NLDC 1

Congestion Management In Real Time

NLDC

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Outline Overview

Causes of Congestion

Congestion in Indian Context

Measures to Relieve Congestion

Regulatory Initiatives

International Experience

Discussion

Congestion Definition

“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_5.04_TB_301

“Congestion” means a situation where the demand for transmission capacity exceeds the Available Transfer Capability (ATC)…..CERC regulation

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Unique Characteristics of Indian Power System Floating Frequency Band (49.2 Hz – 50.3 Hz)

Availability Based Tariff (Unscheduled Interchange)

Weak/Absent Primary Response (FGMO) Continuous Fluctuation of Frequency

Absence of Automatic Generation Control (AGC) by Design

Inadequacy : Generation & Transmission

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Causes of Congestion in Real Time Different from congestion in STOA

Deviation from planned activities

Large interconnected grid Fast growing network Coupling between voltage and frequency accentuates the problem

in a large grid Skewed scenarios

Weather diversity, seasonal demand variation

Interplay with UI mechanism

Load- Generation Imbalance Tie line outage

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Area A Area B

Area A importing from Area B

Scenarios

4D

3D 1S

2D 2S

1D 3S (Congestion)

4S

Skewed Load-Generation Balance

SR

ER+NER

WR

NR

D=> Deficit Region S=> Surplus Region

Seasonal Variation in Power Flow Patterns

NR

WR

ERNER

SR

Bhutan

Scenario-1: Normal Monsoon

NR

WR

ERNER

SR

Bhutan

Scenario-2: Low Load in NR

NR

WR

ERNER

SR

Bhutan

Scenario-3: Low Load in WR

NR

WR

ERNER

SR

Bhutan

Scenario-4: Peak winter

FLOWGATESNR:

Central UP-Western UP

UP-Haryana/Punjab

WR:

Chandrapur-Padghe

Chandrapur-Parli

Bina-Gwalior

Soja-Zerda

SR:

Vijayawada-Nellore

Hossur-Selam

Gutty-Neelamangala

Gutty-Huddy

ER:

Farakka-Malda

Malda-Purnea

Talcher-Rourkela

Jamshedpur-Rourkela

Farakka-Kahalgaon

Kolaghat-Baripada-Rengali

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Measures to Relieve Congestion in Real Time Hydro Rescheduling HVDC set points Topology Change Instructions/ Messages Commercial Mechanisms

Congestion Charge Ancillary Services Counter Trade

Curtailment

Relevant IEGC clauses (1) Clause 5.4.2

(a) …”As mentioned elsewhere, the constituents shall endeavour to restrict their net drawal from the grid to within their respective drawal schedules whenever the system frequency is below 49.5 Hz. When the frequency falls below 49.2 Hz, requisite load shedding (manual) shall be carried out in the concerned State to curtail the over-drawal.”

(b) …” Further, in case of certain contingencies and/or threat to system security, the RLDC may direct an SLDC to decrease its drawal by a certain quantum. Such directions shall immediately be acted upon.”

(c)…” Each Regional constituent shall make arrangements that will enable manual demand disconnection to take place, as instructed by the RLDC/SLDC, under normal and/or contingent conditions. ”

(d)…” The measures taken to reduce the constituents’ drawal from the grid shall not be withdrawn as long as the frequency/voltage remains at a low level, unless specifically permitted by the RLDC. ”

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Relevant IEGC clauses (2)

Clause 6.4.12 “However, notwithstanding the above, the RLDC may direct

the SLDCs/ISGS/other regional entities to increase/decrease their drawal/generation in case of contingencies e.g. overloading of lines/transformers, abnormal voltages, threat to system security. Such directions shall immediately be acted upon. In case the situation does not call for very urgent action, and RLDC has some time for analysis, it shall be checked whether the situation has arisen due to deviations from schedules, or due to any power flows pursuant to short-term open access. These shall be got terminated first, in the above sequence, before an action, which would affect the scheduled supplies from ISGS to the long term customers is initiated..”

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Relevant IEGC clauses (3) Clause 6.5.18

In the event of bottleneck in evacuation of power due to any constraint, outage, failure or limitation in the transmission system, associated switchyard and substations owned by the Central Transmission Utility or any other transmission licensee involved in inter-state transmission (as certified by the RLDC) necessitating reduction in generation, the RLDC shall revise the schedules which shall become effective from the 4th time block, counting the time block in which the bottleneck in evacuation of power has taken place to be the first one. Also , during the first, second and third time blocks of such an event, the scheduled generation of the ISGS shall be deemed to have been revised to be equal to actual generation, and the scheduled drawals of the beneficiaries shall be deemed to have been revised to be equal to their actual drawals.

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CERC(Measures to relieve congestion in real time operation) Regulations, 2009 NLDC to assess TTC, ATC and TRM of inter-regional

corridors in consultation with RLDCs RLDCs to assess TTC, ATC and TRM of regional

control areas Availability in public domain Provision of revision Charge both payable and receivable Warning notice and application of congestion charge Withdrawal of congestion charge Congestion charge account

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Rate of Congestion Charge Order

Rate of Congestion Charge – Rs 5.45/kWh Rate higher than the difference between maximum UI

charge and UI charge at 50 Hz Application of congestion charge

Below 50 Hz – downstream overdrawing entities Above 50 Hz – upstream underdrawing entities

Congestion caused by forced outage of a line in a corridor (after finalisation of drawl scheduled) No congestion charge shall be levied Provided the power flow on the corridor is as per the

schedule Such contingencies to be tackled through emergency

instructions by concerned SLDCs/RLDCs/NLDCs

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Real Time Congestion Management

Procedure

Prepared in compliance to Section 4(2) ofThe Central Electricity Regulatory

Commission(Measures to relieve congestion in real time

operation)Regulations, 2009

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Transfer Capability Assessment

Total Transfer Capability Simulation Studies for Assessment

Network Modeling Input data for Basecase Preparation Operating and Emergency Limits Limiting Conditions

Basecase Violations (N-1) contingency Violations

Transmission Reliability Margin (TRM) Available Transfer Capability Import and Export Capability

Declaration of Congestion

Congestion in Real Time Voltage violations ATC violation in a corridor High loading of transmission elements

ATC violation for 2 time blocks – warning notice by NLDC

Curtailment of open access transactions Revision of Transfer Capability Application of Congestion Charge

Congestion persists after issuance of warning notice No affirmative action by defaulting agency foreseen

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Applicability of Congestion Charge

Applied simultaneously upstream and downstream

Applicable after 2 time blocks from notice

Remain in force for atleast 8 time blocks

Maximum upto 4 times a day

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Thank you !!