Dynamic Reactive Power issue in Wind Integrated Power Systems and LVRT Compliance of WPPs

Zakir H Rather, IIT Bombay RE integration workshop, Chennai Email: [email protected] January 23, 2018 Wind farm in chitradurga-pic taken from IREDA ppt Journey of at global level

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Source: GWEC Indian Power System and 2022 RE target

3 • Installed capacity≈330 GW (1.36 GW in 1947) ; Peak demand ≈ 150 GW Biomass, Small 10 GW • ≈ 300 million people do not have access to Hydro, electricity. 5 GW

RE Wind, 60 GW Solar, 100  302 GW at 100 m height GW  Target by 2022 is 60 GW of wind and 100 GW of solar PV  90% of wind potential is in the Southern and the Western region 120 100 Growth path of wind power 80 60 100 (GW) 40 Large scale solar 20 Solar rooftop 50 0

0 2011-12 2014-15 2016-17 2021-22 Challenges of variable RE (vRE) integration

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Technical  Lack of transmission infrastructure, grid stability, variability of RE sources, weak grid, estimation of effective turbine capacity etc. Regulatory  Complexity of subsidy structure and involvement of too many agencies Industrial barriers  Lack of investment , skilled manpower Wind resource data collection  Wind potential calculation requires proper data of wind speed at site . Social and environmental issues  Noise pollution from wind farm affects the local region.  Deforestation for carrying wind turbine and blades vRE integration-Technical issues 5 • Increased Flexibility requirement (variability issue) • Wind-driven displacement of conventional synchronous power plant – low synchronous inertia and possibly increased operating reserves – Diminishing reactive power reserve and short circuit power • Renewable Energy curtailment • Emerging issues: Post-fault delayed active power recovery from wind turbine/plant Impact on reactive power capability: 6 Evolution of LVRT 7

LVRT curve is representative of worst case realistic voltage recovery profile that may occur once a power system recovers from lowest voltage point. Factors affecting LVRT requirements:

• Current and anticipated wind penetration levels • Strength of grid • Type of load in the system (predominance of induction motor load leads to poor voltage recovery) • Islanding of system • Dynamic voltage support devices in the system and plant reactive power headroom LVRT requirement LVRT priority

1  0.9

0.75 Voltage (p.u.) Voltage

0.25 2004 2016

100 500 750 1500 10000 Time(ms) LVRT curve as per EirGrid and Indian wind grid code LVRT curve for .dk, EirGrid: T= 625 ms, Vpf=0.9 pu; Vf= 0.15 pu IEGC (CERC): T =table below, Vpf= 0.8 pu; Vf= 0.15 pu 1 0.9 Table: T for various voltage levels in India

Nominal rated Fault clearing Time V post fault V fault (kV) voltage (kV) (millisecond) (kV) Voltage (p.u.)Voltage 400 100 360 60

0.15 2004 220 160 200 33 2016 132 160 120 19.8 150 625 1500 3000 Time (ms) 110 160 96.25 16.5 LVRT curve for Tennet TSO, 66 300 60 9.9 5 LVRT Issues 9

• IEC 61400-21/IEC 61400-21-1 – Field testing? • What about old WTGs? • How to ensure WTGs are LVRT compliant after a period of operation? • How to monitor LVRT compliance?

Which LVRT priority? Wind driven displacement of Conventional Power Plants (CPPs)-Danish power system 10

Offshore WF

Source: Energinet.dk Impact on grid security: Danish case study

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400 kV Vester Hassing substation

1 Fault at Vester Hassing substation

0.8

0.6 Voltage (pu)

0.4 VSWTGs trip DCHPs trip 0.2 Old wind turbines trip

4Rather et al.,4.5 2015 Chengxi5 liu et al., 20145.5 6 6.5 7 7.5 Time (sec) Reactive power support from must run CPPs in the Danish grid 12

• Short circuit power Must-run was costly • Dynamic voltage control – Reactive power consumption by old wind turbines and commutation of HVDC LCC • Continuous voltage control

(Active power reserves are

bought in separate markets Source: Energinet.dk (Danish TSO) and do not give rise to must-run) Voltage stability considering dynamic reactive power compensation in 2030 Danish grid

1.1

1 • Refurbished SCs 0.9 • New SCs 0.8 • STATCOM, SVCs Fault at Vester Hassing substation 0.7 Voltage (pu)

• 0.6Dynamic Q support from WPPs

0.5

4 4.5 5 5.5 6 6.5 7 7.5 Time (sec)

Rather et al., 2015 Potential solutions to address lack of dynamic reactive power reserve in RE integrated system 14 • Infrastructure reinforcement: – synchronous condensers, – FACTS devices such as SVC, STATCOM, TSSC Procurement of dynamic reactive power through ancillary service market

Energinet.dk Operating WPP beyond grid code requirement

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Asynchr onous Motor Static Load 345 MW M 207 MW, 80 M VAR 6.6 kV 26.4 kV 345 kV 154 kV PCC fault 33 kV 345 kV

13.8 kV

WTG 5 WTG 1 0 WTG 1 5 SG1 SG2 SG3 SG4 SG5 SG6 100 MVA 150 MVA 200 MVA

WTG WTG 4 9 WTG 1 4 5 MW ≡ 33 kV WTG 3 WTG 8 WTG 1 3 33 kV 2.3 kV

90° WTG 2 WTG 7 WTG 1 2 Wind PWPP VPCC angle 0°

WTG 1 WTG 6 WTG 1 1

Qca p V

P K1 QWTG1_ref Q WPP_cap Qmax K2 VPCC QWTG2_ref _ Σ Π K limiter . Deadband QWPP_ref . Qmin Vcom .

Q Kn QWTGn_ref

ΔVPCC Post-fault delayed active power recovery

Rather et. al, 2017

LVRT priority: active or reactive power?

Voltage at TW1(WPP1 terminal) Grid frequency

Active power from WPP Active and reactive current 19