IET Keynote Address: Offshore Windfarm Design Issues

IET TV offers some good keynote presentations in various engineering sectors from leading engineering experts. Here’s one I found on offshore wind farm design issues from Andrew Donalson, SSE. It gives some good insight into reallife wind farm design, installation, and project challenges, and how SSE is currently dealing with these challenges.

Presentation video link: http://goo.gl/YT7KZ

I hope you will like as much as I did.

Data Checklist for Windfarm Load Flow Studies in IPSA

Wind farm load flow studies are usually preliminary assessment studies; typical investigations include: wind farm equipment/network (e.g. cables, transformers etc.) thermal overloads; network steady state voltages etc.

How much data you need to model a wind farm depends on the type of study being conducted and the connecting DNO/TNO grid voltage level. Here’s a typical wind farm modeling check list for load flow studies in IPSA for new/proposed wind farm. If load flow studies are to be required for an existing wind farm, then additional equipment, such as power factor capacitor, STATCOM etc., at the wind farm site will also have to be included. Some tips are given below where appropriate.

Network Settings

• System base in MVA: Unless explicitly specified, IPSA sets a default value of 100MVA.
• System frequency in Hz: Again unless explicitly specified, IPSA sets a default value of 50Hz.

Grid Source

Typically this information is obtained from the host DNO or through DNO’s Long Term Development Statements (LTDS). In IPSA this is usually represented using a ‘Grid Infeed’ block.

• Voltage level in kV.
• Voltage magnitude in p.u.: This is the anticipated voltage at POC/PCC during normal system operation, and is usually obtained from DNO network load flow studies or site measurements. Usually set as 1p.u if this information is not given.
• Peak and RMS fault MVA levels, and X/R ratio for a LLL fault type.
• Peak and RMS fault MVA levels for a LG fault type: Leave them blank if not given.
• AC decay in seconds: A decay of 2s is typical.
• RMS fault time in seconds: Typically 100ms in UK and 80ms in Ireland systems.

Grid transformer

• HV & LV voltages in kV.
• Power rating in MVA: Helps IPSA identify transformer overloading.
• Winding resistance in p.u: At IPSA system MVA base. If explicitly not given, could be calculated from load losses. Usually set as 10% of reactance if load losses not given.
• Zero sequence winding resistance and reactance in p.u.: Again at system MVA base. Typically assumed as 85-90% of positive sequence impedances if not given.
• Winding vector type: Dyn11, YYno etc.
• Minimum tap, maximum tap and tap step in %.
• Target voltage in p.u.: Most wind farm grid transformers will be providing voltage regulation at the HV side within their tap operating range, and therefore entering this value is recommended. If not given or known set this to 1p.u.

Wind farm cable network

• Positive sequence resistance, reactance and susceptance in p.u.: Don’t panic if you don’t have this data, IPSA has incorporated impedance database for cables and overhead lines for typical voltage levels. So use this information via ‘Database and Harmonics’ tab on line properties.
• Zero sequence resistance and reactance in p.u.: Typically assumed as positive sequence values if not given.

Wind turbine transformers

• Same as the grid transformer, except for the representation of taps are only required if the transformer provides or will to provide voltage regulation at its HV side.

Wind turbine generators

• For load flow studies a full detailed generator representation is not required, and therefore a simple universal machine block will do the job.
• Enter rated real and reactive power output in MW and MVAR respectively.

Reactive power compensation

• If the reactive power compensation required capacitive MVARs is already known then include this in the model using shunt component in IPSA.
• Positive and zero sequence resistance and reactance in p.u.: The reactance value entered is positive when representing an inductive shunt and is negative when representing a capacitive shunt.

Note: One common mistake I did previously was entering the wrong data or entering data with inaccurate calculations or estimation. I have learnt my mistakes, and so I humbly recommend you to check your calculations/data again: It’s worth the pain.

Now, once you are confident on the data and wind farm equipment representation in IPSA, run a load flow. If IPSA prompts you a converged load flow, then you have just conducted a successful wind farm load flow study.

Congratulations!