Transcript Congestion

Congestion
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When transmission demand >capability
When Voltage levels in a corridor beyond operable limits
When Real time line flow exceeds the TTC
Most fundamental transmission management problem
A natural corollary of growth
Occurs in deregulated markets
Commercial signal to Tr. Requirement
N-1 Planning
System security at stake
POWER SYSTEM DE-REGULATION
(RESTRUCTING)
GENCO
GENCO
GENCO
GENCO
GENCO
Tie Lines
TRANSCO
TRANSCO
DISCO
DISCO
TRANSCO
DISCO
DISCO
DISCO
Deregulation or Restructuring denotes breaking up of the
Vertically Integrated Utility(VIU) structure into Competitive
Market Entities.
RESTRUCTURED ELECTRICAL
INDUSTRY
ENTITIES RESULTING FROM DEREGULATION
SO
GENCO
TRANSCO
DISCO
SO is the Power System Operator and the Power Market
Operator, which may include other entities depending on the
market structure. SO, is independent of the other entities
8.0 CASE STUDY OF COGESTIO EXPERIECED O 12-12-2008:
• Due to early morning fog, Talcher-Kolar HVDC had to be operated in
reduced voltage mode resulting in a reduction of the total transfer
capability to 3600 MW from 4000 MW between 0400 Hrs to 0900
Hrs of 12-Dec-2008.
• After accounting for reliability margin, long term transactions and
already approved bilateral transactions, available margin on ER-SR
path was 617 MW and on WR-SR path, available margin was about
490 MW during this period
• Based on the provisional solution received from the Power
Exchanges for the period 0500 Hrs to 0600 Hrs, it was observed that
the total requirement of both Exchanges was more than total import
margin of Southern Grid.
• Accordingly available margin for each Exchange was calculated on
pro-rata basis. The market was split in both the Power Exchanges
and the flow was restricted to the available capacity in the final
solution.
• As against a total provisional requisition of 1430 MW for import to
Southern Grid, 1091 MW was cleared in the final solution
Congestion management methods
• Cost free methods (Physical)
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Generation/ Load Control
Network Reconfiguration (Parallel Paths, Loops)
FACTS/ FSC ETC
Voltage improvement
• Non-cost free methods (Commercial )
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Rescheduling of transactions
Curtailment
Imposition of Congestions charge
Ancillary Services
Congestion occurance
• Real Time :
– Inadequate system conditions
– Temporary outage of Tr. Line / Generator/
Load
• Ex-ante (before fact):
– More transactions by a far end Consumer
– Seasonal skew in L-G balance
– More demand for transmission corridor
Congestion mitigation
• Stage 1 : Ex-ante (before fact):
– Bidding for transmission corridor (for bilateral
trnasactions)
– Market Split (for Collective transactions)
• Stage 2 : (Real time)
– Impose Congestion charges on UI
• Stage 3 : (Real time)
Curtailment of STOA/ Collective/ MTOA/ LTA
Pre-requisites
• Observability of Grid (SCADA)
• Scheduling mechanism
• EMS tools (Contingency Analysis, Security
Constrained Dispatch)
• Commercial Mechanism
Congestion management in India
• Congestion charges in NR @Rs.3/u for OD from 2007
• Congestion Regulations (CERC) w.e.f. 11.06.10
• congestion charge shall be applied as a commercial
measure.
• The congestion charge will be payable by a Regional
entity or entities causing congestion in the inter-regional
link or intra-regional link
• and receivable by a Regional entity or entities relieving
congestion.
• In addition to the Unscheduled Interchange charges
Measures to mitigate Congestion
• Declare ATC by NLDC/ RLDCs / for Inter
Regional/ Intra regional and each control area
• Congestion charge imposed on only Deviations
from schedules
• Rate of congestion charge : Rs.5.45/u
• Notice of
– 2 time blocks for imposing
– 1 time block for lifting congestion charge
– At frequency below 50 Hz, congestion charge would
be levied for
• over drawal or under-injection in the importing control area
• under drawal or over-injection in the exporting control area.
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NLDC/ RLDC display the TTC, ATC,
Actual flow on the congested corridor on
common SCADA display
• No congestion charges if congestion is
due to outage of a transmission line in the
corridor, but schedules are maintained
• In such case, curtailment of STOA/ MTOA
and then LTA
REAL TIME CONGESTION MANAGEMENT
• In case of transmission constraint or threat to
grid security, the scheduled transactions may be
curtailed in the manner as decided by the NLDC
/RLDCs / SLDCs to relieve the transmission
constraint/ to improve grid security.
• Collective Transaction through Power
Exchange(s) would normally be curtailed
subsequent to the Short-Term Bilateral
Transaction(s).
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RLDCs would curtail a Transaction at the periphery of the Regional
Entities. SLDC(s) shall further incorporate the inter-se curtailment of
intra-State Entities to implement the curtailment.
• In case of curtailment of a Transaction caused by transmission
constraints
/ threat to grid security, the Transmission Charges in respect of such
• Transaction shall be payable on pro-rata basis in accordance with
the finally Implemented Schedules. Operating Charges shall not be
revised in case of curtailment.
Power Exchange (s) shall be responsible for the settlement on
account of curtailment, directly with its participants.
• NLDC/RLDCs/SLDCs shall interact only with the respective Power
Exchange(s), for the same
• Payment /receipts though Congestion
charge a/c
• Utilization of fund for studies, SPS, Shunt
capacitrs
Congestion Charge Imposition
Upstream
O/D &U/G relieve
U/D & O/G aggravate
O/D &U/G receive charges
U/D & O/G pay charges
Downstream
U/D & O/G relieve
O/D &U/G aggravate
U/D & O/G receive charges
O/D &U/G pay charges
Congestion accounting
• NLDC/ RLDC provide
– From/To time block
– corridor
– and Upstream /downstream entities
details to RPCs on a weekly basis when
congestion charge is kicked along with
reasons
• RPC to issue congestion account along
with UI accounting