Transcript RES Impact on Transmission Network and Power Reserves

TRANSELECTRICA - DEN
RES-E Impact on Transmission Grid and Power
System Reserves
Florin Balasiu
Director of Operational Planning Division
Update Romanian Renewable Market
02 apr 2012
Content
1. Benefits and Challenges to Integrate RES
2. Technical Topics Regarding RES Integration
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Connection schemes. Network development
Power system stability topics
Shortcircuit withstand
Protective schemes
Power quality
3. Conclusions
1. Benefits and Challenges to Integrate RES-E
Developing and integration of RES (wind and photovoltaic) contribute to:
 Actions to mitigate climate changes
 Secure energy requirements
 Increase competitiveness and wealth
New challenges arise from:
 Variable nature of the RES
 Distributed nature
 Different electrical technologies
 Larger forecast errors
Fluctuating Nature of RES
Eolian [Mw]
Peak - 926 MW
1000
Increase 340 MW; 2 h
Decrease 390 MW; 1 h
900
800
700
600
500
400
300
200
100
0
3/29/2012
0:00
3/29/2012
2:24
3/29/2012
4:48
3/29/2012
7:12
3/29/2012
9:36
3/29/2012
12:00
3/29/2012
14:24
3/29/2012
16:48
3/29/2012
19:12
3/29/2012
21:36
3/30/2012
0:00
Distributed Nature of RES
Zona
CEE Dobrogea
CEE Moldova
CEE Banat
Contract+Functie
P instalat [MW]
2700
840
0
Contract+Functie+ATR
P instalat [MW]
6500
2050
1400
Total 110 kV
CEE
CFE
5280
230
8050
570
TOTAL SEN
CEE
CFE
8820
230
18000
570
RET
400 kV + 220 kV
2. Technical Topics on RES Integration
Connection scheme depends on: region, installed capacity, existing lines,
active power generation-load balance of the region
Power System Stability – rotor angle, frequency and voltage stability
 Frequency stability – balance between total active power generation
and load at Romanian power grid level, including load, export and
storage
 Voltage stability – balance between reactive power generation and
absorption capability
Shortcircuit withstand – symmetrical and asymmetrical (SLG) faults
Protective schemes of the generating units and of the network
Power quality – voltage drops, swings, flicker, operational performance
indexes
Total investment costs
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4
Network development
S/s modernization;
Transmission lines reinforcement vs new lines
increase transmission capacity by use of high temperature conductors
optimal power flow management
New lines:
400 kV Cernavoda-Gura Ialomitei-Stalpu
400 kV Suceava-Gadalin
400 kV Gutinas-Smardan
400 kV Portile de Fier-Resita-(Pancevo)-Timisoara-Arad
Typical 110 kV connection diagrams
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4
Typical 110 kV Connection Layouts for Renewable Medium Size (1)
New Distribution
Substation A
Substation B
Substation
110 kV
110 kV
Renewable
Generating Unit
80 MW
Visible for system operators
UGL 110 kV
Operational security => N-1 fulfilled
110 kV
Generation Substation
110 kV
Reliable protective system:
 Dependability
 Security
 Critical clearing time
ST=40 MVA
20 kV
ST=40 MVA
20 kV
Typical 110 kV Connection Layouts for Renewable Medium Size (2)
Substation B
Substation A
Renewable
Generating Unit
80 MW
OHL 110 kV
Visible for system operators
110 kV
Generation Substation
Operational security => N-1 not fulfilled
Islanding issues
The protective system:
 Difficulties to avoid unwanted trips or delayed ones
 Difficulties to provide remote back-up
thus not recommended
ST=40 MVA
20 kV
ST=40 MVA
20 kV
Power System Stability Topics
Frequency control – balance between load and generation
Aim – to maintain the balance between load and generation within a synchronous area
Based on three control actions:
 Primary frequency control is a local control to maintain load-generation balance and
stabilise frequency after large disturbances
 Secondary frequency control – centralised automatic generation control (AGC) to bring
back the frequency to its reference value. It restores the interchanges with surrounding
power systems
 Tertiary frequency control – to restore primary and secondary reserves
Secure system operation is only possible by close cooperation between owners of Power
Generating Facilities and the Network Operators. In particular, the system behavior in
disturbed operating conditions depends upon the response of Power Generating
Facilities to deviations from nominal values of voltage and frequency.
Effects – frequency range of operation
U/Un [ur]
1.1
60 min
90 min
1
0.95
0.9
90 min
>90 min, pot fi impuse de TSO
1.05
Nelimitat
180 min
0.85
cerinte locale TSO
30 min
0.8
47
47.5
48
48.5
49
49.5
50
50.5
51
51.5
f [Hz]
52
Effects – active power frequency response
P = the change in MW output from the
generator
f = the frequency deviation in the
network
Pmax = the max capacity to which P is
related
Active Power frequency response of Generating Units in Frequency Sensitive Mode
Effects – tertiary reserves
Tertiary frequency control is performed manually in order to restore primary and secondary
reserves.
Tertiary control may be achieved by:
 connection of generating units – fast startup, enough generating units
 changes in the dispatching of units
 changes in the interchanges program
 load control – energy storage
Actual limit for RES in the grid – about 3000 MW installed capacity
Power System Stability Topics
Voltage stability – reactive power control
Voltage stability refers to the ability of the power system to maintain voltages at all busbars
within the operational ranges during normal operation as well as after being subjected to
disturbances in the network.
Sufficient reactive power support is the most important part for voltage control and voltage
stability in a transmission and distribution network. As reactive power can not be
transported over long distances, the reactive power has to be supplied where required.
Consequently, increasing amount of wind generation reduces reactive power reserves in the
transmission system, which is defined by available reactive power of the synchronous
generators, SVCs and shunt capacitors minus reactive power consumption in the network
including reactive power of the switchable inductors.
Effects – voltage range of operation
U/Un [ur]
1.1
60 min
90 min
1
0.95
0.9
90 min
>90 min, pot fi impuse de TSO
1.05
Nelimitat
180 min
0.85
cerinte locale TSO
30 min
0.8
47
47.5
48
48.5
49
49.5
50
50.5
51
51.5
f [Hz]
52
Effects – fault ride through (FRT)
Ability of non-conventional generators to stay connected in the case of network faults
It is of particular importance to transmission system operators, that wind farms and photovoltaic generators stay connected, in case of faults at transmission or distribution levels that
lead to a voltage dips in a wide area.
It is mandatory for RES to be equipped with FRT-capability
FRT profile of a RES connected at
110 kV or above voltage levels.
Boundaries for a voltage-against-time
profile at the Connection Point
Power System Stability Topics
Transient stability – critical fault clearing time
The main aspects having a possible impact on transient stability issues are:
 RES are usually connected at different locations than conventional power stations.
Hence, power flows are considerable different in the presence of a high amount of
renewable power and actual power systems are typically not optimized for renewable
power transport. This aspect is relevant for Dobrogea area
 Renewable generating units are usually based on different technologies than
conventional synchronous generators and new tools for modeling and calculations are
needed
Based on these differences two phenomena can be distinguished, which can be affected by
RES generation:
 Global effects which can result in loss of synchronism of generators:
Transient stability (large-disturbance effect)
 Local effects
Trip of RES generators after subjected to a disturbance (w/o FLTR)
Transient stability – critical fault clearing time
Transient stability = the ability of the power system to maintain synchronism during and
after severe disturbances, for example short circuits or generator trips
The behaviour of the system is highly dependent on the type and duration of disturbance,
thus to ensure transient stability in a system often a number of critical contingencies have
to be simulated at different locations
For transient stability, the Critical Clearing Time is of utmost importance and represents an
useful measure for characterizing the transient stability performance of a given dispatch
scenario
To counteract against transient stability problems:
Fast protection tripping time + fast CB opening time => teleprotection schemes
Fast bus-bar faults clearing time => BBP and BFP
3. Conclusions
Large scale renewable power integration in the Romanian Power System is
possible by taking plenty technical measures
The installed RES (wind and photovoltaic) integration capability depends
on transmission and distribution lines and S/s development as well as
balancing capabilities and available reserves
Secure system operation is only possible by close cooperation among
owners of Power Generating Facilities, Network Operators and ANRE
Thank You !
Florin Balasiu
Update Romanian Renewable Market
02 apr 2012