Transcript An investigation into the technical design, transient

“AN INVESTIGATION INTO
THE TECHNICAL DESIGN,
TRANSIENT STABILITY
STUDIES AND MODELLING
ISSUES FOR LAND BASED
WF INTO SMALL ISLAND
GRID"
Presented by Rohan R.V Seale
PROJECT OBJECTIVES :
•
Develop grid connection requirements and
standards for BLPC that will permit the
development and operation of an efficient, safe,
reliable and well coordinated transmission grid
system.
•
Investigate the power quality impact of wind farm
on BLPC network.
•
Perform relevant Transient studies to assess the
impact due to 24 kv Wind Farm connection on
island grid.
•
Assess the overall protection, design and SCADA
requirements for integration of a land based wind
farm into a small island utility.
BACKGROUND INFORMATION
• CONNECTION OF WF TO NORTH SUB.
• NORMALLY WEAK CONNECTION -POTENTIAL LOW
•
•
•
•
VOLTAGE AT DIST. LEVEL
RADIAL LINE WITH SINGLE OHL FEED
SECOND UG CABLE FEED DUE IN 2007
ADDITIONAL 2 X 132 KV UG CABLES - 2008
POTENTIAL GEN. SITE DEVELOPMENT IN NORTHADDITIONAL 4 x 20MW (2009)
Existing Facilities
• 175km of
transmission
lines
• 3,828km of
distribution
lines
REGENCY PK.
BLPC TRANSMISSION SYSTEM
ADVENT OF WT GENERATION
• Wind generators connect to both the
•
•
•
•
distribution & transmission networks .
An emerging set of renewable energy
generation is under construction or in planning
phase in Caribbean.
The transmission & distribution systems will
require selective reinforcement to support the
volume of renewable generation being
planned.
The technical connection requirements for
generators connecting to the transmission or
distribution systems are set out in Industry
Codes and Intl. Standards.
Framework agreements set out obligations
and contractually binding arrangements
between generators & Utilities.
ELEMENTS OF SYSTEM OPERATION
SECURITY
OF
SUPPLY
DYNAMIC
STABILITY
SYSTEM
VOLTAGE
SYSTEM
OPERATION
RESERVE
CAPACITY
FREQUENCY
CONTROL
INTERNATIONAL STANDARDS
Table I
IEC Wind Energy Standards
The status of the IEC standards is provided in Table I.
Title
Purpose
Working
Document Number
Group
WG-1
Safety Requirements
Principal standard defining design
WG-2
for Large
requirements
WG-3
Wind Turbines
WG-4
Small Wind Turbine
Principal standard defining design
Systems
requirements for small turbines
IEC 1400-1*
IEC 1400-2*
WG-6
Performance
Defines performance measurement
Measurement Techniques techniques
IEC 1400-12*
WG-7
Revision of IEC 1400-1
Edition 2 of IEC 1400-1
1400-1 Ed2
WG-8
Blade Structural Testing
Defines methods for blade structural
testing
1400-23
WG-9
Wind Turbine Certification Defines certification requirements
Requirements
(Harmonized version of several European
standards.)
1400-22
WG-10
Power Quality
Defines power
1400-21
Measurements
quality measurement techniques
International Standards Cont’d
• G59/1 - Recommendations for The Connection of
Embedded Generating Plant to The Public Electricity
Suppliers’ Distribution Systems (1991) (≤20kV,
≤5MW)
• G75/1 - Recommendations for the connection of
embedded generating plant to public distribution
systems >20kV or with outputs ≥5MW
• G 83/1 – Recommendations for connection of Small
Scale EG (<16 A per phase) in parallel with LV Dist.
Network
IEEE P 1547-2003 STANDARD
• Influential standard for interconnection of all
forms of DR is IEEE 1547-2003, Standard for Interconnecting
Distributed Resources with Electric Power Systems.
• IEEE 1547 is the result of a recent effort by
SCC21 to develop a single interconnection
standard that applies to all technologies.
• IEEE 1547 addresses all types of interconnected
generation up to 10 MW.
• The 1547 standard has benefited greatly from
earlier utility industry work documented in IEEE
and IEC standards (ANSI- C37 series for
protective relaying)
RECENT CHANGES TO USA GRID CODE (AWEA):
• Low voltage ride-through (LVRT) capability for wind plants and wind
turbines: AWEA recommended adoption of an LVRT requirement
developed by E.ON Netz. This is a German grid operator faced with a
significant and growing penetration of asynchronous wind generation on
the German grid. This standard requires that the machine stay
connected for voltages at the terminals as low as 15% of nominal per
unit for approximately 0.6 s.
• Supervisory control and data acquisition (SCADA) equipment for remote
control: AWEA recommended the requirement of equipment to enable
•
•
remote command and control for the limitation of maximum plant output
during system emergency and system contingency events.
Reactive power capability: AWEA recommended that wind plants
connected to the transmission system be capable of operating over a
power factor range of ±0.95.
Current wind turbine simulation models: AWEA recommended that
major stakeholders (TSOs and WT manuf.) participate in a formal
process for developing, updating, and improving engineering models
and turbine specifications used for modeling the wind plant
interconnection.
RECENT CHANGES TO UK GRID CODE
The Grid Code incorporates the technical issues raised by the 3 Licensees with
respect to the connection of windfarms:
• Fault ride through: Requirement for generating units to revert to normal
•
•
•
•
operation when a fault on the network is cleared.
Power/frequency characteristics: Requirement for generating units to be able
to deliver power & remain connected to the network when the system
frequency deviates from 50Hz.
Frequency control: Requirement for generating plants to be able to
increase/decrease power output with falling or rising frequency.
Reactive range and voltage control: Requirement for generating plant to be
able to supply lagging/leading reactive power and control the voltage at the
grid connection point.
Negative phase sequence: The requirement for generating units to be able to
withstand negative sequence currents caused by phase voltage unbalance
and phase to phase faults.
WFPS1.4 FAULT RIDE THROUGH REQUIREMENTS
WFPS1.4.1 A Wind Farm Power Station shall remain connected to the Transmission System for
Transmission System Voltage dips on any or all phases, where the Transmission
System Voltage measured at the HV terminals of the Grid Connected Transformer
remains above the heavy black line in Figure WFPS1.1.
Connection process overview
PROJECT PLANNING PHASE
INFORMATION PHASE
DESIGN PHASE
CONSTRUCTION PHASE
TESTING & COMMISSIONING PHASE
CATEGORIES OF WIND PLANTS
• BULK WIND PLANTS: Consist of large wind
farms connected to the Transmission
System (USA)
• DISTRIBUTED WIND PLANTS: refers to
single Turbines / small groups of turbines
dispersed along Distribution System
(popular in Europe , Caribbean )
WIND TURBINE CATEGORIES
WT divided into two categories which
define their electrical characteristics
• FIXED SPEED DEVICES – Simple & Cheap
• VARIABLE SPEED DEVICES – Power
Electronic Interface to Grid
• M/C RATINGS FROM 600 KW – 1.5 MW
WIND TURBINE TECHNOLOGY
•
•
FIXED SPEED
FSIG: Standard squirrel-cage induction
generator connected directly to the grid:
•
These machines have a gearbox to match
the rotational speed of blades with that of
the generator. Mechanical power may be
regulated through an inherent
aerodynamic stall characteristic of blades
or with active control of blade pitch.
WRIG: Wound-rotor induction generator
with variable rotor resistance: These
machines have a gearbox for coupling an
electrical generator to a turbine hub. They
also have pitch control of blades for
maximizing energy capture and controlling
turbine speed within range of the
generator and a small range of variable
speed operation (e.g., 10% of generator
synchronous speed).
•
VARIABLE SPEED
DFIG: Doubly fed asynchronous generator:
These are essentially wound rotor induction
machines with variable frequency excitation of
the rotor circuit, incorporating rotor current
control via power converter. The rotor circuit
power converter may be four-quadrant, allowing
independent control of real and reactive flow in
either direction (rotor to grid or grid to rotor), or
unidirectional real power flow (grid to rotor).
These machines have a gearbox for coupling the
generator shaft to turbine hub, active control of
turbine blade pitch for maximizing production
and controlling mechanical speed, and variable
speed operation depending on the rating of
power converter relative to turbine rating (e.g.,
±30% of generator synchronous speed).
Synchronous or induction generator with full-size
power converter: In these machines, the
generator is coupled to the grid through a fully
rated ac/dc/ac power converter. They also have
a gearbox to match generator speed to variable
rotational speed of blades and variable speed
operation over a wide range, depending on
electrical generator characteristics.
CAPACITY FACTORS
• The Declared Net Capacity (DNC) of a generation
•
•
•
•
scheme is a measure of the expected average power
output of the generation scheme.
DNC = (RATED POWER OUTPUT– POWER
CONSUMED BY PLANT) X CF
Capacity factor for wave energy schemes = 0.33
Capacity factor for wind energy schemes = 0.43
Capacity factor for other types of C-2 generation
schemes = 1.00
POW. SYS. ANALYSIS FOR
DISTRIBUTED WIND:
• Voltage Regulation
• POWER QUALITY- FLICKER,
HARMONICS
• Short Circuit Contribution
Pow. Sys. Analysis Issues for Bulk
Wind include:
• Var Support
• Capacity Constraints
• Stability
• Reserve Capacity Requirements
Factors Impacting System Voltage
• Local Wind Profile (Speed, Turbulence,
Shear)
• Size of Wind Turbine to Short Circuit ratio
• X/R Ratio of system
• Type of WTG and associated Reactive
Power Control
• Loading on Distribution Feeder
VOLTAGE REGULATION:
• Commercial WTG employ Reactive
Compensation
• Variable Speed Gen. use Static Var. Control
to adjust current phase angle
• Fixed and semi variable speed IG use
switched capacitor banks
• Need to Coordinate with other Voltage Reg.
devices e.g. Regulator/switched Caps.
POWER QUALITY
• VOLTAGE FLICKER - Refers to the rapid
•
•
•
•
variations in voltage levels within a certain Mag.
and Freq. range
Synonymous with light or lamp flicker
Arises due to abrupt changes in WT Pow. O/PWind Gusting & Variable Dynamic behaviour
Fluctuations at freq. close to 8 Hz cause most
annoyance
Occurs on weak systems with low X/R ratio
VOLTAGE FLICKER IMPACT
• Peculiar to Fixed speed devices
• Variable speed WT less likely to cause
flicker
• Wind farm with several turbines less likely
to cause flicker as variations of Pow. O/P
tend to cancel out.
CAUSES OF FLICKER BY WTG
• Blade passing of tower results in
oscillations
• Variations of wind speed
• Switching operations- startup & shutdown
• Recommended limits on flicker in Dist.
Networks addressed in IEC 61400.21
SHORT CIRCUIT CONTRIBUTION
• For WTG in 600 kw - 1.3 MW range must
consider Fault Contribution
• 80-90% of Dist faults are SLG which cause
m/c to receive normal excitation voltage
• For voltage > 60% treat IG as Synch. m/c.
(Rule of thumb by W. Feero)
• Obtain Static Ind. m/c model – more
accurate
NETWORK EFFECT OF GEN. TECH.
EFFECTS DUE TO FAULT CONTRIBUTION
• REDUCTION OF RELAY REACH
• SYMPATHETIC TRIPPING OF
BREAKERS/RECLOSERS
• COORDINATION ISSUES- DELAYED
AUTO-RECLOSING 3-5 secs.
Network Design for WTG Connection
• CONNECTION VOLTAGE – 24 KV, 69 KV
• NETWORK FAULT LEVEL
• SYSTEM X/R RATIO
• NETWORK CAPACITY AT PCC – THERMAL
RATINGS, EXP. REQ’MENTS, VOLT.
REGULATION
WF POWER EQUATION
Where,
• ρ = air density (nominally 1.22 kg/m3)
• R = radius of area swept by the turbine
blades
• V = speed of moving air stream
• Cp = “coefficient of performance” for the
composite airfoil (rotating blades)
VAR SUPPORT
• WIND FARMS TYPICALLY NOT USED TO
PROVIDE VOLTAGE CONTROL
• CAN PROVIDE LOCAL VOLTAGE REGULATION
FOR WEAK SYSTEMS
• FLUCTUATING WIND PLANT O/P MEANS AMT.
OF REACTIVE POW. REQ’D VARIES
• FAILURE TO MAINTAIN REACTIVE Q LEADS TO
VOLTAGE COLLAPSE AS WTG O/P INCREASES
REACTIVE COMPENSATION
TECHNIQUES:
• CONSTANT PF - Switched Cap. Banks at each
WTG provide constant PF over range of Gen O/P
• VARIABLE PF – Real time control of each WTG
reactive Q production or absorption
• SUBS. SWITCHED CAP. BANKS – Large Cap
banks located at interconnection Sub.
• STATCOM – FACTS devices that use voltage
source converters to provide reactive current.
POWER SYSTEM STABILITY
• Full Assessment of Network performance
requires study of STEADY STATE and
TRANSIENT STABILITY operation
• Characteristics of WTG must not
compromise the stability of Power System
following CONTINGENCY
DEFINITION OF STABILITY
• STEADY STATE STABILITY - Ability of Pow.
Sys. to remain stable after a small
disturbance e.g load disturbance, switching
• TRANSIENT STABILITY – ability of Pow.
Sys. to maintain synchronism after a
severe transient disturbance. E.g. Short
Circuits, loss of load or Gen.
PURPOSE OF TRANS. STAB. STUDY
• TO PREDICT ABILITY OF GEN. TO RECOVER
AND REMAIN CONNECTED TO POWER SYSTEM
AFTER A FAULT
• TO ASSESS INTERACTION OF GENS. AND
OTHER ROTATING PLANT (WTG) CONNECTED
TO NETWORK AFTER FAULT
• TO ENSURE MINIMUM VOLTAGE DISTURBANCE
DUE TO LOSS OF SYNCHRONISM
SMALL SIGNAL STABILITY
Two forms of Instability
occur under these
conditions:
• Steady Increase in Rotor
Angle due to lack of
sufficient Synchronising
Torque
• Rotor oscillations of
increasing amplitude due
to lack of sufficient
damping torque
TRANSIENT STABILITY
CONSIDERATIONS
• In large complex power systems Transient
instability may not always occur as first
Swing Instability, but may be due to
superposition of several modes of
oscillations.
• Analysing TS - the study period is 3-5 secs.
after disturbance. May be extended to 10
secs. or more.
STABILITY CHALLENGES
CAUSES
• SHORT CIRCUITS
• LOSS OF TIE LINES IN UTILITY
NETWORK
CONSEQUENCES
• AREA WIDE BLACK OUT
• INTERRUPTION OF LOAD
• UNDER VOLTAGE CONDITION
• LOSS OF GENERATION
• DAMAGE TO EQUIPMENT
• SWITCHING OPERATIONS OF LINES,
• RELAY AND PROTECTIVE DEVICE
CAPACITORS ETC.
• SUDDEN LARGE STEP CHANGE OF
GENERATION
MALFUNCTION
SYSTEM OR NETWORK STUDY
• LOAD FLOW STUDY
• TRANSIENT
•
STABILITY STUDY
DYNAMIC SECURITY
ASSESSMENT
•
•
•
•
•
COMMERCIAL
SOFTWARE
PSS/E – PTI LTD.
ERACS – ERA LTD.
IPSA – IPSA
POWER/UMIST
ETAP – OTI INC.
MATLAB / SIMULINK
PS STUDY CONSIDERATIONS
• LOAD FLOWS
• CURRENT FLOWS IN EACH BRANCH OF
NETWORK
• REAL & REACTIVE POWER FLOWS
• VOLTAGES AT EACH NODE
• VOLTAGE BOOST AT CONTROL NODES
• LOSSES
FAULT LEVEL STUDIES
• TOTAL FAULT CURRENT AT FAULTED
NODE
• ANGLE OF FAULT CURRENT RELATIVE
TO REFERENCE VOLTAGE
• FAULT CURRENT DISTRIBUTION
• (CRITICAL TO PROTECTION)
LOAD FLOW ANALYSIS
MATLAB/POWERSIM
ETAP 5.5.0
ETAP 5.5.0 FEATURES
MODELLING ISSUES
• DFIG MODELLED – ALL PARTS
MODELLED FOR DYNAMIC STUDIES
• AERODYNAMICS
• TURBINE
• DRIVE TRAIN - GEARBOX
• GENERATOR
• CONTROL SYSTEM
WIND FARM MODELLING
• Modelling WF requires grouping of m/cs of
similar type into an equivalent single m/c
• Large WF can be split into several equiv.
m/cs
• Layout of WG to be taken into account as
this affects regulation and dynamic
behaviour especially of variable speed m/cs.
• Consider Loss of accuracy vs. simplified
practical model
SIMULATION STUDY
• TRANSIENT STABILITY STUDIES PERFORMED
•
•
•
•
•
FOR (up to 7 secs):
CONTINGENCY ON OHL INFEEDS AND WF CKT
CONTINGENCY ON UG CABLES
LOSS OF GENERATION
BUS FAULT
WIND GUST
SYMETRICAL LV TOLERANCE CURVE
EQUAL AREA CRITERION:
• Divide the machines in the
•
•
•
•
system into two groups:
the critical machines that
are responsible for the loss
of synchronism, and the
remaining non critical ones
Replace the two groups by
two equivalent. machines.
Replace these machines by
an equivalent single
machine, infinite bus
system.
Evaluate the system
stability using the equal
area criterion.
WF SINGLE LINE SIMULATION
CONVERTER
WT MODEL: Cp CURVES
WT AERODYNAMICS MODEL
CONVERTER CONTROL
MACHINE INERTIA CONSTANTS
DFIG MODEL SETUP
WIND CHARACTERISTIC MODEL
ST-NO-OHL-FLT-L25SIM
ST-NO-OHLFLT-L11-PROTSIM
ST-NO-OHLFLT-L25BFSIM
TS- ST-CE-OHLFLT- V & I
TS-ST-CE-OHLFLT- P & Q POWER
ST-CE-OHLFLT-SPEED & MECH. POWER
TS- CH-STUGCABFLTBF
TS- CH-STUGCABFLTBF
TS- CH-STCABBF MECH. POW &
SPEED
WFT-WIND GUST
SWING CURVES: SG 24 BUS FAULT
SWING CURVES- NORTH 24 BUS FAULT
CONCLUSIONS:
• BLPC TO ADOPT RELEVANT INT’L STANDARDSFORMULATE INTERCON. GRID CODES
• DFIG – HAVE CAPACITY TO ASSIST STABILITY
DURING POWER SYSTEM DISTURBANCE
• SIMULATIONS NEEDED TO TEST DFIG &
MANUF. M/C PARAMETERS FOR LVRT
REQUIREMENT & STABILITY ENHANCEMENTS
• PROTECTION PHILOSOPHY TO BE ADOPTED
w.r.t. WFT INTERCONNECTION
COMPARISON OF WT TO TALLEST BUILDING
• B’DOS CENTRAL BANK
Typical 850/900 kW Wind Turbine
Generator
52m Rotor
Diameter
50m
Hub
Height
QUESTIONS?