Under changing scenario of more and more Renewable Energy Penetration replacing conventional rotating electric power sources is leading to gradual diminishing of inertia of system that is often required to maintain stability of power system. The work is aimed at determining of inertia at various points of the system under different loading condition to take care of the system security.

1. Shailendra Verma
Grid Controller of India limited
INDIA
skverma@grid-india.in
Inertia in Indian Grid with Increasing Renewable
Penetration – Modelling and Experience
1
Authors:
K.V.N. Pawan Kumar, S R Narasimhan
Sudhanshu S. Barpanda, Debasis De,
Rajiv K Porwal, Samir C. Saxena,
Vivek Pandey, Rahul Shukla, Aman Gautam,
Shailendra Verma, Subrata Mukhopadhyay
23PESGM4448

2. people served
4.5 GW+
~417 GW
generation capacity
220 GW+
peak demand
> 4.5 TWh
daily energy met 468,977 ckm+
EHV transmission
1.3 Billion+
international exchanges
~173 GW
renewables
(including large Hydro)
14+
HVDCs
3.2 million km²
area footprint
3
power exchanges
~ 120 GW
Operating frequency band
49.90 -50.05 Hz
inter-regional capacity
2
Indian Grid: Overview
74 % Synchronous
Capacity

3. Frequency Profile during major imbalance
events ( PMU based data resolution 40 msec)
Generation Loss:5350 MW
Frequency dropped by 0.48 Hz in
15 seconds
Cascading Effect resulted in Tripping at Multiple Stations
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Outage of 765 kV Substation &
Outage of 6 number of 765 kV EHV line on OV
Generation Loss:7000 MW
AUFLS operated in the event (Freq. ~ 49.4 Hz)
15th May 2023
Frequency dropped by 0.58 HZ

4. 4
ROCOF of 7000 MW Generation loss event

5. Computation of RoCoF from frequency measurements through PMU
Raw data Filtered Data
Average Frequency
Identified Window
curve fitting method for 5th order
polynomial first order coefficient as
initial RoCoF
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ROCOF

6. Calculations of Inertia &
Power Number for a sample event
Initial Frequency (Hz) 49.885
All India Generation (From NLDC SCADA) (MW) 144482
Actual Generation Loss (SCADA) (MW) 780
Calculated ROCOF from Avg Frequency (Hz/s) * 0.0167
Estimated inertia (sec) 8.06
Nadir Frequency (Hz) 49.804
Time to Reach Nadir Frequency (sec) 10.6
Frequency Drop (Hz) 0.0810
Power Number =∆𝑃/∆𝑓 (MW/Hz) 9626.65
*Captive power generation is not under monitoring in India at National/Regional Control centre which ranges
from 10-15 % of total generation.
*Utilisation of monitored MW in place of MVA base in calculation of inertia.
2𝐻
𝑓0
𝑑𝑓
𝑑𝑡
=
𝑃𝑚 − 𝑃𝑒
𝑆
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7. Generation Loss vs calculated RoCoF
Slope is likely to decrease in case of improvement in governor response
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8. Inertia Estimation Results
The Indian power system inertia has varied between 5 to 9 Seconds between Jan 2014-May 2023.
The mean value of inertia is 6.5 seconds.
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9. Inertia with RE penetration
System is becoming lighter with the increase in RE penetration
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10. Kinetic energy based on survey on sources of inertia
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11. All INDIA - Frequency Response Characteristic
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Increasing trend infers Increasing System Strength
FRC calculation for any load or generation loss incident involving net
change of more than 1000 MW or a frequency change 0.1 Hz or more.

12. Challenges in measurement based
inertia estimation
RoCoF values reported by PMU not suitable
Important to avoid initial transient phase in calculations
RoCoF values required at t=0+
Identification of suitable moving average window
Assigning proper weightage to respective location frequency
Identifying appropriate event for inertia estimation (sequential or aggregate)
Factoring Primary response
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13. Flow chart for
online inertia
estimation
𝐻𝑠𝑦𝑠 =
σ𝑖=1
𝑛
𝑆𝑖 ∗ 𝐻𝑖
σ𝑖=1
𝑛
𝑆𝑖
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Online inertia monitoring using SCADA

14. Inertia Monitoring at National level
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15. Inertia Monitoring at Regional level
Capacity on Bar (MVA)
System Inertia of Northern Region
No of Units on Bar
Actual Generation (MW)
Kinetic Energy (MW-sec)
108
28237
109391
39828 Capacity on Bar (MVA)
System Inertia of Western Region
No of Units on Bar 183
78648
Actual Generation (MW) 54076
Kinetic Energy (MW-sec) 222935
Capacity on Bar (MVA)
System Inertia of Southern Region
No of Units on Bar 165
43088
Actual Generation (MW) 36731
Kinetic Energy (MW-sec) 157260
Capacity on Bar (MVA)
No of Units on Bar 92
System Inertia of Eastern Region
29077
Actual Generation (MW) 13966
Kinetic Energy (MW-sec) 100168
Capacity on Bar (MVA)
Kinetic Energy (MW-sec) 11659
System Inertia of North Eastern Region
No of Units on Bar 65
4322
Actual Generation (MW) 3247
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16. Way forward
Provisions in the Indian Electricity Grid Code 2023
• Mandatory tests for Solar/Wind- Real and Reactive Power Capability, Power Plant Controller Function Test, Frequency Response Test, Active
Power and Reactive Power Set Point
• Minimum inertia to be maintained all the time for secure and stable grid operation
• ‘Frequency Response Obligation’ a new mandate in the Grid Code
• Hydro/gas generating units – compensated for synchronous condenser mode operation
• UFR settings and df/dt load shedding schemes depending on local load generation balance of the respective regions
• Provision for unit commitment in the interest of Grid security
Provisions in the Manual on Transmission Planning Criteria
• Inertia studies are included under transmission planning
• ROCOF shall be calculated based on simulation studies for the lowest inertia period
• Generation Contingency, Load Contingency may be considered for ROCOF calculation
• Calculated RoCoF should be lower than the maximum permissible RoCoF value.
• The maximum permissible RoCoF shall be such that the 1st stage UFLS doesn’t get triggered and frequency remains 0.1 Hz above 1st stage of
UFLS.
• BESS, Synchronous Condenser etc. for fast response to arrest the frequency decline and help restore the frequency
• Determination of system inertia is essential for frequency stability assessment
Other Initiatives:
• Possible standards on Fast Frequency Response from IBR / BESS is being deliberated
• Use of retiring thermal plants as synchronous condenser for inertia support
• Spatial Distribution of Inertia
• Load Composition Understanding
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17. References
• Report on Assessment of Inertia in Indian Power System
https://posoco.in/wp-content/uploads/2022/01/Assessment-of-Inertia-in-Indian-Power-System.pdf
• Indian Electricity Grid Code) Regulations, 2023
https://cercind.gov.in/Regulations/180-Regulations.pdf
• Manual on Transmission Planning Criteria
https://cea.nic.in/wp-content/uploads/psp___a_ii/2023/03/Manual_on_Transmission_Planning_Criteria_2023.pdf
• Central Electricity Authority (Technical Standards for Connectivity to the Grid) Regulations, 2007
https://cea.nic.in/wp-content/uploads/regulations_cpt/2023/01/Connectivity_to_Grid.pdf
• Central Electricity Authority (Technical Standards for Connectivity to the Grid) (Amendment) Regulations, 2019.
https://cea.nic.in/wp-content/uploads/2020/02/notified_regulations.pdf
• Central Electricity Authority (Technical Standards for Connectivity to the Grid) Amendment Regulations, 2013.
https://cea.nic.in/wp-content/uploads/2020/02/grid_connectivity_12112013.pdf
• Central Electricity Authority (Grid Standards ) Regulations, 2010
https://cea.nic.in/wp-content/uploads/2020/02/grid_standards_reg.pdf
• Central Electricity Authority (Technical Standards for Connectivity of the Distributed Generation Resources) Regulations, 2013
https://cea.nic.in/wp-content/uploads/regulations_cpt/2020/09/Legal_Annexure-V.pdf
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18. Thank You
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