HVDC in CSG Challenges and Solutions

HVDC in CSG Challenges and Solutions LI, Licheng lilc@csg.cn LI, Peng lipeng@csg.cn China Southern Power Grid Co., Ltd June 2013 1

Overview of CSG Date of Establishment December 29, 2002 Services Power transmission, distribution, and supply in Guangdong, Guangxi, Yunnan, Guizhou, and Hainan, a total area of 1.02 million square kilometers Population Served Xinjiang Tibet National power grid Northwest China North China Central China Northeast China East China Southern power grid A total population of 230 million, accounting for 17.8% of the national population Assets As of the end of 2012, 562.9 billion yuan, ranked 152 in Fortune Global 500 CSG 2013. All rights reserved. 4

Overview of CSG uin 2012, the installed generation capacity within CSG is about 200 GW. GW 78.13 GW 88.86 95.90 67.08 35.27% 108.72 Thermalpower 57.17% pumpedstorage 6.12 3.22% 4.05 2.13% 104.36 4.20 2.21% 113.23 118.08 119.6 447 4478 wind power nuclearpower Hydroelectric power 527 5272 585 5859 670 6708 730 750 7307 7500 TWh 2007 2008 2009 2010 2011 2012 2007 2008 2009 2010 2011 2012 Average annual peak load growth rate of 8.6% in the past five years Average annual electricity consumption growth rate of 10.9% in the past five years CSG 2013. All rights reserved. 5

Overview of CSG 8 AC + 5 DC from west to east Three Gorges Yunnan Guizhou 9.11GW Guangxi 9.54GW Guangdong p p p p Long Distance Ultra High Voltage Bulk Capacity Hybrid Operation of AC/DC Hainan 24.43GW 1/3 of GD Load CSG 2013. All rights reserved. 6

III. Challenges & solutions Interaction in AC//DC systems HVDC block lead to power shift to AC systems and make it more intense. power HVDC HVAC A blackout from ac/dc interaction voltage abnormal ac voltage lead to HVDC commutation failure or block CSG 2013. All rights reserved. 8

III. Challenges & solutions Challenge 1: DC power shift Bulk power will shift from HVDC to HVAC during: HVDC Block or ESOF HVDC Line fault HVDC Power reduction DC BLOCK or ESOF Bulk power shift may lead to : Voltage drop AC line overload Relay malfunction System instability Blackout Dc line fault--recovery--success Dc line fault--recovery--fail DC DC power reduction Power Shift AC//DC AC AC power increase CSG 2013. All rights reserved. 9

III. Challenges & solutions Challenge 2: Commutation Failure of multi infeed HVDC links Concurrent commutation failure of 5 HVDC links will be caused by AC fault in 500kV substations or 220kV substations within GD area. Simultaneous commutation failure of multi-hvdc will cause sharp power reduction of HVDC and bulk power shift to HVAC. If the AC fault couldn t be cleared fast, continuous commutation failure may lead to Multi HVDC Block. Power Shift AC Bulk power flow transfer to AC SYS, may cause blackout AC//DC CSG 2013. All rights reserved. 10

III. Challenges & solutions Challenge 3: Simulation of AC/DC hybrid system Exact simulation of AC/DC hybrid system is the basis for system analysis and control. Traditional simulation tools developed for bulk power systems, such as PSS/E and BPA, can t deal with interaction between AC and DC exactly. For example, they are not able to simulate commutation failures in DC and consequent dynamics in AC systems. Tools for HVDC simulation, such as EMTDC, can only deal with small systems. CSG 2013. All rights reserved. 11

III. Challenges & solutions Solution 1: Wide Area SPS Ł Detecting HVDC bipolar block, N-2 outages and some N-3 outages Ł Start remote generation shedding, or HVDC modulation, or load shedding, run back/up of HVDC Ł Communication by fiber-optical channel Ł Redundancy to enhance reliability Goal: to keep system integrity after a severe contingency MS 500kV grid Prevent CSG from blackout in case of several cascading faults Increase transmission capability SS L L MS SS CSG 2013. All rights reserved. 12

III. Challenges & solutions Solution 2: Coordination between AC and DC Solution 2.1: Coordination on protection & control coordination of AC and DC system 27DC protection 100Hz protection AC Relay coordination SPS 81DC protection 87DCM protection DC P/C to avoid HVDC block during AC fault 13 CSG 2013. All rights reserved.

III. Challenges & solutions Solution 2: Coordination between AC and DC Solution 2.2: Optimization parameters of HVDC control (e.g. VDCOL considering recovery requirement of AC system after fault clear in receiving end of HVDC; DC line fault recovery sequence, etc). Vd CIA CC Im CEA 逆变器 CC 整流器 To enhance the system performance. 最小 α 限制 VDCOL 最小电流限制 Id CSG 2013. All rights reserved. 14

III. Challenges & solutions Solution 2: Coordination between AC and DC Solution 2.3: Wide-area damping control system Ł A closed-loop control system based on WAMS Ł Coordinated damping control for three HVDC links Ł Commercial Operating since 2008 Develop WAMS to WACS Increasing damping and transfer capacity Output of Control Unit (V) 6 5.5 5 4.5 XingRen Control Unit 投入退出 4 0 5 10 15 20 25 30 35 40 time (s) CSG 2013. All rights reserved. 15

III. Challenges & solutions Solution 3: Countermeasures to commutation failure 3.1 Fast fault clear with high reliability Redundancy of all Protection System Elements in all station of 220 kv and above. Special maintenance of important protection and circuit breakers. 3.2 Distribution of converter stations in GD Proposed new index to evaluate interaction between converter stations and to weak the interaction through proper distribution of sites. CSG 2013. All rights reserved. 16

III. Challenges & solutions Solution 3: Countermeasures to commutation failure 3.3 STATCOM Installation of more than 800 MVAR STATCOM in some key stations to support transient voltage. CSG 2013. All rights reserved. 17

III. Challenges & solutions Solution 4: Hybrid simulation Established the world largest RTDS lab, with 33 RACKs, connected with protection and control systems, to simulate dynamics of bulk power system involved HVDC. Developed electromagnetic and electromechanical transient hybrid simulation. HVDC models in the simulation is the same as EMTDC, and it can deal with dynamic of bulk AC systems as well. CSG 2013. All rights reserved. 18

IV. Innovation on HVDC Innovation 1: VSC-MTDC for wind power integration p Wind farms in NanAo Island By 2011, total capacity is 143MW In 2013, more 25MW; In 2015, offshore 50MW (Tayu) VSC-MTDC project in Nanao Island Three sending converter stations, One receiving inverter station Voltage ±160kV Capacity 200 MW Distance:20km Solve key technical issues for a number of large-scale wind farms integration into grid friendly Operating in end 2013 CSG 2013. All rights reserved. 20

IV. Innovation on HVDC Innovation 2: Islanded Operation of UHVDC-- background Large-capacity HVDC power transmission system working in islanded operation, may reduce the effect of power shift on the AC system due to HVDC trip. AC//DC Power Shift DC AC DC Islanded No Power Shift DC AC Because the supporting power plants are far away from the converter station, new problems on overvoltage control appear under the islanded operation mode of YG UHVDC. CSG 2013. All rights reserved. 21

IV. Innovation on HVDC Innovation 2: Islanded Operation of UHVDC overvoltage control Overvoltage control is the biggest problem for islanded operation: pfast tripping of AC filter/capacitor banks by DC control system (overvoltage protection is the backup). And the ferromagnetic saturation characteristics of converter transformers can be used to limit power-frequency overvoltage. ptwo-column arresters for AC busbar at converter stations are used. CSG 2013. All rights reserved. 22

IV. Innovation on HVDC Innovation 2: Islanded Operation of UHVDC frequency control Frequency control is another problem for islanded operation: Even primary frequency control (PFC, set dead zone as ±0.15Hz) of generators and frequency limit control (FLC, set the dead zone as ±0.1Hz) of HVDC are both running, the HVDC control is much faster, and the FLC plays the key role. The frequency of islanded system will be kept within 49.9 to 50.1Hz, which is reasonable. Frequency in Parallel operation Frequency in Islanded operation CSG 2013. All rights reserved. 23

IV. Innovation on HVDC Innovation 3: Back to Back HVDC CSG plan to replace the AC tie-lines between YN and rest of CSG with Back to Back HVDC around 2020, to control the size of synchronized power systems, and to mitigate power shift influence of multi DC. 3000 MW + 1500 MW BTB DC lines and VSC technology are under considering. GZ YN GX GD CSG 2013. All rights reserved. 24

V. Conclusion HVDC play a very important role in CSG. CSG adopted different technical strategies. HVDC//HVAC is a proper choice in initial stage to develop long distance transmission systems. Up to now, CSG is continuing optimizing the hybrid system. There are still many works to do to keep the security and stability of AC/DC hybrid systems. CSG is tracing the technical trend and intends to use the HVDC technology more extensively in the future. CSG 2013. All rights reserved. 27