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Planning for New Zealand’sInter-Island HVDC Pole 1
Replacement
Peter GriffithsMohamed Zavahir
EEA Conference 2007 : Engineering – Our Future
Inter-Island HVDC Pole 1
• A brief history• Benefits• Why replace?• Earliest date for replacement• Retirement planning• Selecting the preferred replacement option• Planning and engineering for replacement• The way forward
EEA Conference 2007 : Engineering – Our Future
Inter-Island HVDC Link
Benmore
Haywards
DC Line - 570 km
DC Cables - 40 km
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Original Inter-Island HVDC Link (1965)
– Mercury arc valves– World’s 4th HVDC scheme; 3rd to include submarine cables– 600MW bipolar +/-250kV link– DC line - 570km; DC cables (x3) – 40km
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Hybrid Upgrade (1993)
– DC line upgraded; new DC cables (x3) – 350kV– Original MAV link upgraded to 270kV and paralleled to form
Pole 1 - 540MW 270kV – New thyristor valve Pole 2 – 700MW 350kV– New control systems– 1240MW bipolar scheme reduced to 1040MW following
decommissioning of the last original cable in 1997
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HVDC Configuration as at present - Total 1040 MW
Pole 1
Pole 2
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Wilton
Bunnythorpe
Linton
220 kV HAYWARDS
110 kV HAYWARDS(8 110 kV Circuits)
216/200/80 MVAT2
C2
60 MvarT5
35 Mvar 35 Mvar
C4 C3
40 Mvar
C1
40 Mvar60 Mvar
47.5Mvar
Filters(5, 7, 11, 13 + HP)
47.5Mvar
T1
y/y
C8
65 Mvar
C9
65 Mvar
y/
VG4
POLE1B
C10
65 Mvar
C7
65 Mvar
y/y150/172/66 Mvar
98.5 kV
VG2
High Speed Switch
POLE1A
0.8 H
0.8 H
0.8 H
0.8 H-270 kV
2 kA
Rated at 1.43 kA
Rated at 1.43 kA
Rated at 1.43 kA
Rated at 1.43 kA
46.3Mvar(24th)
60Mvar(12th)
Filters
46.3MVAr(24th)
60Mvar(12th)
Filters
Filters,(5, 7, 11, 13 + HP)
y
652.6/326.1/326.1 MVA815.4/407.7/407.7 MVA overload220/143.9/143.9 kV3 3
350 kV1.6/2.0 kA
0.16 H
POLE 2
y
y
y
652.6/326.1/326.1 MVA815.4/407.7/407.7 MVA overload220/143.9/143.9 kV
3 3
350 kV1.6/2.0 kA
0.16 H
POLE 2
Neutral Switch
VG3
Te Hikowhenua
Neutral Switch
VG3
Commutating Breaker25 km
Commutating Breaker25 km
Bog Roy
110 kVVG1 135 kV
1200 AVG1135 kV
1200 A
y/
y/
VG2
VG4POLE
1A
POLE1B
187.5 MVA
79.3Mvar
(11/13th)
Filters
79.3Mvar(24th)
Filters
/
/
220 kV BENMORE16 kV BENMORE
G1
G3
G2
G4
G5
G6
y/
Filters(5, 7, 9, 11, 13 + HP)
y/
50.5Mvar
y/
50.5Mvar
200/200/60 MVA
y
y
Filters(5, 7, 9, 11, 13 + HP)
6 x 112.5 MVAHydro Generators
Aviemore 1
Twizel
Ohau C
Ohau B
-350 kV2 kA
HVDC LINK SINGLE LINE DIAGRAM NORTH TRANSFER
Aviemore 2
Haywards Benmore
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Benefits of HVDC link
• Certainty to Energy Market – Linking both island markets– Widening the market base
• Energy security between the two islands• Ramp up and self cover – reduce reserve
requirement• Power system stability
– Modulation functions (voltage, and frequency stabilisation)• Spinning reserve sharing between the islands• Increased choice of locating generation• Balancing renewable and intermittent generation
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Why Replace MAV Pole 1?
• One of only two mercury arc valve (MAV) based HVDC systems still in service– Vancouver Island MAV pole
• Younger• Intermittent operation• Operates in parallel with an AC cable link
• Primary equipment now over 42 years old– 45 years old in 2010– Spares are the same age– Additional spares can’t be source for some key components
• No other HVDC plant using similar technology has reached 40 years of service before replacement or removal
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Why Replace MAV Pole 1?
• Combination of risks factors– Technical obsolescence– Seismic– Fire– Environmental– Main circuit equipment performance– Control system equipment performance
• Higher level of maintenance required for Pole 1• Pole 2 availability and reliability is consistently
superior to Pole 1• Unlock existing infrastructure capacity• Improve functionality
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Earliest Date for Replacement
• If a replacement option is economic - earliest approval would be mid-2008– Economic investment– Expected net market benefit must be > 0
• At least 4 to 5 years from approval to implement (2012)– longer for options with new transmission lines
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MAV Pole 1 Retirement
• Gap between planned retirement (2010) and earliest possible replacement (2012)
• Transpower reviewing strategies for extending operation beyond 2010 through to 2012– Retirement plan under review– Primary equipment will be over 47 years old by 2012– No plan to carry out major life extension works for operation
past 2012
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Level of detail
Long list of options
Long-short list of options
Short list of options
Preferred option
OPTIONS SCREENING
OPTIONS RANKING
GRID INVESTMENT TEST
OPTIONS IDENTIFICATION
Number of options
Exp
lora
tion
Red
uctio
n
Identifying the Preferred Option
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HVDC Preparatory Work
Identifying HVDC Environmental issues, setting up process for approval and resource Consents
Environmental Investigations
Engineering studies relevant to overload rating of Pole 2, synchronous condensers at Haywards, noise assessments, seismic issues, civil work requirements, AC switchyard layouts, submarine cables, and improved cost estimates.
Engineering Investigations
Load flow, dynamic and harmonic analysis, initial design studies, and production of performance specifications.
System Investigations
Scope of WorkActivity
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System Studies
• HVDC power system analysis to identify possible AC/DC system interaction issues
• Enable preparation robust performance specifications including desired control system functionality.
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Identify potential substation configurations, transfer capacity requirements and preliminary design considerations including system strength and reactive support requirements.
Planning Studies
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Determine distortion limits, harmonic levels, harmonic impedances and parameters for inclusion in performance specifications for the harmonic filters and control system.
Planning Studies
Harmonic Analysis
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Planning Studies
Harmonic Analysis
Reliability Assessment
Determine the optimal configuration and converter rating for Pole 1 taking into account the spares requirement and Pole 2 ratings
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Planning Studies
Harmonic Analysis
Reliability Assessment
Initial Design Studies
- Consolidate findings from preceding activities -Identify the preferred system configuration for detailed analysis, and- Provide input into Engineering Investigations.
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Planning Studies
Harmonic Analysis
Reliability Assessment
Initial Design Studies
Transient Analysis
- Verify operation of the HVDC system at possible operating conditions, - Assess dynamic interaction - Identify the need for any special dynamic control or special protection.
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Planning Studies
Harmonic Analysis
Reliability Assessment
Initial Design Studies
Transient Analysis
Control System Analysis
Verify steady state and transient performance and special control functionality for enhancing system performance.
EEA Conference 2007 : Engineering – Our Future
Planning Studies
Harmonic Analysis
Reliability Assessment
Initial Design Studies
Transient Analysis
Control System Analysis
Performance Specifications
Produce performance specifications for all major systems including the converter poles, and control and protection systems for Pole 1, Pole 2 and Bipole.
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Planning Studies
Harmonic Analysis
Reliability Assessment
Initial Design Studies
Transient Analysis
Control System Analysis
Performance Specifications
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Planning criteria
• Economic investment– Energy transfer benefits– Assessment of dynamic benefits difficult– Dry year security is not a determining criteria
• Equivalent short circuit ratio of 2.5– Short circuit ratio, SCR = Short circuit capacity/HVDC_Capacity– ESCR = (Fault Level – Filter MVA)/HVDC_capacity
• N vs N-1 criteria– Application of runbacks
• North vs South flow benefits• Natural transfer limits
– North Flow determines HVDC equipment and augmentation requirement
– Resulting South Flow limits
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Engineering investigations
• Pole 2 Overload Investigation– Pole 1 equipment rating and reserve requirement– Critical equipment being analysed by Supplier
• Submarine Cable Survey and Route Investigation
– Need additional cable for 1400 MW rating– Spare consideration (practicality and economics)– Desktop study of route in Cable Protection Zone– Treatment of disused cables
• Engineering Feasibility Studies…
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..Engineering Feasibility Studies• Synchronous condensers
– Condition assessment– Preferred configurations to connect synchronous
condensers via 110kV or 220kV• Substation
– Detailed noise assessments, particularly Haywards– Seismic design issues at the converter stations and cable
terminal stations– Switchyard layouts and transition staging plans– Civil work investigations for location of additional equipment– Conceptual civil design for high level cost estimates– AC equipment assessment to confirm suitable ratings of
existing equipment– Functional specifications
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Environmental Investigations
• Approvals concerning work – At Benmore and Haywards substations– At Oteranga Bay and Fighting Bay cable terminals– Additional Cook Strait cables
• Ultimately to include – Status confirmation with regional plans; – Confirming suitable approaches with Councils;– Consultation with affected parties; – Preparation of applications for resource consents– Assessments of effects on the environment.
EEA Conference 2007 : Engineering – Our Future
Way Forward
ShortList
To E
lect
ricity
Com
mis
sion
8 June 2007
Consultation/Workshops
31 July 2007
GIT
October 2007
Long/ShortList GUP
December 2007
GIT Data Book Published
22 May to 22 June
EEA Conference 2007 : Engineering – Our Future
www.gridnewzealand.co.nz/n278.html#
EEA Conference 2007 : Engineering – Our Future
Questions?