See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/347651482 Experience of PSS Tuning in Indian Power System Conference Paper · December 2020 DOI: 10.1109/NPSC49263.2020.9331918 CITATIONS READS 0 641 6 authors, including: Chandan Kumar Alok Singh POSOCO POSOCO 49 PUBLICATIONS 130 CITATIONS 15 PUBLICATIONS 10 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Power Oscillation View project Dynamic model building for Indian Power system-POSOCO View project All content following this page was uploaded by Chandan Kumar on 28 December 2021. The user has requested enhancement of the downloaded file. SEE PROFILE Experience of PSS Tuning in Indian Power System Presenter : Chandan Kumar (Author) Co-Author : Saibal Ghosh, Saurav Sahay, Alok Pratap Singh, Akash Modi, Surajit Banerjee Power System Operation Corporation Limited(POSOCO) India 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar Outline Paper summarises • Regulatory Overview and Required Improvements • Non-uniformity in Vendors practice • Experiences and Challenges observed in field exercise for 129 Units • Modified PSS tuning procedure and implementation 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar Power System Stabilizer (PSS) Basic Principle Some Key points : • Part of Synchronous machine excitation system • Additional Input to AVR to improve Damping Torque • Control excitation through voltage regulator for damping power oscillation • Input signal : Speed, Frequency and Power • Efficient and economical Mean to damp Oscillations (LFO) and Small signal stability improvement • Need proper tuning Observed Issues in PSS tuning : • Lack of Simulation study • Widely varying practices among utilities & vendors • Lack of procedure and evaluation guidelines • Field implementation with standard tests for evaluation Paper summarises • Regulatory Overview and Required Improvements • Non-uniformity in Vendors practice • Challenges observed in field exercise • Best Practices for PSS tuning • Modified PSS tuning procedure and implementation 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar Regulatory Overview PSS Mandatory for Excitation System CEA Technical Standard for Construction of Electrical Plants and Electric Lines (Published in 2010): • For Coal or lignite based Thermal Generating Stations (10.2. g.i: ), Gas turbine based Thermal generating stations (18), Internal Combustion(IC) engine based Thermal generating station (27) : Suitable Excitation System, as well as Automatic voltage regulator (AVR), shall be provided with the generator as per CEA (Technical standards for connectivity to the Grid) Regulation, 2007. Power System Stabiliser (PSS) shall be provided in AVR for generator of 100 MW and above rating. • For Hydro power Plan (37.3.e): All the performance requirements of AVR, PSS shall be in accordance shall be in accordance with CEA (Technical standards for connectivity to the Grid) Regulation, 2007 and CEA (Grid standard)regulation as and when they come into force. CEA (Technical standards for connectivity to the Grid) Regulation, 2007: • For New generating Units (part II. 1. C): The AVR of generator of 100 MW and above shall include Power system stabiliser (PSS) • For Old Units: (part II. 2. 2): For thermal generating units of having rated capacity of 200 MW and above and Hydro Units having rated capacity of 100 MW and above, following facility should be provided at the time of renovation and modernization : Every generating unit of capacity having rated capacity higher than 100 MW shall have PSS. PSS Tuning Mandatory • IEGC 5.2.k: All generating units shall normally have their automatic voltage regulators (AVRs) in operation. In particular, if a generating unit of over fifty (50) MW size is required to be operated without its AVR in service, the RLDC shall be immediately intimated about the reason and duration, and its permission obtained. Power System Stabilizers (PSS) in AVRs of generating units (wherever provided), shall be got properly tuned by the respective generating unit owner as per a plan prepared for the purpose by the CTU/RPC from time to time. CTU /RPC will be allowed to carry out checking of PSS and further tuning it, wherever considered necessary. • CEA (Technical standards for connectivity to the Grid) Regulation, 2007 6.g: The requester and user shall cooperate with RPC and appropriate Load despatch centre in respect of matter listed below, but not limited to: Cooperate with RPC for tuning of PSS provided in the excitation system of generating Unit. Report of the Task Force on Power System Analysis under Contingencies: Power System Stabilizers (PSS) as part of the generators installed in the network are also critical for damping the local area oscillations and imparting stability to the networks. Optimal tuning of PSS also enhance effectiveness of other HVDC and FACTs controllers in supporting overall/ inter-area stability. Necessary exercise to retune PSS should be undertaken at interval of 3-4 years or even earlier depending on network additions in vicinity of specific generators. Missing Features : Damping Criteria , Procedure and Periodicity of PSS tuning and Evaluation Review of Damping Criteria : POSOCO, “Report on Low Frequency Oscillation in Indian Power System”, New Delhi, Tech.Rep. March 2016. 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar Vendors & Utility Existing Practices Vendor V1 PSS Tuning Study based on Dynamic Model Model Validation during Actual PSS tuning V2 V3 V4 V5 √ × √ × √ √ × × × × Challenges observed • Non-uniform practice. Gain and Phase margin Calculation using System Study √ × √ × √ PSS Tuning at Site: Step Test √ √ √ √ √ PSS tuning at Site: Disturbance Test × × × √ √ • Focus only on step test response. PSS tuning at Site: Impulse Test √ × × × × • Lack of disturbance/impulse test. PSS tuning at Site: Governor Test × × × × × PSS tuning at Site : OEL and UEL Test × × × × × • Missing Validated model based study and Parameter determination exercise. 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar PSS Tuning : Experience & Challenge Summary of PSS tuning at 129 Units in Eastern and Western Region in Indian Power system • Thermal Power Plant Units: 97 • Hydro Power Plant Units: 21 Model validation • Ensures the study results and actual site tests match • Validation of the local mode of frequency with step test. • Three vendors perform this activity 50 MW-800 MW • Gas Based Power Plant Units : 11 Measurement Data • Lack of high precision data from field testing. • Response/tuning validation difficult. Reference voltage step change • Voltage step of 5 % is good for analyzing the PSS response. • Evaluation based on lower steps (1%-3%) is difficult Generation level • 80-100 % of the rated capacity & All test at same loading • PSS cutoff criteria • Gets bypassed below certain generation level. • Affects overall response evaluation. PSS Gain • Conservative Setting – Lack of study and field test. Governor Status • Free Governor Mode need to be kept off for ideal condition for testing. 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar PSS Tuning Experiences… Step response test • Unit response for change in Excitation system Vref. • Provide PSS response for system voltage change. • Impact of other units in plant affect the testing (irrespective of PSS on/off) • Difficult to assess if plants have units with multiple rating • Better evaluation if unit under test is only kept in service • Response during the lowest possible fault level • Can be done Hydro and Gas • Non-economical in thermal plant. • Does not ensure plant level response. Disturbance test • Provide overall plant response • Most effective yet least performed • Plants (Thermal plant) avoid it on apprehension of disturbance. • If transient study is performed then impact of disturbance test known in advance. 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar PSS Tuning Methodology : Simulation Study Study Requirement • Time domain and Frequency domain study • Data Requirement : • Generator detailed model • Oscillation Frequency Range (System Operator/ Planner) Objective • Study should demonstrate improved damping for : • Voltage step change of 1% -5%. • Defined frequency range. • Within 2 cycles. • No appreciable instability at 3 times proposed PSS gain. • Variable system operating conditions • Network topologies changes. • Short circuit on transmission lines from plant. • No adverse impact/negative interaction on the torsional mode. Task • Find local mode of oscillation for the plant and its damping. • Impact of external network impedance variation • Phase and Gain margin for the given range of frequency. Study • Eigen Value Analysis : Phase lead lag compensation to provide positive damping. • Root Locus Analysis : Gain constant determination. • Time domain study : Perform step and disturbance test at various power output. Outcome of Simulation Study: • Local mode of oscillation frequency • PSS phase and gain margin • Number of cycle required for damping (Damping ratio) 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar PSS Tuning Methodology : Field Testing Requirement : AVR tuning IEEE Std 421.2-2014 Gain margin Test 1. Keep gain as calculated from study and increase it till oscillation starts. 2. Reduce gain to 1/3 of this gain value. Step Response Test • Provide time-domain performance • Application of voltage step changes to VTref • 1-3 % change –PSS ON/OFF • Validates local mode and simulation study Frequency Response Test 1. Injecting low frequency band-limited random noise / sinusoidal signal in VTref 2. Provide PSS performance for a range of frequency and ensures model validation Disturbance Test • Most effective : Opening of line/reactor • All Unit PSS ONor OFF (Plant level response) Impulse Test (Alternative to Disturbance Test) • Low magnitude Impulse type signal superimposed over the VTref for step-change in impulse input. 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar PSS Tuning Methodology : Field Testing OEL/UEL Test: • Ensure under excitation limiter (UEL) & over excitation limiter (OEL) do not interact with PSS . • Unit is under and overexcited till UEL/OEL activation perform step/impulse response test Governor Test: • Test PSS performance during frequency events. • Apply +0.5 Hz frequency injection to the governor and keep unit it frequency sensitive mode. Utilization of Synchrophasor • Proved effective for PSS performance evaluation. • Helps in model validation Precautions • Alert during frequency injection close to the resonant frequencies of the machine or neighboring machines. • Alert during frequency injection higher than 3 Hz as can eb near to lowest shaft torsional mode. Consult OEM • Stop if error between Simulation and field test is high . • Stop if growing/sustained oscillation observed PSS out at 4000 MW plant PSS In at 4000 MW plant 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar Suggested Inclusion in Standard/Regulation • Damping criteria Introduction in power system planning and operation criteria. • Mandatory PSS tuning at periodic interval and criteria • PSS tuning procedure and guideline. • Generator model validation Summary Overall Paper provide a glimpse of : • Challenges faced during PSS tuning study and field testing. • Limited resources on real world experience sharing on PSS tuning. • Challenge in deriving strength from Regulation/Standard on PSS tuning evaluation. • Varying practices by utilities and vendors on PSS tuning. • Field Experience & challenges faced during PSS tuning of more than 129 Units. • Methodology for PSS tuning based on best practices. • Suggested Regulation/Standard Inclusion on PSS tuning. New Methodology and Guideline : Approved in the Eastern Region Operation Committee (OCC) Forum in Sept 2020 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. Central Electricity Authority (Technical standards for connectivity to the Grid) Regulation, 2007. Central Electricity Regulatory Commission, Indian Electricity Grid Code (IEGC), 2010 POSOCO, “Report on Low Frequency Oscillation in Indian Power System”, New Delhi, Tech.Rep. March 2016. P. K. Agarwal, Chandan Kumar. “Oscillation Detection and Mitigation Using Synchrophasor Technology in the Indian Power Grid” in Power System Grid Operation Using Synchrophasor Technology, 1st ed, vol. 1, Nuthalapati, S, Ed. Cham: Springer International Publishing, 2019, pp.195216. C. Kumar et al., "Detection of LFO and Evaluation of Damping Improvement Using Synchrophasor Measurement," 2018 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), Kota Kinabalu, 2018, pp. 701-706, doi: 10.1109/APPEEC.2018.8566336. C. Kumar et al., "Intra-Area Mode: Measurement-Based and Model-Based Assessment in Indian Power System," 2019 IEEE Milan PowerTech, Milan, Italy, 2019, pp. 1-6, doi: 10.1109/PTC.2019.8810729. National Grid Electricity Transmission, Grid Code, Issue 5, Revision 21, 2017. WECC Power System Stabilizer Tuning Guidelines ERPC, 164th OCC Minutes, Jan-2020, Available [online]: http://erpc.gov.in/wpcontent/uploads/2020/01/164-OCC-MINUTES.pdf NERC, VAR-501-WECC-3 – Power System Stabilizer Standard IEEE Std 421.2-2014: IEEE Guide for Identification, Testing, and Evaluation of the Dynamic Performance of Excitation Control Systems IEEE Tutorial Course Power System Stabilization via Excitation Control,2009 ERCOT Nodal Operating Guides E. V. Larsen and D. A. Swann, "Applying Power System Stabilizers Part II: Performance Objectives and Tuning Concepts," in IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 6, pp. 3025-3033, June 1981. E. V. Larsen and D. A. Swann, "Applying Power System Stabilizers Part III: Practical Considerations," in IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 6, pp. 3034-3046, June 1981. POSOCO, “Synchrophasors Initiative in India”, New Delhi, Tech.Rep. June 2012. P. Kundur, G. R. Berube, L. M. Hajagos and R. Beaulieu, "Practical utility experience with and effective use of power system stabilizers," 2003 IEEE Power Engineering Society General Meeting , Toronto, Ont., 2003, pp. 1777-1785 Vol. 3 View publication stats Thank you for your attention Contact : chandan@posoco.in 21st National Power Systems Conference (NPSC 2020), December 17-19, 2020, IIT Gandhinagar