Wigton Wind Farm Ltd by sanmelody

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									Wigton Windfarm Ltd.
 Power Factor and VAR Control Experience
         -Problems and Solutions

    Presented by: Francois A. Lee, PE
     Leecorp Ltd ,Wigton consultant
Background
• Wigton Windfarm started operations in April
    2004
•   Connected to JPS grid under the terms of the
    Power Interchange Agreement (PIA)
•   Main Project Manager/ Design Engineer/
    Contractor: RES Ltd. UK
•   23 Neg-Micon NM900/52 900KW turbines
    installed
•   Total estimated capacity of wind farm: 20.7MW
Wigton single line Summary
System description summary
 23 x NEG Micon NM/52 wind Turbines ,each
 turbine generates at 690V,50 hz, and is
 transformed up to 24KV by 1000KVA step up
 transformers at the base of each turbine.
 Turbines located 100M apart are connected to a
 common collection point at the substation.The24
 KV collection is further transformed up to 69 KV.
The point of interconnction with the local
utility (JPS) is at the terminals of the
windfarm power transformer 69KV
disconnect switch.
The windfarm main substation is
connected to JPSco’s substation rated
139/69 KV at Spur Tree via 11.315 KM of
newly built 69 KV overhead lines
Problems

• Metered MVAR demand indicates
  significant consumption by the wind plant
  up to 8 MVAR.(see P/Q characteristic)
• JPSCO charges for MVAR demand at a rate
  equivalent to its industrial customers.
Solutions
• Consultants hired to look at scenario and
    determine strategy for way forward Nov.2004.
•   Consultants Findings
     - Power Interchange agreements mandates
       Wigton Winfarm must be atleast .9PF
       and simulatenously providing its
       reactive power requirements.
 Consultants Findings contd.

• At 20 MW output there is a shortfall of aprox. 7.8 MVAR
  inductive

• Neg-Micon turbines installed are inductive types and
  consume 275 KVAr @ no load,410 KVAR @ full load.

• Neg-Micon turbines installed have capacitive
  compensation up to 275 KVAR only.
    Consultants Findings contd.

• Cabling and transformers add to reactive
    demand
•   Balance of Plant contractor has mandate to
    deliver facility that fulfills PIA.
•   The utilities charge to Wigton for Var support is
    in line with PIA
•   Capacitive compensation of aprox. 8 MVAR is
    required at Wigton
•   Automatically switched banks at the 24 KV
    substation point is the likely and cost effective
    solution.
Implementation of solution
• QVARX Canada,specialists at Var compensation at
   medium and high voltage
  identified as substation Capacitor bank system designer
   /supplier
• Preliminary harmonic data indicates that tuning reactors
   will be required.
• Preliminary design done ,meetings convened with
   JPS,Wigton ,consultants and design discussed as per
   PIA procedures.
• QVARX commisioned to and undertakes design and
   system study for 24 KV capacitor bank
System and 24 KV Capacitor Study
Highlights
• Study Objectives
  1- Determine the min. no of switched
     steps and suitable control strategy.
  2- Determine if harmonic tuning reactors
     are required to avoid harmonic
    resonance problems.
  3- Examine the potential for switching impact on
     the LV banks when switching in a 24 KV
     capacitor step.
Study Results and Findings

• A capacitor bank of rating 8 MVAR total is
 required to compensate /offset the
 maximum var demand of 7.8 MVAR
 inductive.The capacitor bank should be
 split into 3 identical steps of 2.67 MVAR,in
 order to keep the voltage steps following
 bank switching to less than 3% at the
 24KV bus.
Study Results and Findings contd.

• The step # 1 bank should remain connected at all times
  ,which will be more stable operation when the wind is
  very low and as it picks up.This is because at low wind
  speeds ,the var demand is rapidly changing between
  capacitive and inductive.The steps #2 and #3 will be
  switched in and out as the var demand at the metering
  point will vary.It is recommended to control these 2
  steps in the capacitor PLC which will allow the most
  rapid switching times as opposed to the standard PF
  controller. This will keep the average inductive kvar as
  low as possible in the event of sudden wind gusts.
Study Results and Findings contd.

• The step 3 capacitor will require tuning
 reactors to avoid resonance problems with
 the typical grid harmonic distortion. The
 step 1 will be a combination of 2 tuned
 banks .One tuned at the 5th harmonic and
 one tuned at the 7th harmonic. This bank
 will be permanently connected. The steps
 2 and 3 banks will each be tuned at the
 7th harmonic.
Study Results and Findings contd.

• The switching transient modeled results do not
    indicate there will be any problems of interaction
    on the LV capacitor banks at the turbines when
    a 24 KV step is switched on.
•   The control of all low voltage caps (at turbines)
    should be such that they should all be connected
    as the MW increases ,and should remain
    connected as the 2nd and 3rd steps come on to
    avoid fighting between the both capacitor
    systems.
Design Study approaches
• Impedance modelling done on 69/24 KV network using ATPDRAW power simualtion
   software
 Modelling basis
 - 24 kv cables are installed trefoil
   arrangement,direct buried,ground
   resistivity 36 ohm-m assumed
 - cables modeled as series R,L and parallel C
   to ground
 - Cables are modelled as lumped impedances per identified branch
   between two nodes,each node being a junction box.
 -Cable splices are not considered nodes in the model as the distributed effect of cable
   inductance and capacitance over the section does not have a noticeable impact on
   the lower order parallel resonance ,which is the key frequency of interest.
Design Study approaches
• Transformers
  - 69/24 KV, 25 MVA rating,this transformer has a
   nameplate impedance of 9.09% at 25 MVA. Load losses
   is assumed to be 83 KW at 25 MVA
 - 24KV/690V,1000 KVA rating,the turbine transformer has
   a nameplate impedance of 5.73% at 1.0MVA.
• Turbine Impedance
  - The turbine at 690V is modelled as the stator
   subtransient reactance which is assumed at 20%.
  -Each turbine has LV capacitor bank of 275 KVAR,which
   is assumed to be fully connected.
Design Study approaches
• Grid Connection
 - The windfarm is connected to the 69KV grid
 via a 25MVA step up transfomer.The 69 KV has
 a 3phase fault level of between 487 t0 544 MVA
 with x/r ratio of 4.8.There are no capacitor
 banks directly on the 69 KV network. There is
 one main breaker controlling all collector circuits
 at 24 KV.See appendix 1 for impedance diagram
 of 69/24 KV network.
Design Study aproaches

• Total capacitor KVAR size
 - Load flow model without substation
 capacitors shows apparent load at 24 KV
 of 20.8 MW and 6.1 MVAr inductive
 - Load flow done with 8 Mvar capacitor
 bank shows correction of max.demand
 vars to 0.3 Mvar capacitive.
Design Study aproaches
• Minimum Switch ON Time Delay
 - Capacitors must be discharged via internal resistors before re-energizing and also
    consideration made for rapid wind gusts which would tend to drive up MVAr demand
    rapidly hence minimum switch on time is critical
• Mode of switching control
  - 3 options available 1st is basic control device of PFC which works on separate time
    delay setpoints,2nd option is var control within the capacitor system PLC
    (programable logic controller) .This option also has fixed time delay setpoints for
    switching on and switching off however PLC can determine whether it is necessary to
    enforce time delays.3rd option is 3 steps connected permanently which is mot
    advisable due to voltage increase at low output.
• 2nd option of Var control in the PLC chosen .In this mode the PLC controller will
    switch off a step when it detects the load is decreasing and the metered var is
    capacitive and exceeds the MVAr size of one step (2.67 MVAr). As such the reactive
    power at the metering point will be controlled aproximately in he range of 0 vars to
    2700 Capacitive ,averaged over 15 min intervals with the rare possibility of inductive
    vars up to 2 MVar.
Design Study aproaches
• Harmonic and transient Analyses
 -The system is modelled in the EMPT (Electro-Magnetic Transients
   Program)computer simulator program.This programme is used to model the
   harmonic impedances ,currents and voltages of electric power systems.
• Between Jan 31- Feb.1,2005 recordings were made at the 24 KV bus,the
   dominant harmonics were the 5th and the 7th.Voltage distortion at 24 KV is
   in the order 2.5 to 3.5% which is acceptable.
• Ratings of the Capacitors and tuning reactors
  -The ratings of the capcitor and tuning reactor components need to be such
   that the equipment will withstand the max.level of harmonic currents as
   well as fundamental voltage magnitude without overloading.Measurements
   on site of harmonic conditions were used as input for calcualtions of the
   required harmonic duties and equipment ratings.See the single line idagram
   of the bank step configurations in the following slide.
Final Design and equipment
selection
Site Design and construction phase
-Contract awarded Feb.05
-Contract completed Aug.05
-Contractors-QVARX,LEECORP
Plant Performance data after
capacitor project
Performance of compensation
system
• Var imports now in the order of 200KVar
  peak per mth at peak (20 MW) output
• Minimal downtime experienced
• Negligible payments to JPS

								
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