TRANSELECTRICA - DENTRANSELECTRICA - DENTRANSELECTRICA - DENTRANSELECTRICA - DEN

RES-E Impact on Transmission Grid and Power RES-E Impact on Transmission Grid and Power System ReservesSystem Reserves

RES-E Impact on Transmission Grid and Power RES-E Impact on Transmission Grid and Power System ReservesSystem Reserves

Update Romanian Renewable Market02 apr 2012

Florin BalasiuDirector of Operational Planning Division

1. Benefits and Challenges to Integrate RES1. Benefits and Challenges to Integrate RES

2. Technical Topics Regarding RES Integration2. Technical Topics Regarding RES Integration

Connection schemes. Network development Power system stability topics Shortcircuit withstand Protective schemes Power quality

Connection schemes. Network development Power system stability topics Shortcircuit withstand Protective schemes Power quality

ContentContent

3. Conclusions3. Conclusions

1. Benefits and Challenges to Integrate RES-E1. Benefits and Challenges to Integrate RES-E

New challenges arise from:

Variable nature of the RES

Distributed nature

Different electrical technologies

Larger forecast errors

New challenges arise from:

Variable nature of the RES

Distributed nature

Different electrical technologies

Larger forecast errors

Developing and integration of RES (wind and photovoltaic) contribute to:

Actions to mitigate climate changes

Secure energy requirements

Increase competitiveness and wealth

Developing and integration of RES (wind and photovoltaic) contribute to:

Actions to mitigate climate changes

Secure energy requirements

Increase competitiveness and wealth

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Eolian [Mw]

Fluctuating Nature of RESFluctuating Nature of RES

Increase 340 MW; 2 h Decrease 390 MW; 1 h

Peak - 926 MW

Contract+Functie Contract+Functie+ATR Zona P instalat [MW] P instalat [MW]

CEE Dobrogea 2700 6500 CEE Moldova 840 2050

RET 400 kV + 220 kV

CEE Banat 0 1400

CEE 5280 8050 Total 110 kV CFE 230 570

CEE 8820 18000 TOTAL SEN CFE 230 570

Distributed Nature of RESDistributed Nature of RES

2. Technical Topics on RES Integration2. 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• 4

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• 4

Network developmentNetwork 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• 4

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• 4

Typical 110 kV Connection Layouts for Renewable Medium Size (1)Typical 110 kV Connection Layouts for Renewable Medium Size (1)

Visible for system operators

Operational security => N-1 fulfilled

Reliable protective system: Dependability Security Critical clearing time

Visible for system operators

Operational security => N-1 fulfilled

Reliable protective system: Dependability Security Critical clearing time

Substation A

Renewable Generating Unit

80 MW

Substation BNew Distribution

Substation

UGL 110 kV

ST=40 MVA

20 kV

ST=40 MVA

20 kV

110 kV

110 kV 110 kV

110 kV

Generation Substation

Visible for system operators

Operational security => N-1 not fulfilledIslanding issues

The protective system: Difficulties to avoid unwanted trips or delayed ones Difficulties to provide remote back-up

thus not recommended

Visible for system operators

Operational security => N-1 not fulfilledIslanding issues

The protective system: Difficulties to avoid unwanted trips or delayed ones Difficulties to provide remote back-up

thus not recommended

Typical 110 kV Connection Layouts for Renewable Medium Size (2)Typical 110 kV Connection Layouts for Renewable Medium Size (2)

Substation A Substation B

OHL 110 kV

ST=40 MVA

20 kV

ST=40 MVA

20 kV

Renewable Generating Unit

80 MW

110 kV

Generation Substation

Power System Stability TopicsPower System Stability Topics

Frequency control – balance between load and generationFrequency 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

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.

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 operationEffects – frequency range of operation

0.8

0.85

0.9

0.95

1

1.05

1.1

47 47.5 48 48.5 49 49.5 50 50.5 51 51.5 52

Nelimitat

90 m

in

>90

min

, pot

fi im

puse

de

TSO

90 m

in

180 min

30 min

60 min

U/Un [ur]

f [Hz]

cerinte locale TSO

Effects – active power frequency responseEffects – active power frequency response

Active Power frequency response of Generating Units in Frequency Sensitive ModeActive Power frequency response of Generating Units in Frequency Sensitive Mode

P = the change in MW output from the generatorf = the frequency deviation in the networkPmax = the max capacity to which P is related

P = the change in MW output from the generatorf = the frequency deviation in the networkPmax = the max capacity to which P is related

Effects – tertiary reservesEffects – tertiary reserves

Tertiary frequency control is performed manually in order to restore primary and secondaryreserves.

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

Tertiary frequency control is performed manually in order to restore primary and secondaryreserves.

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

Voltage stability – reactive power controlVoltage stability – reactive power control

Voltage stability refers to the ability of the power system to maintain voltages at all busbarswithin the operational ranges during normal operation as well as after being subjected todisturbances 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 thetransmission system, which is defined by available reactive power of the synchronousgenerators, SVCs and shunt capacitors minus reactive power consumption in the networkincluding reactive power of the switchable inductors.

Voltage stability refers to the ability of the power system to maintain voltages at all busbarswithin the operational ranges during normal operation as well as after being subjected todisturbances 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 thetransmission system, which is defined by available reactive power of the synchronousgenerators, SVCs and shunt capacitors minus reactive power consumption in the networkincluding reactive power of the switchable inductors.

Power System Stability TopicsPower System Stability Topics

Effects – voltage range of operationEffects – voltage range of operation

0.8

0.85

0.9

0.95

1

1.05

1.1

47 47.5 48 48.5 49 49.5 50 50.5 51 51.5 52

Nelimitat

90 m

in

>90

min

, pot

fi im

puse

de

TSO

90 m

in

180 min

30 min

60 min

U/Un [ur]

f [Hz]

cerinte locale TSO

Effects – fault ride through (FRT)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 photo-voltaic 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

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 photo-voltaic 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

FRT profile of a RES connected at 110 kV or above voltage levels. Boundaries for a voltage-against-time profile at the Connection Point

Transient stability – critical fault clearing timeTransient 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)

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)

Power System Stability TopicsPower System Stability Topics

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 schemesFast bus-bar faults clearing time => BBP and BFP

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 schemesFast bus-bar faults clearing time => BBP and BFP

Transient stability – critical fault clearing timeTransient stability – critical fault clearing time

3. Conclusions3. 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

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 !Thank You !Thank You !Thank You !

Florin Balasiu

Update Romanian Renewable Market02 apr 2012