Wigton Windfarm Ltd.

1
Wigton Windfarm Ltd.

• Power Factor and VAR Control Experience
• -Problems and Solutions
• Presented by Francois A. Lee, PE
• Leecorp Ltd ,Wigton consultant

2
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

3
Wigton single line Summary
4
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.

5

• 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
  JPScos substation rated 139/69 KV at Spur Tree
  via 11.315 KM of newly built 69 KV overhead lines

6
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.

7
(No Transcript)
8
(No Transcript)
9
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.

10
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 _at_ no load,410 KVAR _at_ full
  load.
• Neg-Micon turbines installed have capacitive
  compensation up to 275 KVAR only.

11
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.

12
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

13
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.

14
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.

15
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.

16
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.

17
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.

18
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.

19
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.

20
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.

21
(No Transcript)
22
(No Transcript)
23
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.

24
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.

25
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.

26
(No Transcript)
27
Final Design and equipment selection
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Site Design and construction phase-Contract
awarded Feb.05-Contract completed
Aug.05-Contractors-QVARX,LEECORP
37
(No Transcript)
38
(No Transcript)
39
Plant Performance data aftercapacitor project
40
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