Flexible National Grid Operation

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N. Nallarasan

Senior General Manager – System Operation

National Load Despatch Centre, New Delhi

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Indian Grid…Large Footprint

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NR

WR

SR

ERNER

Ennore

KudankulamKayamkulam

Partabpur

Talcher/Ib Valley

Vindhyachal

Korba

LEGEND

Coal

Hydro

Lignite

Coastal

Nuclear

VizagSimhadri

Kaiga

Tarapur

Mangalore

Krishnapatnam

RAPP

SIKKIM

MYANM

MAR

CHICKEN NECK

Cuddalore

SRI LANKACOLOMBO

NEPALBHUTAN

DESHBANGLA

South Madras

Pipavav

Generation Load-Centre

Kolkata

Bhubaneswar

PatnaLucknow

Delhi

Mumbai

ChennaiBangalore

Bhopal

Guwahati

Jammu

Ludhiana

Jaipur

Gandhinagar

Indore

Raipur

Thiruvananthapuram

Kozhikode

Hyderabad

Coal

Hydro

Wind and Solar Courtesy: NASA

Indian Power System

• Generating Stations > 900 Nos.

• Generating Units > 2200 Nos.

• > 7000 Sub-stations,

• > 3100 transformers

• 11 Nos. HVDC Bi-pole/BtB

• > 150 nos. 765 kV lines

• > 1300 nos. 400 kV lines,

• > 3200 nos. 220 kV lines

Nepal Bhutan

Bangladesh

Myanmar

• Demand met – 182610 MW on 30th May 2019

• Energy met – 4145 MU on 30th May 2019

• Hydro Generation – 816 MU on 9th Sep 2019

• Solar Generation – 147 MU on 6th May 2019

High growth International Interconnections

Diversity of Demand and Generation

Demand variability ~ 3-5 GW/block of 15 minutesTypical Ramp Rate ~ 250 MW/min

Special Days (Festivals…) ~ 500 MW/min

Thermal

Solar

Wind

Hydro

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Ramping in All India Demand

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All India Thermal Generation

5

MW

All India Hydro Generation

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MW

Solar Generation

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Pumped Storage

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MW +gen

MW -Pump

Kadamparai

Pumped Storage Plants in India

Source: “ Large scale integration of Renewable Energy Sources-Way forward” Report by CEA

Frequency Profile over the years…

Slow Tertiary implemented from April, 2016

Maximum and Minimum Frequency patterns

Frequency Variation Index

Frequency Control Continuum in India

Pilot

Signs of Inflexibility

• Difficulty in balancing demand and supply

– Frequency excursions

• Renewable curtailment

– Inability to balance

• Area Balance Violations (Deviations)

• Electricity Markets

– Price volatility

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Source: Cochran, J. et al. (2012), “Flexibility in 21st Century Power Systems, A 21st Century Power Partnership Report”. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/docs/fy14osti/61721.pdf

Future Ready AGC for 175 GW of RE by 2022

• Forecasting of Load & RE• Use of Pumped Storage Plants• Automatic controls

EASTERN

REGION

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Region considered as an Area for secondary control

Ia = Actual net interchange, negative for NR meaning import by NR

Is= Scheduled net interchange, negative for NR meaning import by NR

Bf = Frequency Bias Coefficient in MW/0.1 Hz, positive value

Fa = Actual System Frequency

ACE positive means NR is surplus and NR internal generation has to back down

ACE negative means NR is deficit and NR internal generation has to increase

SOUTHERN

REGION

WESTERN

REGION

Eastern

REGION

NORTHERN

REGION

NORTH-EASTERN REGION

ACE = (Ia - Is) + 10 * Bf * (Fa - 50)

• Tie line bias mode and Frequency bias only mode both possible

New

Existing New

Architecture of the Project

Solar Plant AGC signal hierarchy

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Blog on zero inertia Power system by Prof. Vijay Vittalhttps://www.esig.energy/zero-inertia-power-systems/

RFA for Solar AGC Pilot project issued:https://www.gtg-india.com/work-with-us/

Tertiary ControlCues for System Operator

• Weather Forecast

• Load Forecast

• Availability of Reserves

• Monitoring of Renewables

• Outages of Transmission Lines / Generating units

• Anticipated Congestion

• Monitoring of Area Control Error (ACE)

• SCADA Visualization in Real Time

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• CERC order in Petition No. 07/SM/2018 (Suo-Motu) dtd. 16 Jul’18

– Pilot on 05-Minute Scheduling, Metering, Accounting and Settlement for Thermal/Hydro

– 26th Nov’18- Pilot on Hydro as Fast Response Ancillary Services (FRAS)

– In house Software

Fast Response Ancillary Services (FRAS)

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Sample Hydro Station Data

Security Constrained Economic Despatch (SCED)

• Objective: to minimize production cost of

Inter-State Generating Stations (ISGS)

• Pilot project on w.e.f. 1 Apr 2019

• 134 units with ~ 57 GW capacity covered

• All constraints including ramp rates, technical

minimum, transfer capability honoured

• Integration of scheduling applications at

National level with in-house developed

software

• 1-2 % saving in production cost being

observed 22

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Provisions Regarding Ramping (1)Provisions in the Indian Electricity Grid Code (IEGC):

Operating Code (Section 5.2):

System Security Aspects - Ramping of

All thermal units greater than 200 MW.

All Hydro units greater than 10 MW

Sudden change in generation / load by the utilities of more than 100 MW without prior intimation to and consent of the RLDC.

Scheduling and Despatch Code (Section 6.4)

Generators to declare rate of ramping up / ramping down in a 15 minute block.

Acceptable ramping rate – 200 MW/Hour (in NER 50 MW/Hour)

CEA Standard Technical Features of Super-Critical Units

Ramp rate: + 3% per minute (above 30% loading)

Technical minimum load of super critical units – 40%

Two shift operation mandated

Provisions regarding Ramping (2)

CERC Terms and Conditions of Tariff, 2019

Minimum ramp rate: 1% per minute for thermal ISGS

Reduction in rate of return of equity (RoE) by 0.25% for failure to provide minimum ramp rate

For providing ramp rate over 1%/min, additional rate of RoE of 0.25% allowed for every additional 1%/min

NLDC 24

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Increasing granularity of Despatch Interval

Quarter-hour vs Hourly Schedules Typical Hourly & 15-Minute Schedules

5-minute scheduling:Reduced the steep ramps

Eliminates sharp discreet changes

Reduced frequency fluctuations

Facilitates better load management

Facilitates integration of renewables

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200

400

600

800

1000

1200

1400

1600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Sch

edu

le M

W

Hour

15-Minute Schedule

Hourly Schedule

Flexibility - Ramping Requirement and Provision over the years

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Thermal Flexibility – lower turn down levels

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Simhadri Unit –1 500 MW

Grid Code 4th Amendment - 55% Technical Minimum for Central Generating Stations; effective from 15.05.17

Change in Technical Minimum from 70% to 55%

Thermal Flexibilization during Summer High Demand/Solar: May’19

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Thermal Flexibilization during High Hydro: 2014, 2016 & 2018

Dadri Thermal at High end of Merit order Stack !

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Analysis of Ramping Capability of Thermal Power Plants

Steeper net demand ramps expected in future with increasing RE

More flexibility needed from conventional generation

Attempt to quantify historical ramp rates of thermal generating units

Exhaustive report based on analysis of 7 years’ generation data of 438 units

Report released on 15th May 2019

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Hydro Flexibilization during Lean Hydro Season

2011: Flatter Hydro Curve between the peaks

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Gas Flexibilization during Summer High Demand/Solar: May’19

The gas availability is a subjective issue !

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Flexible Generation

• Hydro– Plan and implement more pumped storage

– High head stations; Pelton vs Francis turbine

– Operational norms to incentivize flexibility

• Thermal– Grid Code clauses on flexibility (ramp rate, minimum)

– Incentives for flexible generation

– Two-shift operation of thermal plants

– Primary, Secondary and Tertiary Controls

• Renewables– Low Voltage Ride Through (LVRT)

– Draft CEA standards notified33

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• HVDCs in India – 5 back to back HVDCs

– 6 bipole HVDC links

– 1 MTDC

– 1 more planned

• CEA Transmission Planning Criterion (Section 18)

– More than 2000 MW over long distance more than 700 km.

– Corridors of AC lines carrying heavy power flows (total more than 5000 MW)

Flexible Transmission

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Way Forward

Power systems are already flexible, designed to accommodate variable and uncertain load.

New actors RE, distributed generation, storage etc. to be accommodated

Need for ‘Flexible’ Systems

Flexible Generation

Flexible Transmission – FACTs, HVDC

Flexible Distribution – Price responsive demand

Flexible Markets -

More Frequent market operation, Ancillary services, Demand response

Policy / Regulatory Framework for Flexibility

Measuring Flexibility

Metrics for performance

Incentivizing and paying for flexibility

Policy support to anticipate flexibility needs and support system flexibility

Flexibility considerations can be integrated into the design of procurement policies

POSOCO 36

Thank You