border capacity than commercially available, the interconnection is also treated as congested, meaning no additional power can be transferred. This congestion is visible for market players as a limit on their cross-border transactions.”- CIGRE_WG_C5.04_TB_301

• Invisible to the market players– “It is possible that even though the available commercial

interconnection capacity is not fully allocated to market players, some lines, being internal or cross-border, become overloaded. This physical congestion is a problem of the System Operator and has to be dealt with by this entity.” CIGRE_WG_C5.04_TB_301

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To be handled before-the fact

To be handled in real-time

Congestion visible to the market• “The more transactions and the more meshed the

network, the higher the chance for mismatch between commercial exchange and physical flows.” CIGRE_WG_C5.04_TB_301

Congestion Sign of growth and vibrant market Natural corollary to Open Access

Existing transmission system was not planned with short-term open access in mind

Security margins have been squeezed ‘Pseudo congestion’ needs to be checked

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Real-time Congestion types

• Internal congestion (Intra-zonal)– Within a single System Operator’s control area

• Cross-border (Inter zonal)– Also called seams issue– Several System Operators involved

Was not experienced -Regional grids were small- Trades were limited

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Experienced occasionally under- Grid Contingencies

- Skewed conditions in gridAggressive Open Access trades

Open Access Theory & PracticeForum of Regulators report, Nov-08

“For successful implementation of OA, the assessment of available transfer capability (ATC) is very important. A pessimistic approach in assessing the ATC will lead to under utilisation of the transmission system. Similarly, over assessment of ATC will place the grid security in danger.”

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Declaration of Security Limits

• “In order to prevent the violation of security limits, System Operator SO must define the limits on commercially available transfer capacity between zones.” CIGRE_WG_C5.04_TB_301

• “System Operators try to avoid such unforeseen congestion by carefully assessing the commercially available capacities and reliability margins.” CIGRE_WG_C5.04_TB_301

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Cross border capacity available for trade

• “Physical capacity connecting zones A and B is sum of 1-3 and 2-3 physical line capacities. However, the cross border capacity available for commercial trade would be less or at most equal to the sum of capacities of cross border lines individually.” CIGRE_WG_5.04_TB_301

1

2

3

A B

12

13

Intra-day STOA

Day-ahead STOA

Collective (PX) STOA

First Come First Served STOA

Advance Short Term Open Access (STOA)

Medium Term Open Access (MTOA)

Long Term Open Access (LTOA)

Reliability Margin (RM)

Available Transfer Capability is

Total Transfer Capability less Reliability Margin

TTC ATC

RM

Diagram- Europe

POWERGRID 14

NTC map for season: Winter 2008/2009

Gross Transmission Capacity (GTC) vis a vis Net Transmission Capacity (NTC) in Europe

Corridor GTC NTC Difference NTC/GTC (%)France to United Kingdom 2000 2000 0 100%United Kingdom to France 2000 0 2000 0%Denmark (East) to Sweden 2010 1700 310 85%Sweden to Denmark (East) 2010 1300 710 65%Italy to Slovenia 2017 480 1537 24%Slovenia to Italy 2017 380 1637 19%Austria to Hungary 2124 500 1624 24%Hungary to Austria 2124 200 1924 9%Sweden to Finland 2230 1800 430 81%Finland to Sweden 2230 1600 630 72%Czech Republic to Austria 2249 600 1649 27%Austria to Czech Republic 2249 0 2249 0%Italy to Austria + Slovenia 2274 0 2274 0%Lituania to Kaliningrad 2287 700 1587 31%Slovakia to Hungary 2492 1100 1392 44%Hungary to Slovakia 2492 200 2292 8%Poland to Slovakia 2504 750 1754 30%Slovakia to Poland 2504 750 1754 30%

Courtesy:ENTSOE 15

NTC Vs GTC Among EU CountriesFor Corridors Up to 1000 MW

NTC Vs GTC Among EU CountriesFor Corridors Up to 5000 MW

NTC Vs GTC Among EU CountriesFor Corridors Up to 16000 MW

Gross Total Capacity & Net Transfer Capability Among EU Countries

y = 0.21x

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000

Gross Total Capacity (MW)

Net

Tra

nsfe

r Cap

abili

ty (M

W)

~ 21%

NTC As % of GTC Among EU Countries

Transmission Capacity ( TC ) vis-à-vis Available Transfer Capability ( ATC ) in Brazil

TRUNKTC

( MW )ATC

( MW ) ATC/TC(%)

North - Southeast/Midwest Interconnection

( from North to Southeast)

4200

n-1 3400 81

n-2 1700 40

WITH SPS 4100 98

North - Southeast/Midwest Interconnection

( from Southeast to North )n-1 3000 71

Foz do Iguaçu – Ivaiporã765 kV trunk 6450

n-2 3600 56

WITH SPS 5300 82

Southeast/Midwest - South Interconnection 17180 n-2 9500 55

440 kV trunk feeding São Paulo 14500

n-2 9600 66

WITH SPS 10200 70

20Courtesy: ONS Brazil

Handling congestion in different time horizons• Long term planning……….3-5 years time frame

– Several scenarios and uncertainties to be factored– Probabilistic vs deterministic– High Impact Low probability events– Operational feedback by NLDC/RLDCs as per

section 4j of NLDC Rules 2005. http://www.posoco.in/documents/operational-feedback

Handling congestion in different time horizons• Medium term planning……….0-3 years time

frame– Network augmentation difficult– Temporary re-configuration of network possible– Pro-rata still the main method in Medium Term

Open Access (MTOA)• Auctions another possibility

Lanco Amarkantak (2 x 300 MW)

400 kV Lanco to Sipat section used to constraint West to East TTC

Lanco Amarkantak (2 x 300 MW)

Contingency Arrangement Implemented in May 2010

Contingency arrangement at CGPL Mundra in 2011

Single line sketch showing proposed bunching arrangement for Bhachau to Vadavi & Chorania D/C TL

D/C CGPL

Mundra

400 kV

Bhachau S/S

PGCILS/C S/C

400 kV 25 km 400 kV

Chorania S/S D/C Bunching point D/C Vadavi S/S

GETCO 192 kms 257 kms GETCO

400 kV Maithon-Koderma arrangement

• Final arrangement– 400 kV Maithon- Gaya D/C (Quad)– 400 kV Koderma-Gaya D/C (Quad)– Forest clearance and ROW problem near Gaya

• Interim arrangement– 400 kV Maithon-Koderma D/C

Benefit

• Reduction in flow of 400 kV Kahalgaon-Biharsariff D/C and Kahalgaon–Banka-Biharshariff D/C, which is a constraint for ER-NR TTC

• Enhancement of ER-NR TTC.

Congestion in Operational Planning horizon

• Priority based rules• Pro-rata rationing• Auctioning

– Explicit Auction…………e-bidding under STOA– Implicit Auction…………Power Exchange Day Ahead

– Hybrid

• Market splitting• Market coupling

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Congestion Management Lessons learnt in Indian context

• Firmness in STOA schedules– “Use it or Lose it”

• Valuing transmission instead of pro rata

• Market splitting

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Congestion Management in real time– Classical

– Compliance to Standards and Grid Code– Topology change– Re-dispatch– Curtailment

– Market based– Commercial signals (Congestion Charge)– Ancillary Market

• Out of merit generation scheduled to pool• Reactive power charge- synchronous condenser operation

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Congestion Management in real time

• Counter trading• Re-dispatching (Out of merit generation)• Locational Marginal Pricing (LMP)

λnode = λ deviation price + λcongestion charge + λlosses

• Transmission Loading Relief (TLR)All these methods would result in significant rise in total cost. “Price for system security”

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Regulatory initiatives• Modifications in Grid Code & other regulations

– Frequency band tightening – Cap on UI volume, Additional UI charge– Inclusion of new definitions (TTC, ATC, Congestion)

• Congestion Charge Regulation– Congestion Charge Value, Geographical

discrimination – Procedure for Assessment of Transfer Capability– Procedure for Implementation of Congestion Charge

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Congestion charges in real time……..CERC orders

• Order dated 7th Nov 2007 in petition no 116/2007– Congestion charges @300 paise/kWh for Northern region– Flexibility given to NRLDC– Irrespective of frequency– Applied on two occasions in NR.

• Regulations dated 22nd Dec 2009 on congestion charges in real time– Procedure approved by CERC vide order dated 11th June 2010– Modified procedure ordered on 22nd April 2013

Imposition of Congestion Charge in NR on 31st Jan-08

1400 hrs0945 hrs 1930 hrs

Antecedent condition31st Jan-08

Morning hours

Congestion Charge

1400 hrs0945 hrs 2000 hrs

Improvement in voltage profile subsequent to imposition of

congestion charge

31st Jan-08, 1400 hrs- 1830 hrs

Imposition of Congestion charge in NR15th September 2008, 0300 hrs to 0800 hrs

Exactly a week later, NTPC Dadri complex plus HVDC Rihand Dadri bipole tripped During night hours. Low load conditions in NR averted a major blackout.

Comments on congestion charge procedure submitted to CERC in

Jan/Feb 2010

Congestion alleviation

Gen: G2

Load: P2

Gen: G1

Load: P1

Downstream system

Upstream system

Line flow = (G1 – P1) OR (P2 – G2)

For congestion alleviation viz. reducing flow on the lines connecting the two systemsboth upstream and downstream actionsare required for maximum benefitconsidering thefrequency dependence on load

Congestion alleviation –only upstream actions

Gen: G2

Load: P2

Gen: G1

Load: P1

Downstream system

Upstream system

Line flow = (G1 – P1) OR (P2 – G2)

For a reduction of generation ∆ Pin upstream system,

the line flow would reduce by

∆ P ( P2 )(P1 + P2)

Congestion alleviation – only downstream actions

Gen: G2

Load: P2

Gen: G1

Load: P1

Downstream system

Upstream system

Line flow = (G1 – P1) OR (P2 – G2)

For a reduction of load ∆ Pin downstream system, the line flow would reduce by

∆ P ( P1 )(P1 + P2)

Congestion alleviation – both upstream and downstream actions

Gen: G2

Load: P2

Gen: G1

Load: P1

Downstream system

Upstream system

Line flow = (G1 – P1) OR (P2 – G2)

For a reduction of generation and load ∆ Peach in upstream and downstream system, the line flow would reduce by

∆ P

Relative size of systems

Downstream system

Upstream system

If upstream system is very smallcompared to the downstream system maximum benefit accrues from generation reduction upstreamviz. actions in the smaller sub-system

Relative size of systems

Downstream system

Upstream system

If downstream system is very smallcompared to the upstream system maximum benefit accrues from load reduction downstreamviz. actions in the smaller sub-system

CONGESTION MANAGEMENT PROCEDURES :: -REV-1 DTD.22/04/13

• Deviations w.r.t Procedure: -Rev-0 Dtd.05/04/10

• Congestion charge procedure: - Declaration

- Applicability

Areas under which modifications have been carried out

• Methodology for assessment of TTC/TRM/ATC

• Declaration of congestion in real time

• Applicability of congestion charge

Declaration of Congestion in real time-Procedures

• 5.1. SLDCs/ RLDCs/ NLDC shall have a display available in their web-sites showing TTC, TRM, ATC declared in advance. Real time power flow in the corridor for which TTC has been declared shall be displayed alongside for comparison. The voltage of the important nodes in the grid downstream/ upstream of the corridor shall also be displayed(Format II)

• 5.2. A corridor shall be considered congested under the following circumstances:

• 5.2.1. Grid voltage in the important nodes downstream/ upstream of the corridor is beyond the operating range specified in the IEGC and/or

• 5.2.2. The real time power flow along a corridor is such that n-1 criteria may not be satisfied.

• 5.2.3. One or more transmission lines in the corridor are loaded beyond the normal limit specified in CEA Manual on Transmission Planning Criteria.

Declaration of Congestion in real time-Procedures

• 5.3. Whenever actual flow on inter/ intra regional link/ corridor exceeds ATC and security criteria as mentioned in clause 5.2 above are violated RLDC, NLDC may issue a warning notice. In case SLDC observes congestion within the intra State grid it shall inform the respective RLDC which in turn shall inform the NLDC. The notice for congestion shall be communicated to all the Regional entities telephonically or through fax/ voice message/ e-mail and through postings on website and making the same available on the common screen at NLDC/ RLDCs/ SLDCs. The format of the notice is enclosed as Format III.

• 5.4 If the power flow on the corridor is as per the schedule, but the congestion has been caused by forced outages of a transmission line in the corridor, which occurs after the drawal schedule has been fixed, then open access transactions shall be curtailed in the priority given in the Central Electricity Regulatory Commission (Grant of Connectivity, Long-term Access and Medium-term Open Access in inter-State Transmission and related matters) Regulations, 2009 followed by revision of TTC, TRM and ATC.

Declaration of Congestion in real time-Procedures

• 5.5 If the power flow on the corridor is as per the schedule and the corridor is congested due to either of the circumstances mentioned in clauses 5.2.1 and 5.2.3 of this procedure then TTC, TRM and ATC shall be revised accordingly.

• 5.6 If violation of TTC limits persists for 2 time-blocks not counting the time-block in which warning notice was issued by RLDC and no affirmative action is taken by the defaulting agency, NLDC/ RLDC(s) shall issue a notice for application of congestion charge. This notice shall be communicated to all the concerned Regional entities telephonically or through fax message and through postings on website and the same shall also be made available at the common screen at NLDC/ RLDCs/ SLDCs. The format is enclosed as Format-IV.

Declaration of Congestion in real time-Relevant Modifications

• 5.2.2:The real-time power flow along a corridor exceeds the ATC for that corridor for continuously one time block of 15-minute

-deleted under points for consideration of corrridor congestion• The real time power flow along a corridor is such that n-1 criteria may not be

satisfied.-modified clause

• 5.6:If congestion persists for 2 time-blocks not counting the time-block in which warning notice was issued by RLDC and no affirmative action by the defaulting agency is taken, NLDC/ RLDC(s) shall issue a notice for application of congestion charge. This notice shall be communicated to all the concerned

-deleted under applicability of congestion where ATC was meant• If violation of TTC limits persists for 2 time-blocks not counting the time-block

in which warning notice was issued by RLDC and no affirmative action is taken by the defaulting agency, NLDC/ RLDC(s) shall issue a notice for application of congestion charge.

-inserted clause

Applicability of Congestion Charge-Summary

• 6.1. Congestion Charge –Rs.5.45/- per unit(not defined in the procedures)• 6.2. Congestion charge would be levied for• a) over drawal or under-injection in the importing control area and• b) under drawal or over-injection in the exporting control area.• 6.3. Congestion charges may also become applicable for an intra-regional

corridor of one region, if the congestion is attributable to other regional entities of other region.

• 6.4. Congestion charge shall be applicable only after two time blocks from the time of issuing the notice, not counting the time block in which notice is issued.

• 6.5. Congestion charge shall be withdrawn after the power flow on the affected transmission link/ corridor has come down to the ATC and remains at this level for one time block. NLDC/ RLDC shall communicate to all concerned Regional entities telephonically or through fax message/ e-mail and through postings on website and making available the same on the common screen available at NLDC/ RLDCs/ SLDCs for lifting of congestion charge. The format of the notice is enclosed as Format-V.

Applicability of Congestion Charge-Relevant Modifications

• 6.2:At frequency below 50 Hz, congestion charge would be levied for over drawal or under-injection in the importing control area and at frequencies above 50 Hz, congestion charge would be levied for under drawal or over-injection in the exporting control area

-deleted under applicability of congestion charge

• 6.2:Congestion charge would be levied fora) over drawal or under-injection in the importing control area andb) under drawal or over-injection in the exporting control area.

-inserted

• Minor changes in format-I

Methodology for TTC/RM/ATC computation-Relevant Modifications

• 3.6.9:Normal operating limit for an Inter connecting transformer shall be 90 % of its Maximum Continuous Rating (MCR)

-deleted• 3.6.9Permissible Normal and emergency limits for transmission elements shall be

as defined in the (CEA Manual on Transmission Planning Criteria).-final clause

• 3.9During assessment of Total Transfer Capability it shall be ensured that:• 3.9.1. All transmission element loadings in the base case are within normal

operating limits and the voltages remain within operating range defined in the IEGC.

• 3.9.2. All transmission element loadings after a credible contingency are within emergency ratings and grid voltage is within the operating range as defined in the IEGC.

-deleted • 3.9:During assessment of Total Transfer Capability it shall be ensured that the

conditions specified in CEA Manual on Transmission Planning Criteria are met after credible n-1 and n-1-1 contingencies.

-final clause

Methodology for TTC/RM/ATC computation-Relevant Modifications

• 3.10.4: Stability under n-1-1 contingency of a temporary single phase to ground fault on a 765 kV line close to the bus or a permanent single phase to ground fault on a 400 kV line close to the bus

• 3.10.5:Angular difference of 30 degrees between adjacent buses under n-1 contingency

-additional insertion

• 3.11.2: Single largest anticipated in feed into the control area/ group of control area (which could be a combination of States for the purpose of Power Exchange and for others)/ region.

-deleted under basis of TRM computation

Thank You