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Emerging Scenario with Renewable Energy in Sri Lanka. Meeting the Challenges in Power System Operations & Economic Consequences.
Lakshitha Weerasinghe Ceylon Electricity Board
∗Basics of Power System Operations in the Sri Lankan context.
∗Understanding the problem! ∗Solutions!
Contents
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Basics of Power System Operations
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Time Line of activities G
ener
atio
n Pl
anni
ng
Cons
truc
tion
of
Gen
erat
ing
Asse
ts
Cons
truc
tion
of
Tran
smis
sion
In
fras
truc
ture
Uni
t Com
mitm
ent
Freq
. Con
trol
Tran
smis
sion
Pl
anni
ng
Econ
omic
Dis
patc
h
Supp
ly-D
eman
d Ba
lanc
ing
Seconds Minutes Hrs./ Days
Gov
erno
r Act
ion
Years
Ope
ratio
ns P
lann
ing
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Time Line of activities U
nit C
omm
itmen
t
Freq
. Con
trol
Econ
omic
Dis
patc
h
Supp
ly-D
eman
d Ba
lanc
ing
Seconds Minutes Hrs./ Days
Gov
erno
r Act
ion
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
50Hz
51Hz 49Hz
Demand Generation
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Supply-Demand Balancing
Supp
ly-D
eman
d Ba
lanc
ing
Seconds
20:0
0
16:0
0
12:0
0
08:0
0
04:0
0
00:0
0
24:0
0
Intermediate load
Peak load
Load MW
Base Load
1400MW 1600MW
2000MW
900 MW
Understanding the Demand curve
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Frequency (Hz)
Power (MW)
50Hz
100 MW
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Supp
ly-D
eman
d Ba
lanc
ing
Seconds
Gov
erno
r Act
ion
Minutes Hrs./ Days
Frequency (Hz)
Power (MW)
50Hz
100 MW
49.5Hz
110 MW © Lakshitha Weerasinghe Ceylon Electricity Board 2014
Supp
ly-D
eman
d Ba
lanc
ing
Seconds
Gov
erno
r Act
ion
Minutes Hrs./ Days
Freq. Error
Without Governor Control
With Governor Control
Frequency
50 Hz Time
Disturbance (Generator Trips!)
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Supp
ly-D
eman
d Ba
lanc
ing
Gov
erno
r Ac
tion
Frequency Control
Supp
ly-D
eman
d Ba
lanc
ing
Seconds
Gov
erno
r Act
ion
Minutes Hrs./ Days
Freq
uenc
y Co
ntro
l
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Frequency
50 Hz Freq. Error
With Frequency Control
Time
Disturbance (Generator Trips!)
With Governor Control (Primary ALFC)
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Bringing Frequency back to 50Hz.
Hydro*
Thermal
CEB 1361 MW
•CEB 1164 MW
•IPP 771 MW
*Note :- Mini Hydro and wind not included
Understanding the Frequency Controller
0MW 67
Kothmale single unit maximum capacity = 67MW
Eg.
50 49 51
52 48
Hz
30 60
50Hz
51Hz 49Hz
Demand Generation
50Hz
51Hz 49Hz
Demand
Generation
50Hz
51Hz 49Hz
Demand Generation
Any one of the following power stations is assigned at any given time to look after the system frequency. 1. Victoria (unit size = 71MWx3) 2. Kothmale (Unit size x 67 x 3) 3. New Laxapana (50MW x 2) 4. Samanala Wewa (60MW x 2)
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Time Line of activities U
nit C
omm
itmen
t
Freq
. Con
trol
Econ
omic
Dis
patc
h
Supp
ly-D
eman
d Ba
lanc
ing
Seconds Minutes Hrs./ Days
Gov
erno
r Act
ion
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
∗Economic Dispatch – What load to be kept on each machine that is already in operation. ∗Unit Commitment – What are the
machines to start or stop to serve load within a given period.
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Other Constraints/ Considerations (1) Hydro Power comes last in the water utilization Priority order
1. Water Service and Drainage 2. Environment 3. Irrigation 4. Power
(2) Pond balancing (3) Reservoir Operations
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Annual Inflow 3500 GWh
Annual Hydro Generation 3500 GWh
Spill
MOL
Storage Capacity ≅ 1250 GWh
Rese
rvoi
r 1
Rese
rvoi
r 7
Understanding the problem.
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Resource Attributes that causes problems to System Operations
Small Hydro Non Dispatchability.
Wind Non- Dispatchability and Intermittency.
Solar Non-Dispatchability and Intermittency.
Problems associated with Non Conventional Renewable Technologies.
Over 260 MW of Small NCRE generators are connected to the Distribution network. They appear as “Negative Loads” to system operators.
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Issues due to Non Dispatchability.
20:0
0
16:0
0
12:0
0
08:0
0
04:0
0
00:0
0
24:0
0
Load MW
Minimum Demand
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Issues due to non Dispatchable nature
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Issues due to non Dispatchable nature
20:0
0
16:0
0
12:0
0
08:0
0
04:0
0
00:0
0
24:0
0
Load MW
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Issues due to non Dispatchable nature
3 Base Load Coal plants. Minimum stable load is 180MW. Base Load Thermals such as Sapugaskanda HFO plant, CC plants. Frequency Controlling Hydro Plant Plants providing (Up/Down) Operating Reserves. “Must Run” Hydro plants Hydro plants operated to balance ponds. 360MW of non dispatchable small renewable plants.
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Issues due to Intermittency
Technical • Violation of operating frequency
limits. (±1%) • Operation of Under Frequency Load
Shedding (starting from 48.75Hz). • Severe Frequency instabilities leading
to cascaded total collapse.
Economical • Cost of maintaining high spinning
reserve. • Underutilization of energy from other
sources which may be cheaper or at zero cost (such as from Run-of-the-river plants that are spilling).
• Cycling of base load thermal plants.
How Intermittent is Wind SPEED ?
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Jan
Feb
Mar
Apr
May Jun
Jul
Aug
Sep
Oct
Nov Dec
Velo
city
m/s
Seasonal Variation of Wind Velocity
8.80
9.00
9.20
9.40
9.60
9.80
10.00
10.20
10.40
1 2 3 4 5 6 7 8 9 101112131415161718192021222324
velo
city
m/s
Diurnal Variation of Wind Velocity
0123456789
10
0 50 100 150 200 250 300 350 400 450 500
Source: SEA
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
How Intermittent is Wind Power ? Minute to Minute variation of out put (MW) of a wind Farm over
3 hour period.
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
How Intermittent is Solar?
Perfect Solar Day Pre-monsoon Clouds Passing Over
Source - SEA
Cost of Spinning Reserves.
Gradient = Incremental cost Rs/kWh
Generation Cost per
hour
Output (MW)
No Load Cost per
hour
Plant No Load Cost per Hour (Rs million)
(September 2014)
Kalanitissa CCP (Diesel) 1.17 AES CCP 1.3 Kerawalapitiya Yougadanavi 1.6 Victoria 10 m3 /s (25% of full load )
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Cost of Cycling
Plant Start/Stop Cost (Rs million)
Hot (<8 h) Warm (8<h<48)
Cold (48<h)
Kalanithissa CC (Diesel)
3.9 4.6 5.3
AES CC 3.3 8.6 10.5 Kerawalapitiya Yougadanavi
5.9 7.1 9.5
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Solutions
© Lakshitha Weerasinghe Ceylon Electricity Board 2014
Solutions Supply Side Solutions
• Maintaining larger spinning reserve to do Load-Frequency Control on supply side. • Operating intermittent sources (such as Wind) below capable output and utilize the balance
capacity to cushion out fluctuations at the source itself. • Group Control & AGC at Load dispatch Centre. • Secondary Automatic Load-Frequency regulation using Integral Controllers.
Demand Side Solutions • Valley Filling measures to improve Low demand period • Introducing variable loads to be called upon low demand periods. • Changing Customer demand using smart Grid options. • Introducing local loads such as Hydrogen, Compressed Air and Battery technologies to utilize
part of the generation to cushion out intermittency/variability at the terminal.
Other Solutions • Forecasting Wind speeds to do improved Operations Planning. • Interconnect with neighboring Grids. • Geographical scattering of Wind and Solar park locations.
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