Preferred Bipole III route. • Bipole I and II both use interlake transmission corridor.
• About 75% of the province generating capacity is carried over this corridor.
A Preliminary Look at the Feasibility of VSC HVDC Technology in Manitoba M. Mohaddes, M. Rashwan, R. Ostash TransGrid SoluFons D. Jacobson, P. Wang Manitoba Hydro
IEEE 2011 Electrical Power and Energy Conference
Manitoba System – HVDC Bipoles • Bipole I and II both use interlake transmission corridor Preferred Bipole III route Bipole I & II route
• About 75% of the province generating capacity is carried over this corridor • Both Bipole I and II terminate at Dorsey converter station • Bipole III (2000 to 2500MW) improves system reliability by adding a new line and converter station • Bipole III termination electrically close to Dorsey converter station
IEEE 2011 Electrical Power and Energy Conference
Plans for the HVDC Bipoles • Bipole III – Present plan to use convenFonal LCC HVDC technology
• Bipoles I and II – Future plans to eventually replace the HVDC valves
• Preliminary feasibility studies to investigate VSC HVDC – Fast-‐growing raFngs – Possibility to operate with overhead lines – Reduced losses due to change in VSC topology from PWM to mulF-‐ level – For these reasons, becoming possible to consider VSC technology instead of convenFonal LCC IEEE 2011 Electrical Power and Energy Conference
Manitoba System & VSC Studies • How would using VSC instead f network MHoac BP1the nBP2 LCC affect eed for 1854 MW 2000 MW BP3 synchronous condensers? 2000-2500 MW Synch condensers: • Synchronous condensers 3x300 MVAr
Synch condensers: 4x250 MVAr
6x160 MVAr
– Large capital costs – Require lots of maintenance
Riel 500 kV
Dorsey 500 kV
Three 230kV • Feasibility Studies compared ties to SK VSC and LCC in terms of:
Transient Stability Scenarios: Two ties to ON 1. All Bipoles LCC (present plan) – Need for synchronous condensers 2. BP3 VSC / BP1 and BP2 LCC Manitoba 3. BP3 and BP2 VSC / BP1 LCC – Performance of interconnected US D602F G82R R50M L20D future system 500kV line 4. All Bipoles VSC IEEE 2011 Electrical Power and Energy Conference
Study Models/Methodology • Four Key Faults:
BP1 1854 MW
3 HVDC inverters very near each other, a single disturbance – Solid 3PF at inverter can cause sudden temporary loss of – Remote 3PF at inverter large HVDC infeed
– Solid 3PF at recFfier
BP2 2000 MW
– DC line fault (LCC and VSC)
• Main focus of study results
Result: Frequency dip in southern system ac network
– Southern system frequency response IEEE 2011 Electrical Power and Energy Conference
BP3 2000-2500 MW
MH ac network
Study Results: 3PF at Rec or Inv • Not much difference in system BP1 1854 MW response whether the Bipoles Low AC voltage at use VSC or LCC • Low AC voltage at rec or inv = minimal power transfer, regardless of type of DC technology
BP2 2000 MW
BP3 2000-2500 MW
rec or inv leads to minimal DC power transfer
• In all cases, large southern system frequency dip due to temporary loss of large amount of power infeed in the southern system
MH ac network
Result: Frequency dip in southern system ac network same for VSC or LCC
IEEE 2011 Electrical Power and Energy Conference
Study Results: VSC Advantage – Remote Inverter Faults VSC without Riel syncs gives be`er performance than LCC with Riel syncs Why? Because VSC does not fail commutaFon like LCC The more LCC links, the more power temporarily lost = more underfrequency
Better voltage performance with VSC
Dorsey voltage
0.3 Hz better underfrequency with VSC
Dorsey frequency
~2 cycles
BP1 Power
BP2 Power
Blue: VSC no Riel syncs Green: LCC with Riel syncs
Less power loss with VSC (no comm fail)
IEEE 2011 Electrical Power and Energy Conference
BP3 Power
Study Results: VSC Disadvantage – DC Overhead Line Faults
VSC without Riel syncs gives worse performance than LCC with Riel syncs Why? Because VSC DC fault draws currents from AC system, looks like remote fault, causes other LCC to fail commutaFon. Also longer restart Fme. Response improves if more bipoles are VSC, less LCC bipoles to fail commutaFon
Blue: VSC no Riel syncs Green: LCC with Riel syncs
Reduction in AC voltage with VSC DC line fault
Dorsey voltage
0.3 Hz worse underfrequency with VSC
Dorsey frequency BP1 Power
BP1 LCC comm fail during VSC DC line fault
BP2 Power
BP2 LCC comm fail during VSC DC line fault
BP3 Power
VSC longer restart time compared to LCC DC fault
IEEE 2011 Electrical Power and Energy Conference
Findings: Need for Synchronous Condensers for BP3 VSC? • Studies suggest building BP3 as VSC would not require any new synchronous condensers – Save in capital and maintenance costs for 1000 MVAR of synchronous condensers that are needed if BP3 is LCC – Must be kept in mind that although VSCs can provide steady state and dynamic reacFve power support, cannot provide the inerFa that synchronous condensers do
• The worst case fault for the BP3 VSC scenario was a VSC DC line fault, but sFll acceptable system response without any new syncs IEEE 2011 Electrical Power and Energy Conference
Findings: OperaFon in Very Weak System
• Possibility of replacing all HVDC bipoles with VSC in distant future • How many exisFng synchronous condensers could be reFred? No firm answer yet. – ReFring all syncs results in very weak system (next nearest generaFon quite far from the inverters) – Possibility of oscillaFons between VSC and AC system – started around 1.6 SCR – Idea to use frequency control on VSC inverter to act more like generator to stabilize phase angle/frequency in south – Further study with appropriate VSC control models and more system power flow scenarios needed to make conclusions IEEE 2011 Electrical Power and Energy Conference
Findings: MVA RaFng of the VSC Links • Studies done based on 2432 MVA raFng, not 2000 MVA (due to available PSS/E VSC model) • SensiFvity analysis showed difference in amount of VSC power lost during remote faults • ConsideraFons regarding syncs and VSC raFngs: – Even if all bipoles VSC, may sFll want some syncs for inerFa – Higher MVA raFng so less power lost transiently during AC undervoltage events, especially true for more VSC links – Further studies of VSC controls: • P priority over Q to a`empt to lose less VSC power • VSC in frequency control to help stabilize Dorsey frequency IEEE 2011 Electrical Power and Energy Conference
Conclusions & Future ConsideraFons • Bipole 3 – VSC appears technically feasible – Eliminates need for 1000 MVAR of new synchronous condensers – VSC advantage: remote faults, no comm fail – VSC disadvantage: DC line faults, longer restart Fme, bigger disturbance to AC system than LCC
IEEE 2011 Electrical Power and Energy Conference
Conclusions & Future ConsideraFons • Bipoles 1 and 2 – VSC appears technically feasible – How many exisFng synchronous condensers could/should be reFred yet to be answered – System very weak without any syncs, further study required
IEEE 2011 Electrical Power and Energy Conference
The End
Thank You! Any QuesFons?
IEEE 2011 Electrical Power and Energy Conference
