37
Supergen Theme 3 – The Connection Durham, Strathclyde, Manchester, RAL
Supergen Theme 3 – The Connection
Durham, Strathclyde, Manchester, RAL
SUPERGEN Wind Wind Energy Technology
Work Package 3.1 Durham University – System Performance
Evaluation – Reliability/Connection Overview, March 2012
Li Ran
Part A - Reliability evaluation of offshore connection – for example:
Gearbox Gen
~
=
=
~
Inside Nacelle
Gearbox Gen
~
=
=
~
Inside Nacelle Offshore Platform
Submarine AC Cable to the offshore platform (typically
a few kilometers for a 5MW turbine)
Variable frequency and voltage
transformer (Step-Up)
Variable frequency and voltage transformer
(Step-Down)
(A) a.c.string
(B) a.c. star
RA: Dr Behzad Kazemtabrizi
Started February 2012
Offshore downtimes (Egmond aan Zee Wind Farm 2009 Survey)
Source: Operation Report for Egmond aan Zee Wind Farm in 2009
(accessed in noordzeewind.nl)
Availability comparison
Connection Scheme/ Main Component
Individual Unavailability (%) Total System Availability (%)
Total System Unavailability (%)
Generator
Converter
Grid
Markov Markov
LWKD (onshore) 0.0188% 0.0249% 0.1287% 99.83% 0.1724%
Configuration A 9.9662% 2.3733% 0.3644% 87.67% 12.33%
Configuration B 9.9662% 0.5034% to 2.3733
0.3644% 87.67% to 89.25%
10.746% to 12.33%
Note: Other components in the turbine system are assumed
to be 100% reliable.
Part B - Static & dynamic limits: offshore connection network
• Overall Aim: Connection technology for large offshore wind farms – achieving control, performance, reliability, maintainability and cost effectiveness.
HVDC
Offshore Substation
Shore
Onshore Substation
Wind turbines to Grid
PhD candidate Terry Ho
Started October 2010
Power electronics centralisation at substation topology
Offshore platform Wind Turbine Generators
Po
wer co
llection
system
to HVDC
• Power electronics are easier to access in a centralised location
• Assuming steady-state connection for a 5MW turbine and a 5km connection, minimum voltage were found to be 4.6kV for a thick cable (1000mm2) and 9.7kV for a thin cable (95mm2)
• Transfomerless connection is
possible with multi-level
converters in a one to one
radial connection and MV
machine
• More work will be done in the dynamics and reliability evaluation in this area
For 1000mm2
Offshore a.c. network voltage control
• How to define and maintain a.c. voltage for the offshore network?
• The converter in VSC HVDC link should always be subject to a.c.
side current control.
offshore a.c. network
Offshore a.c. network voltage control
VSC HVDC filter wind farm
Prof Aurelio García-Cerrada
University of Pontificia Comillas, Spain
Visiting professor, Durham University
January2012-July 2012
Offshore a.c. network voltage control
• Outer loop voltage controller is decoupled
• Less interaction between d and q
• Better response in maintaining the voltage for changing loads
• Internal loop current control is conventional
Response without dq decoupling
Response with decoupling
simulation with large load disturbance
SUPERGEN Wind Wind Energy Technology
Work Package 3.2 Strathclyde University – Offshore
Control Schemes Overview, March 2012
Olimpo Anaya-Lara
Offshore arrays and wind farm cluster control (Research at Strathclyde)
1. Assessment of collection network designs for offshore wind farms
2. Basic connections for wind farm clusters and dynamic performance evaluation
3. Design of generalised droop control for power management in multi-terminal connected wind farms
1. Electrical collectors for offshore wind farms
AC String:
Electrical collectors for offshore wind farms
AC Cluster:
Electrical collectors for offshore wind farms
Example wind farm layout: 1 GW wind farm; 10 MW turbines, 170m swept
diameter; 7 diameters turbine spacing; ±300kV HVDC
link
Turbine
TransmissionPlatform
RedundancyLinks
Links betweenTurbines
Links toPlatform
Electrical collectors for offshore wind farms
Breakdown of losses
0
50
100
150
200
250
300
350
400
DC Star AC Star DC String
AC String
DC Cluster
AC Cluster
An
nu
al L
oss
(G
Wh
)
Transformers
Power Electronics
Cables
Generator
Clustering Loss
Electrical collectors for offshore wind farms
Breakdown of costs
0
100
200
300
400
500
600
DC Star AC Star DC String
AC String
DC Cluster
AC Cluster
Co
st (£
M)
Platform
Cable Installation
Cable
Loss
Electrical collectors for offshore wind farms
Conclusions:
Overall, DC networks were found to have a lower capital cost and
lower loss than the AC equivalent, due to the lower cost of DC
cables and the reduced number of conversion steps.
However, costs and losses are less certain, due to the lack of
commercially available DC collection network cables and
equipment.
SUPERGEN Wind Wind Energy Technology
Work Package 3.3 Manchester University – Connection
to Shore Overview, March 2012
Mike Barnes
Connection to Shore (University of Manchester)
1. Background Component Study
2. Protection and Circuit Breaker study
3. Reliability and Unavailability Analysis of Connection Topologies
VSC-HVDC
ABB.com
First Offshore Installation
• Troll – 1&2 – 88MW (2005), 3&4 – 100MW (2015)
– +/-60kV DC, 70km
– 132kV AC on shore to 56kV or 66kV offshore
2. Breakers Available - Limited
• Passive Resonance Breaker – Test designs constructed – Relatively low interruption speed
• Based on Metallic Return Transfer Breaker in CS-HVDC – Full Current, Limited Voltage
BRKLs
SA
I Ib
Ic
Is
CL
Circuit Breakers
How to manage DC fault? – No DC circuit breakers
– Faults cleared on AC side (at present)
State of Art - Review
Presently few credible solutions
Lead candidate: ABB Medium Voltage Prototype
Other manufacturers also working in field
At Manchester – Patent idea filed.
Disconnector
Auxiliary DC Breaker
Main DC Breaker
Current Limiting
Reactor
Residual
DC Current
Breaker
Hybrid DC Breaker
3. VSC-HVDC Availability Analysis
• Typical Radial Scheme for an UK Round 3 Windfarm:
– Determine overall availability of scheme
– Identify key components which effect the scheme
• Availability statistics are next to non-existent
165km ±300kV DC Cable
165km ±300kV DC Cable
Id
Id
400kV AC Grid220kV AC
Convertor
Reactor
DC Capacitor
MMCTransformer
GIS
Subsystem 1 – Offshore System
Subsystem 2 – DC System
Subsystem 3 – Onshore System
Offshore
Cooling
System
Control
System
Offshore
Cooling
System
Control
System
Subsystem 4 Subsystem 5
Ventilation
System
Ventilation
System
Radial VSC-HVDC Scheme
Results
54%
10%
9%
8%
9%10%
Component Importance for Availability
DC Cable Offshore MMC
Offshore Reactor Offshore DC Switchyard
Other Offshore Equipment Onshore Equipment
Overall energy availability of 96.5%
Cable Sensitivity Analysis
Cable Failure Rate (occ/yr/100km) Energy Availability (%)
0.007 98.2
0.07 96.5
0.7 79.7
•Round 3 offshore windfarms commercially unviable if true failure rate is in the vicinity of 0.7
Greatest cause of damage MTTR – 2 months
Availability Analysis of HVDC Grid
600MW
Stations
1200MW
or 900MW
DC cables
Cost-benefit Analysis Radial scheme has a very slightly higher availability than HVDC grid with no additional capacity
HVDC grid with additional capacity has significantly higher availability than a radial scheme
Higher availability means greater revenue and can result in a more profitable investment.
Cable Scheme
Capital Cost
Avail-ability
Loss £m/yr
Saving £m/yr
Extra Cap Cost £m
Payback (yr)
900MW 876.5 0.963 35.0 0 0 0
Radial 908.25 0.965 33.2 1.82 31.8 17
1200MW 982.5 0.972 26.1 8.92 106 12
SUPERGEN Wind Wind Energy Technology
Work Package 3.4 STFC-RAL Integration of Energy Storage
Overview, March 2012 Alan Ruddell
Potential needs for energy storage in a far-offshore connection / transmission scheme
Turbine trips Stability
Power High (per turbine) Low-medium (per
wind farm)
Storage time Seconds - minutes Seconds
Response Sub-second Sub-second
Cycling Low High
Storage technology Supercapacitor,
Flywheel, Battery
Offshore Wind Farm
Offshore
Network
Onshore
Grid 1
(UK)
Td1
OT -> DC
Research basis for Theme 3: HVDC VSC 900MW +/- 320kV up to 150km transmission Ref: North Sea Offshore Transmission Basic Connection Schemes, Theme 3, Olimpo Anaya-Lara, Strathclyde)
Avoiding curtailment
Power High
Storage time Hours
Response Minutes
Cycling Low
Storage
technology
Flow cell
Battery
Integration of energy storage
Wind turbine rotor inertial storage
Relationships between turbine power, rotor diameter, mass, inertia can be derived (based on fit to data for available turbines)
The rotor inertia constant is highly sensitive to rotor diameter and tip speed for any power (as shown by the spread for 2011 Vestas turbines), and is generally increasing with turbine power
0
1
2
3
4
5
6
7
8
9
10
11
12
0 1 2 3 4 5 6
roto
r in
ert
ia c
on
sta
nt
[s]
Rated power [MW]
Total rotor inertia constant
formula
Vestas 2011
Tip speed
Power
Rotor diameter
Rotor mass
The total inertia constant can be around 10 seconds for large wind turbines.
Flywheel energy storage
Manufacturers include: – Beacon Power, Vycon, Kinetic Traction Systems, Piller, Temporal Power and Active Power
Applications include UPS, transportation, hybrid vehicle, rail trackside support, and grid support
Commercialisation has been slow
Beacon Power
100kW / 25kWh
flywheel
Manufacturer Rotor
Type
Rotor
Speed
(rpm)
Bearings Power
Rating
Energy Standby
Loss
Main application
Beacon Power Carbon-
fibre
Composite
16,000 Active
Magnetic
100kW 25 kWh
(15 min)
2% of rated
power
(2kW)
grid-stabilisation
Vycon Energy 4340 Steel 36,750 Active
Magnetic
300kW 1.1 kWh
(40 s)
UPS market
Kinetic
Traction
Systems (KTS)
Carbon
fibre
36,000 Magnetic and
hydrodynamic
200kW 1.5kWh
(30 s)
1% of rated
power
(2kW)
railway regenerative
braking
Ultracapacitor energy storage
(Supercapacitors are also known as electric double layer capacitors (EDLC), ultracapacitors, electrochemical capacitors)
Major manufacturers include: – Maxwell (USA), IOXUS (USA), NESSCAP (S.Korea), EPCOS (Europe) and Okamura
Laboratory (Japan)
Commercialisation and market growth is rapid: – in the last 10 years the market has grown 25% per year, and the growth rate is
increasing (NESSCAP)
– over the last 10 years the cost has fallen by 99% and is continuing to fall, due to automation of the manufacturing process and development of more efficient technologies
– the cost of ultracapacitors is falling at a faster rate than the cost of batteries
Maxwell have a range of ultracapacitors designed specifically for use in wind turbine blade pitch control systems
– Reduces lifetime maintenance costs
– Durable and reliable > 1,000,000 cycles
– Eliminates reliance on batteries or maintenance issues with hydraulic systems
– High performance in all weather conditions from -40° to +65° C
Parameter Spec.
Capacitance 94 F
Rated voltage 75 V
Continuous current 48 A (@ 15°C)
Weight 25 kg
Maximum energy 73 Wh
Specific power 2,100 W/kg
Specific energy 2.9 Wh/kg
Lithium ion battery energy storage
AES Energy Storage has 70 MW of grid storage in operation in:
– 6 US systems and Chile
– provides ancillary services
– stores excess wind power during curtailment
Xtreme Power - Dynamic Power Resources (DPR) – DPR containerised module 1.5MVA, 1MWh
– Container size 40x11x11 ft, total weight 100,000 lbs
– Overall system approx. 33 W/kg; 11 W/litre
– Overall system round trip efficiency > 90%
– Uses XP’s 12V 1kWh PowerCell module
Wind farm applications, e.g. – Maui 20MW wind farm (2011), storage 10 MW / 20 MWh
– stores excess power during curtailment periods
– also provides ramp control, frequency and voltage ancillary services
Laurel Mountain Wind farm:
61 turbines, 98MW
AES energy storage:
approx 32MW / 8MWh / $23M
A123 Systems supplies lithium ion batteries to system developers
– is to supply 6 systems to Northern Powergrid
– for peak load shifting, voltage fluctuations
– systems use stacks of multiple cells
A123 Lithium ion cell 3.3V 2.5Ah (8.25Wh nom.)
26mm dia x 65mm long, 76 g
2,600 W/kg 5,800 W/litre
> 1000 full cycles
Xtreme Power DPR 15-100C Containerised Unit
Size comparison of flywheels and Li-ion batteries systems (20MW / 5MWh system – 15min storage)
AES Energy Storage / A123 Systems Li-ion battery plant
Phase 1 + 2: 20MW / 5 MWh (Phase 1: 8MW shown)
Battery only costs generally around $1M / MW
2MW / 0.5MWh in container module (each 53ft long)
Provides ancillary services and regulation
Smaller than flywheel system
A large space is required ! Beacon Power – 1st large scale system
20MW / 5MWh
Installed July 2011 in New York – cost $69M
Provides fast-response frequency regulation
Plant connected to NYSEG network at 115kV
1 MW module:
Power electronics interface and ancillaries
Ten 100kW flywheels (blue lid, underground)
The complete 20 MW system comprises 20 modules
