ANCILLARY SERVICES SUPPLIED TO THE GRID: THE CASE OF THISVI CCGT POWER PLANT (GREECE) - Claudio Cavandoli, Alessandro Crippa EDISON S.p.A. ...
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Claudio Cavandoli, Alessandro Crippa
EDISON S.p.A., Engineering Department
ANCILLARY SERVICES
SUPPLIED TO THE GRID:
THE CASE OF THISVI CCGT
POWER PLANT (GREECE)
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 1
ANCILLARY SERVICES SUPPLIED TO THE GRID: THE CASE OF THISVI CCGT
POWER PLANT (GREECE) - GENERAL DATA
Combined Cycle Power Plant, 421.6 MWe Registered Capacity
Multi-Shaft arrangement, 1+1 Configuration
33 MWth Supplementary Firing
Designed for Dual Fuel operation (emergency)
Air Cooled Condenser
ANSALDO NOOTER ERIKSEN
ENERGIA 3 Pressure Levels + RH
V.94.3A4 – 275 MW
ANSALDO
ENERGIA GEA (21 fans)
MT – 146 MW
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 2
ANCILLARY SERVICES SUPPLIED TO THE GRID: THE CASE OF THISVI CCGT
POWER PLANT (GREECE)
GREEK ELECTRICAL GRID CODE REQUIREMENTS
• Each Generation Unit must have primary frequency control capability;
• The operating reserve shall be not less than 3% of the registered capacity in the
range between 50% and 97% of the registered capacity;
• The operating reserve in the range between 97% and 100% shall be not less than
that indicated by a straight line with fixed slope from 3% of registered capacity
at 97% output and 0% at full load;
• The production license holder must be capable of activating, within 30 seconds,
the total primary operating reserve and of maintaining supply for at least 15
minutes;
• The primary operating reserve must be available again 15 minutes after
activation.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 3
GREEK ELECTRICAL GRID CODE REQUIREMENTS
Load variation Vs plant load
14
12
Greek Grid Code Requirements:
10
• 12.6 MW/30s from minimum load to 97%
[MW/30 s]
8
registered capacity
6
4
• Linear decrease to zero between 97% and
Grid required load variation MW /30s 100% registered capacity
2
0
95% 96% 97% 98% 99% 100%
Power Plant Load [%]
Gas Turbine Load Ramps (AEN V.94.3A.4):
1. Normal Operation:
• 13 MW/min 60% - 98% Base Load
• 6.5 MW/min 98% - 100% Base Load
2. Frequency Regulation:
• ≈ 24 MW/min 60% - 98% Base Load
• 13 MW/min 98% - 100% Base Load
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 4
GREEK ELECTRICAL GRID CODE REQUIREMENTS
IMPLEMENTED CONTROL STRATEGY (1/3):
The HP steam header is controlled in modified sliding pressure throttling the Steam
Turbine HP Control valve (fixed pressure increase of 10 bar with respect to natural sliding
pressure, following steam flow-rate).
ST HP SECTION - NATURAL SLIDING Vs. MODIFIED SLIDING PRESSURE
150
140
130
HP ST INLET PRESSURE [barg]
120
110
100
90
80
70
60
50
120 140 160 180 200 220 240 260 280 300
HP STEAM FLOW-RATE [t/h]
The ST reacts to Grid frequency disturbs greater than 20 mHz (dead-band), in order to avoid
unnecessary depressurization of the headers and fluctuations. The ST Active Power response will be
proportional to the frequency disturbance, according to the defined droop control.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 5
GREEK ELECTRICAL GRID CODE REQUIREMENTS
IMPLEMENTED CONTROL STRATEGY (2/3):
The “bridge valve” located at the IP superheater outlet is used to keep slightly pressurized
the IP steam drum in order to prevent steam back-flow during the transient (which would
limit the contribution of the Steam Turbine IP section).
A pressure drop of 2 bar is maintained across the bridge valve during normal operation; the bridge
valve is fully opened when the ST contribution to primary frequency regulation is requested.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 6
GREEK ELECTRICAL GRID CODE REQUIREMENTS
IMPLEMENTED CONTROL STRATEGY (3/3):
The Supplementary-firing load will follow GT load, from 0%, with GT at 70% load, to
100%, with GT at cold base load. Note: post firing maximum load is limited to its
maximum load (MWth) or maximum exhaust gases temperature (°C), whichever is
reached first.
Supplementary firing load[%]
GT load[%]
This configuration avoids plant load ramp rate reduction while during operation at fired load. As far as
HRSG burners are operated according to GT load, the relevant impact on plant load variation rate is
negligible (the flexibility is equivalent to an unfired power plant).
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 7
GREEK ELECTRICAL GRID CODE REQUIREMENTS
IMPLEMENTED CONTROL STRATEGY (SUMMARY):
From 93% to cold From cold to hot
% GT load Up to 70% From 70% to 93%
base load base load
On at maximum
Post-firing Off On On
load
Load control + Load control + Load control + Load control +
GT control
frequency frequency frequency frequency
mode participation participation participation participation
Pressure control + Pressure control +
ST control
Pressure control Pressure control frequency frequency
mode participation participation
Open loop as a Open loop as a
Post-firing On at maximum
- function of the GT function of the GT
control mode load
load load
Steam
pressure Natural sliding Modified sliding Modified sliding Constant pressure
control mode
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 8GREEK ELECTRICAL GRID CODE REQUIREMENTS
CONTROL SYSTEM SCHEMATIC DIAGRAM:
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 9GREEK ELECTRICAL GRID CODE REQUIREMENTS
DYNAMIC SIMULATION
A dynamic simulation study of the plant has been developed together with Politecnico di
Milano University and ACT Solutions, in order to evaluate in advance the plant response
to a frequency disturbance and with the aim to optimize the above described procedure
as well as the involved control system logics and parameters. The following aspects
have been considered:
• process model of the relevant parts of entire BOP (water, steam, flue gas, PF
combustor);
• GT model, with the aim of reproducing its power generation response so as to
present realistic boundary conditions at the post-firing chamber inlet (on the plant
model side) and to the control system;
• ST model with the aim of reproducing its power generation response and main
process parameters;
• boundary conditions impressed by the electric system, limiting the scope to the
behaviour of the generator frequency;
• model of control system, integrating all the involved features of GT/ST controllers
and the Distributed Control System of the plant.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 10GREEK ELECTRICAL GRID CODE REQUIREMENTS
DYNAMIC SIMULATION RESULTS
[MW]
[MW]
[kg/s]
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 11GREEK ELECTRICAL GRID CODE REQUIREMENTS
TESTS RESULTS
The following tests have been carried out in order to assess Thisvi Power Plant compliance with the Greek Grid
Code requirements in terms of Primary Frequency Contribution:
- Plant at 97% load: Frequency error injection of ± 200 mHz maintained for 15 min
- Plant at 90% load: Frequency error injection of ± 200 mHz maintained for 15 min
- Plant at 80% load: Frequency error injection of ± 200 mHz maintained for 15 min
- Plant at 60% load: Frequency error injection of ± 200 mHz maintained for 15 min
Plant Load Frequency Error Primary Frequency Contribution
[%] [mHz] [MW]
30 seconds 15 minutes
97 % - 200 + 15.0 + 16.9
97 % + 200 - 13.5 - 13.8
90 % - 200 + 11.6 + 15.3
90 % + 200 - 14.0 - 12.9
80 % - 200 + 13.7 + 13.5
80 % + 200 - 16.4 - 16.2
60 % - 200 + 15.5 + 14.2
60 % + 200 - 16.0 - 13.0
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 12GREEK ELECTRICAL GRID CODE REQUIREMENTS - CONCLUSIONS
1. As a general statement, the ST participation to the frequency regulation can be
considered an effective method to share the regulating contribution between the GT
and the ST, thus reducing the thermal stresses on the GT and the necessary load
reduction, as well as the consequent ST load reduction in combined cycle operation.
2. In Thisvi case moreover, the ST participation is necessary to meet the Greek Grid
Code requirements, due to the high contribution requested and to the GT allowable
loading gradient.
3. The foreseen control strategy (properly pre-tuned using dynamic simulation tools and
finally fine-tuned in site) is an effective method to meet the Greek Grid Code
requirements in terms of primary frequency regulation.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 13ELECTRICITY FROM RENEWABLE ENERGY SOURCES (RES-e): IMPACT ON
TRANSMISSION SYSTEM OPERATION
1. Greece has a photovoltaic and wind potential comparable to central-southern
Italy.
2. The development feasibility evaluation needs a detailed analysis on how typical
daily PV and wind generation expected profiles.
3. Unpredictability can comply with the load diagram of a typical day.
4. The lack of firmness of PV and wind generation (i.e. the intermittency) and the
lack of forecast precision (on day ahead and on day ongoing) play the most
important role in the balancing energy of the system.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 14LOAD DIAGRAM OF A TYPICAL DAY IN GREECE
(source: www.admie.gr )
peak load at h 21-22: ~ 6GW
[MW]
first peak h 13-14
base load ~ 3GW:
about 50% of peak load
[h]
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 15TYPICAL DAILY PHOTOVOLTAIC GENERATION PROFILE IN GREECE
(source: Development of future scenarios and EU network data collection – SIEMENS WORKPAPER - 2008)
peak generation
at h 12-14
NO generation
from h 17-20
peak load
to h 6-7
at h 21-22
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 16TYPICAL DAILY WIND GENERATION PROFILE IN GREECE
(source: Development of future scenarios and EU network data collection – SIEMENS WORKPAPER - 2008)
daily variability: peak load
~ 60% of Pmax at h 21-22
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 17ELECTRICITY FROM RENEWABLE ENERGY SOURCES (RES-e): PHOTOVOLTAIC
AND WIND GENERATION PROFILES vs LOAD DIAGRAM
• Greek’s load diagram has deep fluctuations and two peaks.
• PV generation profile (in its typical shape) covers part of the first load peak
around 13.00 – 14.00 h; however the highest load peak is between 21.00 h
and 22.00 h when PV production is certainly equal to zero.
• Wind generation profile is extremely variable (both in time and in magnitude)
and unpredictable. Therefore it is completely unmatched in comparison to
load diagram.
• Variability and uncertainty (difficult to forecast accurately) introduce power
imbalances, lower levels of firm generation capacity and loss of services
from displaced generation.
• The challenge is to maintain stable operation of an electrical grid with high
penetration of RES.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 18ELECTRICITY FROM RENEWABLE ENERGY SOURCES (RES-e): IMPACT ON
TRANSMISSION AND DISTRIBUTION SYSTEMS OPERATION
Traditionally, the amount of balancing energy, or reserve, provided by controllable thermal or
hydro generation had to be sized to balance variations in demand or forced outages of the
largest production units.
Large penetration of intermittent and in particular wind and photovoltaic generation
introduces additional requirements for balancing energy.
The reasons are twofold:
• since RES generation has limited predictability, in order to cope with the forecast error,
larger amounts of flexible sources are necessary;
• also considering that the predictability of RES will improve in the future, however, even with
perfect forecasting, PV and wind generation will remain intermittent, non-controllable and
very variable from one hour to another. Therefore, additional flexibility is required.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 19ELECTRICITY FROM RENEWABLE ENERGY SOURCES (RES-e): IMPACT ON
TRANSMISSION AND DISTRIBUTION SYSTEMS OPERATION
The evolution in the composition of the optimal portfolio changes with increasing RES-e:
- Some of the less flexible base-load conventional plants will be forced out of the markets.
- Peak load and Medium load plants will cope with the variability of intermittent sources.
- Consequently, the grid needs more and more flexible plants like hydro, pump storage,
OCGT and CCGT, as well as high capacity wind power plants technically able to participate
in frequency control and the provision of reserve power capacity;
- Every MW of wind capacity requires 1 MW of backup firm capacity, to ensure 90%
availability.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 20ELECTRICITY FROM RENEWABLE ENERGY SOURCES (RES-e): IMPACT ON
TRANSMISSION SYSTEM OPERATION - CONCLUSIONS
1. Electricity systems with high penetration of wind and photovoltaic generation
have a higher exposure to problems related to grid stability.
2. There is an increasing need for flexible generating units, as a backup firm
capacity able to supply ancillary services, for dealing with intermittency and
RES-e forecast errors.
3. Ancillary services markets should be developed so that producers could
“offer” such flexibility to system operators and other market participants.
4. There should be a level playing field for balancing responsibility which applies
to all producers, including RES ones, in order to stimulate all market
participants to carry out thorough proper scheduling and forecasting, limiting
system costs.
Convegno ANIMP-ATI, 27 giugno 2012, Auditorium ABB - Sesto San Giovanni (MI) 21You can also read
