The Challenges of Small ScaleIslanded Power Systems
Craig Harrison12th November 2014
Presentation Overview
Summary of Challenges
Focus on the Technical Challenges – Engineering
Real Life Perspective – Examples
Renewable Energy & its Impact on Generation
Generation Dynamics & Modelling
The Challenges
Political – short term objectives, optimistic plans & promises, corruption
Environmental – limited land, volcanic islands & atolls, global warming & rising sea levels
Funding – Capex - ADB, World Bank, IRENA, EU Agencies, SPREP, Australian, NZ and Japanese Governments, US Aid Agencies (US Territories)
Opex – limited utility funding!
Engineering Skills – low skill levels, low staff retention, system complexity limits
Technical Challenges – improving generation efficiencies, integration of RE, reduce losses (technical & non technical)
The Reality
FSM, Pohnpei, Power Station
FSM, Pohnpei, Power Station
FSM, Pohnpei, Power Station
Typical Island Power Station
Multiple Generators Different Sizes Different Ages & Condition
A Day in the Lifeof a
Nauruan Genset
High Speed V & I Recordings
With a self powered iba PADU-C data acquisition unit high speed recording of genset voltage and current signals can be recorded for several days.
iba PADU-C
1250kVA415V
1740A
1kHz Sampling & Recording, All Day Long
100s Span
50ms Span
0.5s Span
This Particular 24hr Period Calculations for RMS voltage & current, real & reactive power flow over 24hrs (@1000pts/s!)to get an overview of the day.
RMS Voltage (pu)
RMS Current (A)
Real Power (kW)
Reactive Power (kVar)
Flag Transient Points of InterestRaise a flag whenever the rms voltage deviates by >5% and inspect more closely.
Example1 Example2Example3
Example 1 – Effect of Sudden Load Shed on Voltage & Frequency
Example 2 – Effect of Sudden Load Changes on Voltage & Frequency
Example 3 – Transformer Inrush EventNote change of scales to cope with magnitude of event (current reaches 3500A, ~2pu). See next slide for zoom in on raw data.
Initial speed/frequency response
Example 3 - Zoom In on Raw Data
Clipped at 4000A (PADU input range limit for CT’s used)
Sub Transient
The Island Vision – 100% RE
Impediments as above!
Current Activities
PV systems being installed – small scale as % of generation capacity
Small number of battery systems – small scale
Large number of RE studies being funded – e.g. IRENA
* desk top studies focused on “hosting capacity”* input data often estimated values* generation dynamics is not known or considered
Some unsatisfactory outcomes - building on weak base!
Outcomes – The Evidence
American Samoa – 19MW Demand – 1.6MW PV Installed
* PV fluctuations audible in slow speed engines – slow response* Small High Speed Sets being run as additional spinning reserve!* Net outcome is questionable!
Tonga – 7MW Demand – 2 * 1MW PV & LA battery storage
* Cloud Events cause the PV to trip – gen. frequency variations* Batteries ineffective for demand shifting – inadequate ratings
Island Power SystemsSome Problem Areas
Low Fault Levels – Weak
Generation Dynamic Behaviour – Poor (e.g. Nauru)
Protection Discrimination – Black Outs
Island Power SystemsProblem Areas
Generation Dynamic Behaviour
Parallel Generators – Droop Load Share
Most Common Generator ConfigurationDroop typically 3 to 5%
Parallel Generators – Droop Load Share
Step Load Response
Movement downthe droop curve
Engine Model – Droop Mode
Engine & Governor – Basic Model
Governor
Engine Model – Droop Mode
Governor – Model
Governor – Transfer Function
GovernorTime Constant
Engine Model – Droop Mode
Engine & Governor – Complete
Two Poles2nd Order System
System Modelling
2nd Order Response
H(s)
Opportunities for Optimisation
Improve Generator Control Dynamics
Reduction of Spinning Reserve
Improved Performance & Fuel Efficiency
End with a Good News StoryGroote Eylandt
3% fuel saving = $300k pa Improved dynamics behaviour – reduced trips & blackouts
Thankyou
Questions
