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